scholarly journals Future Projections of Antarctic Ice Shelf Melting Based on CMIP5 Scenarios

2018 ◽  
Vol 31 (13) ◽  
pp. 5243-5261 ◽  
Author(s):  
Kaitlin A. Naughten ◽  
Katrin J. Meissner ◽  
Benjamin K. Galton-Fenzi ◽  
Matthew H. England ◽  
Ralph Timmermann ◽  
...  
Keyword(s):  
Sea Ice ◽  
First Century ◽  
Ice Formation ◽  
Cmip5 Models ◽  
Ice Shelf ◽  
Amundsen Sea ◽  
Future Projections ◽  
Twenty First Century ◽  
Basal Melting ◽  
The Antarctic

Basal melting of Antarctic ice shelves is expected to increase during the twenty-first century as the ocean warms, which will have consequences for ice sheet stability and global sea level rise. Here we present future projections of Antarctic ice shelf melting using the Finite Element Sea Ice/Ice-Shelf Ocean Model (FESOM) forced with atmospheric output from models from phase 5 of the Coupled Model Intercomparison Project (CMIP5). CMIP5 models are chosen based on their agreement with historical atmospheric reanalyses over the Southern Ocean; the best-performing models are ACCESS 1.0 and the CMIP5 multimodel mean. Their output is bias-corrected for the representative concentration pathway (RCP) 4.5 and 8.5 scenarios. During the twenty-first-century simulations, total ice shelf basal mass loss increases by between 41% and 129%. Every sector of Antarctica shows increased basal melting in every scenario, with the largest increases occurring in the Amundsen Sea. The main mechanism driving this melting is an increase in warm Circumpolar Deep Water on the Antarctic continental shelf. A reduction in wintertime sea ice formation simulated during the twenty-first century stratifies the water column, allowing a warm bottom layer to develop and intrude into ice shelf cavities. This effect may be overestimated in the Amundsen Sea because of a cold bias in the present-day simulation. Other consequences of weakened sea ice formation include freshening of High Salinity Shelf Water and warming of Antarctic Bottom Water. Furthermore, freshening around the Antarctic coast in our simulations causes the Antarctic Circumpolar Current to weaken and the Antarctic Coastal Current to strengthen.

scholarly journals Interannual-to-Multidecadal Responses of Antarctic Ice Shelf–Ocean Interaction and Coastal Water Masses during the Twentieth Century and the Early Twenty-First Century to Dynamic and Thermodynamic Forcing

2020 ◽  
Vol 33 (12) ◽  
pp. 4941-4973
Author(s):  
Kazuya Kusahara
Keyword(s):  
Twentieth Century ◽  
Southern Ocean ◽  
Sea Ice ◽  
Coastal Water ◽  
Water Masses ◽  
First Century ◽  
Ice Shelf ◽  
Early Twenty ◽  
Basal Melting ◽  
The Antarctic

AbstractMuch attention has been paid to ocean–cryosphere interactions over the Southern Ocean. Basal melting of Antarctic ice shelves has been reported to be the primary ablation process for the Antarctic ice sheets. Warm waters on the continental shelf, such as Circumpolar Deep Water (CDW) and Antarctic Surface Water (AASW), play a critical role in active ice shelf basal melting. However, the temporal evolution and mechanisms of the basal melting and warm water intrusions throughout the twentieth century and the early twenty-first century have not been rigorously examined and are not fully understood. Here, we conduct a numerical experiment of an ocean–sea ice–ice shelf model forced with a century-long atmospheric reanalysis for the period 1900–2010. To begin with, we provide an assessment of the atmospheric conditions by comparing with available observation and show biases in warming and stronger westerly trends. Taking into account the limitation, we examine the interannual-to-multidecadal variability in the Antarctic ice shelf basal melting and the role of coastal water masses. A series of numerical experiments demonstrate that wind stress changes over the Southern Ocean drive enhanced poleward heat transport by stronger subpolar gyres and reduce coastal sea ice and cold-water formations, both of which result in an increased ocean heat flux into Antarctic ice shelf cavities. Furthermore, an increase of sea ice–free days leads to enhanced regional AASW contribution to the basal melting. This study demonstrates that changes in Antarctic coastal water masses are key metrics for better understanding of the ocean–cryosphere interaction over the Southern Ocean.

scholarly journals Contrasting the Antarctic and Arctic Atmospheric Responses to Projected Sea Ice Loss in the Late Twenty-First Century

2018 ◽  
Vol 31 (16) ◽  
pp. 6353-6370 ◽  
Author(s):  
Mark England ◽  
Lorenzo Polvani ◽  
Lantao Sun
Keyword(s):  
Sea Ice ◽  
Climate Model ◽  
Arctic Sea Ice ◽  
First Century ◽  
The Arctic ◽  
Minor Role ◽  
Systems Model ◽  
Antarctic Sea Ice ◽  
Twenty First Century ◽  
The Antarctic

Abstract Models project that Antarctic sea ice area will decline considerably by the end of this century, but the consequences remain largely unexplored. Here, the atmospheric response to future sea ice loss in the Antarctic is investigated, and contrasted to the Arctic case, using the Community Earth Systems Model (CESM) Whole Atmosphere Coupled Climate Model (WACCM). Time-slice model runs with historic sea ice concentrations are compared to runs with future concentrations, from the late twenty-first century, in each hemisphere separately. As for the Arctic, results indicate that Antarctic sea ice loss will act to shift the tropospheric jet equatorward, an internal negative feedback to the poleward shift associated with increased greenhouse gases. Also, the tropospheric response to Antarctic sea ice loss is found to be somewhat weaker, more vertically confined, and less seasonally varying than in the case of Arctic sea ice loss. The stratospheric response to Antarctic sea ice loss is relatively weak compared to the Arctic case, although it is here demonstrated that the latter is still small relative to internal variability. In contrast to the Arctic case, the response of the ozone layer is found to be positive (up to 5 Dobson units): interestingly, it is present in all seasons except austral spring. Finally, while the response of surface temperature and precipitation is limited to the southern high latitudes, it is nonetheless unable to impact the interior of the Antarctic continent, suggesting a minor role of sea ice loss on recent Antarctic temperature trends.

scholarly journals Modeling intensive ocean–cryosphere interactions in Lützow-Holm Bay, East Antarctica

2020 ◽  
Author(s):  
Kazuya Kusahara ◽  
Daisuke Hirano ◽  
Masakazu Fujii ◽  
Alexander D. Fraser ◽  
Takeshi Tamura
Keyword(s):  
Sea Ice ◽  
Bottom Topography ◽  
East Antarctica ◽  
Ice Shelf ◽  
Atlantic Sector ◽  
Ice Shelves ◽  
Water Intrusion ◽  
Fast Ice ◽  
Basal Melting ◽  
The Antarctic

Abstract. Basal melting of Antarctic ice shelves accounts for more than half of the mass loss from the Antarctic Ice Sheet. Many studies have focused on active basal melting at ice shelves in the Amundsen-Bellingshausen Seas and the Totten Ice shelf, East Antarctica. In these regions, the intrusion of Circumpolar Deep Water (CDW) onto the continental shelf is a key component for the localized intensive basal melting. Both regions have a common oceanographic feature: southward deflection of the Antarctic Circumpolar Current on the eastern flank of ocean gyres brings CDW onto the continental shelves. The physical setting of Shirase Glacier Tongue (SGT) in Lützow-Holm Bay corresponds to a similar configuration for the Weddell Gyre in the Atlantic sector. Here, we conduct a 2–3 km resolution simulation of an ocean-sea ice-ice shelf model using a newly-compiled bottom topography dataset in the bay. The model can reproduce the observed CDW intrusion along the deep trough. The modeled SGT basal melting reaches a peak in summer and minimum in autumn and winter, consistent with the wind-driven seasonality of the CDW thickness in the bay. The model results suggest the existence of eastward-flowing undercurrent on the upper continental slope in summer, and the undercurrent contributes to the seasonal-to-interannual variability of the warm water intrusion into the bay. Furthermore, numerical experiments with and without fast-ice cover in the bay demonstrate that fast ice plays a role as an effective thermal insulator and reduces local sea-ice formation, resulting in much warmer water intrusion into the SGT cavity.

scholarly journals Modeling intensive ocean–cryosphere interactions in Lützow-Holm Bay, East Antarctica

2021 ◽  
Vol 15 (4) ◽  
pp. 1697-1717
Author(s):  
Kazuya Kusahara ◽  
Daisuke Hirano ◽  
Masakazu Fujii ◽  
Alexander D. Fraser ◽  
Takeshi Tamura
Keyword(s):  
Sea Ice ◽  
Bottom Topography ◽  
East Antarctica ◽  
Ice Shelf ◽  
Atlantic Sector ◽  
Ice Shelves ◽  
Water Intrusion ◽  
Fast Ice ◽  
Basal Melting ◽  
The Antarctic

Abstract. Basal melting of Antarctic ice shelves accounts for more than half of the mass loss from the Antarctic ice sheet. Many studies have focused on active basal melting at ice shelves in the Amundsen–Bellingshausen seas and the Totten ice shelf, East Antarctica. In these regions, the intrusion of Circumpolar Deep Water (CDW) onto the continental shelf is a key component for the localized intensive basal melting. Both regions have a common oceanographic feature: southward deflection of the Antarctic Circumpolar Current brings CDW toward the continental shelves. The physical setting of the Shirase Glacier tongue (SGT) in Lützow-Holm Bay corresponds to a similar configuration on the southeastern side of the Weddell Gyre in the Atlantic sector. Here, we conduct a 2–3 km resolution simulation of an ocean–sea ice–ice shelf model using a recently compiled bottom-topography dataset in the bay. The model can reproduce the observed CDW intrusion along the deep trough. The modeled SGT basal melting reaches a peak in summer and a minimum in autumn and winter, consistent with the wind-driven seasonality of the CDW thickness in the bay. The model results suggest the existence of an eastward-flowing undercurrent on the upper continental slope in summer, and the undercurrent contributes to the seasonal-to-interannual variability in the warm water intrusion into the bay. Furthermore, numerical experiments with and without fast-ice cover in the bay demonstrate that fast ice plays a role as an effective thermal insulator and reduces local sea ice formation, resulting in much warmer water intrusion into the SGT cavity.

scholarly journals CMIP5 Diversity in Southern Westerly Jet Projections Related to Historical Sea Ice Area: Strong Link to Strengthening and Weak Link to Shift

2017 ◽  
Vol 31 (1) ◽  
pp. 195-211 ◽  
Author(s):  
Thomas J. Bracegirdle ◽  
Patrick Hyder ◽  
Caroline R. Holmes
Keyword(s):  
Sea Ice ◽  
Weak Link ◽  
Coupled Model ◽  
First Century ◽  
Sea Surface ◽  
Cmip5 Models ◽  
Cross Model ◽  
Near Surface ◽  
Westerly Jet ◽  
Twenty First Century

Abstract A major feature of projected changes in Southern Hemisphere climate under future scenarios of increased greenhouse gas concentrations is the poleward shift and strengthening of the main eddy-driven belt of midlatitude, near-surface westerly winds (the westerly jet). However, there is large uncertainty in projected twenty-first-century westerly jet changes across different climate models. Here models from the World Climate Research Programme’s phase 5 of the Coupled Model Intercomparison Project (CMIP5) were evaluated to assess linkages between diversity in simulated sea ice area (SIA), Antarctic amplification, and diversity in projected twenty-first-century changes in the westerly jet following the representative concentration pathway 8.5 (RCP8.5) scenario. To help disentangle cause and effect in the coupled model analysis, uncoupled atmosphere-only fixed sea surface experiments from CMIP5 were also evaluated. It is shown that across all seasons, approximately half of the variance in projected RCP8.5 jet strengthening is explained statistically by intermodel differences in simulated historical SIA, whereby CMIP5 models with larger baseline SIA exhibit more ice retreat and less jet strengthening in the future. However, links to jet shift are much weaker and are only statistically significant in austral autumn and winter. It is suggested that a significant cross-model correlation between historical jet strength and projected strength change (r = −0.58) is, at least in part, a result of atmospherically driven historical SIA biases, which then feed back into the atmosphere in future projections. The results emphasize that SIA appears to act in concert with proximal changes in sea surface temperature gradients in relation to model diversity in westerly jet projections.

scholarly journals Tracing Future Spring and Summer Drying in Southern Africa to Tropical Lows and the Congo Air Boundary

2020 ◽  
Vol 33 (14) ◽  
pp. 6205-6228
Author(s):  
Emma Howard ◽  
Richard Washington
Keyword(s):  
Southern Africa ◽  
Austral Summer ◽  
Summer Rainfall ◽  
First Century ◽  
Cmip5 Models ◽  
Spatial Change ◽  
Wet Season ◽  
Austral Spring ◽  
Future Projections ◽  
Twenty First Century

AbstractIn southern Africa, models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) predict robust future drying associated with a delayed rainy-season onset in the austral spring and a range of wetting and drying patterns in the austral summer. This paper relates these rainfall changes to dynamical shifts in two classes of weather systems: the Congo Air Boundary (CAB) and tropical lows. Objective algorithms are used to track these features in CMIP5 model output. It is then established that the climatological locations and frequencies of these systems are reasonably well represented in the CMIP5 models. RCP8.5 end-of-twenty-first-century projections are compared with historical end-of-twentieth-century simulations. Future projections in tropical-low locations and frequencies diverge, but indicate an overall average decrease of 15% and in some cases a northward shift. The projected spatial change in the tropical-low frequency distribution is weakly positively correlated to the projected spatial change in the austral summer rainfall distribution. Meanwhile, future projections indicate a 13% increase in CAB frequency from October to December. This is associated with the gradual climatological CAB breakdown occurring half a month later on average in end-of-twenty-first-century RCP8.5 projections. A delay in the gradual seasonal decline of the CAB prevents rainfall to the south of the CAB’s mean position, most of which is shown to occur on CAB breakdown days, hence creating the austral spring drying signal and delayed wet-season onset. Intermodel variability in the magnitude of CAB frequency increase is able to explain intermodel variability in the projected drying.

The role of sea ice in the fresh-water budget of the Weddell Sea, Antarctica

2001 ◽  
Vol 33 ◽  
pp. 419-424 ◽  
Author(s):  
R. Timmermann ◽  
A. Beckmann ◽  
H. H. Hellmer
Keyword(s):  
Sea Ice ◽  
Fresh Water ◽  
Water Budget ◽  
Ocean Model ◽  
Weddell Sea ◽  
Ice Formation ◽  
Necessary Condition ◽  
Ice Shelf ◽  
Basal Melting ◽  
Good Agreement

AbstractA coupled sea-ice-ocean model of the Weddell Sea, Antarctica, has been developed as part of the Bremerhaven Regional Ice-Ocean Simulations (BRIOS) project. It is based on the s-Coordinate Primitive Equation ocean Model (SPEM) and a dynamic-thermodynamic sea-ice model with viscous-plastic rheology which also provides the thermohaline forcing at the base of the Antarctic ice shelves. Model runs are forced with wind, cloudiness, temperature and precipitation fields of the European Centre for Medium-range Weather Forecasts and U.S. National Centers for Environmental Prediction re-analyses. Model results show good agreement with observations of ice extent, thickness and drift. Water-mass properties and the large-scale circulation are in good agreement with observations. Fresh-water fluxes from sea-ice formation as well as from ice-shelf basal melting and from precipitation are computed and compiled to the fresh-water budget of the Weddell Sea. Supporting estimates based on hydrographic observations, model results indicate that fresh-water loss due to sea-ice formation and export (34mSv) is roughly balanced by ice-shelf basal melting (9 mSv) and net precipitation (19 mSv). Furthermore, sea-ice formation appears to be a necessary condition for bottom-water production in the Weddell Sea.

scholarly journals Factors affecting projected Arctic surface shortwave heating and albedo change in coupled climate models

2015 ◽  
Vol 373 (2045) ◽  
pp. 20140162 ◽  
Author(s):  
Marika M. Holland ◽  
Laura Landrum
Keyword(s):  
Sea Ice ◽  
Surface State ◽  
Climate Models ◽  
First Century ◽  
The Arctic ◽  
Cmip5 Models ◽  
Ice Surface ◽  
Area Loss ◽  
Twenty First Century ◽  
Arctic Surface

We use a large ensemble of simulations from the Community Earth System Model to quantify simulated changes in the twentieth and twenty-first century Arctic surface shortwave heating associated with changing incoming solar radiation and changing ice conditions. For increases in shortwave absorption associated with albedo reductions, the relative influence of changing sea ice surface properties and changing sea ice areal coverage is assessed. Changes in the surface sea ice properties are associated with an earlier melt season onset, a longer snow-free season and enhanced surface ponding. Because many of these changes occur during peak solar insolation, they have a considerable influence on Arctic surface shortwave heating that is comparable to the influence of ice area loss in the early twenty-first century. As ice area loss continues through the twenty-first century, it overwhelms the influence of changes in the sea ice surface state, and is responsible for a majority of the net shortwave increases by the mid-twenty-first century. A comparison with the Arctic surface albedo and shortwave heating in CMIP5 models indicates a large spread in projected twenty-first century change. This is in part related to different ice loss rates among the models and different representations of the late twentieth century ice albedo and associated sea ice surface state.

scholarly journals Observed interannual changes beneath Filchner-Ronne Ice Shelf linked to large-scale atmospheric circulation

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Tore Hattermann ◽  
Keith W. Nicholls ◽  
Hartmut H. Hellmer ◽  
Peter E. D. Davis ◽  
Markus A. Janout ◽  
...  
Keyword(s):  
Sea Ice ◽  
Atmospheric Circulation ◽  
Large Scale ◽  
Numerical Models ◽  
Ice Sheet ◽  
Hot Water ◽  
Ice Formation ◽  
Ice Shelf ◽  
Amundsen Sea ◽  
Large Scale Atmospheric Circulation

AbstractFloating ice shelves are the Achilles’ heel of the Antarctic Ice Sheet. They limit Antarctica’s contribution to global sea level rise, yet they can be rapidly melted from beneath by a warming ocean. At Filchner-Ronne Ice Shelf, a decline in sea ice formation may increase basal melt rates and accelerate marine ice sheet mass loss within this century. However, the understanding of this tipping-point behavior largely relies on numerical models. Our new multi-annual observations from five hot-water drilled boreholes through Filchner-Ronne Ice Shelf show that since 2015 there has been an intensification of the density-driven ice shelf cavity-wide circulation in response to reinforced wind-driven sea ice formation in the Ronne polynya. Enhanced southerly winds over Ronne Ice Shelf coincide with westward displacements of the Amundsen Sea Low position, connecting the cavity circulation with changes in large-scale atmospheric circulation patterns as a new aspect of the atmosphere-ocean-ice shelf system.

scholarly journals Tracing future spring and summer drying in southern Africa to tropical lows and the Congo Air Boundary

2020 ◽  
Author(s):  
Emma Howard ◽  
Richard Washington
Keyword(s):  
Southern Africa ◽  
Austral Summer ◽  
Summer Rainfall ◽  
First Century ◽  
Cmip5 Models ◽  
Spatial Change ◽  
Wet Season ◽  
Austral Spring ◽  
Future Projections ◽  
Twenty First Century

In southern Africa, models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) predict robust future drying associated with a delayed rainy-season onset in the austral spring and a range of wetting and drying patterns in the austral summer. This paper relates these rainfall changes to dynamical shifts in two classes of weather systems: the Congo Air Boundary (CAB) and tropical lows. Objective algorithms are used to track these features in CMIP5 model output. It is then established that the climatological locations and frequencies of these systems are reasonably well represented in the CMIP5 models. RCP8.5 end-of-twenty-first-century projections are compared with historical end-of-twentieth-century simulations. Future projections in tropical-low locations and frequencies diverge, but indicate an overall average decrease of 15% and in some cases a northward shift. The projected spatial change in the tropical-low frequency distribution is weakly positively correlated to the projected spatial change in the austral summer rainfall distribution. Meanwhile, future projections indicate a 13% increase in CAB frequency from October to December. This is associated with the gradual climatological CAB breakdown occurring half a month later on average in end-of-twenty-first-century RCP8.5 projections. A delay in the gradual seasonal decline of the CAB prevents rainfall to the south of the CAB’s mean position, most of which is shown to occur on CAB breakdown days, hence creating the austral spring drying signal and delayed wet-season onset. Intermodel variability in the magnitude of CAB frequency increase is able to explain intermodel variability in the projected drying.

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