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Author Topic: Risks and Challenges for Regional Circulation Models of the Southern Ocean  (Read 47834 times)

AbruptSLR

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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 »
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AbruptSLR

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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."
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AbruptSLR

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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."
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AbruptSLR

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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."
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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."
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AbruptSLR

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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."
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AbruptSLR

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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 »
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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.”
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AbruptSLR

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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

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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

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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

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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
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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.”
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AbruptSLR

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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