Support the Arctic Sea Ice Forum and Blog

Author Topic: Risks and Challenges for Regional Circulation Models of the Southern Ocean  (Read 61529 times)

AbruptSLR

  • ASIF Emperor
  • Posts: 16478
    • View Profile
  • Liked: 178
  • Likes Given: 12
Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #100 on: January 05, 2016, 08:17:38 PM »
The linked article discusses a ground based initiative to gather high-quality data about Antarctic clouds; which are critical for the accurate calibration of regional models:

Alexandra Witze  (07 January 2016), "Antarctic clouds studied for first time in five decades
AWARE project will help unravel effects of global warming", Nature, Volume: 529, Pages: 12, doi:10.1038/529012a


http://www.nature.com/news/antarctic-clouds-studied-for-first-time-in-five-decades-1.19110

Extract: "On Antarctica’s Ross Island, a short drive from the US McMurdo research station, high-tech radar antennas and other atmospheric instruments gaze skyward, gathering detailed measurements of West Antarctic clouds. Remarkably, these are the first such data to be gathered in five decades — even though weather patterns in the region can influence those half a world away.
The US$5-million project, known as the Atmospheric Radiation Measurement West Antarctic Radiation Experiment (AWARE), began to observe the skies near McMurdo in November and will run until early 2017. A second measurement station, 1,600 kilometres away in the ice sheet’s interior, will operate until the end of this month. (The site is so remote that it can be used only during the Antarctic summer.)
A similar experiment in the Arctic in 1997–98 relied on an instrument-laden ship that was deliberately frozen into sea ice. It yielded fundamental insights into the physics of northern polar clouds, and AWARE scientists hope that their project will do the same for the south. “This is going to be a sea change in our understanding,” says Lynn Russell, an atmospheric scientist at the Scripps Institution of Oceanography in La Jolla, California, and a co-principal investigator on AWARE.
Antarctica’s massive ice sheet acts as a global heat sink. As a result, changes in Antarctic clouds, such as the amount of ground they cover or how much radiation they absorb, can have ripple effects as far away as the tropics. Climate modellers need to understand the physics of these clouds if they are to correctly work out how weather around the globe will change as the polar regions warm.

AWARE, which is led by Scripps atmospheric scientist Dan Lubin, aims to get the best data yet on clouds and aerosol particles above West Antarctica. That includes mixed phase clouds, which occur in polar regions and combine supercooled water with ice. Studies have shown that clouds moving across Antarctica’s interior are mostly ice, whereas those moving onshore from the coast contain more liquid water. The composition of these clouds plays a major part in determining how much sunlight they reflect into space — which helps to shape atmospheric circulation and weather patterns below."
« Last Edit: July 01, 2016, 11:08:32 PM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 16478
    • View Profile
  • Liked: 178
  • Likes Given: 12
Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #101 on: January 24, 2016, 03:52:02 AM »
The linked reference discusses new model results about Mechanisms of Southern Ocean heat uptake and transport; which indicate to me that heat sequestered in the deep ocean in Antarctica does not stay sequestered as long as previously thought due to global eddying that results in mixing:


Adele K. Morrison, Stephen M. Griffies, Michael Winton, and Whit G. Anderson & Jorge L. Sarmiento (2016 ), "Mechanisms of Southern Ocean heat uptake and transport in a global eddying climate model", Journal of Climate, doi: http://dx.doi.org/10.1175/JCLI-D-15-0579.1


http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0579.1

Abstract: "The Southern Ocean plays a dominant role in anthropogenic oceanic heat uptake. Strong northward transport of the heat content anomaly limits warming of the sea surface temperature in the uptake region and allows the heat uptake to be sustained. Using an eddy-rich global climate model, the processes controlling the northward transport and convergence of the heat anomaly in the mid-latitude Southern Ocean are investigated in an idealized 1% yr−1 increasing CO2 simulation. Heat budget analyses reveal that different processes dominate to the north and south of the main convergence region. The heat transport northward from the uptake region in the south is driven primarily by passive advection of the heat content anomaly by the existing time mean circulation, with a smaller 20% contribution from enhanced upwelling. The heat anomaly converges in the mid-latitude deep mixed layers, because there is not a corresponding increase in the mean heat transport out of the deep mixed layers northward into the mode waters. To the north of the deep mixed layers, eddy processes drive the warming and account for nearly 80% of the northward heat transport anomaly. The eddy transport mechanism results from a reduction in both the diffusive and advective southward eddy heat transports, driven by decreasing isopycnal slopes and decreasing along-isopycnal temperature gradients on the northern edge of the peak warming."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 16478
    • View Profile
  • Liked: 178
  • Likes Given: 12
Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #102 on: January 29, 2016, 02:41:33 PM »
The linked reference introduces freshwater flux into a CESM1-CAM5 model (i.e. hosing, which was not included in the CMIP5 projections) to produce updated projections indicating that currently the relatively small amounts of freshwater introduced to the Southern Ocean by Antarctic Ice Sheet mass loss is contributing to sea ice extent expansion; but that this trend will reverse itself over a period of 20-years (or longer) due to global warming (even if the freshwater flux/hosing increases several times and/or at different water depths).  This finding could represent a worse-case scenario for abrupt sea level contribution from the WAIS, as it promotes the accumulation of warm CDW in the Southern Ocean for the time being (which facilitates grounding line retreat for heat marine glacier) followed by subsequent sea ice reductions that will both:
(a) Promote austral summer surface ice melting (due to reduced summertime albedo) and associated hydrofracturing, and
(b) Reduce the amount of land fast sea ice that can pin icebergs in place.  This would result in the loss of buttressing action from the associated ice mélange.

Andrew G. Pauling, Cecilia M. Bitz, Inga J. Smith and Patricia J. Langhorne (2016), "The Response of the Southern Ocean and Antarctic Sea Ice to Fresh Water from Ice Shelves in an Earth System Model", Journal of Climate, doi: http://dx.doi.org/10.1175/JCLI-D-15-0501.1


http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0501.1


Abstract: "The possibility that recent Antarctic sea ice expansion resulted from an increase in fresh water reaching the Southern Ocean is investigated here. The freshwater flux from ice sheet and ice shelf mass imbalance is largely missing in models that participated in the Coupled Model Intercomparison Project Phase 5 (CMIP5). However, on average P-E reaching the Southern Ocean has increased in CMIP5 models to a present value that is about 2600 Gt yr−1 greater than pre-industrial times and 5-22 times larger than estimates of the mass imbalance of Antarctic ice sheets and shelves (119 to 544 Gt yr−1). Two sets of experiments were conducted from 1980-2013 in CESM1-CAM5, one of the CMIP5 models, artificially distributing fresh water either at the ocean surface to mimic iceberg melt, or at the ice shelf fronts at depth. An anomalous reduction in vertical advection of heat into the surface mixed layer resulted in sea surface cooling at high southern latitudes, and an associated increase in sea ice area. Enhancing the freshwater input by an amount within the range of estimates of the Antarctic mass imbalance did not have any significant effect on either sea ice area magnitude or trend. Freshwater enhancement of 2000 Gt yr−1 raised the total sea ice area by 1×106 km2, yet this and even an enhancement of 3000 Gt yr−1 was insufficient to offset the sea ice decline due to anthropogenic forcing for any period of 20 years or longer. Further, the sea ice response was found to be insensitive to the depth of fresh water injection."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 16478
    • View Profile
  • Liked: 178
  • Likes Given: 12
The linked reference corrects a long know bias in the CESM regarding ASR for the Southern Ocean.  This correction resulted in a pre-industrial era increase in tropical temperatures and a decrease in Southern Ocean temperatures:

Jennifer E. Kay, Casey Wall, Vineel Yettella, Brian Medeiros, Cecile Hannay, Peter Caldwell and Cecilia Bitz (2016), "Global climate impacts of fixing the Southern Ocean shortwave radiation bias in the Community Earth System Model (CESM)",  Journal of Climate, doi: 10.1175/JCLI-D-15-0358.1.

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0358.1

Abstract: "A large, long-standing, and pervasive climate model bias is excessive absorbed shortwave radiation (ASR) over the mid-latitude oceans, especially the Southern Ocean. This study investigates both the underlying mechanisms for and climate impacts of this bias within the Community Earth System Model with the Community Atmosphere Model version 5 (CESM-CAM5). Excessive Southern Ocean ASR in CESM-CAM5 results in part because low-level clouds contain insufficient amounts of supercooled liquid. In a present-day atmosphere-only run, an observationally motivated modification to the shallow convection detrainment increases supercooled cloud liquid, brightens low-level clouds, and substantially reduces the Southern Ocean ASR bias. Tuning to maintain global energy balance enables reduction of a compensating tropical ASR bias. In the resulting pre-industrial fully coupled run with a brighter Southern Ocean and dimmer Tropics, the Southern Ocean cools and the Tropics warm. As a result of the enhanced meridional temperature gradient, poleward heat transport increases in both hemispheres (especially the Southern Hemisphere) and the Southern Hemisphere atmospheric jet strengthens. Because Northward cross-equatorial heat transport reductions occur primarily in the ocean (80%) not the atmosphere (20%), a proposed atmospheric teleconnection linking Southern Ocean ASR bias reduction and cooling with northward shifts in tropical precipitation has little impact. In summary, observationally motivated supercooled liquid water increases in shallow convective clouds enable large reductions in long-standing climate model shortwave radiation biases. Of relevance to both model bias reduction and climate dynamics, quantifying the influence of Southern Ocean cooling on tropical precipitation requires a model with dynamic ocean heat transport."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 16478
    • View Profile
  • Liked: 178
  • Likes Given: 12
As both of the linked references are on the technical side I am posting them in this thread; however, they both could be seen as support Hansen et al (2016)'s ice-climate feedback mechanism if their findings were to be incorporated within a suitable climate model:

K. Hutchinson, S. Swart, A. Meijers, I. Ansorge & S. Speich (19 April 2016), "Decadal-scale thermohaline variability in the Atlantic sector of the Southern Ocean", Journal of Geophysical Research Oceans, DOI: 10.1002/2015JC011491


http://onlinelibrary.wiley.com/doi/10.1002/2015JC011491/abstract

Abstract: "An enhanced Altimetry Gravest Empirical Mode (AGEM), including both adiabatic and diabatic trends, is developed for the Antarctic Circumpolar Current (ACC) south of Africa using updated hydrographic CTD sections, Argo data, and satellite altimetry. This AGEM has improved accuracy compared to traditional climatologies and other proxy methods. The AGEM for the Atlantic Southern Ocean offers an ideal technique to investigate the thermohaline variability over the past two decades in a key region for water mass exchanges and transformation. In order to assess and attribute changes in the hydrography of the region, we separate the changes into adiabatic and diabatic components. Integrated over the upper 2000 dbar of the ACC south of Africa, results show mean adiabatic changes of 0.16 ± 0.11°C.decade−1 and 0.006 ± 0.014 decade−1, and diabatic differences of -0.044 ± 0.13°C.decade−1 and -0.01 ± 0.017 .decade−1 for temperature and salinity, respectively. The trends of the resultant AGEM, that include both adiabatic and diabatic variability (termed AD-AGEM), show a significant increase in the heat content of the upper 2000dbar of the ACC with a mean warming of 0.12 ± 0.087°C.decade−1. This study focuses on the Antarctic Intermediate Water (AAIW) mass where negative diabatic trends dominate positive adiabatic differences in the Subantarctic Zone (SAZ), with results indicating a cooling (-0.17°C.decade−1) and freshening (-0.032 decade−1) of AAIW in this area, whereas south of the SAZ positive adiabatic and diabatic trends together create a cumulative warming (0.31°C.decade−1) and salinification (0.014 decade−1) of AAIW."

Patrick F. Cummins, Diane Masson & Oleg A. Saenko (21 April 2016), "Vertical heat flux in the ocean: Estimates from observations and from a coupled general circulation model", Journal of Geophysical Research Oceans, DOI: 10.1002/2016JC011647

http://onlinelibrary.wiley.com/doi/10.1002/2016JC011647/abstract

Abstract: ”The net heat uptake by the ocean in a changing climate involves small imbalances between the advective and diffusive processes that transport heat vertically. Generally, it is necessary to rely on global climate models to study these processes in detail. In the present study, it is shown that a key component of the vertical heat flux, namely that associated with the large-scale mean vertical circulation, can be diagnosed over extra-tropical regions from global observational data sets. This component is estimated based on the vertical velocity obtained from the geostrophic vorticity balance, combined with estimates of absolute geostrophic flow. Results are compared with the output of a non-eddy resolving, coupled atmosphere-ocean general circulation model. Reasonable agreement is found in the latitudinal distribution of the vertical heat flux, as well as in the area-integrated flux below about 250 meters depth. The correspondence with the coupled model deteriorates sharply at depths shallower than 250 m due to the omission of equatorial regions from the calculation. The vertical heat flux due to the mean circulation is found to be dominated globally by the downward contribution from the Southern Hemisphere, in particular the Southern Ocean. This is driven by the Ekman vertical velocity which induces an upward transport of seawater that is cold relative to the horizontal average at a given depth. The results indicate that the dominant characteristics of the vertical transport of heat due to the mean circulation can be inferred from simple linear vorticity dynamics over much of the ocean."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 16478
    • View Profile
  • Liked: 178
  • Likes Given: 12
The linked (open access) reference focuses on the impacts of marine instability primarily of the Wilkes Basin (but also other basins as indicated by the attached images showing impacts on AABW formation due to different assumed marine glacier instability scenarios in different basins) on Southern Ocean dynamics.  This research supports the Hansen et al (2016) findings:

Phipps, S. J., Fogwill, C. J., and Turney, C. S. M.: Impacts of marine instability across the East Antarctic Ice Sheet on Southern Ocean dynamics, The Cryosphere Discuss., doi:10.5194/tc-2016-111, in review, 2016.

http://www.the-cryosphere-discuss.net/tc-2016-111/

Abstract. Recent observations and modelling studies have demonstrated the potential for rapid and substantial retreat of large sectors of the East Antarctic Ice Sheet (EAIS). This has major implications for ocean circulation and global sea level. Here we examine the effects of increasing meltwater from the Wilkes Basin, one of the major marine-based sectors of the EAIS, on Southern Ocean dynamics. Climate model simulations reveal that the meltwater flux rapidly stratifies surface waters, leading to a dramatic decrease in the rate of Antarctic Bottom Water formation. The surface ocean cools but, critically, the Southern Ocean warms by more than 1 ºC at depth. This warming is accompanied by a Southern Ocean-wide "domino effect", whereby the warming signal propagates westward with depth. Our results suggest that melting of one sector of the EAIS could result in accelerated warming across other sectors, including the Weddell Sea sector of the West Antarctic Ice Sheet. Thus localised melting of the EAIS could potentially destabilise the wider Antarctic Ice Sheet.


Caption for attached image: "Figure 3. Rate of AABW formation (Sv) in the control simulation (black), and in experiments WILKES (red), WEST (green) and EAST (blue). Thin lines indicate individual ensemble members; thick lines indicate the ensemble means. The values shown are 100-year running means. Vertical dashed lines indicate the years in which the freshwater hosing begins and ends."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 16478
    • View Profile
  • Liked: 178
  • Likes Given: 12
Calibrating ESMs (like ACME) to match the rather abrupt change in ocean circulation patterns observed for the PETM, may contribute to our confidence that such models can accurately project where we are headed in the coming decades:

Abbott, A. N., Haley, B. A., Tripati, A. K., and Frank, M.: Constraints on ocean circulation at the Paleocene–Eocene Thermal Maximum from neodymium isotopes, Clim. Past, 12, 837-847, doi:10.5194/cp-12-837-2016, 2016.


http://www.clim-past.net/12/837/2016/cp-12-837-2016.pdf

Abstract. Global warming during the Paleocene–Eocene Thermal Maximum (PETM)  ∼  55 million years ago (Ma) coincided with a massive release of carbon to the ocean–atmosphere system, as indicated by carbon isotopic data. Previous studies have argued for a role of changing ocean circulation, possibly as a trigger or response to climatic changes. We use neodymium (Nd) isotopic data to reconstruct short high-resolution records of deep-water circulation across the PETM. These records are derived by reductively leaching sediments from seven globally distributed sites to reconstruct past deep-ocean circulation across the PETM. The Nd data for the leachates are interpreted to be consistent with previous studies that have used fish teeth Nd isotopes and benthic foraminiferal δ13C to constrain regions of convection. There is some evidence from combining Nd isotope and δ13C records that the three major ocean basins may not have had substantial exchanges of deep waters. If the isotopic data are interpreted within this framework, then the observed pattern may be explained if the strength of overturning in each basin varied distinctly over the PETM, resulting in differences in deep-water aging gradients between basins. Results are consistent with published interpretations from proxy data and model simulations that suggest modulation of overturning circulation had an important role for initiation and recovery of the ocean–atmosphere system associated with the PETM.

Edit: For those who do not like to click on open access references, I provide both the first associated image of Fig 1 with the following caption: "Figure 1. Nd and C isotope data ("Nd and _13C) across the PETM from the Southern Ocean (a), Pacific Ocean (b), and Atlantic Ocean (c).  The sediment leach "Nd are shown with circles and solid lines; the fish teeth/debris "Nd from Thomas et al. (2003) are shown as dots. All data are presented on directly comparable scales for both "Nd and _13C. The sample ages are based on the _13C age models. In (b) the age model of Site 1209B has been slightly adjusted (second x axis) such that the _13C excursion coincides with the age of the PETM in the other cores. The shaded vertical bar indicates the timing of the PETM as defined by the CIE in the cores."  Also, I provide the second attached image of Fig 3.  Both of these images show the relatively high sensitivity of ocean currents following the PETM triggering event, particularly with regards to upwelling in the Southern Ocean and along the west coast of South America. 
« Last Edit: June 02, 2016, 05:22:20 PM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 16478
    • View Profile
  • Liked: 178
  • Likes Given: 12
The linked reference provides field data from deep diving elephant seals to better characterize the nature and movements of the modified CDW that is crossing the continental shelves in West Antarctica to cause basal ice melting for associated ice shelves and grounding line retreat for key marine glaciers:

Xiyue Zhang, Andrew F. Thompson, Mar M. Flexas, Fabien Roquet & Horst Bornemann (1 June 2016), "Circulation and meltwater distribution in the Bellingshausen Sea: from shelf break to coast", Geophysical Research Letters, DOI: 10.1002/2016GL068998

http://onlinelibrary.wiley.com/doi/10.1002/2016GL068998/full

Abstract: "West Antarctic ice shelves have thinned dramatically over recent decades. Oceanographic measurements that explore connections between offshore warming and transport across a continental shelf with variable bathymetry towards ice shelves are needed to constrain future changes in melt rates. Six years of seal-acquired observations provide extensive hydrographic coverage in the Bellingshausen Sea, where ship-based measurements are scarce. Warm but modified Circumpolar Deep Water floods the shelf and establishes a cyclonic circulation within the Belgica Trough with flow extending towards the coast along the eastern boundaries and returning to the shelf break along western boundaries. These boundary currents are the primary water mass pathways that carry heat towards the coast and advect ice shelf meltwater offshore. The modified Circumpolar Deep Water and meltwater mixtures shoal and thin as they approach the continental slope before flowing westward at the shelf break, suggesting the presence of the Antarctic Slope Current. Constraining meltwater pathways is a key step in monitoring the stability of the West Antarctic Ice Sheet."


See also:
https://www.washingtonpost.com/news/energy-environment/wp/2016/06/08/seals-wearing-little-sensors-are-showing-scientists-why-antarctica-is-melting/
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 16478
    • View Profile
  • Liked: 178
  • Likes Given: 12

The linked PowerPoint presentation discusses the atmospheric response to the Weddell Polynya (the attached image shows this polynya in the 1970's):

 Weijer, Veneziani, Hecht, Jeffery, Jonko, Stössel & Hodos (2016) "Atmospheric Response to the Weddell Polynya"

http://climatemodeling.science.energy.gov/sites/default/files/presentations/Wilbert_Polynyas.pdf

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

AbruptSLR

  • ASIF Emperor
  • Posts: 16478
    • View Profile
  • Liked: 178
  • Likes Given: 12
As a follow-on to my Reply #100, the linked open access pdf describes a recently initiated field campaign to gather direct atmospheric data (generally related to cloud cover & radivative forcing) between the WAIS Divide & McMurdo Station.  The document is entitled: "ARM West Antarctic Radiation Experiment (AWARE) Science Plan", and hopefully finding from this effort will improve regional modeling of cloud cover in West Antarctica (as most current climate models exhibit low skill levels in this area):

https://www.arm.gov/publications/programdocs/doe-sc-arm-15-040.pdf

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

sidd

  • ASIF Governor
  • Posts: 3858
    • View Profile
  • Liked: 70
  • Likes Given: 0
Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #110 on: October 19, 2016, 01:09:54 AM »
http://www.ocean-sci-discuss.net/os-2016-54/

discusses AAIW freshening, decreasing Agulhas leakage and more. paper is open access, in review stage.

AbruptSLR

  • ASIF Emperor
  • Posts: 16478
    • View Profile
  • Liked: 178
  • Likes Given: 12
Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #111 on: December 12, 2016, 06:43:47 PM »
The linked reference provides field evidence supporting Hansen's ice-climate interaction mechanism.

Pepijn Bakker et al, Centennial-scale Holocene climate variations amplified by Antarctic Ice Sheet discharge, Nature (2016). DOI: 10.1038/nature20582

http://www.nature.com/nature/journal/vaop/ncurrent/full/nature20582.html

Abstract: "Proxy-based indicators of past climate change show that current global climate models systematically underestimate Holocene-epoch climate variability on centennial to multi-millennial timescales, with the mismatch increasing for longer periods. Proposed explanations for the discrepancy include ocean–atmosphere coupling that is too weak in models, insufficient energy cascades from smaller to larger spatial and temporal scales, or that global climate models do not consider slow climate feedbacks related to the carbon cycle or interactions between ice sheets and climate. Such interactions, however, are known to have strongly affected centennial- to orbital-scale climate variability during past glaciations, and are likely to be important in future climate change. Here we show that fluctuations in Antarctic Ice Sheet discharge caused by relatively small changes in subsurface ocean temperature can amplify multi-centennial climate variability regionally and globally, suggesting that a dynamic Antarctic Ice Sheet may have driven climate fluctuations during the Holocene. We analysed high-temporal-resolution records of iceberg-rafted debris derived from the Antarctic Ice Sheet, and performed both high-spatial-resolution ice-sheet modelling of the Antarctic Ice Sheet and multi-millennial global climate model simulations. Ice-sheet responses to decadal-scale ocean forcing appear to be less important, possibly indicating that the future response of the Antarctic Ice Sheet will be governed more by long-term anthropogenic warming combined with multi-centennial natural variability than by annual or decadal climate oscillations."


See also the linked article entitled: "Antarctic Ice Sheet study reveals 8,000-year record of climate change".

http://phys.org/news/2016-12-antarctic-ice-sheet-reveals-year.html

Extract: "An international team of researchers has found that the Antarctic Ice Sheet plays a major role in regional and global climate variability - a discovery that may also help explain why sea ice in the Southern Hemisphere has been increasing despite the warming of the rest of the Earth.


Global climate models that look at the last several thousand years have failed to account for the amount of climate variability captured in the paleoclimate record, according to lead author Pepijn Bakker, a climate modeller from the MARUM Center for Marine Environmental Studies at the University of Bremen in Germany.

The researchers first turned their attention to the Scotia Sea. "Most icebergs calving off the Antarctic Ice Sheet travel through this region because of the atmospheric and oceanic circulation," explained Weber. "The icebergs contain gravel that drop into the sediment on the ocean floor - and analysis and dating of such deposits shows that for the last 8,000 years, there were centuries with more gravel and those with less."

The research team's hypothesis is that climate modellers have historically overlooked one crucial element in the overall climate system. They discovered that the centuries-long phases of enhanced and reduced Antarctic ice mass loss documented over the past 8,000 years have had a cascading effect on the entire climate system.

Using sophisticated computer modelling, the researchers traced the variability in iceberg calving (ice that breaks away from glaciers) to small changes in ocean temperatures."


See also the following linked article entitled: "New study shows impact of Antarctic Ice Sheet on climate change"

https://www.eurekalert.org/pub_releases/2016-12/osu-nss120816.php
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 16478
    • View Profile
  • Liked: 178
  • Likes Given: 12
Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #112 on: February 17, 2017, 03:40:12 PM »
The linked open access reference uses a model to likely associate eddies in the Southern Ocean to atmospheric CO₂ content.

David P. Marshall, Maarten H. P. Ambaum, James R. Maddison, David R. Munday & Lenka Novak (9 January 2017), "Eddy saturation and frictional control of the Antarctic Circumpolar Current", Geophysical Research Letters, DOI: 10.1002/2016GL071702

http://onlinelibrary.wiley.com/doi/10.1002/2016GL071702/abstract

Abstract: "The Antarctic Circumpolar Current is the strongest current in the ocean and has a pivotal impact on ocean stratification, heat content, and carbon content. The circumpolar volume transport is relatively insensitive to surface wind forcing in models that resolve turbulent ocean eddies, a process termed “eddy saturation.” Here a simple model is presented that explains the physics of eddy saturation with three ingredients: a momentum budget, a relation between the eddy form stress and eddy energy, and an eddy energy budget. The model explains both the insensitivity of circumpolar volume transport to surface wind stress and the increase of eddy energy with wind stress. The model further predicts that circumpolar transport increases with increased bottom friction, a counterintuitive result that is confirmed in eddy-permitting calculations. These results suggest an unexpected and important impact of eddy energy dissipation, through bottom drag or lee wave generation, on ocean stratification, ocean heat content, and potentially atmospheric CO2."

See also the associated EOS article entitled: "Swirling Eddies in the Antarctic May Have Global Impacts"

https://eos.org/research-spotlights/swirling-eddies-in-the-antarctic-may-have-global-impacts?utm_source=eos&utm_medium=email&utm_campaign=EosBuzz021717

Extract: "A new model examines how eddies in the Antarctic Circumpolar Current affect volume transport of the world's strongest current.

According to the authors, because of the ACC’s high-volume transport, this eddy energy dissipation in the Southern Ocean may have an outsized impact on global oceanic stratification and heat content. Because ocean stratification in turn impacts the ocean carbon cycle, the authors emphasize the potential role of these eddies in influencing atmospheric CO2. Further research into the mechanisms behind the current’s movement will help scientists to more fully understand the complex interactions between Earth’s oceans and atmosphere."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 16478
    • View Profile
  • Liked: 178
  • Likes Given: 12
I do not find it reassuring that the behavior of the Southern Ocean plays large roles in both Frey & Kay (2017)'s estimate of an ECS of 5.6C and in Hansen et al (2016)'s ice-climate feedback mechanism, and yet scientists do not adequately understand the decadal variability of this unique region as discussed in the reference below:

Latif, M., Martin, T., Reintges, A. et al. (2017) "Southern Ocean Decadal Variability and Predictability", Curr Clim Change Rep, doi:10.1007/s40641-017-0068-8

https://link.springer.com/article/10.1007%2Fs40641-017-0068-8?utm_content=bufferc013d&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "The Southern Ocean featured some remarkable changes during the recent decades. For example, large parts of the Southern Ocean, despite rapidly rising atmospheric greenhouse gas concentrations, depicted a surface cooling since the 1970s, whereas most of the planet has warmed considerably. In contrast, climate models generally simulate Southern Ocean surface warming when driven with observed historical radiative forcing. The mechanisms behind the surface cooling and other prominent changes in the Southern Ocean sector climate during the recent decades, such as expanding sea ice extent, abyssal warming, and CO2 uptake, are still under debate. Observational coverage is sparse, and records are short but rapidly growing, making the Southern Ocean climate system one of the least explored. It is thus difficult to separate current trends from underlying decadal to centennial scale variability. Here, we present the state of the discussion about some of the most perplexing decadal climate trends in the Southern Ocean during the recent decades along with possible mechanisms and contrast these with an internal mode of Southern Ocean variability present in state-of-the art climate models."

For Frey & Kay (2017) see:

William R. Frey & Jennifer E. Kay (2017), "The influence of extratropical cloud phase and amount feedbacks on climate sensitivity", Climate Dynamics; pp 1–20, doi:10.1007/s00382-017-3796-5
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 16478
    • View Profile
  • Liked: 178
  • Likes Given: 12
The linked reference indicates that new decadal-scale model projections for the Southern Ocean indicate that some component of the recent high levels of sea ice extents has been associated with weakening of the AABW cell in the Weddell Sea.  To me this weakening of this AABW cell supports Hansen's ice-climate feedback mechanism:

Zhang, Liping, Thomas L Delworth, Xiaosong Yang, Richard G Gudgel, Liwei Jia, Gabriel A Vecchi, and Fanrong Zeng, July 2017: Estimating decadal predictability for the Southern Ocean using the GFDL CM2.1 model. Journal of Climate, 30(14), DOI:10.1175/JCLI-D-16-0840.1

http://journals.ametsoc.org/doi/10.1175/JCLI-D-16-0840.1

Abstract: “This study explores the potential predictability of the Southern Ocean (SO) climate on decadal time scales as represented in the GFDL CM2.1 model using prognostic methods. Perfect model predictability experiments are conducted starting from 10 different initial states, showing potentially predictable variations of Antarctic bottom water (AABW) formation rates on time scales as long as 20 years. The associated Weddell Sea (WS) subsurface temperatures and Antarctic sea ice have potential predictability comparable to that of the AABW cell. The predictability of sea surface temperature (SST) variations over the WS and the SO is somewhat smaller, with predictable scales out to a decade. This reduced predictability is likely associated with stronger damping from air–sea interaction. As a complement to this perfect predictability study, the authors also make hindcasts of SO decadal variability using the GFDL CM2.1 decadal prediction system. Significant predictive skill for SO SST on multiyear time scales is found in the hindcast system. The success of the hindcasts, especially in reproducing observed surface cooling trends, is largely due to initializing the state of the AABW cell. A weak state of the AABW cell leads to cooler surface conditions and more extensive sea ice. Although there are considerable uncertainties regarding the observational data used to initialize the hindcasts, the consistency between the perfect model experiments and the decadal hindcasts at least gives some indication as to where and to what extent skillful decadal SO forecasts might be possible.”
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 16478
    • View Profile
  • Liked: 178
  • Likes Given: 12
Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #115 on: August 04, 2017, 01:17:12 AM »
The linked reference finds that "... localized changes in coastal winds off East Antarctica can produce significant subsurface temperature anomalies (>2 °C) around much of the continent."

Paul Spence, Ryan M. Holmes, Andrew McC. Hogg, Stephen M. Griffies, Kial D. Stewart & Matthew H. England  (2017), "Localized rapid warming of West Antarctic subsurface waters by remote winds", Nature Climate Change, Volume: 7, Pages: 595–603, doi:10.1038/nclimate3335

http://www.nature.com/nclimate/journal/v7/n8/full/nclimate3335.html

Abstract: "The highest rates of Antarctic glacial ice mass loss are occurring to the west of the Antarctica Peninsula in regions where warming of subsurface continental shelf waters is also largest. However, the physical mechanisms responsible for this warming remain unknown. Here we show how localized changes in coastal winds off East Antarctica can produce significant subsurface temperature anomalies (>2 °C) around much of the continent. We demonstrate how coastal-trapped barotropic Kelvin waves communicate the wind disturbance around the Antarctic coastline. The warming is focused on the western flank of the Antarctic Peninsula because the circulation induced by the coastal-trapped waves is intensified by the steep continental slope there, and because of the presence of pre-existing warm subsurface water offshore. The adjustment to the coastal-trapped waves shoals the subsurface isotherms and brings warm deep water upwards onto the continental shelf and closer to the coast. This result demonstrates the vulnerability of the West Antarctic region to a changing climate."

Edit, for an open access pdf see:


http://web.science.unsw.edu.au/~matthew/nclimate3335.pdf


« Last Edit: December 13, 2017, 06:02:22 PM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 16478
    • View Profile
  • Liked: 178
  • Likes Given: 12
Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #116 on: August 05, 2017, 03:57:55 AM »
The linked open access reference helps to quantify the influence of the Equatorial Pacific on the Southern Ocean, and indicates that the variability of the Southern Ocean has significantly increased since the 1940's:

Turney, C. S. M., Fogwill, C. J., Palmer, J. G., van Sebille, E., Thomas, Z., McGlone, M., Richardson, S., Wilmshurst, J. M., Fenwick, P., Zunz, V., Goosse, H., Wilson, K.-J., Carter, L., Lipson, M., Jones, R. T., Harsch, M., Clark, G., Marzinelli, E., Rogers, T., Rainsley, E., Ciasto, L., Waterman, S., Thomas, E. R., and Visbeck, M.: Tropical forcing of increased Southern Ocean climate variability revealed by a 140-year subantarctic temperature reconstruction, Clim. Past, 13, 231-248, https://doi.org/10.5194/cp-13-231-2017, 2017.

https://www.clim-past.net/13/231/2017/

Abstract: “Occupying about 14 % of the world's surface, the Southern Ocean plays a fundamental role in ocean and atmosphere circulation, carbon cycling and Antarctic ice-sheet dynamics. Unfortunately, high interannual variability and a dearth of instrumental observations before the 1950s limits our understanding of how marine–atmosphere–ice domains interact on multi-decadal timescales and the impact of anthropogenic forcing. Here we integrate climate-sensitive tree growth with ocean and atmospheric observations on southwest Pacific subantarctic islands that lie at the boundary of polar and subtropical climates (52–54° S). Our annually resolved temperature reconstruction captures regional change since the 1870s and demonstrates a significant increase in variability from the 1940s, a phenomenon predating the observational record. Climate reanalysis and modelling show a parallel change in tropical Pacific sea surface temperatures that generate an atmospheric Rossby wave train which propagates across a large part of the Southern Hemisphere during the austral spring and summer. Our results suggest that modern observed high interannual variability was established across the mid-twentieth century, and that the influence of contemporary equatorial Pacific temperatures may now be a permanent feature across the mid- to high latitudes.”
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 16478
    • View Profile
  • Liked: 178
  • Likes Given: 12
Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #117 on: August 31, 2017, 06:36:26 PM »
The linked reference discusses how global deep waters spiral to the surface of the Southern Ocean (see the attached image):

Tamsitt V, Drake HF, Morrison AK, et al. (2017), "Spiraling Pathways of Global Deep Waters to the Surface of the Southern Ocean." Nature Communications.;8:172, DOI: 10.1038/s41467-017-00197-0

https://www.nature.com/articles/s41467-017-00197-0

Abstract: "Upwelling of global deep waters to the sea surface in the Southern Ocean closes the global overturning circulation and is fundamentally important for oceanic uptake of carbon and heat, nutrient resupply for sustaining oceanic biological production, and the melt rate of ice shelves. However, the exact pathways and role of topography in Southern Ocean upwelling remain largely unknown. Here we show detailed upwelling pathways in three dimensions, using hydrographic observations and particle tracking in high-resolution models. The analysis reveals that the northern-sourced deep waters enter the Antarctic Circumpolar Current via southward flow along the boundaries of the three ocean basins, before spiraling southeastward and upward through the Antarctic Circumpolar Current. Upwelling is greatly enhanced at five major topographic features, associated with vigorous mesoscale eddy activity. Deep water reaches the upper ocean predominantly south of the Antarctic Circumpolar Current, with a spatially nonuniform distribution. The timescale for half of the deep water to upwell from 30° S to the mixed layer is ~60–90 years."

Caption for attached image: "The three dimensional upward spiral of North Atlantic Deep Water through the Southern Ocean. a Observed warm water (>1.6 °C) on the 28.05 kg m−3 neutral density surface from hydrographic observations27, south of 40° S, colored by depth (m). The isoneutral surface is masked in regions with potential temperature below 1.6 °C. 1/4° ocean bathymetry70 is shown in gray. b Modeled (CM2.6) particle pathways from the Atlantic Ocean, with particles released in the depth range 1000–3500 m along 30° S. Colored boxes mark 1° latitude × 1° longitude × 100 m depth grid boxes visited by >3.5% of the total upwelling particle-transport from release at 30° S to the mixed layer. Boxes are colored by depth, similar to a. c Two example upwelling particle trajectories from CM2.6, one originating from the western Atlantic and the other from the eastern Atlantic. Trajectories are colored by depth as in a and b, blue spheres show the particle release locations and red spheres show the location where the particles reach the mixed layer. Three-dimensional maps were produced using Python and Mayavi"
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 16478
    • View Profile
  • Liked: 178
  • Likes Given: 12
Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #118 on: September 17, 2017, 11:05:26 AM »
Interesting information on the correlation of ozone depletion over Antarctica and the Southern Annular Mode (SAM):

Jiao Yang & Cunde Xiao (15 September 2017), "The evolution and volcanic forcing of the southern annular mode during the past 300 years", International Journal of Climatology, DOI: 10.1002/joc.5290 

http://onlinelibrary.wiley.com/doi/10.1002/joc.5290/abstract?utm_content=buffer77291&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Extract: "A positive change in the southern annular mode (SAM), which is the primary pattern of climate variability in the Southern Hemisphere, has been induced predominantly by polar stratospheric ozone depletion. However, the lack of long-term observational records limits our understanding of the long-term SAM behaviour. In this study, we found that the geochemical record of the LGB69 ice core from the eastern coast of Antarctica was significantly correlated with the winter SAM index (SAMI). In addition, we developed an annual mean SAMI beginning in 1701 based on 15 annually resolved ice cores and relevant proxy–climate relationships. Our reconstruction accounted for 54.8% of the total variance from 1957 to 2000 (the calibration period). We demonstrate that the recent positive phase shift in the annual mean SAMI since the 1970s is unprecedented, with the estimate for the latest regime in the 1990s reaching values 2.5 times the standard deviation above the baseline (1701–2000). This peak value also coincides with the largest 30- and 50-year trends, which have occurred at the end of the 20th century. From the reconstructed SAMI, we also found that the response to large volcanic events was likely positive in the 3 years after the eruption, but this positive response can be masked by internal climate variability when a strong El Niño event occurs in the eruption year."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

solartim27

  • ASIF Middle Class
  • Posts: 528
    • View Profile
  • Liked: 13
  • Likes Given: 15
Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #119 on: September 19, 2017, 09:02:34 PM »
Quote
A NASA study has located the Antarctic glaciers that accelerated the fastest between 2008 and 2014 and finds that the most likely cause of their speedup is an observed influx of warm water into the bay where they're located.

The water was only 1 to 2 degrees Fahrenheit (0.5 to 1 degree Celsius) warmer than usual water temperatures in the area, but it increased the glaciers' flow speeds by up to 25 percent and multiplied the rate of glacial ice loss by three to five times -- from 7 to 10 feet of thinning per year (2 to 3 meters) up to 33 feet per year (10 meters).

https://www.jpl.nasa.gov/news/news.php?feature=6949
FNORD

AbruptSLR

  • ASIF Emperor
  • Posts: 16478
    • View Profile
  • Liked: 178
  • Likes Given: 12
Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #120 on: September 30, 2017, 06:43:41 PM »
The linked reference used climate models that include eddies in the ocean to confirm many of the ice-climate feedback mechanisms cited by Hansen.  Hopefully, CMIP6 models will benefit these lessons:

Paul B. Goddard, Carolina O. Dufour, Jianjun Yin, Stephen M. Griffies & Michael Winton (17 September 2017), "CO2-Induced Ocean Warming of the Antarctic Continental Shelf in an Eddying Global Climate Model", JGR Oceans, DOI: 10.1002/2017JC012849

http://onlinelibrary.wiley.com/doi/10.1002/2017JC012849/abstract

Abstract: "Ocean warming near the Antarctic ice shelves has critical implications for future ice sheet mass loss and global sea level rise. A global climate model with an eddying ocean is used to quantify the mechanisms contributing to ocean warming on the Antarctic continental shelf in an idealized 2xCO2 experiment. The results indicate that relatively large warm anomalies occur both in the upper 100 m and at depths above the shelf floor, which are controlled by different mechanisms. The near-surface ocean warming is primarily a response to enhanced onshore advective heat transport across the shelf break. The deep shelf warming is initiated by onshore intrusions of relatively warm Circumpolar Deep Water (CDW), in density classes that access the shelf, as well as the reduction of the vertical mixing of heat. CO2-induced shelf freshening influences both warming mechanisms. The shelf freshening slows vertical mixing by limiting gravitational instabilities and the upward diffusion of heat associated with CDW, resulting in the build-up of heat at depth. Meanwhile, freshening near the shelf break enhances the lateral density gradient of the Antarctic Slope Front (ASF) and disconnect isopycnals between the shelf and CDW, making cross-ASF heat exchange more difficult. However, at several locations along the ASF, the cross-ASF heat transport is less inhibited and heat can move onshore. Once onshore, lateral and vertical heat advection work to disperse the heat anomalies across the shelf region. Understanding the inhomogeneous Antarctic shelf warming will lead to better projections of future ice sheet mass loss."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 16478
    • View Profile
  • Liked: 178
  • Likes Given: 12
Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #121 on: October 12, 2017, 02:54:05 PM »
The linked reference highlights how counterproductive the current glacial models are when they estimate that the Dotson Ice Shelf would not collapse for another 250 years when due to oceanic melting it might collapse within 40 to 50 years, and if hydrofracturing occurs it might collapse 25 to 30 years.

Noel Gourmelen et al (2017), "Channelized Melting Drives Thinning Under a Rapidly Melting Antarctic Ice Shelf", Geophysical Research Letters, DOI: 10.1002/2017GL074929 

http://onlinelibrary.wiley.com/doi/10.1002/2017GL074929/abstract

Abstract: "Ice shelves play a vital role in regulating loss of grounded ice and in supplying freshwater to coastal seas. However, melt variability within ice shelves is poorly constrained and may be instrumental in driving ice shelf imbalance and collapse. High-resolution altimetry measurements from 2010 to 2016 show that Dotson Ice Shelf (DIS), West Antarctica, thins in response to basal melting focused along a single 5 km-wide and 60 km-long channel extending from the ice shelf's grounding zone to its calving front. If focused thinning continues at present rates, the channel will melt through, and the ice shelf collapse, within 40–50 years, almost two centuries before collapse is projected from the average thinning rate. Our findings provide evidence of basal melt-driven sub-ice shelf channel formation and its potential for accelerating the weakening of ice shelves."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 16478
    • View Profile
  • Liked: 178
  • Likes Given: 12
Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #122 on: October 12, 2017, 03:02:02 PM »
The linked article explores the relationship between the Antarctic Ozone hole and sea ice extent.  To me the results indicate that our current models are not adequate to simulate the complexities of the Southern Ocean and Antarctica subjected to anthropogenic forcing:

Laura Landrum, Marika Holland, Marilyn Raphael & Lorenzo Polvani (11 October 2017), "Stratospheric ozone depletion: an unlikely driver of the regional trends in Antarctic sea ice in austral fall in the late 20th Century", Geophysical Research Letters, DOI: 10.1002/2017GL075618 

http://onlinelibrary.wiley.com/doi/10.1002/2017GL075618/abstract?utm_content=bufferbf6ea&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "It has been suggested that recent regional trends in Antarctic sea ice might have been caused by the formation of the ozone hole in the late 20th century. Here we explore this by examining two ensembles of a climate model over the ozone hole formation period (1955-2005). One ensemble includes all known historical forcings; the other is identical except for ozone levels, which are fixed at 1955 levels. We demonstrate that the model is able to capture, on interannual and decadal time scales, the observed statistical relationship between summer Amundsen Sea Low strength (when ozone loss causes a robust deepening) and fall sea-ice concentrations (when observed trends are largest). In spite of this, the modeled regional trends caused by ozone depletion are found to be almost exactly opposite to the observed ones. We deduce that the regional character of observed sea ice trends is likely not caused by ozone depletion."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 16478
    • View Profile
  • Liked: 178
  • Likes Given: 12
Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #123 on: October 15, 2017, 04:59:00 PM »
CMIP5 did not include freshwater hosing from Antarctic ice mass loss to the ocean and thus produced projections of Antarctic sea ice that correlated poorly with the observations from 1980 to 2013.  However, when the linked reference included this freshwater hosing into CESM1(CAM5) they found much improved correlation:

Andrew G. Pauling, Inga J. Smith, Patricia J. Langhorne & Cecilia M. Bitz (9 October 2017), "Time-dependent freshwater input from ice shelves: impacts on Antarctic sea ice and the Southern Ocean in an Earth System Model", Geophysical Research Letters, DOI: 10.1002/2017GL075017 

http://onlinelibrary.wiley.com/doi/10.1002/2017GL075017/abstract?utm_content=buffer0aa71&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "Earth System Models do not reproduce the observed increase in Antarctic sea ice extent which may be due to the unrealistic representation of ice shelves. Here we investigate the response of sea ice to increasing freshwater input from ice shelves using the Community Earth System Model with the Community Atmosphere Model version 5 [CESM1(CAM5)]. Including the effect of heat loss from the ocean to melt ice shelves resulted in significantly more positive trends in sea ice area. We have conducted model experiments adding fresh water as if from ice shelf melt with a linear increase in the rate of input over the period 1980-2013. We found that an increase in the rate of change of freshwater input of ∼45 Gt yr−2 was sufficient to offset the negative trend in sea ice area in CESM1(CAM5), although the freshwater input by the end of the experiment was larger than observed at that time."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 16478
    • View Profile
  • Liked: 178
  • Likes Given: 12
Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #124 on: November 10, 2017, 05:39:29 PM »
The linked reference provides an update on progress being made on modeling the complex Southern Ocean- Antarctic Ice Sheet interaction:

Asay-Davis, X.S., Jourdain, N.C. & Nakayama, Y. (2017), "Developments in Simulating and Parameterizing Interactions Between the Southern Ocean and the Antarctic Ice Sheet", Curr Clim Change Rep, https://doi.org/10.1007/s40641-017-0071-0

https://link.springer.com/article/10.1007%2Fs40641-017-0071-0

Abstract: "Recent advances in both ocean modeling and melt parameterization in ice-sheet models point the way toward coupled ice sheet–ocean modeling, which is needed to quantify Antarctic mass loss and the resulting sea-level rise. The latest Antarctic ocean modeling shows that complex interactions between the atmosphere, sea ice, icebergs, bathymetric features, and ocean circulation on many scales determine which water masses reach ice-shelf cavities and how much heat is available to melt ice. Meanwhile, parameterizations of basal melting in standalone ice-sheet models have evolved from simplified, depth-dependent functions to more sophisticated models, accounting for ice-shelf basal topography, and the evolution of the sub-ice-shelf buoyant flow. The focus of recent work has been on better understanding processes or adding new model capabilities, but a broader community effort is needed in validating models against observations and producing melt-rate projections. Given time, community efforts in coupled ice sheet–ocean modeling, already underway, will tackle the considerable challenges involved in building, initializing, constraining, and performing projections with coupled models, leading to reduced uncertainties in Antarctica’s contribution to future sea-level rise."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 16478
    • View Profile
  • Liked: 178
  • Likes Given: 12
Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #125 on: November 26, 2017, 06:23:18 PM »
Current ESMs do not model either aerosols and/or aerosol cloud interactions very well in the Southern Ocean and Antarctica.  The two linked (& related) references provides new information about paleo aerosols over central Antarctica based on ice cores.  Hopefully, such information can be used to reduce the bias of current ESMs projections with regard to the climate response to warming in the high latitudes of the SH:

Legrand, M., Preunkert, S., Wolff, E., Weller, R., Jourdain, B., and Wagenbach, D.: Year-round records of bulk and size-segregated aerosol composition in central Antarctica (Concordia site) – Part 1: Fractionation of sea-salt particles, Atmos. Chem. Phys., 17, 14039-14054, https://doi.org/10.5194/acp-17-14039-2017, 2017.

https://www.atmos-chem-phys.net/17/14039/2017/

Abstract. Multiple year-round records of bulk and size-segregated composition of aerosol were obtained at the inland site of Concordia located at Dome C in East Antarctica. In parallel, sampling of acidic gases on denuder tubes was carried out to quantify the concentrations of HCl and HNO3 present in the gas phase. These time series are used to examine aerosol present over central Antarctica in terms of chloride depletion relative to sodium with respect to freshly emitted sea-salt aerosol as well as depletion of sulfate relative to sodium with respect to the composition of seawater. A depletion of chloride relative to sodium is observed over most of the year, reaching a maximum of  ∼ 20 ng m−3 in spring when there are still large sea-salt amounts and acidic components start to recover. The role of acidic sulfur aerosol and nitric acid in replacing chloride from sea-salt particles is here discussed. HCl is found to be around twice more abundant than the amount of chloride lost by sea-salt aerosol, suggesting that either HCl is more efficiently transported to Concordia than sea-salt aerosol or re-emission from the snow pack over the Antarctic plateau represents an additional significant HCl source. The size-segregated composition of aerosol collected in winter (from 2006 to 2011) indicates a mean sulfate to sodium ratio of sea-salt aerosol present over central Antarctica of 0.16 ± 0.05, suggesting that, on average, the sea-ice and open-ocean emissions equally contribute to sea-salt aerosol load of the inland Antarctic atmosphere. The temporal variability of the sulfate depletion relative to sodium was examined at the light of air mass backward trajectories, showing an overall decreasing trend of the ratio (i.e., a stronger sulfate depletion relative to sodium) when air masses arriving at Dome C had traveled a longer time over sea ice than over open ocean. The findings are shown to be useful to discuss sea-salt ice records extracted at deep drilling sites located inland Antarctica.

&

Legrand, M., Preunkert, S., Weller, R., Zipf, L., Elsässer, C., Merchel, S., Rugel, G., and Wagenbach, D.: Year-round record of bulk and size-segregated aerosol composition in central Antarctica (Concordia site) – Part 2: Biogenic sulfur (sulfate and methanesulfonate) aerosol, Atmos. Chem. Phys., 17, 14055-14073, https://doi.org/10.5194/acp-17-14055-2017, 2017.

https://www.atmos-chem-phys.net/17/14055/2017/

Abstract. Multiple year-round (2006–2015) records of the bulk and size-segregated composition of aerosol were obtained at the inland site of Concordia located in East Antarctica. The well-marked maximum of non-sea-salt sulfate (nssSO4) in January (100 ± 28 ng m−3 versus 4.4 ± 2.3 ng m−3 in July) is consistent with observations made at the coast (280 ± 78 ng m−3 in January versus 16 ± 9 ng m−3 in July at Dumont d'Urville, for instance). In contrast, the well-marked maximum of MSA at the coast in January (60 ± 23 ng m−3 at Dumont d'Urville) is not observed at Concordia (5.2 ± 2.0 ng m−3 in January). Instead, the MSA level at Concordia peaks in October (5.6 ± 1.9 ng m−3) and March (14.9 ± 5.7 ng m−3). As a result, a surprisingly low MSA-to-nssSO4 ratio (RMSA) is observed at Concordia in mid-summer (0.05 ± 0.02 in January versus 0.25 ± 0.09 in March). We find that the low value of RMSA in mid-summer at Concordia is mainly driven by a drop of MSA levels that takes place in submicron aerosol (0.3 µm diameter). The drop of MSA coincides with periods of high photochemical activity as indicated by high ozone levels, strongly suggesting the occurrence of an efficient chemical destruction of MSA over the Antarctic plateau in mid-summer. The relationship between MSA and nssSO4 levels is examined separately for each season and indicates that concentration of non-biogenic sulfate over the Antarctic plateau does not exceed 1 ng m−3 in fall and winter and remains close to 5 ng m−3 in spring. This weak non-biogenic sulfate level is discussed in the light of radionuclides (210Pb, 10Be, and 7Be) also measured on bulk aerosol samples collected at Concordia. The findings highlight the complexity in using MSA in deep ice cores extracted from inland Antarctica as a proxy of past dimethyl sulfide emissions from the Southern Ocean.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 16478
    • View Profile
  • Liked: 178
  • Likes Given: 12
The linked reference cites model output that indicates: "… that isopycnal eddy stirring is the principal mechanism of shoreward heat transport around Antarctica, though likely modulated by tides and surface forcing."

Andrew L. Stewart, Andreas Klocker & Dimitris Menemenlis (19 January 2018), "Circum-Antarctic Shoreward Heat Transport Derived From an Eddy- and Tide-Resolving Simulation", Geophysical Research Letters, DOI: 10.1002/2017GL075677

http://onlinelibrary.wiley.com/doi/10.1002/2017GL075677/full

Extract: "Almost all heat reaching the bases of Antarctica's ice shelves originates from warm Circumpolar Deep Water in the open Southern Ocean. This study quantifies the roles of mean and transient flows in transporting heat across almost the entire Antarctic continental slope and shelf using an ocean/sea ice model run at eddy- and tide-resolving (1/48°) horizontal resolution. Heat transfer by transient flows is approximately attributed to eddies and tides via a decomposition into time scales shorter than and longer than 1 day, respectively. It is shown that eddies transfer heat across the continental slope (ocean depths greater than 1,500 m), but tides produce a stronger shoreward heat flux across the shelf break (ocean depths between 500 m and 1,000 m). However, the tidal heat fluxes are approximately compensated by mean flows, leaving the eddy heat flux to balance the net shoreward heat transport. The eddy-driven cross-slope overturning circulation is too weak to account for the eddy heat flux. This suggests that isopycnal eddy stirring is the principal mechanism of shoreward heat transport around Antarctica, though likely modulated by tides and surface forcing."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

aperson

  • ASIF Citizen
  • Posts: 137
    • View Profile
  • Liked: 40
  • Likes Given: 69
Antarctic SIE predictions on multi-yearly time scales

Marchi, S., Fichefet, T., Goosse, H. et al. Clim Dyn (14 June 2018)., Reemergence of Antarctic sea ice predictability and its link to deep ocean mixing in global climate models, https://doi.org/10.1007/s0038

Quote
"This first multi-model study of Antarctic sea ice predictability reveals that the ice edge location can potentially be predicted up to 3 years in advance. However, the ice edge location predictability shows contrasted seasonal performances, with high predictability in winter and no predictability in summer. The reemergence of the predictability from one winter to next is provided by the ocean through its large thermal inertia. Sea surface heat anomalies are stored at depth at the end of the winter and influences the sea ice advance the following year as they resurface. The effectiveness of this mechanism across models is found to depend upon the depth of the mixed layer."

If we want to understand forecasting Antarctic Sea Ice, we should be looking at the ocean in winter.

morganism

  • ASIF Citizen
  • Posts: 102
    • View Profile
  • Liked: 1
  • Likes Given: 0
Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #128 on: August 12, 2018, 01:49:37 AM »
Holocene warming effect of southern ocean

"Because of the enhanced Southern Ocean upwelling, the biological pump weakened over the Holocene, allowing more carbon dioxide to leak from the deep ocean into the atmosphere and thus possibly explaining the 20 ppm rise in atmospheric carbon dioxide.

“This process is allowing some of that deeply stored carbon dioxide to invade back to the atmosphere,” said Sigman. “We’re essentially punching holes in the membrane of the biological pump.”

https://www.astrobio.net/alien-life/carbon-leak-may-have-warmed-the-planet-for-11000-years-encouraging-human-civilization/

AbruptSLR

  • ASIF Emperor
  • Posts: 16478
    • View Profile
  • Liked: 178
  • Likes Given: 12
Re: Risks and Challenges for Regional Circulation Models of the Southern Ocean
« Reply #129 on: August 12, 2018, 04:07:44 AM »
Holocene warming effect of southern ocean

"Because of the enhanced Southern Ocean upwelling, the biological pump weakened over the Holocene, allowing more carbon dioxide to leak from the deep ocean into the atmosphere and thus possibly explaining the 20 ppm rise in atmospheric carbon dioxide.

“This process is allowing some of that deeply stored carbon dioxide to invade back to the atmosphere,” said Sigman. “We’re essentially punching holes in the membrane of the biological pump.”

https://www.astrobio.net/alien-life/carbon-leak-may-have-warmed-the-planet-for-11000-years-encouraging-human-civilization/

Newly identified evidence indicates that the Southern Ocean will likely stop absorbing as much CO₂ as it recently has been doing, with continuing anthropogenic radiative forcing:

Title: "How much longer will Southern Ocean slow climate change?"

http://www.newstalkzb.co.nz/news/national/how-much-longer-will-southern-ocean-slow-climate-change/

Extract: "The vast and wild ocean current sucks up more than 40 per cent of the carbon dioxide we produce, acting as a temporary climate-change buffer by slowing down the accumulation of greenhouse gases in our atmosphere.

Yet the same westerly winds that play a critical role in regulating its storing capacity are now threatening its future as a CO2 bank, by bringing deep carbon-rich waters up to the surface.
Many climate models predict that the westerly winds overlying the ocean would get stronger if atmospheric greenhouse gas concentrations continued to risk.

A new international study suggests that in the past, strong westerlies have been linked to higher levels of atmospheric CO2 due to their impact on the Southern Ocean carbon balance.

That meant stronger westerlies could actually speed up climate change if mankind continued to emit as much CO2 as it does today.

"Our new records of the Southern Hemisphere westerly winds suggest there have been large changes in wind intensity over the past 12,000 years.

"This is in marked contrast to climate model simulations that predict only relatively small wind speed changes over the same period."

Yet, Mikaloff-Fletcher added, sea surface carbon data suggested that there was a reversal of this trend in the early 2000s, when the Southern Ocean began taking up carbon much more quickly, even though the westerlies didn't slow.

"The mechanisms behind this change still aren't fully explained, which makes it hard to predict whether this is a short-term effect or a long-term one," she said.

"The Macquarie study suggests that the sudden increase in Southern Ocean carbon uptake may not persist on longer timescales.""
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson