scholarly journals On the Role of Coastal Troughs in the Circulation of Warm Circumpolar Deep Water on Antarctic Shelves

2013 ◽  
Vol 43 (1) ◽  
pp. 51-64 ◽  
Author(s):  
Pierre St-Laurent ◽  
John M. Klinck ◽  
Michael S. Dinniman
Keyword(s):  
Deep Water ◽  
Ice Sheets ◽  
Ocean Model ◽  
Mean Flow ◽  
Ice Shelf ◽  
Circumpolar Deep Water ◽  
Onshore Flow ◽  
Continental Shelves ◽  
Bellingshausen Sea

Abstract Oceanic exchanges across the continental shelves of Antarctica play an important role in biological systems and the mass balance of ice sheets. The focus of this study is on the mechanisms responsible for the circulation of warm Circumpolar Deep Water (CDW) within troughs running perpendicular to the continental shelf. This is examined using process-oriented numerical experiments with an eddy-resolving (1 km) 3D ocean model that includes a static and thermodynamically active ice shelf. Three mechanisms that create a significant onshore flow within the trough are identified: 1) a deep onshore flow driven by the melt of the ice shelf, 2) interaction between the longshore mean flow and the trough, and 3) interaction between a Rossby wave along the shelf break and the trough. In each case the onshore flow is sufficient to maintain the warm temperatures underneath the ice shelf and basal melt rates of O(1 m yr−1). The third mechanism in particular reproduces several features revealed by moorings from Marguerite Trough (Bellingshausen Sea): the temperature maximum at middepth, a stronger intrusion on the downstream edge of the trough, and the appearance of warm anticyclonic anomalies every week. Sensitivity experiments highlight the need to properly resolve the small baroclinic radii of these regions (5 km on the shelf)—simulations at 3-km resolution cannot reproduce mechanism 3 and the associated heat transport.

scholarly journals Glacial Meltwater Identification in the Amundsen Sea

2017 ◽  
Vol 47 (4) ◽  
pp. 933-954 ◽  
Author(s):  
Louise C. Biddle ◽  
Karen J. Heywood ◽  
Jan Kaiser ◽  
Adrian Jenkins
Keyword(s):  
Dissolved Oxygen ◽  
Deep Water ◽  
Ocean Model ◽  
Water Type ◽  
Ice Shelf ◽  
Amundsen Sea ◽  
Glacial Meltwater ◽  
Circumpolar Deep Water ◽  
Water Characteristics ◽  
Multiparameter Analysis

AbstractPine Island Ice Shelf, in the Amundsen Sea, is losing mass because of warm ocean waters melting the ice from below. Tracing meltwater pathways from ice shelves is important for identifying the regions most affected by the increased input of this water type. Here, optimum multiparameter analysis is used to deduce glacial meltwater fractions from water mass characteristics (temperature, salinity, and dissolved oxygen concentrations), collected during a ship-based campaign in the eastern Amundsen Sea in February–March 2014. Using a one-dimensional ocean model, processes such as variability in the characteristics of the source water masses on shelf and biological productivity/respiration are shown to affect the calculated apparent meltwater fractions. These processes can result in a false meltwater signature, creating misleading apparent glacial meltwater pathways. An alternative glacial meltwater calculation is suggested, using a pseudo–Circumpolar Deep Water endpoint and using an artificial increase in uncertainty of the dissolved oxygen measurements. The pseudo–Circumpolar Deep Water characteristics are affected by the under ice shelf bathymetry. The glacial meltwater fractions reveal a pathway for 2014 meltwater leading to the west of Pine Island Ice Shelf, along the coastline.

scholarly journals Origin of Circumpolar Deep Water intruding onto the Amundsen and Bellingshausen Sea continental shelves

2018 ◽  
Vol 9 (1) ◽  
Author(s):  
Yoshihiro Nakayama ◽  
Dimitris Menemenlis ◽  
Hong Zhang ◽  
Michael Schodlok ◽  
Eric Rignot
Keyword(s):  
Deep Water ◽  
Circumpolar Deep Water ◽  
Continental Shelves ◽  
Bellingshausen Sea

scholarly journals Warm Circumpolar Deep Water at the Western Getz Ice Shelf Front, Antarctica

2019 ◽  
Vol 46 (2) ◽  
pp. 870-878 ◽  
Author(s):  
K. M. Assmann ◽  
E. Darelius ◽  
A. K. Wåhlin ◽  
T. W. Kim ◽  
S. H. Lee
Keyword(s):  
Deep Water ◽  
Ice Shelf ◽  
Circumpolar Deep Water

scholarly journals Circulation of modified Circumpolar Deep Water and basal melt beneath the Amery Ice Shelf, East Antarctica

2015 ◽  
Vol 120 (4) ◽  
pp. 3098-3112 ◽  
Author(s):  
Laura Herraiz-Borreguero ◽  
Richard Coleman ◽  
Ian Allison ◽  
Stephen R. Rintoul ◽  
Mike Craven ◽  
...  
Keyword(s):  
Deep Water ◽  
East Antarctica ◽  
Ice Shelf ◽  
Circumpolar Deep Water ◽  
Amery Ice Shelf

scholarly journals Eddy-Resolving Model Estimate of the Cabbeling Effect on the Water Mass Transformation in the Southern Ocean

2012 ◽  
Vol 42 (8) ◽  
pp. 1288-1302 ◽  
Author(s):  
L. Shogo Urakawa ◽  
Hiroyasu Hasumi
Keyword(s):  
Southern Ocean ◽  
Deep Water ◽  
Water Mass ◽  
Formation Rate ◽  
Ocean Model ◽  
Intermediate Water ◽  
Mode Water ◽  
Model Estimate ◽  
Circumpolar Deep Water ◽  
Water Mass Transformation

Abstract Cabbeling effect on the water mass transformation in the Southern Ocean is investigated with the use of an eddy-resolving Southern Ocean model. A significant amount of water is densified by cabbeling: water mass transformation rates are about 4 Sv (1 Sv ≡ 106 m3 s−1) for transformation from surface/thermocline water to Subantarctic Mode Water (SAMW), about 7 Sv for transformation from SAMW to Antarctic Intermediate Water (AAIW), and about 5 Sv for transformation from AAIW to Upper Circumpolar Deep Water. These diapycnal volume transports occur around the Antarctic Circumpolar Current (ACC), where mesoscale eddies are active. The water mass transformation by cabbeling in this study is also characterized by a large amount of densification of Lower Circumpolar Deep Water (LCDW) into Antarctic Bottom Water (AABW) (about 9 Sv). Large diapycnal velocity is found not only along the ACC but also along the coast of Antarctica at the boundary between LCDW and AABW. It is found that about 3 Sv of LCDW is densified into AABW by cabbeling on the continental slopes of Antarctica in this study. This densification is not small compared with observational and numerical estimates on the AABW formation rate, which ranges from 10 to 20 Sv.

scholarly journals Sensitivity of Circumpolar Deep Water Transport and Ice Shelf Basal Melt along the West Antarctic Peninsula to Changes in the Winds

2012 ◽  
Vol 25 (14) ◽  
pp. 4799-4816 ◽  
Author(s):  
Michael S. Dinniman ◽  
John M. Klinck ◽  
Eileen E. Hofmann
Keyword(s):  
Continental Shelf ◽  
Antarctic Peninsula ◽  
Deep Water ◽  
Constant Factor ◽  
Ice Shelf ◽  
The West ◽  
Ice Shelves ◽  
Circumpolar Deep Water ◽  
West Antarctic ◽  
West Antarctic Peninsula

Abstract Circumpolar Deep Water (CDW) can be found near the continental shelf break around most of Antarctica. Advection of this relatively warm water (up to 2°C) across the continental shelf to the base of floating ice shelves is thought to be a critical source of heat for basal melting in some locations. A high-resolution (4 km) regional ocean–sea ice–ice shelf model of the west Antarctic Peninsula (WAP) coastal ocean was used to examine the effects of changes in the winds on across-shelf CDW transport and ice shelf basal melt. Increases and decreases in the strength of the wind fields were simulated by scaling the present-day winds by a constant factor. Additional simulations considered effects of increased Antarctic Circumpolar Current (ACC) transport. Increased wind strength and ACC transport increased the amount of CDW transported onto the WAP continental shelf but did not necessarily increase CDW flux underneath the nearby ice shelves. The basal melt underneath some of the deeper ice shelves actually decreased with increased wind strength. Increased mixing over the WAP shelf due to stronger winds removed more heat from the deeper shelf waters than the additional heat gained from increased CDW volume transport. The simulation results suggest that the effect on the WAP ice shelves of the projected strengthening of the polar westerlies is not a simple matter of increased winds causing increased (or decreased) basal melt. A simple budget calculation indicated that iron associated with increased vertical mixing of CDW could significantly affect biological productivity of this region.

The role of ocean circulation in the propagation of rifts on ice shelves.

2020 ◽  
Author(s):  
Mattia Poinelli ◽  
Eric Larour ◽  
Riccardo Riva
Keyword(s):  
Ocean Circulation ◽  
Regional Climate ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Rift Propagation ◽  
Break Up ◽  
The Stability

<p>The break-up of large ice shelves and the associated loss of ice are thought to play a destabilizing role in the ice sheet dynamics. Although ice shelves are a substantial buttressing source in the stability of continental ice sheets, the propagation of large rifts eventually leads to the break-up of icebergs into the ocean. As consequence, this loss of ice would trigger further glacier acceleration and ice sheets retreat, destabilizing the ice cap. Retreat and collapse of ice sheets are also thought to be related to regional climate warming. Indeed, satellite observations suggest that a warming surrounding would induce the ice sheet to progressive thinning and weakening.</p><p>The prolongation of un-grounded ice into the ocean is often interrupted by the propagation of fractures that eventually separates large icebergs from the ice shelf. These fractures are called rifts and range from dimensions of 10 to 100 km. A recent example of such phenomena is the massive break-up of the Larsen C in July, 2017 which followed the disintegration of Larsen A in 1995 and the partial break-up of Larsen B in 2002. The tabular iceberg formed by Larsen C was limited by the propagation of a large rift that began in summer 2016, although the ice shelf had already been thinning since 1992.</p><p>Rift initiation and propagation are thought to be the result of glaciological and oceanographic sources that trigger ice to break. Nonetheless, exact mechanisms remain elusive. The on-going project focuses on ice-ocean interactions in ice shelves that accommodate rifts by using oceanographic models. The goal is to couple rift propagation and ocean circulation underneath ice cavities in order to infer how basal melting affects the development of rifts. The numerical framework is developed within the capabilities of the MITgcm. We aim to identify the sensitivity of propagation rate and opening rate of rifts to variations in the ocean circulation that have occurred during the separation of part of the ice shelf.</p><p>On a larger scale, we are interested in the role of rifting in the stability of Antarctic shelves. Therefore, we work toward a better understanding of which processes are involved in the triggering of rift propagation.</p>

The role of cephalopods in the world’s oceans: general conclusions and the future

1996 ◽  
Vol 351 (1343) ◽  
pp. 1105-1112 ◽  
Keyword(s):  
Shallow Water ◽  
Deep Water ◽  
Sampling Methods ◽  
Total Biomass ◽  
Continental Shelves ◽  
Direct Sampling ◽  
Almost All ◽  
Neutrally Buoyant ◽  
Negatively Buoyant

In this volume we have considered the problems of investigation special to cephalopods. Almost all our knowledge of their general biology is restricted to the shelf-living, muscular, negatively buoyant (the Loliginidae and Octopodidae) or gas-supported species (the Sepiidae and Nautilidae) and members of the Ommastrephidae which move on to the continental shelves at certain seasons. These species of the continental shelves comprise only about 15% of all cephalopod genera and live in water of less than 300 m depth, which covers only 6% of the Earth’s surface. They do not represent the majority of cephalopod species or much of their total biomass; 85 % of genera are spread in the upper 2000 m and across the bottom of the deep oceans, which occupy 66 % of the Earth’s surface. Over 40% of these genera are neutrally buoyant by oil or chemical means and may have very different lifestyles from the forms we know from shallow water. Improvement of our knowledge of the ecology of deep water forms is hindered by our poor direct sampling methods and rests largely upon sampling from stomachs or regurgitations of the predators that eat cephalopods.

scholarly journals Tropical forcing of Circumpolar Deep Water Inflow and outlet glacier thinning in the Amundsen Sea Embayment, West Antarctica

2012 ◽  
Vol 53 (60) ◽  
pp. 19-28 ◽  
Author(s):  
E.J. Steig ◽  
Q. Ding ◽  
D.S. Battisti ◽  
A. Jenkins
Keyword(s):  
Wind Stress ◽  
Deep Water ◽  
Reanalysis Data ◽  
Ocean Model ◽  
Tropical Pacific ◽  
Amundsen Sea ◽  
Outlet Glacier ◽  
Circumpolar Deep Water ◽  
Tropical Forcing ◽  
The North

AbstractOutlet glaciers draining the Antarctic ice sheet into the Amundsen Sea Embayment (ASE) have accelerated in recent decades, most likely as a result of increased melting of their ice-shelf termini by warm Circumpolar Deep Water (CDW). An ocean model forced with climate reanalysis data shows that, beginning in the early 1990s, an increase in westerly wind stress near the continental shelf edge drove an increase in CDW inflow onto the shelf. The change in local wind stress occurred predominantly in fall and early winter, associated with anomalous high sea-level pressure (SLP) to the north of the ASE and an increase in sea surface temperature (SST) in the central tropical Pacific. The SLP change is associated with geopotential height anomalies in the middle and upper troposphere, characteristic of a stationary Rossby wave response to tropical SST forcing, rather than with changes in the zonally symmetric circulation. Tropical Pacific warming similar to that of the 1990s occurred in the 1940s, and thus is a candidate for initiating the current period of ASE glacier retreat.

Late Holocene advance of the Müller Ice Shelf, Antarctic Peninsula: sedimentological, geochemical and palaeontological evidence

1995 ◽  
Vol 7 (2) ◽  
pp. 159-170 ◽  
Author(s):  
Eugene W. Domack ◽  
Scott E. Ishman ◽  
Andrew B. Stein ◽  
Charles E. McClennen ◽  
A.J. Timothy Jull
Keyword(s):  
Antarctic Peninsula ◽  
Deep Water ◽  
Sediment Cores ◽  
Austral Summer ◽  
Ice Age ◽  
Geochemical Data ◽  
Organic Carbon Content ◽  
Ice Shelf ◽  
Circumpolar Deep Water ◽  
The Antarctic

Marine sediment cores were obtained from in front of the Müller Ice Shelf in Lallemand Fjord, Antarctic Peninsula in the austral summer of 1990–91. Sedimentological and geochemical data from these cores document a warm period that preceded the advance of the Müller Ice Shelf into Lallemand Fjord. The advance of the ice shelf is inferred from a reduction in the total organic carbon content and an increase in well-sorted, aeolian, sand in cores proximal to the present calving line. This sedimentological change is paralleled by a change in the foraminiferal assemblages within the cores. Advance of the ice shelf is indicated by a shift from assemblages dominated by calcareous benthic and planktonic forms to those dominated by agglutinated forms. A 14C chronology for the cores indicates that the advance of the Müller Ice Shelf took place c. 400 years ago, coincident with glacier advances in other high southern latitude sites during the onset of the Little Ice Age. Ice core evidence, however, documents this period as one of warmer temperatures for the Antarctic Peninsula. We suggest that the ice shelf advance was linked to the exclusion of circumpolar deep water from the fjord. This contributed to increased mass balance of the ice shelf system by preventing the rapid undermelt that is today associated with warm circumpolar deep water within the fjord. We also document the recent retreat of the calving line of the Müller Ice Shelf that is apparently in response to a recent (four decade long) warming trend along the western side of the Antarctic Peninsula.

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