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Author Topic: Risks and Challenges for Regional Circulation Models of the Southern Ocean  (Read 49376 times)

AbruptSLR

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Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #50 on: January 23, 2014, 01:29:15 AM »
The linked article indicates that warming of the north and tropical Atlantic Ocean is reducing the atmospheric pressure and the sea ice offshore of the Amundsen Sea Embayment, in a manner that may have adverse consequences for SLR:

Xichen Li, David M. Holland, Edwin P. Gerber & Changhyun Yoo, (2014), "Impacts of the north and tropical Atlantic Ocean on the Antarctic Peninsula and sea ice"; Nature; 505, 538–542; doi:10.1038/nature12945

http://www.nature.com/nature/journal/v505/n7484/full/nature12945.html

Abstract: "In recent decades, Antarctica has experienced pronounced climate changes. The Antarctic Peninsula exhibited the strongest warming of any region on the planet, causing rapid changes in land ice. Additionally, in contrast to the sea-ice decline over the Arctic, Antarctic sea ice has not declined, but has instead undergone a perplexing redistribution. Antarctic climate is influenced by, among other factors, changes in radiative forcing and remote Pacific climate variability, but none explains the observed Antarctic Peninsula warming or the sea-ice redistribution in austral winter. However, in the north and tropical Atlantic Ocean, the Atlantic Multidecadal Oscillation (a leading mode of sea surface temperature variability) has been overlooked in this context. Here we show that sea surface warming related to the Atlantic Multidecadal Oscillation reduces the surface pressure in the Amundsen Sea and contributes to the observed dipole-like sea-ice redistribution between the Ross and Amundsen–Bellingshausen–Weddell seas and to the Antarctic Peninsula warming. Support for these findings comes from analysis of observational and reanalysis data, and independently from both comprehensive and idealized atmospheric model simulations. We suggest that the north and tropical Atlantic is important for projections of future climate change in Antarctica, and has the potential to affect the global thermohaline circulation and sea-level change."
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AbruptSLR

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Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #51 on: January 23, 2014, 04:09:51 PM »
It has been a while since I posted the attached figure from Bertler et al 2006 (see reference at bottom of this post), which shows pictorially the relationship between the location of the Amundsen Sea Low (or Amundsen Bellingshausen Sea Low), ASL (or ABSL) and either a La Nina or an El Nino event.  Taken together with the information in my immediately preceding post (which stated that sea surface warming related to the Atlantic Multidecadal Oscillation, AMO, reduces the surface pressure in the Amundsen Sea), this implies that when the next El Nino event occurs (which may be the austral summer of 2014 to 2015) and shifts the location of the ASL to blow wind directly into the ASE, the winds will likely be stronger due to the lower Amundsen sea pressure associated with AMO effect; which will drive more warm CDW into the ASE resulting in higher than previously expected ice mass loss from the glaciers in this area.

Bertler, N.A., Naish, T.T., Mayewski, P.A. and Barrett, P.J., (2006), "Opposing oceanic and atmospheric ENSO influences on the Ross Sea Region, Antarctica", Advances in Geosciences, 6, pp 83-88, SRef-ID: 1680-7359/adgeo/2006-6-83.
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AbruptSLR

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Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #52 on: January 24, 2014, 04:17:16 PM »
The following link leads to a nice summary (from October 2013) of the ARGO findings through the end of 2012:

http://ceres.larc.nasa.gov/documents/STM/2013-10/14_Global_averages.pdf

As indicated in the attached figure, one key finding is that all of the ocean heat gain in the ARGO era has been in the Southern Hemisphere (which indicates that all of the steric SLR in in the ARGO era has been in the Southern Hemisphere).  This provides additional support to my position that when the current EL Nino hiatus period ends, there is an excess of heat in the Southern Ocean that can accelerate ice mass loss from Antarctica once the local winds/current shift sufficiently to increase the ocean interaction with the grounded ice.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #53 on: January 27, 2014, 07:11:55 PM »
Articles such as that found at the link below, indicate that science is only now beginning to delineate the nature of a deep ocean current 40-times larger than the Amazon in the critical area near the Kerguelen Plateau in the Southern Ocean.  These finding indicate that the flows and velocities are higher than previously expected, indicating the relatively high degree of uncertainty associated with Regional Circulation Models of the Southern Ocean; which indicates an associated lower confidence level in sea level rise projections, than previously acknowledged in reports such as the AR5:

http://www.worldbulletin.net/science-technology/57641/scientists-uncover-deep-ocean-current-near-antarctica
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AbruptSLR

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Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #54 on: January 31, 2014, 10:18:51 PM »
The linked AGU poster discusses the influence of the ozone hole over Antarctica and the impact of the SAM on cross shelf heat exchange around Antarctica:

Yoo, C., E. P. Gerber, L.-S. Bai, D. H. Bromwich, M. S. Dinniman, K. M. Hines, D. M. Holland, and J. M. Klinck: Impact of Souther Annular Mode on cross shelf exchange around the Antarctica. 2013 AGU Fall Meeting, San Francisco, CA, Dec. 9-13, 2013.

http://polarmet.osu.edu/ACCIMA/ACCIMA_yoo_etal_201312.pdf
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AbruptSLR

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Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #55 on: February 01, 2014, 08:13:16 PM »
The linked (free access) paper describes progress being made on the Regional Ocean Model System (ROMS) focused on the Southern Ocean (& in this case study the Weddell Sea).  This work confirms the importance of including ice-ocean coupling within RCMs:

V. Meccia, I.Wainer, M. Tonelli, and E. Curchitser, (2013), "Coupling a thermodynamically active ice shelf to a regional simulation of the Weddell Sea", Geosci. Model Dev., 6, 1209–1219, 2013, www.geosci-model-dev.net/6/1209/2013/; doi:10.5194/gmd-6-1209-2013

http://www.geosci-model-dev.net/6/1209/2013/gmd-6-1209-2013.pdf

"Abstract. A thermodynamically interactive ice shelf cavity parameterization is coupled to the Regional Ocean Model System (ROMS) and is applied to the Southern Ocean domain with enhanced resolution in the Weddell Sea. This implementation is tested in order to assess its degree of improvement to the hydrography (and circulation) of the Weddell Sea. Results show that the inclusion of ice shelf cavities in the model is feasible and somewhat realistic (considering the lack of under-ice observations for validation). Ice shelf–ocean interactions are an important process to be considered in order to obtain realistic hydrographic values under the ice shelf. The model framework presented in this work is a promising tool for analyzing the Southern Ocean’s response to future climate change scenarios."
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AbruptSLR

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Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #56 on: February 01, 2014, 08:31:00 PM »
Papers such as the linked article by Sigmond et al 2014, indicate that the current CMIP5 results (which do not simulated the observed sea ice pattern in Antarctica) have not had time to incorporate the findings of Li et al 2014 (see reference at end of post) of how the north and tropical Atlantic Ocean influences sea ice in the Southern Ocean.  It will take time (decades)  to correctly calibrate the current generation of GCMs and RCMs.

Sigmond, Michael, John C. Fyfe, 2014: The Antarctic Sea Ice Response to the Ozone Hole in Climate Models. J. Climate, 27, 1336–1342.  doi: http://dx.doi.org/10.1175/JCLI-D-13-00590.1

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-13-00590.1

Abstract: "It has been suggested that the increase of Southern Hemisphere sea ice extent since the 1970s can be explained by ozone depletion in the Southern Hemisphere stratosphere. In a previous study, the authors have shown that in a coupled atmosphere–ocean–sea ice model the ozone hole does not lead to an increase but to a decrease in sea ice extent. Here, the robustness of this result is established through the analysis of models from phases 3 and 5 of the Coupled Model Intercomparison Project (CMIP3 and CMIP5). Comparison of the mean sea ice trends in CMIP3 models with and without time-varying stratospheric ozone suggests that ozone depletion is associated with decreased sea ice extent, and ozone recovery acts to mitigate the future sea ice decrease associated with increasing greenhouse gases. All available historical simulations with CMIP5 models that were designed to isolate the effect of time-varying ozone concentrations show decreased sea ice extent in response to historical ozone trends. In most models, the historical sea ice extent trends are mainly driven by historical greenhouse gas forcing, with ozone forcing playing a secondary role."

Xichen Li, David M. Holland, Edwin P. Gerber & Changhyun Yoo, (2014), "Impacts of the north and tropical Atlantic Ocean on the Antarctic Peninsula and sea ice"; Nature; 505, 538–542; doi:10.1038/nature12945
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #57 on: February 03, 2014, 05:12:53 PM »
The following link leads to a pdf of New Zealand's Antarctic Science program for 2013-2014.  The Kiwis are doing a lot of great science relevant to SLR, including: (a) K049: Roosevelt Island Climate Evolution – RICE Project; (b) K055: Assessment of the Current State of the Antarctic Middle Atmosphere and Climate Model Validation; (c) K060: Space Weather Monitoring (AARDDVARK), (d) K063: Antarctic sea ice thickness mapping at McMurdo Sound, and (e) K085: Investigating ozone depletion and climate change: trace gas measurements in the Antarctic atmosphere:

http://antarcticanz.govt.nz/images/downloads/science/Science_Programme-201314.pdf
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #58 on: February 04, 2014, 01:29:43 AM »
The following link cites the findings of field work by the Alfred Wegener Institute where the researchers took marine sediment cores from the Pacific sector of the Southern Ocean (the Pacific Sector accounts for 50% of the Southern Ocean), that records about 1 million year worth of dust deposition on the seafloor.  This is significant because during past ice ages the dust over the Southern Ocean increased by about 3-times normal; and the calibration of past GCMs over the past 1 million years assumed that there should be very little dust in the Pacific sector of the Southern Ocean during past ice ages, while the cores should that the amounts and origins of the dust in the Pacific sector was the same in the other sectors of the Southern Ocean.  This implies that during these past ice age periods, large band of westerly winds extended so far northward that they gather dust from Australia and New Zealand (as well as the previously recognized dust source from Argentina).  This implies that all existing GCMs need to be re-calibrated so that they project the occurrence of this large band of westerly wind during past ice ages:

F. Lamy, R. Gersonde, G. Winckler, O. Esper, A. Jaeschke, G. Kuhn, J. Ullermann, A. Martinez-Garcia, F. Lambert, & R. Kilian, (2014), "Increased Dust Deposition in the Pacific Southern Ocean During Glacial Periods", Science 24 January 2014: Vol. 343 no. 6169 pp. 403-407, DOI: 10.1126/science.1245424

http://environmentalresearchweb.org/cws/article/yournews/56052
http://www.sciencemag.org/content/343/6169/403.short

Abstract: "Dust deposition in the Southern Ocean constitutes a critical modulator of past global climate variability, but how it has varied temporally and geographically is underdetermined. Here, we present data sets of glacial-interglacial dust-supply cycles from the largest Southern Ocean sector, the polar South Pacific, indicating three times higher dust deposition during glacial periods than during interglacials for the past million years. Although the most likely dust source for the South Pacific is Australia and New Zealand, the glacial-interglacial pattern and timing of lithogenic sediment deposition is similar to dust records from Antarctica and the South Atlantic dominated by Patagonian sources. These similarities imply large-scale common climate forcings, such as latitudinal shifts of the southern westerlies and regionally enhanced glaciogenic dust mobilization in New Zealand and Patagonia."

Editor's Summary: "The effect of windblown dust on marine productivity in the Southern Ocean is thought to be a key determinant of atmospheric CO2 concentrations. Lamy et al. (p. 403) present a record of dust supply to the Pacific sector of the Southern Ocean for the past one million years, derived from a suite of deep-sea sediment cores. Dust deposition during glacial periods was 3 times greater than during interglacials, and its major source region was probably Australia or New Zealand."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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sidd

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Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #59 on: February 04, 2014, 01:38:29 AM »
Interesting. I wonder if dust induced phytoplankton bloom played a part in increasing CO2 drawdown during glacials.

AbruptSLR

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Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #60 on: February 04, 2014, 01:43:35 AM »
sidd,

Yes, the article clearly states that the iron rich dust causes the plankton in the Southern Ocean to bloom which decreased atmospheric carbon dioxide levels during past ice ages (resulting in a feedback for addition cooling).

Best,
ASLR
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #61 on: February 04, 2014, 06:43:56 PM »
The linked reference discusses how animal-borne instruments have improved estimates of the Southern Ocean general circulation over the last decade:

Roquet, F., et al. (2013), Estimates of the Southern Ocean general circulation improved by animal-borne instruments, Geophys. Res. Lett., 40, 6176–6180, doi:10.1002/2013GL058304.

http://onlinelibrary.wiley.com/doi/10.1002/2013GL058304/abstract

Abstract
"Over the last decade, several hundred seals have been equipped with conductivity-temperature-depth sensors in the Southern Ocean for both biological and physical oceanographic studies. A calibrated collection of seal-derived hydrographic data is now available, consisting of more than 165,000 profiles. The value of these hydrographic data within the existing Southern Ocean observing system is demonstrated herein by conducting two state estimation experiments, differing only in the use or not of seal data to constrain the system. Including seal-derived data substantially modifies the estimated surface mixed-layer properties and circulation patterns within and south of the Antarctic Circumpolar Current. Agreement with independent satellite observations of sea ice concentration is improved, especially along the East Antarctic shelf. Instrumented animals efficiently reduce a critical observational gap, and their contribution to monitoring polar climate variability will continue to grow as data accuracy and spatial coverage increase."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #62 on: February 05, 2014, 12:33:14 AM »
The following link leads to an article indicating that NOAA and the U.S. Navy are teaming up with academic and other government scientists to design the next generation of powerful supercomputer models to predict weather, ocean conditions and regional climate change:

http://research.noaa.gov/News/NewsArchive/LatestNews/TabId/684/ArtMID/1768/ArticleID/10430/NOAA-launches-research-on-next-generation-of-high-performance-weather-climate-models.aspx
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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The following linked reference (with a free access pdf) discusses the new ACCIMA regional climate system model for the Southern Ocean and Antarctica.  This model contains numerous improvements on earlier models, but still needs improvement:

Bromwich, D. H, C. Yoo, K. M. Hines, L.-S. Bai, D. Holland, J. Klinck, M. Dinniman, and E. Gerber, 2014: ACCIMA: A regional climate system model for the Southern Ocean and Antarctica. J. Climate,


http://polarmet.osu.edu/ACCIMA/bromwich_yoo_jc_2014.pdf

“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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wili

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The Antarctic Half of the Global Thermohaline Circulation is Collapsing

http://www.dailykos.com/story/2014/03/05/1281907/-The-Antarctic-Half-of-the-Global-Thermohaline-Circulation-is-Collapsing

The largest source of Antarctic Bottom Water in the global thermohaline circulation (labelled W) has ceased production.

...this study probably underestimates the amount of fresh water around Antarctica and its effects on Antarctic Bottom Water (ABW) formation...

 Global political policies are not keeping up with the rate of change and our models have, to date, underestimated the rate of change. We are witnessing a total failure of global leadership to deal with changes we caused that are spiraling out of control.


Peter Ward on the consequences of this development: "When [the global ocean current conveyor belt] stops, we lose oxygen at the bottom, and we start the process toward mass extinction."

http://climatestate.com/2014/03/05/the-antarctic-half-of-the-global-thermohaline-circulation-is-collapsing/
« Last Edit: March 06, 2014, 02:51:06 AM by wili »
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AbruptSLR

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wili,

The topic of the AABW is a serious matter and has been discussed extensively, in many different threads in the Antarctic folder; but rather than referencing these past discussions, I will limit myself now to noting that the following research by Rose et al. (2014) indicates that ocean heat uptake (OHU) in the polar regions has three times the influence on climate sensitivity as does the same OHU in the tropics.  This implies that the reduction in OHU into the AABW will have an amplified effect on global warming:

Rose BEJ, KC Armour, DS Battisti, N Feldl and DDB Koll (2014) The dependence of transient climate sensitivity and radiative feedbacks on the spatial pattern of ocean heat uptake, Geophysical Research Letters, 41, doi: 10.1002/2013GL058955

http://web.mit.edu/karmour/www/Rose_etal_GRL2014.pdf

Abstract: "The effect of ocean heat uptake (OHU) on transient global warming is studied in a multimodel framework. Simple heat sinks are prescribed in shallow aquaplanet ocean mixed layers underlying atmospheric general circulation models independently and combined with CO2 forcing. Sinks are localized to either tropical or high latitudes, representing distinct modes of OHU found in coupled simulations.  Tropical OHU produces modest cooling at all latitudes, offsetting only a fraction of CO2 warming. High latitude OHU produces three times more global mean cooling in a strongly polar-amplified pattern. Global sensitivities in each scenario are set primarily by large differences in local shortwave cloud feedbacks, robust across models. Differences in atmospheric energy transport set the pattern of temperature change.  Results imply that global and regional warming rates depend sensitively on regional ocean processes setting the OHU pattern, and that equilibrium climate sensitivity cannot be reliably estimated from transient observations."

Best,
ASLR
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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The following link leads to a free access pdf of a paper about the findings of a regional circulation model that focuses on basal ice melting for Antarctic ice shelves (& include atmospheric effects):

http://polarmet.osu.edu/ACCIMA/dinniman_klinck_jc_2014.pdf
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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The following link leads to a free access pdf of the Bromwich et al 2014 paper entitled: "ACCIMA: A Regional Climate System Model for the Southern Ocean and Antarctica"; which of course is about the ACCIMA RCM:

http://polarmet.osu.edu/ACCIMA/bromwich_yoo_jc_2014.pdf
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Shared Humanity

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Hah! I've finally  found the proper home for this article which was just recently posted on ASIB.

http://www.dailykos.com/story/2014/03/05/1281907/-The-Antarctic-Half-of-the-Global-Thermohaline-Circulation-is-Collapsing

What are the implications?


SteveMDFP

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Hah! I've finally  found the proper home for this article which was just recently posted on ASIB.

http://www.dailykos.com/story/2014/03/05/1281907/-The-Antarctic-Half-of-the-Global-Thermohaline-Circulation-is-Collapsing

What are the implications?


Worse than either the author or comments there suggest.  The main mechanism of mass extinctions during the end-Permian event ("the great dying") was probably not heat itself, but collapse of oxygen delivery to the ocean floors, resulting in highly toxic hydrogen sulfide (H2S). 
Formation of deep water from cooled surface waters doesn't just distribute heat, it's the only major way for oxygen to get to the deep ocean waters.

Organic matter is taken up by organisms to grow.  Ordinarily, they use oxygen to react with carbon compounds to create the energy they need.  When the oxygen is used up, anaerobic bacteria will use dissolved sulfate, converting sulfate to hydrogen sulfide (the stuff with a rotten egg smell). 
H2S is highly toxic, it's been compared to cyanide gas.  Released at ocean depths it will simply kill all the ocean creatures we're familiar with.  When levels are high enough, it can be released into the atmosphere.
I think we're rapidly transitioning the globe to a Permian Extinction state.  Once started, that can continue, with positive feedback mechanisms, for many millenia to come.
We're already seeing more areas of ocean with hypoxic dead zones.  Expect to see more.

sidd

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Re: euxinic ocean

these papers by Kidder and Worsley are relevant

doi:10.1016/S0031-0182(03)00667-9

doi:10.1016/j.palaeo.2010.05.036

doi: 10.1130/G131A.1

the last at least is open access, and very good. There is another recent paper by (among others) Canfield, of Canfield ocean fame, but i do not immediately recall the reference.

I think you will find that widespread euxinia will take longer than centuries; however my guess is  acidic and possible euxinic conditions in the Red Sea or Mediterranean first.

sidd

AbruptSLR

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Although this post could go into either the Paleo, or the Trends of the Southern Ocean, threads, I am putting it here because the paleo data presented in the linked reference (with a free access paper) represents a challenge of both Global and Regional Circulation Models related to the influence of the Southern Ocean during the Holocene (8,000 yrs age the mean global temperatures were a bit higher than now so calibrating the GCMs, & RCMs, to match the observed Holocene record should improve the model projections).  This challenge particularly focuses on the ventilation of the Northwest Pacific Ocean trigger by wind-driven changes in the Southern Ocean, as indicated by the title, abstract and attached image:

S. F. Rella    & M. Uchida, (2014),"A Southern Ocean trigger for Northwest Pacific ventilation during the Holocene?", Scientific Reports 4, Article number: 4046 doi:10.1038/srep0404

http://www.nature.com/srep/2014/140210/srep04046/full/srep04046.html?WT.ec_id=SREP-20140218

Abstract: "Holocene ocean circulation is poorly understood due to sparsity of dateable marine archives with submillennial-scale resolution. Here we present a record of mid-depth water radiocarbon contents in the Northwest (NW) Pacific Ocean over the last 12.000 years, which shows remarkable millennial-scale variations relative to changes in atmospheric radiocarbon inventory. Apparent decoupling of these variations from regional ventilation and mixing processes leads us to the suggestion that the mid-depth NW Pacific may have responded to changes in Southern Ocean overturning forced by latitudinal displacements of the southern westerly winds. By inference, a tendency of in-phase related North Atlantic and Southern Ocean overturning would argue against the development of a steady bipolar seesaw regime during the Holocene."
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AbruptSLR

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The following abstract comes from the International Glacial Society Proceeding 65 at the following link:

http://www.igsoc.org/symposia/2014/chamonix/proceedings/procsfiles/procabstracts_65.htm

The Pollard and DeConto  2014 reference indicates that a new generation of Antarctic ice sheet modeling indicates that these ice sheets are less stable than previously expected:

70A0977
Modeling past and future ice retreat in Antarctic subglacial basins
David POLLARD, Robert DECONTO
Corresponding author: David Pollard
Corresponding author e-mail: pollard@essc.psu.edu

Abstract: "Geological data indicate that global mean sea level has fluctuated on O(104 to 105 year) timescales during the last ~25 million years. Peak levels are uncertain, but some estimated high stands are ~20 m or more above modern, for instance during the mid-Pliocene. If correct, this implies substantial variations in the size of the East Antarctic ice sheet (EAIS). However, climate and ice-sheet models have not been able to simulate significant EAIS retreat from continental size, given low proxy atmospheric CO2 levels during this time. Here, we use a continental Antarctic ice sheet model with two mechanisms based on previous studies and observations: (1) structural failure of large tidewater ice cliffs, and (2) enhanced ice-shelf calving due to meltwater drainage into crevasses. With climate forcing representing Pliocene warm periods, the two mechanisms accelerate West Antarctic collapse and produce retreat in major East Antarctic basins. Equivalent global mean sea-level rise is ~15 m, in better agreement with past sea-level data. The model is applied to specific past periods and to the long-term (100s to 1000s years) future, in which the ice sheet is found to be considerably more vulnerable to climate warming than previously modeled."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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The following abstract comes from the International Glacial Society Proceeding 65 at the following link:

http://www.igsoc.org/symposia/2014/chamonix/proceedings/procsfiles/procabstracts_65.htm

The Whitehouse et al 2014 reference indicates the importance and the challenges of including the impacts of relative sea-level changes on dynamic ice sheet models:

70A0997
Evaluating the impact of relative sea-level change on ice-sheet dynamics
Pippa WHITEHOUSE, Glenn MILNE, Andreas VIELI
Corresponding author: Pippa Whitehouse
Corresponding author e-mail: pippa.whitehouse@durham.ac.uk

Abstract: "The water depth of the surrounding ocean is a key factor in determining the dynamics of a marine-based ice sheet. In this study we outline two key ways in which sea-level changes impact ice-sheet dynamics, and we highlight potential errors that can be made if sea-level changes are not consistently modelled in parallel with the evolution of a marine-based ice sheet. Changes in relative sea level, i.e. water depth, will influence grounding line dynamics, both in terms of the location of the grounding line and the flux of ice across the grounding line. We explore the implications of considering realistic, spatially variable relative sea-level changes – derived using a glacial isostatic adjustment (GIA) model – as opposed to uniform, or ‘eustatic’, sea-level changes when determining the likely configuration of two key Antarctic outlet glaciers during the LGM. In particular, we highlight the different sea-level change experienced by East and West Antarctica due to rotational feedback. Secondly, changes in water depth will determine which portions of the ice sheet are grounded or floating. In the context of a GIA model, this information is needed to determine the magnitude of the ice and ocean load changes that are applied to the solid Earth. We demonstrate that if the evolving topography is incorrectly defined, particularly across ice-shelf regions, errors on the order of 10 mm a–1 can be made when predicting present-day uplift rates due to past ice mass changes. The correct modelling of water depth change is also necessary to study the evolution of ice rises, whose presence will impact the stress regime of an ice shelf and hence the dynamics of the upstream ice sheet, and to determine former ice-sheet thicknesses via the interpretation of iceberg scours."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Hopefully, scientist can get their GCMs & RCMs to replicate the following paleo-evidence that the Southern Ocean can vent large amounts of  carbon dioxide back into the atmosphere during periods of global warming and of accelerating circumpolar Antarctic wind velocities (see the first post in this thread), discussed in the following linked reference:


Luke C. Skinner, Claire Waelbroeck, Adam E. Scrivner, and Stewart J. Fallon, (2014), "Radiocarbon evidence for alternating northern and southern sources of ventilation of the deep Atlantic carbon pool during the last deglaciation", PNAS, doi: 10.1073/pnas.1400668111, (March 31, 2014)



http://www.pnas.org/content/early/2014/03/27/1400668111.abstract

Significance: "This study sheds light on the mechanisms of deglacial atmospheric CO2 rise and, more specifically, on the hypothesized role of a “bipolar seesaw” in deep Atlantic ventilation. Comparing new high-resolution radiocarbon reconstructions from the Northeast Atlantic with existing data from the Southern Ocean, we show that a bipolar ventilation seesaw did indeed operate during the last deglaciation. Whereas today the deep Atlantic’s carbon pool is “flushed” from the north by North Atlantic Deep Water export, it was flushed instead from the south during Heinrich Stadial 1 and the Younger Dryas, in time with sustained atmospheric CO2 rise."


Abstract: "Recent theories for glacial–interglacial climate transitions call on millennial climate perturbations that purged the deep sea of sequestered carbon dioxide via a “bipolar ventilation seesaw.” However, the viability of this hypothesis has been contested, and robust evidence in its support is lacking. Here we present a record of North Atlantic deep-water radiocarbon ventilation, which we compare with similar data from the Southern Ocean. A striking coherence in ventilation changes is found, with extremely high ventilation ages prevailing across the deep Atlantic during the last glacial period. The data also reveal two reversals in the ventilation gradient between the deep North Atlantic and Southern Ocean during Heinrich Stadial 1 and the Younger Dryas. These coincided with periods of sustained atmospheric CO2 rise and appear to have been driven by enhanced ocean–atmosphere exchange, primarily in the Southern Ocean. These results confirm the operation of a bipolar ventilation seesaw during deglaciation and underline the contribution of abrupt regional climate anomalies to longer-term global climate transitions."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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The linked research on the paleo- absorption of CO2 by the Southern Ocean (considering the influence of sea ice), represents another challenge for RCM hind-casts to match and calibrate to before projection future responses to AGW:

Raffaele Ferrari, Malte F. Janse, Jess F. Adkins, Andrea Burke, Andrew L. Stewart, and Andrew F. Thompson,  (2014), "Antarctic sea ice control on ocean circulation in present and glacial climates", Proceedings of the National Academy of Sciences, doi: 10.1073/pnas.1323922111

http://www.pnas.org/content/early/2014/05/29/1323922111.abstract?sid=7f015fc3-4a3b-4d0a-8250-bfdce8fb1324


Abstract: "In the modern climate, the ocean below 2 km is mainly filled by waters sinking into the abyss around Antarctica and in the North Atlantic. Paleoproxies indicate that waters of North Atlantic origin were instead absent below 2 km at the Last Glacial Maximum, resulting in an expansion of the volume occupied by Antarctic origin waters. In this study we show that this rearrangement of deep water masses is dynamically linked to the expansion of summer sea ice around Antarctica. A simple theory further suggests that these deep waters only came to the surface under sea ice, which insulated them from atmospheric forcing, and were weakly mixed with overlying waters, thus being able to store carbon for long times. This unappreciated link between the expansion of sea ice and the appearance of a voluminous and insulated water mass may help quantify the ocean’s role in regulating atmospheric carbon dioxide on glacial–interglacial timescales. Previous studies pointed to many independent changes in ocean physics to account for the observed swings in atmospheric carbon dioxide. Here it is shown that many of these changes are dynamically linked and therefore must co-occur."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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As we are beginning to enter mid-Pliocene type conditions, I provide the following link to the Zhang et al (2013) research (with a free access pdf) providing clear evidence that as the westerly (circumpolar) winds move poleward (towards the South Pole) as they currently are doing (due to the ozone hole and GHG increases), that the Southern Ocean vented large quantities of CO₂ into the mid-Pliocene atmosphere, less than 3 million years ago.  Hopefully, currently researchers can use such data to calibrate their RCM models, to see whether the Southern Ocean will soon vent large amounts of CO2 into the our modern atmosphere:

Zhongshi Zhang, Kerim H. Nisancioglu & Ulysses S. Ninnemann, (2013), "Increased ventilation of Antarctic deep water during the warm mid-Pliocene", Nature Communications, Volume: 4, Article number: 1499, doi:10.1038/ncomms2521


http://www.nature.com/ncomms/journal/v4/n2/full/ncomms2521.html

Abstract: "The mid-Pliocene warm period is a recent warm geological period that shares similarities with predictions of future climate. It is generally held the mid-Pliocene Atlantic Meridional Overturning Circulation must have been stronger, to explain a weak Atlantic meridional δ13C gradient and large northern high-latitude warming. However, climate models do not simulate such stronger Atlantic Meridional Overturning Circulation, when forced with mid-Pliocene boundary conditions. Proxy reconstructions allow for an alternative scenario that the weak δ13C gradient can be explained by increased ventilation and reduced stratification in the Southern Ocean. Here this alternative scenario is supported by simulations with the Norwegian Earth System Model (NorESM-L), which simulate an intensified and slightly poleward shifted wind field off Antarctica, giving enhanced ventilation and reduced stratification in the Southern Ocean. Our findings challenge the prevailing theory and show how increased Southern Ocean ventilation can reconcile existing model-data discrepancies about Atlantic Meridional Overturning Circulation while explaining fundamental ocean features."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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The linked reference provides projections from a Global Circulation Model, GCM, that continued AGW will result in a rapid advection of warm ocean water exceeding 2 degrees C (up to 4 degrees C) into the 200-700m water depth (in the range of the bottom of the Antarctic ice shelves and adjoining grounding line) induced by weakened near-shore Ekman pumping, which is associated with weakened coastal currents.  While not unexpected, this is seriously bad news, and this indicates that the ASE glaciers may begin a rapid phase of collapse sooner, rather than latter:

Spence, P, S. Griffies, M. England, A. Hogg, O. Saenko, N. Jourdain, (2014), "Rapid subsurface warming and circulation changes of Antarctic coastal waters by poleward shifting winds", GRL; DOI: 10.1002/2014GL060613

http://onlinelibrary.wiley.com/doi/10.1002/2014GL060613/abstract

Abstract: "The southern hemisphere westerly winds have been strengthening and shifting poleward since the 1950s. This wind trend is projected to persist under continued anthropogenic forcing, but the impact of the changing winds on Antarctic coastal heat distribution remains poorly understood. Here we show that a poleward wind shift at the latitudes of the Antarctic Peninsula can produce an intense warming of subsurface coastal waters that exceeds 2 °C at 200-700 m depth. The model simulated warming results from a rapid advective heat flux induced by weakened near-shore Ekman pumping, and is associated with weakened coastal currents. This analysis shows that anthropogenically induced wind changes can dramatically increase the temperature of ocean water at ice sheet grounding lines and at the base of floating ice shelves around Antarctica, with potentially significant ramifications for global sea level rise."

See also:

https://www.climatescience.org.au/content/751-changing-antarctic-winds-create-new-sea-level-threat

See also:

http://www.sciencecodex.com/changing_antarctic_winds_create_new_sea_level_threat-136994

Extract: "Changes to Antarctic winds have already been linked to southern Australia's drying climate but now it appears they may also have a profound impact on warming ocean temperatures under the ice shelves along the coastline of West and East Antarctic.
"When we included projected Antarctic wind shifts in a detailed global ocean model, we found water up to 4°C warmer than current temperatures rose up to meet the base of the Antarctic ice shelves," said lead author Dr Paul Spence from the ARC Centre of Excellence for Climate System Science (ARCCSS).
"The sub-surface warming revealed in this research is on average twice as large as previously estimated with almost all of coastal Antarctica affected. This relatively warm water provides a huge reservoir of melt potential right near the grounding lines of ice shelves around Antarctica. It could lead to a massive increase in the rate of ice sheet melt, with direct consequences for global sea level rise.""

See also:

http://www.laboratoryequipment.com/news/2014/07/changing-antarctic-winds-are-threat-sea-level
« Last Edit: July 07, 2014, 08:11:35 PM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #78 on: November 02, 2014, 02:14:28 AM »
The following linked reference, and associated extracts, indicates that a new DoE (see also Replies #11, 12 & 13 regarding prior efforts from DoE labs) state-of-the-art Earth Systems Model, ESM, named Accelerated Climate Modeling for Energy (ACME), will include extensive sub-routines focused on the Antarctic Ice Sheet, AIS, (as well as the Greenland Ice Sheet, GIS) and possible abrupt SLR:

Bader D, W Collins, R Jacob, P Jones, P Rasch, M Taylor, P Thornton, and D Williams. "Accelerated Climate Modeling for Energy (ACME) Project Strategy and Initial Implementation Plan." 2014

http://climatemodeling.science.energy.gov/sites/default/files/publications/acme-project-strategy-plan_0.pdf

Extract: "2.2.1.3 Cryosphere System
Could a dynamical instability in the Antarctic Ice Sheet be triggered within the next 40 years?

The objective is to examine the near-term risk of initiating the dynamic instability and onset of the collapse of the Antarctic Ice Sheet due to rapid melting by warming waters adjacent to the ice-sheet grounding lines. The experiment would be the first fully coupled global simulation to include dynamic ice shelf–ocean interactions for addressing the potential instability associated with grounding line dynamics in marine ice sheets around Antarctica. It will utilize several significant advances in the new ACME model, including the ability to enhance spatial resolution in both the ice sheet and ocean model to resolve grounding-line processes while still maintaining global extent in a coupled system and throughput for decadal simulations. The simulation will include an eddy-resolving Southern Ocean as well to better represent Circumpolar Deep Water (CDW) and dynamics associated with bringing this water onto the continental shelf under the ice sheet. Including the sea-ice model captures the process of buttressing at the ice shelf–sea-ice boundary. Finally, a fully coupled system is able to simulate changes in atmospheric forcing (e.g., poleward displacement of jets) that could influence the behavior of the Southern Ocean and sea ice.
The specific experiment will be a fully coupled simulation from 1970–2050 to explore whether rapid ice-sheet instability is triggered in this time frame. An ensemble would be desirable to address the likelihood of such an event, though this is not likely to be affordable in our configuration in this timeframe. The model configuration for this experiment will be a modified version of the standard high-resolution ACME configuration described below. The base configuration includes the atmosphere/land on a 0.25° cubed-sphere grid using the ACME-modified CAM5-SE atmosphere model. The subgrid orography modifications will be needed to resolve Antarctic surface mass balance at the ice-sheet margins. The ocean component will be MPAS-O on a Spherical Centroidal Voronoi Tesselations (SCVT) mesh with 15-km grid spacing at the equator, decreasing to 5 km in the Southern Ocean region. The default mesh will be extended southward to include critical Antarctic embayments and the resolution in these regions will be further enhanced if affordable. The vertical grid will be a hybrid coordinate with 100 vertical levels. The sea-ice component will be MPAS-CICE on the same ocean grid. Finally, we will add an Antarctic Ice Sheet model with resolution of 0.5–1 km near likely grounding-line locations and coarser resolution (~10 km) throughout the interior. For initial conditions, we will follow a similar spin-up procedure as with previous high-resolution simulations, with an ocean/ice state from an ocean/ice reanalysis-forced spin-up. For the ice sheet, an optimized initial condition should be available from the PISCEES project.
This first-of-its-kind coupled simulation will be focused largely on the ocean–ice shelf feedbacks and potential for dynamical instability and rapid SLR. It represents a first step toward a comprehensive SLR and impacts capability needed by the DOE to assess threats to coastal facilities. As work proceeds toward the more comprehensive experiments planned in the 10-year timeframe, we will be incrementally adding additional features. For example, work will begin under this project to develop an initial implementation of icebergs and primitive calving laws to capture the transport and distribution of ice and other material as the ice sheets flow into the ocean. Work also continues (as part of related projects) on a Greenland Ice Sheet model so that we can capture SLR contributions from both major ice sheets. We will also begin to include isostasy and ice-sheet self-gravity that can have a first-order effect on the regional SLR signature around the coastal U.S. We anticipate all of these effects to be included in a following ACME version. Further releases will begin to include wave models, further focusing of resolution in coastal and storm-track regions, and other capabilities needed to further refine SLR impact at regional scales.

2.2.2.3 Cryosphere System
How will regional variations in sea level rise interact with more extreme storms to enhance the coastal impacts of SLR?
The aim of this simulation is to determine the potential impacts on the nation’s coastal zones due to SLR exacerbated by regional variations in SLR and extreme storm surges. The novel aspects of this simulation are:
1. Fully coupled models of the cryosphere, including both major land ice sheets, the floating ice shelves surrounding Antarctica, the interactions with surrounding sea ice, and icebergs calved from Antarctica and Greenland
2. Complete treatments of the impacts of time-evolving isostasy and ice-sheet self-gravity on SLR
3. Addition of wave models to the ocean component
4. Deployment of enhanced resolution in all components to resolve dynamics at ice-sheet margins, sea-ice behavior, and the effects of severe weather on sea state in the major storm tracks

This experiment is based upon DOE’s advances in dynamic and adaptive ice-sheet modeling combined with the capacity for ultrahigh resolution of the land ice sheets and surrounding oceans using upcoming advances toward extreme-scale computing.

4.4 Ice Sheets
The ice-sheet model brings in a new set of interactions that must be understood and monitored for development or reduction of biases. The state of the atmosphere is essential to the surface mass balance, which in turn must be compared against other mass loss terms (iceberg calving, submarine melting). Along with monitoring of changes in grounded ice area and volume and these related mass balance terms, some of which may prove useful as metrics in a coupled context, a research problem we intend to take on is the development of Circumpolar Deep Water (CDW) metrics. Where waters are all near freezing, the relatively warm CDW, often found below colder and fresher waters, has a strong potential to accelerate submarine melting and therefore to strongly impact the overall mass balance of the Antarctic Ice Sheet. Stronger winds can drive greater upwelling and bring these warm waters in contact with the ice shelf. Research to understand the controls on CDW state and variability will be undertaken, facilitating the establishment of metrics focused on CDW mean state and variability, ensuring that transitions to or from rapid submarine melt states are not modeling artifacts but are robust and well understood. This effort will be critical for successfully answering the cryospheric driving question."

See also:
http://www.forbes.com/sites/jamesconca/2014/10/13/the-great-climate-model/

Extract: "We need a Great Climate Model.

The national laboratories of the Department of Energy are working on just such a model. Teamed with the National Center for Atmospheric Research, four academic institutions and one private company to form the Accelerated Climate Modeling for Energy, or ACME project, the national labs will help develop the most complete, fully coupled, state-of-the-science Earth system model to date.

Pacific Northwest National Laboratory (PNNL), Argonne, Brookhaven, Lawrence Berkeley, Lawrence Livermore, Los Alamos, Oak Ridge and Sandia will conduct simulations and modeling on the highest performance computing systems in the world. That includes over a hundred petaflop machines and the soon-to-be-operational exascale supercomputers."

&

http://www.scientificcomputing.com/news/2014/09/developing-most-advanced-earth-system-computer-model-yet-created

Extract: "LOS ALAMOS, NM — With President Obama announcing climate-support initiatives at the 2014 United Nations Climate Summit, the U.S. Department of Energy national laboratories are teaming with academia and the private sector to develop the most advanced climate and Earth system computer model yet created. For Los Alamos National Laboratory researchers, it is a welcome advance for an already vibrant high-performance computing community.
Accelerated Climate Modeling for Energy, or ACME, is designed to accelerate the development and application of fully coupled, state-of-the-science Earth system models for scientific and energy applications."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

steve s

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Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #79 on: November 02, 2014, 07:47:56 AM »
The effort is so hopeful, and if it could be pulled off it would very useful. Seems like a difficult or even impossible model to debug, though. If debugged, an incredibly difficult model to fit with accurate parameters. Many statistical difficulties would have to be ignored, any of which could throw off results.

I hope that it points the way to better back-of-the-napkin thinking by showing critical bottlenecks.   

(I'm not picking on this effort, for it is impossible to test the computational validity/accuracy of large complex computer solutions under the theoretically simplest scenarios -- and this is not simple.)

AbruptSLR

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Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #80 on: November 10, 2014, 11:14:44 PM »
The following reference shows a large-scale climate response to a retreat of the WAIS, including associated feedbacks in the oceanic and atmospheric circulation patterns:

F. Justino, A. S. Silva, M. P. Pereira, F. Stordal, D. Lindemann and F. Kucharski, (2014), "The large-scale climate in response to the retreat of the West Antarctic Ice Sheet", Journal of Climate; doi: http://dx.doi.org/10.1175/JCLI-D-14-00284.1

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-14-00284.1

Abstract: "Based upon coupled climate simulations driven by present day and conditions resembling the Marine Isotope Stage 31 (WICE-EXP), insofar the West Antarctic Ice Sheet (WAIS) configuration is concerned, we demonstrate that changes in the WAIS orography lead to noticiable changes in the oceanic and atmospheric circulations. Compared with the present day climate, the WICE-EXP is characterized by warmer conditions in the Southern Hemisphere (SH) by up to 5°C in the polar oceans and up to 2°C in the Northern Hemisphere (NH). These changes feed back on the atmospheric circulation weakening (strengthening) the extratropical westerlies in the SH (northern Atlantic). Calculations of the Southern Annular Mode (SAM) show that modification of the WAIS induces warmer conditions and a northward shift of the westerly flow, in particular there is a clear weakening of the polar jet. These changes lead to modification of the rate of deep water formation reducing the magnitude of the North Atlantic Deep Water, but enhancing the Antarctic Bottom Water. By evaluating the density flux we have found that the thermal density flux has played a main role in the modification of the meridional overturning circulation. Moreover, the climate anomalies between the WICE-EXP and the present day simulations resemble a bipolar seesaw pattern. These results are in good agreement with paleorecontructions in the framework of the Ocean Drilling and ANDRILL Programs."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #81 on: November 17, 2014, 11:38:07 PM »
The linked reference (with an open access pdf) indicates that two coupled climate models show that in response to an ozone depletion the Southern Ocean responded with two processes for sea ice extent change.  The first process based on a northward Ekman drift occurred relatively quickly and served to expand Antarctic sea ice extent about three decades ago.  The second process acted relatively more slowly (years to decades), results in a warming trend for the Southern Ocean leading to a reduction in projected sea ice extent (see attached figure).  Based on these findings we can expect Antarctic amplification to begin accelerating in the next decade or so.

David Ferreira, John Marshall, Cecilia M. Bitz, Susan Solomon, and Alan Plumb, (2014) "Antarctic ocean and sea ice response to ozone depletion: a two timescale problem", Journal of Climate, In press.

http://www.met.rdg.ac.uk/~gf905417/Publications_files/Twotimescale_final.pdf


Abstract: "The response of the Southern Ocean to a repeating seasonal cycle of ozone loss is studied in two coupled climate models and found to comprise both fast and slow processes. The fast response is similar to the inter-annual signature of the Southern Annular Mode (SAM) on Sea Surface Temperature (SST), on to which the ozone-hole forcing projects in the summer. It comprises enhanced northward Ekman drift inducing negative summertime SST anomalies around Antarctica, earlier sea ice freeze-up the following winter, and northward expansion of the sea ice edge year-round. The enhanced northward Ekman drift, however, results in upwelling of warm waters from below the mixed layer in the region of seasonal sea ice. With sustained bursts of westerly winds induced by ozone-hole depletion, this warming from below eventually dominates over the cooling from anomalous Ekman drift. The resulting slow-timescale response (years to decades) leads to warming of SSTs around Antarctica and ultimately a reduction in sea-ice cover year-round. This two-timescale behavior – rapid cooling followed by slow but persistent warming - is found in the two coupled models analysed, one with an idealized geometry, the other a complex global climate model with realistic geometry. Processes that control the timescale of the transition from cooling to warming, and their uncertainties are described. Finally we discuss the implications of our results for rationalizing previous studies of the effect of the ozone-hole on SST and sea-ice extent."

“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

sidd

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Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #82 on: November 18, 2014, 01:02:05 AM »
That Ferreira paper is interesting. Forcing that analysis with the observed freshening signal in the southern ocean might actually yield good regional level results.

AbruptSLR

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Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #83 on: January 19, 2015, 08:11:26 PM »
The linked research indicates that thermodynamics (warming and near-surface stability) control 21st century Southern Ocean shortwave climate feedbacks.  Besides illustrating how challenging it is to correctly model the Antarctic region, this research indicates to me that if the telecommunication of Pacific Tropical energy to the WAIS occurs (as many models project), then the West Antarctic could be subject to more positive feedback (warming) in the 21st century than previous assumed in the AR5 models.

Kay, J. E., B. Medeiros, Y.-T. Hwang, A. Gettelman, J. Perket, and M. G. Flanner (2014), Processes controlling Southern Ocean shortwave climate feedbacks in CESM, Geophys. Res. Lett., 41, 616–622, doi:10.1002/2013GL058315.

http://onlinelibrary.wiley.com/doi/10.1002/2013GL058315/abstract

Abstract: "A climate model (Community Earth System Model with the Community Atmosphere Model version 5 (CESM-CAM5)) is used to identify processes controlling Southern Ocean (30–70°S) absorbed shortwave radiation (ASR). In response to 21st century Representative Concentration Pathway 8.5 forcing, both sea ice loss (2.6 W m−2) and cloud changes (1.2 W m−2) enhance ASR, but their relative importance depends on location and season. Poleward of ~55°S, surface albedo reductions and increased cloud liquid water content (LWC) have competing effects on ASR changes. Equatorward of ~55°S, decreased LWC enhances ASR. The 21st century cloud LWC changes result from warming and near-surface stability changes but appear unrelated to a small (1°) poleward shift in the eddy-driven jet. In fact, the 21st century ASR changes are 5 times greater than ASR changes resulting from large (5°) naturally occurring jet latitude variability. More broadly, these results suggest that thermodynamics (warming and near-surface stability), not poleward jet shifts, control 21st century Southern Ocean shortwave climate feedbacks."

Also see:
http://cires.colorado.edu/science/groups/kay/Publications/
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #84 on: January 21, 2015, 01:38:37 AM »
The linked reference indicates that improved modeling of external freshwater flux (from ice melting) significantly improved the accuracy of the Earth System Models of the High-Latitude Southern Ocean region:

Achim Stössel, Dirk Notz, F. Alexander Haumann, Helmuth Haak, Johann Jungclaus & Uwe Mikolajewicz, (2015), "Controlling high-latitude Southern Ocean convection in climate models", Ocean Modelling, Volume 86, February 2015, Pages 58–75, doi:10.1016/j.ocemod.2014.11.008


http://www.sciencedirect.com/science/article/pii/S1463500314001760


Abstract: "Earth System Models (ESMs) generally suffer from a poor simulation of the High-Latitude Southern Ocean (HLSO). Here we aim at a better understanding of the shortcomings by investigating the sensitivity of the HLSO to the external freshwater flux and the horizontal resolution in forced and coupled simulations with the Max-Planck-Institute Ocean Model (MPIOM). Forced experiments reveal an immediate reduction of open-ocean convection with additional freshwater input. The latter leads to a remarkably realistic simulation of the distinct water-mass structure in the central Weddell Sea featuring a temperature maximum of +0.5 °C at 250 m depth. Similar, but more modest improvements occur over a time span of 40 years after switching from a forced to a coupled simulation with an eddy-resolving version of MPIOM. The switch is accompanied with pronounced changes of the external freshwater flux and the wind field, as well as a more realistic heat flux due to coupling. Similar to the forced freshwater-flux experiments, a heat reservoir develops at depth, which in turn decreases the vertically integrated density of the HLSO and reduces the Antarctic Circumpolar Current to rather realistic values. Coupling with a higher resolution version of the atmosphere model (ECHAM6) yields distinct improvements of the HLSO water-mass structure and sea-ice cover. While the coupled simulations reveal a realistic amount of Antarctic runoff, its distribution appears too concentrated along the coast. Spreading the runoff over a wider region, as suggested in earlier studies to mimic the effect of freshwater transport through icebergs, also leads to noticeable improvements of the HLSO water-mass properties, predominantly along the coast. This suggests that the spread of the runoff improves the representation of Antarctic Bottom Water formation through enhanced near-boundary convection rather than weakened open-ocean convection."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #85 on: January 22, 2015, 04:32:56 PM »
The authors of the linked reference about atmospheric river events in Antarctica found that:

(a) The nine atmospheric rivers that hit East Antarctica between 2009 and 2011 accounted for 80 per cent of the exceptional snow accumulation at Princess Elisabeth station; and
(b) "The unusually high snow accumulation in Dronning Maud Land in 2009 that we attributed to atmospheric rivers added around 200 gigatons of mass to Antarctica, which alone offset 15 per cent of the recent 20-year ice sheet mass loss," see the attach image and associated caption below.

I would like to point-out:
 
(a) First, that atmospheric river events have been historically rare and to have nine such events hit Dronning Maud Land between 2009 and 2011 indicates that extreme weather is becoming more common in the Southern Ocean; and
(b) Second, as global warming continues future atmospheric events may more frequenctly drop rain instead of snow on Antarctica; which would be a positive feedback for ice mass loss & SLR:

Also, I would like to point-out that modeling such future atmospheric river events represents a significant challenge for regional modelers to get right:

Gorodetskaya, I. V., M. Tsukernik, K. Claes, M. F. Ralph, W. D. Neff, and N. P. M. Van Lipzig, (2014), "The role of atmospheric rivers in anomalous snow accumulation in East Antarctica", Geophys. Res. Lett., 41, 6199–6206, doi:10.1002/2014GL060881.


http://onlinelibrary.wiley.com/doi/10.1002/2014GL060881/abstract

Abstract: "Recent, heavy snow accumulation events over Dronning Maud Land (DML), East Antarctica, contributed significantly to the Antarctic ice sheet surface mass balance (SMB). Here we combine in situ accumulation measurements and radar-derived snowfall rates from Princess Elisabeth station (PE), located in the DML escarpment zone, along with the European Centre for Medium-range Weather Forecasts Interim reanalysis to investigate moisture transport patterns responsible for these events. In particular, two high-accumulation events in May 2009 and February 2011 showed an atmospheric river (AR) signature with enhanced integrated water vapor (IWV), concentrated in narrow long bands stretching from subtropical latitudes to the East Antarctic coast. Adapting IWV-based AR threshold criteria for Antarctica (by accounting for the much colder and drier environment), we find that it was four and five ARs reaching the coastal DML that contributed 74–80% of the outstanding SMB during 2009 and 2011 at PE. Therefore, accounting for ARs is crucial for understanding East Antarctic SMB."

Caption: "A meteorological image of an atmospheric river slamming into the East Antarctic coast on 15 February 2011. L indicates the atmospheric river's low-pressure trough and H indicates the blocking high-pressure ridge further downstream, directing moisture transport (red arrows) into the Dronning Maud Land and the Princess Elisabeth base (white square). The colours show total moisture amounts (in centimetres equivalent of water). Credit: Irina Gorodetskaya"


See also:
http://www.spacedaily.com/reports/Giant_atmospheric_rivers_add_mass_to_Antarcticas_ice_sheet_999.html

http://phys.org/news/2015-01-giant-atmospheric-rivers-mass-antarctica.html
« Last Edit: January 22, 2015, 04:51:40 PM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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The linked reference (with an open access pdf) shows how basal ice-shelf channels in Antarctic ice shelves imprint the ice flowfield with enhanced horizontal shearing across the channels.  This presents the possibility of identifying and classifying such channels from satellite observations; which would be an important step in incorporating the effects of these channels in ice-ocean models for Antarctic ice shelves.

Drews, R. (2015), "Evolution of ice-shelf channels in Antarctic ice shelves", The Cryosphere Discuss., 9, 1603-1631, doi:10.5194/tcd-9-1603-2015

http://www.the-cryosphere-discuss.net/9/1603/2015/tcd-9-1603-2015.html

Abstract: "Ice shelves buttress the continental ice flux and mediate ice–ocean interactions. They are often traversed by channels in which basal melting is enhanced, impacting ice-shelf stability. Here, channel evolution is investigated using a transient, three-dimensional full Stokes model and geophysical data collected on Roi Baudouin Ice Shelf (RBIS), Antarctica. The modeling confirms basal melting as a feasible mechanism for channel creation, although channels may also advect without melting for many tens of kilometers. Channels can be out of hydrostatic equilibrium depending on their width and the upstream melt history. Inverting surface elevation for ice thickness in those areas is erroneous and corresponding observational evidence is presented at RBIS by comparing the hydrostatically inverted ice thickness with radar measurements. The model shows that channelized melting imprints the flowfield characteristically, which can result in enhanced horizontal shearing across channels. This is exemplified for a channel at RBIS using observed surface velocities and opens up the possibility to classify channelized melting from space, an important step towards incorporating these effects in ice–ocean models."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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If you click on the pdf links before the end of March 2015 you can down load pdfs of all of these 2014 Phil. Trans. papers on the Southern Ocean.

Andrew J. Watson, Michael P. Meredith, John Marshall (2014), "The Southern Ocean, carbon and climate", Phil Trans R Soc A., 372 2019 20130057; doi: 10.1098/rsta.2013.0057

http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130057.full.pdf


Marshall J, Armour KC, Scott, JR, Kostov Y, Hausmann U, Ferreira D, Shepherd, TG, Bitz CM. (2014) "The ocean’s role in polar climate change: asymmetric Arctic and Antarctic responses to greenhouse gas and ozone forcing". Phil. Trans. R. Soc. A 372: 20130040. http://dx.doi.org/10.1098/rsta.2013.0040

http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130040.full.pdf

Meijers AJS. (2014), "The Southern Ocean in the Coupled Model Intercomparison Project phase 5". Phil. Trans. R. Soc. A 372: 20130296. http://dx.doi.org/10.1098/rsta.2013.0296

http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130296.full.pdf

http://rsta.royalsocietypublishing.org/content/372/2019/20130296


Heywood KJ et al. (2014) "Ocean processes at the Antarctic continental slope". Phil. Trans. R. Soc. A 372: 20130047. http://dx.doi.org/10.1098/rsta.2013.0047

http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130047.full.pdf

http://rsta.royalsocietypublishing.org/content/372/2019/20130047



Gille ST. (2014) "Meridional displacement of the Antarctic Circumpolar Current". Phil. Trans. R. Soc. A 372: 20130273.
http://dx.doi.org/10.1098/rsta.2013.0273

http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130273.full.pdf

http://rsta.royalsocietypublishing.org/content/372/2019/20130273

Meredith MP, Jullion L, Brown PJ, Naveira Garabato AC, Couldrey MP. (2014), "Dense waters of theWeddell and Scotia Seas: recent changes in properties and circulation". Phil. Trans. R. Soc. A 372: 20130041. http://dx.doi.org/10.1098/rsta.2013.0041

http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130041.full.pdf

http://rsta.royalsocietypublishing.org/content/372/2019/20130041

Abstract: " The densest waters in the Atlantic overturning circulation are sourced at the periphery of Antarctica, especially the Weddell Sea, and flow northward via routes that involve crossing the complex bathymetry of the Scotia Arc. Recent observations of significant warming of these waters along much of the length of the Atlantic have highlighted the need to identify and understand the time-varying formation and export processes, and the controls on their properties and flows. Here, we review recent developments in understanding of the processes that control the changing flux of water through the main export route from the Weddell Sea into the Scotia Sea, and the transformations of the waters within the Scotia Sea and environs. We also present a synopsis of recent findings that relate to the climatic change of dense water properties within the Weddell Sea itself, in the context of known Atlantic-scale changes. Among the most significant findings are the discovery that the warming of waters exported from the Weddell Sea has been accompanied by a significant freshening, and that the episodic nature of the overflow into the Scotia Sea is markedly wind-controlled and can lead to significantly enhanced abyssal stratification. Key areas for focusing future research effort are outlined."

Brown PJ, Meredith MP, Jullion L, Naveira Garabato A, Torres-Valdés S, Holland P, Leng MJ, Venables H. 2014 Freshwater fluxes in theWeddell Gyre: results from δ18O. Phil. Trans. R. Soc. A 372: 20130298. http://dx.doi.org/10.1098/rsta.2013.0298

http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130298.full.pdf

http://rsta.royalsocietypublishing.org/content/372/2019/20130298

Abstract: "Full-depth measurements of δ18O from 2008 to 2010 enclosing the Weddell Gyre in the Southern Ocean are used to investigate the regional freshwater budget. Using complementary salinity, nutrients and oxygen data, a four-component mass balance was applied to quantify the relative contributions of meteoric water (precipitation/glacial input), sea-ice melt and saline (oceanic) sources. Combination of freshwater fractions with velocity fields derived from a box inverse analysis enabled the estimation of gyre-scale budgets of both freshwater types, with deep water exports found to dominate the budget. Surface net sea-ice melt and meteoric contributions reach 1.8% and 3.2%, respectively, influenced by the summer sampling period, and −1.7% and +1.7% at depth, indicative of a dominance of sea-ice production over melt and a sizable contribution of shelf waters to deep water mass formation. A net meteoric water export of approximately 37 mSv is determined, commensurate with local estimates of ice sheet outflow and precipitation, and the Weddell Gyre is estimated to be a region of net sea-ice production. These results constitute the first synoptic benchmarking of sea-ice and meteoric exports from the Weddell Gyre, against which future change associated with an accelerating hydrological cycle, ocean climate change and evolving Antarctic glacial mass balance can be determined."

Hogg AMcC, Munday DR. (2014), "Does the sensitivity of Southern Ocean circulation depend upon bathymetric details?", Phil. Trans. R. Soc. A 372: 20130050. http://dx.doi.org/10.1098/rsta.2013.0050

http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130050.full.pdf

http://rsta.royalsocietypublishing.org/content/372/2019/20130050

Abstract: "The response of the major ocean currents to changes in wind stress forcing is investigated with a series of idealized, but eddy-permitting, model simulations. Previously, ostensibly similar models have shown considerable variation in the oceanic response to changing wind stress forcing. Here, it is shown that a major reason for these differences in model sensitivity is subtle modification of the idealized bathymetry. The key bathymetric parameter is the extent to which the strong eddy field generated in the circumpolar current can interact with the bottom water formation process. The addition of an embayment, which insulates bottom water formation from meridional eddy fluxes, acts to stabilize the deep ocean density and enhances the sensitivity of the circumpolar current. The degree of interaction between Southern Ocean eddies and Antarctic shelf processes may thereby control the sensitivity of the Southern Ocean to change."

Waugh DW (2014), "Changes in the ventilation of the southern oceans", Phil. Trans. R. Soc. A 372, 20130269. DOI: 10.1098/rsta.2013.0269

http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130269.full.pdf

http://rsta.royalsocietypublishing.org/content/372/2019/20130269

Abstract: "Changes in the ventilation of the southern oceans over the past few decades are examined using ocean measurements of CFC-12 and model simulations. Analysis of CFC-12 measurements made between the late 1980s and late 2000s reveal large-scale coherent changes in the ventilation, with a decrease in the age of subtropical Subantarctic Mode Waters (SAMW) and an increase in the age of Circumpolar Deep Waters. The decrease in SAMW age is consistent with the observed increase in wind stress curl and strength of the subtropical gyres over the same period. A decrease in the age of SAMW is also found in Community Climate System Model version 4 perturbation experiments where the zonal wind stress is increased. This decrease is due to both more rapid transport along isopycnals and the movement of the isopycnals. These results indicate that the intensification of surface winds in the Southern Hemisphere has caused large-scale coherent changes in the ventilation of the southern oceans."


van Heuven SMAC, Hoppema M, Jones EM, de Baar HJW. (2014), "Rapid invasion of anthropogenic CO2 into the deep circulation of the Weddell Gyre". Phil. Trans. R. Soc. A 372: 20130056. http://dx.doi.org/10.1098/rsta.2013.0056

http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130056.full.pdf

http://rsta.royalsocietypublishing.org/content/372/2019/20130056

Abstract: "Data are presented for total carbon dioxide (TCO2), oxygen and nutrients from 14 cruises covering two repeat sections across the Weddell Gyre, from 1973 to 2010. Assessments of the rate of increase in anthropogenic CO2 (Cant) are made at three locations. Along the Prime Meridian, TCO2 is observed to steadily increase in the bottom water. Accompanying changes in silicate, nitrate and oxygen confirm the non-steady state of the Weddell circulation. The rate of increase in TCO2 of +0.12±0.05 μmol kg−1 yr−1 therefore poses an upper limit to the rate of increase in Cant. By contrast, the bottom water located in the central Weddell Sea exhibits no significant increase in TCO2, suggesting that this water is less well ventilated at the southern margins of the Weddell Sea. At the tip of the Antarctic Peninsula (i.e. the formation region of the bottom water found at the Prime Meridian), the high rate of increase in TCO2 over time observed at the lowest temperatures suggests that nearly full equilibration occurs with the anthropogenic CO2 of the atmosphere. This observation constitutes rare evidence for the possibility that ice cover is not a major impediment for uptake of Cant in this prominent deep water formation region."


Majkut JD, Carter BR, Frölicher TL, Dufour CO, Rodgers KB, Sarmiento JL. (2014), "An observing system simulation for Southern Ocean carbon dioxide uptake". Phil. Trans. R. Soc. A 372: 20130046. http://dx.doi.org/10.1098/rsta.2013.0046

http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130046.full.pdf

http://rsta.royalsocietypublishing.org/content/roypta/372/2019/20130046.full.pdf

Abstract: "The Southern Ocean is critically important to the oceanic uptake of anthropogenic CO2. Up to half of the excess CO2 currently in the ocean entered through the Southern Ocean. That uptake helps to maintain the global carbon balance and buffers transient climate change from fossil fuel emissions. However, the future evolution of the uptake is uncertain, because our understanding of the dynamics that govern the Southern Ocean CO2 uptake is incomplete. Sparse observations and incomplete model formulations limit our ability to constrain the monthly and annual uptake, interannual variability and long-term trends. Float-based sampling of ocean biogeochemistry provides an opportunity for transforming our understanding of the Southern Ocean CO2 flux. In this work, we review current estimates of the CO2 uptake in the Southern Ocean and projections of its response to climate change. We then show, via an observational system simulation experiment, that float-based sampling provides a significant opportunity for measuring the mean fluxes and monitoring the mean uptake over decadal scales."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

jai mitchell

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The following link leads to a nice summary (from October 2013) of the ARGO findings through the end of 2012:

http://ceres.larc.nasa.gov/documents/STM/2013-10/14_Global_averages.pdf

As indicated in the attached figure, one key finding is that all of the ocean heat gain in the ARGO era has been in the Southern Hemisphere (which indicates that all of the steric SLR in in the ARGO era has been in the Southern Hemisphere).  This provides additional support to my position that when the current EL Nino hiatus period ends, there is an excess of heat in the Southern Ocean that can accelerate ice mass loss from Antarctica once the local winds/current shift sufficiently to increase the ocean interaction with the grounded ice.


This seems to confirm to me my suspicion re: NH aerosol loading and the implications of Durack et. al (2014)  back of the napkin calculation lends itself to .5-.7 watts per meter squared negative aerosol loading in the northern hemisphere, though this feels low to me.

ahh yes, that would be the average value from 2007. . .ok that makes sense.
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AbruptSLR

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As one of the three stated goals that ACME focuses on is improved projections for the cryosphere, I decided to post the following references funded by the ACME program here:


Storer, R. L., Griffin, B. M., Höft, J., Weber, J. K., Raut, E., Larson, V. E., Wang, M., and Rasch, P. J. (2015), "Parameterizing deep convection using the assumed probability density function method", Geosci. Model Dev., 8, 1-19, doi:10.5194/gmd-8-1-2015


http://www.geosci-model-dev.net/8/1/2015/gmd-8-1-2015.html


Abstract: "Due to their coarse horizontal resolution, present day climate models must parameterize deep convection. This paper presents single-column simulations of deep convection using a probability density function (PDF) parameterization. The PDF parameterization predicts the PDF of subgrid variability of turbulence, clouds, and hydrometeors. That variability is interfaced to a prognostic microphysics scheme using a Monte Carlo sampling method.
The PDF parameterization is used to simulate tropical deep convection, the transition from shallow to deep convection over land, and midlatitude deep convection. These parameterized single-column simulations are compared with 3-D reference simulations. The agreement is satisfactory except when the convective forcing is weak.

The same PDF parameterization is also used to simulate shallow cumulus and stratocumulus layers. The PDF method is sufficiently general to adequately simulate these five deep, shallow, and stratiform cloud cases with a single equation set. This raises hopes that it may be possible in the future, with further refinements at coarse time step and grid spacing, to parameterize all cloud types in a large-scale model in a unified way."

Le Page Y, Morton D, Bond-Lamberty B, J Pereira MC, Hurtt G. (2015), "HESFIRE: A Global Fire Model to Explore the Role of Anthropogenic and Weather Drivers", Biogeosciences;12:887-903, doi:10.5194/bg-12-887-2015


http://www.biogeosciences.net/12/887/2015/bg-12-887-2015.html


Abstract. Vegetation fires are a major driver of ecosystem dynamics and greenhouse gas emissions. Anticipating potential changes in fire activity and their impacts relies first on a realistic model of fire activity (e.g., fire incidence and interannual variability) and second on a model accounting for fire impacts (e.g., mortality and emissions). In this paper, we focus on our understanding of fire activity and describe a new fire model, HESFIRE (Human–Earth System FIRE), which integrates the influence of weather, vegetation characteristics, and human activities on fires in a stand-alone framework. It was developed with a particular emphasis on allowing fires to spread over consecutive days given their major contribution to burned areas in many ecosystems. A subset of the model parameters was calibrated through an optimization procedure using observation data to enhance our knowledge of regional drivers of fire activity and improve the performance of the model on a global scale. Modeled fire activity showed reasonable agreement with observations of burned area, fire seasonality, and interannual variability in many regions, including for spatial and temporal domains not included in the optimization procedure. Significant discrepancies are investigated, most notably regarding fires in boreal regions and in xeric ecosystems and also fire size distribution. The sensitivity of fire activity to model parameters is analyzed to explore the dominance of specific drivers across regions and ecosystems. The characteristics of HESFIRE and the outcome of its evaluation provide insights into the influence of anthropogenic activities and weather, and their interactions, on fire activity.


See also:
http://news.sciencemag.org/climate/2014/12/new-u-s-climate-model-project-getting-cautious-praise
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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The linked website contains numerous presentations related to Earth Systems Modeling from a May 2014 meeting associated with the ACME program:

http://climatemodeling.science.energy.gov/presentations/2014
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Oceanic gravity wave can have a significant impact on the rate of calving from ice shelves (which is important to the stability of Antarctic marine glaciers), and the linked reference provide new insights into efforts to improve the accuracy of climate models (including ACME) projecting the changes in gravity waves with continued warming:

Liu, H.-L., J. M. McInerney, S. Santos, P. H. Lauritzen, M. A. Taylor, and N. M. Pedatella (2014), "Gravity waves simulated by high-resolution Whole Atmosphere Community Climate Model", Geophys. Res. Lett., 41, 9106–9112, doi:10.1002/2014GL062468.

http://onlinelibrary.wiley.com/enhanced/doi/10.1002/2014GL062468/

Abstract: "For the first time a mesoscale-resolving whole atmosphere general circulation model has been developed, using the National Center for Atmospheric Research Whole Atmosphere Community Climate Model with ∼0.25° horizontal resolution and 0.1 scale height vertical resolution above the middle stratosphere (higher resolution below). This is made possible by the high accuracy and high scalability of the spectral element dynamical core from the High-Order Method Modeling Environment. For the simulated January–February period, the latitude-height structure and the magnitudes of the temperature variance compare well with those deduced from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) observations. The simulation reveals the increasing dominance of gravity waves (GWs) at higher altitudes through both the height dependence of the kinetic energy spectra, which display a steeper slope (∼−3) in the stratosphere and an increasingly shallower slope above, and the increasing spatial extent of GWs (including a planetary-scale extent of a concentric GW excited by a tropical cyclone) at higher altitudes. GW impacts on the large-scale flow are evaluated in terms of zonal mean zonal wind and tides: with no GW drag parameterized in the simulations, forcing by resolved GWs does reverse the summer mesospheric wind, albeit at an altitude higher than climatology, and only slows down the winter mesospheric wind without closing it. The hemispheric structures and magnitudes of diurnal and semidiurnal migrating tides compare favorably with observations."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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The linked reference emphasizes the importance of using a high resolution wind model when trying to project the amount of oceanic heat advected to Antarctic ice shelves and subsequently the amount of associated ice mass loss.

Michael S. Dinniman, John M. Klinck, Le-Sheng Bai, David H. Bromwich, Keith M. Hines, and David M. Holland (2015), "The effect of atmospheric forcing resolution on delivery of ocean heat to the Antarctic floating ice shelves", Journal of Climate, doi: http://dx.doi.org/10.1175/JCLI-D-14-00374.1


http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-14-00374.1


Abstract: "Oceanic melting at the base of the floating Antarctic ice shelves is now thought to be a more significant cause of mass loss for the Antarctic ice sheet than iceberg calving. In this study, we use a 10 km horizontal resolution circum-Antarctic ocean/sea ice/ice shelf model (based on ROMS) to study the delivery of ocean heat to the base of the ice shelves. The atmospheric forcing comes from the ERA-Interim reanalysis (~80 km resolution) and from simulations using the Polar-optimized Weather Research and Forecasting model (30 km resolution) where the upper atmosphere was relaxed to the ERA-Interim reanalysis. The modeled total basal ice shelf melt is low compared to observational estimates, but increases by 14% with the higher resolution winds and just 3% with both the higher resolution winds and atmospheric surface temperatures. The higher resolution winds lead to more heat being delivered to the ice shelf cavities from the adjacent ocean and an increase in the efficiency of heat transfer between the water and the ice. The higher resolution winds also lead to changes in the heat delivered from the open ocean to the continental shelves as well as changes in the heat lost to the atmosphere over the shelves and the sign of these changes varies regionally. Addition of the higher resolution temperatures to the winds results in lowering, primarily during summer, the wind driven increase in heat advected into the ice shelf cavities due to colder summer air temperatures near the coast."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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As we are currently entering a period with a potentially strong El Nino event the following research can help us understand the associate changes in the currents around Antarctica (with implications for the potential acceleration of ice mass loss due to the accelerated advection of warm CDW to the grounding lines of key marine glaciers):

Clothilde E. Langlais, Stephen R. Rintoul, and Jan D. Zika, 2015: Sensitivity of Antarctic Circumpolar Current Transport and Eddy Activity to Wind Patterns in the Southern Ocean. J. Phys. Oceanogr., 45, 1051–1067; doi: http://dx.doi.org/10.1175/JPO-D-14-0053.1


http://journals.ametsoc.org/doi/abs/10.1175/JPO-D-14-0053.1


Abstract: "The Southern Hemisphere westerly winds have intensified in recent decades associated with a positive trend in the southern annular mode (SAM). However, the response of the Antarctic Circumpolar Current (ACC) transport and eddy field to wind forcing remains a topic of debate. This study uses global eddy-permitting ocean circulation models driven with both idealized and realistic wind forcing to explore the response to interannual wind strengthening. The response of the barotropic and baroclinic transports and eddy field of the ACC is found to depend on the spatial pattern of the changes in wind forcing. In isolation, an enhancement of the westerlies over the ACC belt leads to an increase of both barotropic and baroclinic transport within the ACC envelope, with lagged enhancement of the eddy kinetic energy (EKE). In contrast, an increase in wind forcing near Antarctica drives a largely barotropic change in transport along closed f/H contours (“free mode”), with little change in eddy activity. Under realistic forcing, the interplay of the SAM and the El Niño–Southern Oscillation (ENSO) influences the spatial distribution of the wind anomalies, in particular the partition between changes in the wind stress over the ACC and along f/H contours. This study finds that the occurrence of a negative or positive ENSO during a positive SAM can cancel or double the wind anomalies near Antarctica, altering the response of the ACC and its eddy field. While a negative ENSO and positive SAM favors an increase in EKE, a positive ENSO and positive SAM lead to barotropic transport changes and no eddy response."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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The two attached images show some of the results of the Los Alamos National Laboratory's (LANL's) contributions to the ACME program.  The first image shows ocean currents & eddies in the Southern Ocean; while the second image shows an example of LANL's efforts to model the degradation of the permafrost with continued warming.

http://www.lanl.gov/newsroom/picture-of-the-week/pic-week-9.php

Caption for first Image: "The oceans play an important role in the earth's climate; they transport heat from equator to pole, provide moisture for rain, and absorb carbon dioxide from the atmosphere. Ocean models, such as this one from Los Alamos National Laboratory, help explain interactions between individual eddies that may be altered in a changing climate. This visualization, courtesy of the Lab's MPAS-Ocean Model, shows ocean currents and eddies in a high-resolution global ocean simulation with the Antarctic in the center. Colors show speed, where white is fast and blue is slow."

http://www.lanl.gov/newsroom/picture-of-the-week/pic-week-8.php

Caption for second Image: "Arctic soils currently store nearly 20 years worth of human emissions of carbon in frozen permafrost, but the Arctic is warming faster than most of the rest of the Earth, meaning that this carbon may soon thaw and be released as greenhouse gases. Los Alamos National Laboratory scientists work to understand the fate of this carbon using computer simulations such as this model of snowmelt draining from polygonal ground near Barrow, Alaska."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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The linked reference provides new insight on modeling the ACC and the Southern Ocean MOC:

Farneti, R., S.M. Downes, S.M. Griffies, S.J. Marsland, E. Behrens, M. Bentsen, D. Bi, A. Biastoch, C. Böning, A. Bozec, V.M. Canuto, E. Chassignet, G. Danabasoglu, S. Danilov, N. Diansky, H. Drange, P.G. Fogli, A. Gusev, R.W. Hallberg, A. Howard, M. Ilicak, T. Jung, M. Kelley, W.G. Large, A. Leboissetier, M. Long, J. Lu, S. Masina, A. Mishra, A. Navarra, A.J. George Nurser, L. Patara, B.L. Samuels, D. Sidorenko, H. Tsujino, P. Uotila, Q. Wang, and S.G. Yeager (2015), "An assessment of Antarctic Circumpolar Current and Southern Ocean Meridional Overturning Circulation during 1958-2007 in a suite of interannual CORE-II simulations", Ocean Model., doi:10.1016/j.ocemod.2015.07.009.

http://www.sciencedirect.com/science/article/pii/S1463500315001183

Abstract: "In the framework of the second phase of the Coordinated Ocean-ice Reference Experiments (CORE-II), we present an analysis of the representation of the Antarctic Circumpolar Current (ACC) and Southern Ocean Meridional Overturning Circulation (MOC) in a suite of seventeen global ocean-sea ice models. We focus on the mean, variability and trends of both the ACC and MOC over the 1958-2007 period, and discuss their relationship with the surface forcing. We aim to quantify the degree of eddy saturation and eddy compensation in the models participating in CORE-II, and compare our results with available observations, previous fine-resolution numerical studies and theoretical constraints. Most models show weak ACC transport sensitivity to changes in forcing during the past five decades, and they can be considered to be in an eddy saturated regime. Larger contrasts arise when considering MOC trends, with a majority of models exhibiting significant strengthening of the MOC during the late 20th and early 21st century. Only a few models show a relatively small sensitivity to forcing changes, responding with an intensified eddy-induced circulation that provides some degree of eddy compensation, while still showing considerable decadal trends. Both ACC and MOC interannual variability are largely controlled by the Southern Annular Mode (SAM). Based on these results, models are clustered into two groups. Models with constant or two-dimensional (horizontal) specification of the eddy-induced advection coefficient κ show larger ocean interior decadal trends, larger ACC transport decadal trends and no eddy compensation in the MOC. Eddy-permitting models or models with a three-dimensional time varying κ show smaller changes in isopycnal slopes and associated ACC trends, and partial eddy compensation. As previously argued, a constant in time or space κ is responsible for a poor representation of mesoscale eddy effects and cannot properly simulate the sensitivity of the ACC and MOC to changing surface forcing. Evidence is given for a larger sensitivity of the MOC as compared to the ACC transport, even when approaching eddy saturation. Future process studies designed for disentangling the role of momentum and buoyancy forcing in driving the ACC and MOC are proposed.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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The linked reference indicates that model results show that the Southern Hemisphere Hadley cell is expanding due to GHG forcing:

H. Nguyen, C. Lucas, A. Evans, B. Timbal, and L. Hanson (2015), "Expansion of the Southern Hemisphere Hadley Cell in response to greenhouse gas forcing", Journal of Climate, doi: http://dx.doi.org/10.1175/JCLI-D-15-0139.1


http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0139.1


Abstract: "Changes of the southern hemisphere Hadley cell over the twentieth Century are investigated using the twentieth Century Reanalysis (20CR) and coupled model simulations from the Coupled Model Intercomparison Project phase 5 (CMIP5). Trends computed on a 30-year sliding window on the 20CR dataset reveal a statistically significant expansion of the Hadley cell from 1968 forced by an increasing surface global warming. This expansion is strongly associated with the intensification and poleward shift of the subtropical dry zone, which potentially explain the increasing trends of droughts in the subtropical regions such as Southern Australia, South America and Africa. Coupled models from the CMIP5 do not adequately simulate the observed amount of the Hadley expansion, only showing an average of one fourth of the expansion as determined from the 20CR and only when simulations include greenhouse gas forcing as opposed to simulations including natural forcing only."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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The linked reference provides new insight on the roles of the different tropical ocean basins on telecommunication of energy to the West Antarctic Ice Sheet.  However, while the reference correctly models many responses they acknowledge that still better understanding needs to be gain about the associate jet stream structure that are influence by a large number of phenomena including the: ENSO, IPO, PDO, AMO, SAM, the ozone hole, global warming, ocean currents, cyclonic activity etc. etc.; all of which could influence ice mass loss rates from the WAIS in the future.

Xichen Li, David M. Holland, Edwin P. Gerber and Changhyun Yoo (2015), "Rossby waves mediate impacts of tropical oceans on West Antarctic atmospheric circulation in austral winter", Journal of Climate; doi: http://dx.doi.org/10.1175/JCLI-D-15-0113.1



http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0113.1


Abstract: "Recent studies link climate change around Antarctica to the sea surface temperature of tropical oceans, with teleconnections from the Pacific, Atlantic, and Indian Oceans making different contributions to Antarctic climate. In this study, we identify the impacts of each ocean basin on the wintertime Southern Hemisphere circulation, by comparing simulation results using a comprehensive atmospheric model, an idealized dynamical core model, and a theoretical Rossby-wave model. Our results show that Tropical Atlantic Ocean warming, Indian Ocean warming, and Eastern Pacific cooling are all able to deepen the Amundsen Sea Low located adjacent to West Antarctica, while Western Pacific warming increases the pressure to the west of the international date line, encompassing the Ross Sea and regions south of the Tasman Sea. In austral winter, these tropical ocean basins work together linearly to modulate the atmospheric circulation around Western Antarctica. Further analyses indicate that these teleconnections critically depend on stationary Rossby-wave dynamics, and are thus sensitive to the background flow, in particular, the sub-tropical/mid-latitude jet. Near these jets, wind shear is amplified, which strengthens the generation of Rossby waves. On the other hand, near the edges of the jets, the meridional gradient of the absolute vorticity is also enhanced. As a consequence of the Rossby-wave dispersion relationship, the jet edge may reflect stationary Rossby-wave trains, serving as a wave-guide. Our simulation results not only identify the relative roles of each of the tropical ocean basins in the tropical – Antarctica teleconnection, but also suggest that a deeper understanding of teleconnections requires a better estimation of the atmospheric jet structures."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #98 on: September 14, 2015, 08:07:39 PM »
The linked reference finds that considering only hosing from the PIG collapse is sufficient to alter climate model projections for such matters as: CDW temperatures, surface water temperatures, Southern Ocean sea ice extent, and AMOC activity.  This work clearly substantiates the Hansen et al. 2015 findings, and also indicates how sensitive climate response is to different input combinations:

J.A.M. Green and A. Schmittner (2015), "Climatic consequences of a Pine Island Glacier collapse", Journal of Climate; doi: http://dx.doi.org/10.1175/JCLI-D-15-0110.1


http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0110.1


Abstract: "An intermediate complexity climate model is used to simulate the impact of an accelerated Pine Island Glacier mass loss on the large-scale ocean circulation and climate. Simulations are performed for pre-industrial conditions using hosing levels consistent with present day observation of 3,000 m3 s-1, at an accelerated rate of 6,000 m3 s-1, and at a total collapse rate of 100,000 m3 s-1, and in all experiments the hosing lasted 100 years. It is shown that even a modest input of meltwater from the glacier can introduce an initial cooling over the upper part of the Southern Ocean due to increased stratification and ice cover leading to a reduced upward heat flux from Circumpolar Deep Water. This causes global ocean heat content to increase and global surface air temperatures to decrease. The Atlantic Meridional Overturning Circulation (AMOC) increases, presumably due to changes in the density difference between Antarctic Intermediate Water and North Atlantic Deep Water. Simulations with a simultaneous hosing and increases of atmospheric CO2 concentrations show smaller effects of the hosing on global surface air temperature and ocean heat content, which we attribute to the melting of Southern Ocean sea ice. The sensitivity of the AMOC to the hosing is also reduced as the warming by the atmosphere completely dominates the perturbations."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #99 on: November 27, 2015, 05:32:37 PM »
With a hat-tip to Laurent, I re-post the following from the "What's new in Antarctica?" thread:

Big data reveals glorious animation of Antarctic bottom water
http://nci.org.au/2015/11/24/big-data-reveals-glorious-animation-of-antarctic-bottom-water/

https://www.youtube.com/watch?feature=player_embedded&v=8VMSF28J9H4
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson