Evaluation of four coupled climate models in the Amundsen Sea, Antarctica

2021 ◽  
Author(s):  
Kyriaki M. Lekakou ◽  
Ben G.M. Webber ◽  
Karen J. Heywood ◽  
David P. Stevens ◽  
Patrick Hyder
Keyword(s):  
Sea Ice ◽  
Continental Shelf ◽  
Deep Water ◽  
Climate Models ◽  
Warm Water ◽  
Low Resolution ◽  
Amundsen Sea ◽  
Ice Shelves ◽  
Medium Resolution ◽  
Warm Deep Water

<p>The Amundsen Sea glaciers, in West Antarctica, are among the world’s fastest discharges of ice into the ocean. The rapid thinning of these ice shelves can be largely explained by basal melting driven by the ocean. Relatively warm water reaches the continental shelf in the Amundsen Sea and deep bathymetric troughs facilitate warm deep water flow to the base of the ice shelves. However, time sparse observational data, and even poorly known bathymetry, contribute to the difficulty of quantifying the key ocean mechanisms, and their variability, that transport warm water onto the Amundsen Sea continental shelf and guide it southward into the ice shelf cavities. Nonetheless these processes should be represented in the coupled climate models, such as those used for CMIP6, which are being used to project future sea level rise.</p><p>Here we leverage recent observational campaigns and gains in process understanding to assess how well four of these models, UKESM1 and the HadGEM-GC3.1 family of models, represent the ocean processes forcing warm water onto the Amundsen Sea continental shelf. The three HadGEM models have the same external forcing but different horizontal resolutions, 1/12, ¼ and 1 degree. The 1 degree resolution UKESM1 is based on HadGEM3.1 but includes atmospheric chemistry, aerosols and marine biogeochemistry. A key finding is the medium resolution (1/4°) HadGEM-GC3.1 model’s inability to allow warm deep water intrusion onto the continental shelf, associated with a strong westward slope current that is not present in the other models. The medium resolution model represents well the annual cycle of sea ice in the Amundsen Sea, but overall has significantly less sea ice around Antarctica, compared with the other models and satellite observations. Despite its low resolution, UKESM1 represents well all the main ocean features, including the shelf-break undercurrent, warm deep water and realistic sea ice. It captures more significant interannual variability, in contrast to the low resolution HadGEM, for which the interannual variability is more suppressed. Of the four models considered here, the best performing models are the 1/12° HadGEM and UKESM1, followed by the low resolution HadGEM model, which reasonably represents warmer deep water on the continental shelf and a shallower mixed layer. The medium resolution HadGEM, despite its better resolution is less realistic than the two low resolution models.</p>

Circulation and Modification of Warm Deep Water on the Central Amundsen Shelf

2014 ◽  
Vol 44 (5) ◽  
pp. 1493-1501 ◽  
Author(s):  
H. K. Ha ◽  
A. K. Wåhlin ◽  
T. W. Kim ◽  
S. H. Lee ◽  
J. H. Lee ◽  
...  
Keyword(s):  
Heat Transport ◽  
Deep Water ◽  
Shelf Area ◽  
Amundsen Sea ◽  
Glacial Ice ◽  
Ice Shelves ◽  
Oceanic Heat Transport ◽  
Eastern Side ◽  
Warm Deep Water ◽  
Western Side

Abstract The circulation pathways and subsurface cooling and freshening of warm deep water on the central Amundsen Sea shelf are deduced from hydrographic transects and four subsurface moorings. The Amundsen Sea continental shelf is intersected by the Dotson trough (DT), leading from the outer shelf to the deep basins on the inner shelf. During the measurement period, warm deep water was observed to flow southward on the eastern side of DT in approximate geostrophic balance. A northward outflow from the shelf was also observed along the bottom in the western side of DT. Estimates of the flow rate suggest that up to one-third of the inflowing warm deep water leaves the shelf area below the thermocline in this deep outflow. The deep current was 1.2°C colder and 0.3 psu fresher than the inflow, but still warm, salty, and dense compared to the overlying water mass. The temperature and salinity properties suggest that the cooling and freshening process is induced by subsurface melting of glacial ice, possibly from basal melting of Dotson and Getz ice shelves. New heat budgets are presented, with a southward oceanic heat transport of 3.3 TW on the eastern side of the DT, a northward oceanic heat transport of 0.5–1.6 TW on the western side, and an ocean-to-glacier heat flux of 0.9–2.53 TW, equivalent to melting glacial ice at the rate of 83–237 km3 yr−1. Recent satellite-based estimates of basal melt rates for the glaciers suggest comparable values for the Getz and Dotson ice shelves.

Variability of warm water intrusions onto the Bellingshausen Sea continental shelf

2021 ◽  
Author(s):  
Ria Oelerich ◽  
Karen J. Heywood ◽  
Gillian M. Damerell ◽  
Andrew F. Thompson
Keyword(s):  
Continental Shelf ◽  
Continental Slope ◽  
Antarctic Peninsula ◽  
Deep Water ◽  
Warm Water ◽  
The West ◽  
Ice Shelves ◽  
West Antarctic ◽  
Bellingshausen Sea ◽  
West Antarctic Peninsula

<p>The continental shelf of the Bellingshausen Sea, located between the West Antarctic Peninsula and the Amundsen Sea, Antarctica, is poorly investigated, compared with its neighbours. Here, the southernmost frontal jet of the Antarctic Circumpolar Current is adjacent to the continental slope which impacts the transport of warm Circumpolar Deep Water onto the shelf. This in turn can influence the transport of heat southward across the shelf and therefore the melting of vulnerable ice shelves.</p><p>We present model-based investigations using the GLORYS12V1 1/12° reanalysis monthly output (GLOBAL_REANALYSIS_PHY_001_030) over 19 years from 2000 to 2018. By connecting the location of the frontal jet to SSH contours we identify seasonal and interannual variability in this current system and demonstrate that the closer the frontal jet is to the continental slope, the greater the flow of warm deep water onto the shelf. This onshore flow is limited to specific areas closest to the frontal jet, predominantly in the eastern Bellingshausen Sea. In contrast, other areas, specifically those troughs where water flows towards the West Antarctic Peninsula and close to the coastline of Antarctica show opposite behaviour with respect to onshelf heat content. Further analyses of flow patterns also indicate the involvement of a coastal jet close to the shore that is weaker when more warm water is on the shelf. Understanding the variability in the current structures throughout the continental shelf of the Bellingshausen Sea in response to a changing frontal jet is essential to gain knowledge about the distribution of heat and therefore the melting of ice shelves.</p>

scholarly journals Variability of Warm Deep Water Inflow in a Submarine Trough on the Amundsen Sea Shelf

2013 ◽  
Vol 43 (10) ◽  
pp. 2054-2070 ◽  
Author(s):  
A. K. Wåhlin ◽  
O. Kalén ◽  
L. Arneborg ◽  
G. Björk ◽  
G. K. Carvajal ◽  
...  
Keyword(s):  
Deep Water ◽  
Bottom Layer ◽  
Shelf Break ◽  
Ocean Currents ◽  
Local Wind ◽  
Amundsen Sea ◽  
Ice Shelves ◽  
Warm Deep Water ◽  
Buoyancy Forces ◽  
Lower Circumpolar Deep Water

Abstract The ice shelves in the Amundsen Sea are thinning rapidly, and the main reason for their decline appears to be warm ocean currents circulating below the ice shelves and melting these from below. Ocean currents transport warm dense water onto the shelf, channeled by bathymetric troughs leading to the deep inner basins. A hydrographic mooring equipped with an upward-looking ADCP has been placed in one of these troughs on the central Amundsen shelf. The two years (2010/11) of mooring data are here used to characterize the inflow of warm deep water to the deep shelf basins. During both years, the warm layer thickness and temperature peaked in austral fall. The along-trough velocity is dominated by strong fluctuations that do not vary in the vertical. These fluctuations are correlated with the local wind, with eastward wind over the shelf and shelf break giving flow toward the ice shelves. In addition, there is a persistent flow of dense lower Circumpolar Deep Water (CDW) toward the ice shelves in the bottom layer. This bottom-intensified flow appears to be driven by buoyancy forces rather than the shelfbreak wind. The years of 2010 and 2011 were characterized by a comparatively stationary Amundsen Sea low, and hence there were no strong eastward winds during winter that could drive an upwelling of warm water along the shelf break. Regardless of this, there was a persistent flow of lower CDW in the bottom layer during the two years. The average heat transport toward the ice shelves in the trough was estimated from the mooring data to be 0.95 TW.

scholarly journals Brief communication: A submarine wall protecting the Amundsen Sea intensifies melting of neighboring ice shelves

2019 ◽  
Author(s):  
Özgür Gürses ◽  
Vanessa Kolatschek ◽  
Qiang Wang ◽  
Christian B. Rodehacke
Keyword(s):  
Sea Ice ◽  
Sea Level Rise ◽  
Sea Level ◽  
Ocean Model ◽  
Warm Water ◽  
Ice Shelf ◽  
Ice Streams ◽  
Amundsen Sea ◽  
Ice Shelves

Abstract. Disintegration of ice shelves in the Amundsen Sea has the potential to cause sea level rise by inducing an acceleration of grounded ice streams. Moore et al. (2018) proposed that using a submarine wall to block the penetration of warm water into the ice shelf cavities could reduce this risk. We use a global sea ice-ocean model to show that a wall shielding the Amundsen Sea below 350 m depth successfully suppresses the inflow of warm water and reduces ice shelf melting. However, the warm water gets redirected towards neighboring ice shelves, which reduces the effectiveness of the wall.

scholarly journals Simulating or prescribing the influence of tides on the Amundsen Sea ice shelves

2019 ◽  
Vol 133 ◽  
pp. 44-55 ◽  
Author(s):  
Nicolas C. Jourdain ◽  
Jean-Marc Molines ◽  
Julien Le Sommer ◽  
Pierre Mathiot ◽  
Jérôme Chanut ◽  
...  
Keyword(s):  
Sea Ice ◽  
Amundsen Sea ◽  
Ice Shelves

scholarly journals On the freshening of the northwestern Weddell Sea continental shelf

Ocean Science ◽  
2011 ◽  
Vol 7 (3) ◽  
pp. 305-316 ◽  
Author(s):  
H. H. Hellmer ◽  
O. Huhn ◽  
D. Gomis ◽  
R. Timmermann
Keyword(s):  
Sea Ice ◽  
Continental Shelf ◽  
Weddell Sea ◽  
Central Basin ◽  
Thermal Front ◽  
Late 20Th Century ◽  
Ice Shelves ◽  
Ice Retreat ◽  
Reduced Salt ◽  
Sea Ice Retreat

Abstract. We analyzed hydrographic data from the northwestern Weddell Sea continental shelf of the three austral winters 1989, 1997, and 2006 and two summers following the last winter cruise. During summer a thermal front exists at ~64° S separating cold southern waters from warm northern waters that have similar characteristics as the deep waters of the central basin of the Bransfield Strait. In winter, the whole continental shelf exhibits southern characteristics with high Neon (Ne) concentrations, indicating a significant input of glacial melt water. The comparison of the winter data from the shallow shelf off the tip of the Antarctic Peninsula, spanning a period of 17 yr, shows a salinity decrease of 0.09 for the whole water column, which has a residence time of <1 yr. We interpret this freshening as being caused by a combination of reduced salt input due to a southward sea ice retreat and higher precipitation during the late 20th century on the western Weddell Sea continental shelf. However, less salinification might also result from a delicate interplay between enhanced salt input due to sea ice formation in coastal areas formerly occupied by Larsen A and B ice shelves and increased Larsen C ice loss.

scholarly journals Impact of ocean forcing on the Aurora Basin in the 21st and 22nd centuries

2016 ◽  
Vol 57 (73) ◽  
pp. 79-86 ◽  
Author(s):  
S. Sun ◽  
S. L. Cornford ◽  
D. E. Gwyther ◽  
R. M. Gladstone ◽  
B. K. Galton-Fenzi ◽  
...  
Keyword(s):  
Climate Models ◽  
Global Climate ◽  
Ice Sheet ◽  
Adaptive Mesh ◽  
Global Climate Models ◽  
Ice Shelf ◽  
Amundsen Sea ◽  
Ice Shelves ◽  
Future Warming ◽  
East West

ABSTRACTThe grounded ice in the Totten and Dalton glaciers is an essential component of the buttressing for the marine-based Aurora basin, and hence their stability is important to the future rate of mass loss from East Antarctica. Totten and Vanderford glaciers are joined by a deep east-west running subglacial trench between the continental ice sheet and Law Dome, while a shallower trench links the Totten and Dalton glaciers. All three glaciers flow into the ocean close to the Antarctic circle and experience ocean-driven ice shelf melt rates comparable with the Amundsen Sea Embayment. We investigate this combination of trenches and ice shelves with the BISICLES adaptive mesh ice-sheet model and ocean-forcing melt rates derived from two global climate models. We find that ice shelf ablation at a rate comparable with the present day is sufficient to cause widespread grounding line retreat in an east-west direction across Totten and Dalton glaciers, with projected future warming causing faster retreat. Meanwhile, southward retreat is limited by the shallower ocean facing slopes between the coast and the bulk of the Aurora sub-glacial trench. However the two climate models produce completely different future ice shelf basal melt rates in this region: HadCM3 drives increasing sub-ice shelf melting to ~2150, while ECHAM5 shows little or no increase in sub-ice shelf melting under the two greenhouse gas forcing scenarios.

Warm water flow and mixing beneath Thwaites Glacier ice shelf, West Antarctica

2020 ◽  
Author(s):  
Anna Wåhlin ◽  
Bastien Queste ◽  
Alastair Graham ◽  
Kelly Hogan ◽  
Lars Boehme ◽  
...  
Keyword(s):  
Water Flow ◽  
Deep Water ◽  
Autonomous Underwater Vehicle ◽  
Warm Water ◽  
Ice Shelf ◽  
Mixing Processes ◽  
Spatial Gradients ◽  
West Antarctic ◽  
Warm Deep Water ◽  
Glacier Ice

&lt;p&gt;The fate of the West Antarctic Ice Sheet is the largest remaining uncertainty in predicting sea-level rise through the next century, and its most vulnerable and rapidly changing outlet is Thwaites Glacier . Because the seabed slope under the glacier is retrograde (downhill inland), ice discharge from Thwaites Glacier is potentially unstable to melting of the underside of its floating ice shelf and grounding line retreat, both of which are enhanced by warm ocean water circulating underneath the ice shelf. Recent observations show surprising spatial variations in melt rates, indicating significant knowledge gaps in our understanding of the processes at the base of the ice shelf. Here we present the first direct observations of ocean temperature, salinity, and oxygen underneath Thwaites ice shelf collected by an autonomous underwater vehicle, a Kongsberg Hugin AUV. These observations show that while the western part of Thwaites has outflow of meltwater-enriched circumpolar deep water found in the main trough leading to Thwaites, the deep water (&gt; 1000 m) underneath the central part of the ice shelf is in connection with Pine Island Bay - a previously unknown westward branch of warm deep water flow. Mid-depth water (700 - 1000 m) enters the cavity from both sides of a buttressing point and large spatial gradients of salinity and temperature indicate that this is a region of active mixing processes. The observations challenge conceptual models of ice-ocean interactions at glacier grounding zones and identify a main buttressing point as a vulnerable region of change currently under attack by warm water inflow from all sides: a scenario that may lead to ungrounding and retreat more quickly than previously expected.&lt;/p&gt;

scholarly journals Tropical Pacific SST Drivers of Recent Antarctic Sea Ice Trends

2016 ◽  
Vol 29 (24) ◽  
pp. 8931-8948 ◽  
Author(s):  
Ariaan Purich ◽  
Matthew H. England ◽  
Wenju Cai ◽  
Yoshimitsu Chikamoto ◽  
Axel Timmermann ◽  
...  
Keyword(s):  
Sea Ice ◽  
Climate Models ◽  
Climate Model ◽  
Ross Sea ◽  
Surface Wind ◽  
Tropical Pacific ◽  
Sea Ice Concentration ◽  
Amundsen Sea ◽  
Model Simulations ◽  
Antarctic Sea Ice

Abstract A strengthening of the Amundsen Sea low from 1979 to 2013 has been shown to largely explain the observed increase in Antarctic sea ice concentration in the eastern Ross Sea and decrease in the Bellingshausen Sea. Here it is shown that while these changes are not generally seen in freely running coupled climate model simulations, they are reproduced in simulations of two independent coupled climate models: one constrained by observed sea surface temperature anomalies in the tropical Pacific and the other by observed surface wind stress in the tropics. This analysis confirms previous results and strengthens the conclusion that the phase change in the interdecadal Pacific oscillation from positive to negative over 1979–2013 contributed to the observed strengthening of the Amundsen Sea low and the associated pattern of Antarctic sea ice change during this period. New support for this conclusion is provided by simulated trends in spatial patterns of sea ice concentrations that are similar to those observed. These results highlight the importance of accounting for teleconnections from low to high latitudes in both model simulations and observations of Antarctic sea ice variability and change.

scholarly journals Explicit and parametrised representation of under ice shelf seas in a z<sup>*</sup> coordinate ocean model

2017 ◽  
Author(s):  
Pierre Mathiot ◽  
Adrian Jenkins ◽  
Christopher Harris ◽  
Gurvan Madec
Keyword(s):  
Sea Ice ◽  
Continental Shelf ◽  
Weddell Sea ◽  
Depth Range ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Antarctic Continental Shelf ◽  
Shelf Seas ◽  
Ocean Properties ◽  
The Antarctic

Abstract. Ice shelf/ocean interactions are a major source of fresh water on the Antarctic continental shelf and have a strong impact on ocean properties, ocean circulation and sea ice. However, climate models based on the ocean/sea ice model NEMO currently do not include these interactions in any detail. The capability of explicitly simulating the circulation beneath ice shelves is introduced in the non-linear free surface model NEMO. Its implementation into the NEMO framework and its assessment in an idealised and realistic circum-Antarctic configuration is described in this study. Compared with the current prescription of ice shelf melting (i.e. at the surface) inclusion of open sub-ice-shelf leads to a decrease sea ice thickness along the coast, a weakening of the ocean stratification on the shelf, a decrease in salinity of HSSW on the Ross and Weddell Sea shelves and an increase in the strength of the gyres that circulate within the over-deepened basins on the West Antarctic continental shelf. Mimicking the under ice shelf seas overturning circulation by introducing the meltwater over the depth range of the ice shelf base, rather than at the surface is also tested. It yields similar improvements in the simulated ocean properties and circulation over the Antarctic continental shelf than the explicit ice shelf cavity representation. With the ice shelf cavities opened, the widely-used “3 equations” ice shelf melting formulation enables an interactive computation of melting that has been assessed. Comparison with observational estimates of ice shelf melting indicates realistic results for most ice shelves. However, melting rates for Amery, Getz and George VI ice shelves are considerably overestimated.

Sign in / Sign up

Export Citation Format

Share Document