Antarctic Slope Current modulates ocean heat intrusions towards Totten Glacier

The Antarctic margin is surrounded by two westward flowing currents: the Antarctic Slope Current and the Antarctic Coastal Current. The former influences key processes near the Antarctic margin by regulating the flow of heat and nutrients onto and off the continental shelf, while together they advect nutrients, biological organisms, and temperature and salinity anomalies around the coastline, providing a connective link between different shelf regions. However, the extent to which these currents transport water from one sector of the continental shelf to another, and the timescales over which this occurs, remain poorly understood. Concern that crucial water formation sites around the Antarctic coastline could respond to non-local freshwater forcing from ice shelf meltwater motivates a more thorough understanding of zonal connectivity around Antarctica. In this study, we use daily velocity fields from a global high-resolution ocean-sea ice model, combined with the Lagrangian tracking software Parcels, to investigate the pathways and timescales connecting different regions of the Antarctic continental shelf with a view to understanding the timescales of meltwater transport around the continent. Virtual particles are released over the continental shelf, poleward of the 1000 metre isobath, and are tracked for 20 years. Our results show a strong seasonal cycle connecting different sectors of the Antarctic continent, with more particles arriving further downstream during winter than during summer months. Strong advective links exist between West Antarctica and the Ross Sea while shelf geometry in some other regions acts as barriers to transport. We also highlight the varying importance of the Antarctic Slope Current and Antarctic Coastal Current in connecting different sectors of the coastline. Our results help to improve our understanding of circum-Antarctic connectivity and the timescales of meltwater transport from source regions to downstream shelf locations. Furthermore, the timescales and pathways we present provide a baseline from which to assess long-term changes in Antarctic coastal circulation due to local and remote forcing.

Download Full-text

Variability of the Antarctic Slope Current System in the Northwestern Weddell Sea

Journal of Physical Oceanography ◽

10.1175/jpo-d-17-0030.1 ◽

2017 ◽

Vol 47 (12) ◽

pp. 2977-2997 ◽

Cited By ~ 11

Author(s):

Marina Azaneu ◽

Karen J. Heywood ◽

Bastien Y. Queste ◽

Andrew F. Thompson

Keyword(s):

Current System ◽

Water Layer ◽

Bottom Layer ◽

Weddell Sea ◽

The South ◽

Orkney Islands ◽

Dense Water ◽

South Orkney Islands ◽

Antarctic Slope Current ◽

The Antarctic

AbstractThe dense water outflow from the Antarctic continental shelf is closely associated with the strength and position of the Antarctic Slope Front. This study explores the short-term and spatial variability of the Antarctic Slope Front system and the mechanisms that regulate cross-slope exchange using highly temporally and spatially resolved measurements from three ocean gliders deployed in 2012. The 22 sections along the eastern Antarctic Peninsula and west of the South Orkney Islands are grouped regionally and composited by isobaths. There is consistency in the front position around the Powell Basin, varying mostly between the 500- and 800-m isobaths. In most of the study area the flow is bottom intensified. The along-slope transport of the Antarctic Slope Current (upper 1000 m) varies between 0.2 and 5.9 Sv (1 Sv ≡ 106 m3 s−1) and does not exhibit a regional pattern. The magnitude of the velocity field shows substantial variability, up to twice its mean value. Higher eddy kinetic energy (0.003 m2 s−2) is observed in sections with dense water, possibly because of baroclinic instabilities in the bottom layer. Distributions of potential vorticity show an increase toward the shelf along isopycnals and also in the dense water layer. Glider sections located west of the South Orkney Islands indicate a northward direction of the flow associated with the Weddell Front, which differs from previous estimates of the mean circulation. This study provides some of the first observational confirmation of the high-frequency variability associated with an active eddy field that has been suggested by recent numerical simulations in this region.

Download Full-text

Modelling the seasonal variability of the Antarctic Slope Current

Ocean Science ◽

10.5194/os-7-455-2011 ◽

2011 ◽

Vol 7 (4) ◽

pp. 455-470 ◽

Cited By ~ 34

Author(s):

P. Mathiot ◽

H. Goosse ◽

T. Fichefet ◽

B. Barnier ◽

H. Gallée

Keyword(s):

Wind Speed ◽

Mass Transport ◽

Sea Ice ◽

Seasonal Cycle ◽

Water Mass ◽

Atmospheric Forcing ◽

Sensitivity Experiments ◽

The Mean ◽

Antarctic Slope Current ◽

The Antarctic

Abstract. One of the main features of the oceanic circulation along Antarctica is the Antarctic Slope Current (ASC). This circumpolar current flows westwards and contributes to communication between the three major oceanic basins around Antarctica. The ASC is not very well known due to remote location and the presence of sea ice during several months, allowing in situ studies only during summertime. Moreover, only few modelling studies of this current have been carried out. Here, we investigate the sensitivity of this simulated current to four different resolutions in a coupled ocean-sea ice model and to two different atmospheric forcing sets. Two series of simulations are conducted. For the first series, global model configurations are run at coarse (2°) to eddy-permitting (0.25°) resolutions with the same atmospheric forcing. For the second series, simulations with two different atmospheric forcings are performed using a regional circumpolar configuration (south of 30° S) at 0.5° resolution. The first atmospheric forcing is based on a global atmospheric reanalysis and satellite data, while the second is based on a downscaling of the global atmospheric reanalysis by a regional atmospheric model calibrated to Antarctic meteorological conditions. Sensitivity experiments to resolution indicate that a minimum model resolution of 0.5° is needed to capture the dynamics of the ASC in terms of water mass transport and recirculation. Sensitivity experiments to atmospheric forcing fields shows that the wind speed along the Antarctic coast strongly controls the water mass transport and the seasonal cycle of the ASC. An increase in annual mean of easterlies by about 30 % leads to an increase in the mean ASC transport by about 40 %. Similar effects are obtained on the seasonal cycle: using a wind forcing field with a larger seasonal cycle (+30 %) increases by more than 30 % the amplitude of the seasonal cycle of the ASC. To confirm the importance of wind seasonal cycle, a simulation without wind speed seasonal cycle is carried out. This simulation shows a decrease by more than 50 % of the amplitude of the ASC transport seasonal cycle without changing the mean value of ASC transport.

Download Full-text

Coupled ocean/sea ice dynamics of the Antarctic Slope Current driven by topographic eddy suppression and sea ice momentum redistribution

10.1002/essoar.10507558.1 ◽

2021 ◽

Author(s):

Yidongfang Si ◽

Andrew Stewart ◽

Ian Eisenman

Keyword(s):

Sea Ice ◽

Ice Dynamics ◽

Sea Ice Dynamics ◽

Antarctic Slope Current ◽

The Antarctic

Download Full-text

Acceleration and Overturning of the Antarctic Slope Current by Winds, Eddies, and Tides

Journal of Physical Oceanography ◽

10.1175/jpo-d-18-0221.1 ◽

2019 ◽

Vol 49 (8) ◽

pp. 2043-2074 ◽

Cited By ~ 10

Author(s):

Andrew L. Stewart ◽

Andreas Klocker ◽

Dimitris Menemenlis

Keyword(s):

Sea Ice ◽

Continental Shelf ◽

Continental Slope ◽

Mesoscale Eddy ◽

Shelf Break ◽

Ekman Transport ◽

Global Ocean ◽

Antarctic Slope Current ◽

The Antarctic ◽

Continental Shelf Break

AbstractAll exchanges between the open ocean and the Antarctic continental shelf must cross the Antarctic Slope Current (ASC). Previous studies indicate that these exchanges are strongly influenced by mesoscale and tidal variability, yet the mechanisms responsible for setting the ASC’s transport and structure have received relatively little attention. In this study the roles of winds, eddies, and tides in accelerating the ASC are investigated using a global ocean–sea ice simulation with very high resolution (1/48° grid spacing). It is found that the circulation along the continental slope is accelerated both by surface stresses, ultimately sourced from the easterly winds, and by mesoscale eddy vorticity fluxes. At the continental shelf break, the ASC exhibits a narrow (~30–50 km), swift (>0.2 m s−1) jet, consistent with in situ observations. In this jet the surface stress is substantially reduced, and may even vanish or be directed eastward, because the ocean surface speed matches or exceeds that of the sea ice. The shelfbreak jet is shown to be accelerated by tidal momentum advection, consistent with the phenomenon of tidal rectification. Consequently, the shoreward Ekman transport vanishes and thus the mean overturning circulation that steepens the Antarctic Slope Front (ASF) is primarily due to tidal acceleration. These findings imply that the circulation and mean overturning of the ASC are not only determined by near-Antarctic winds, but also depend crucially on sea ice cover, regionally-dependent mesoscale eddy activity over the continental slope, and the amplitude of tidal flows across the continental shelf break.

Download Full-text

Genesis of the Antarctic Slope Current in West Antarctica

Geophysical Research Letters ◽

10.1029/2020gl087802 ◽

2020 ◽

Vol 47 (16) ◽

Author(s):

Andrew F. Thompson ◽

Kevin G. Speer ◽

Lena M. Schulze Chretien

Keyword(s):

West Antarctica ◽

Antarctic Slope Current ◽

The Antarctic

Download Full-text

Spatial and temporal variability of the Antarctic Slope Current in an eddying ocean-sea ice model

10.5194/egusphere-egu21-13947 ◽

2021 ◽

Author(s):

Wilma Huneke ◽

Adele Morrison ◽

Andy Hogg

Keyword(s):

Continental Shelf ◽

Temporal Variability ◽

Shelf Break ◽

Spatial And Temporal Variability ◽

Shelf Water ◽

Antarctic Continental Shelf ◽

Antarctic Slope Current ◽

The Antarctic ◽

Continental Shelf Break ◽

Ice Model

The basal melt rate of Antarctica's ice shelves is largely controlled by heat delivered from the Southern Ocean to the Antarctic continental shelf. The Antarctic Slope Current (ASC) is an almost circumpolar feature that encircles Antarctica along the continental shelf break in an anti-clockwise direction. Because the circulation is to first order oriented along the topographic slope, it inhibits exchange of water masses between the Southern Ocean and the Antarctic continental shelf and thereby impacts cross-slope heat supply. Direct observations of the ASC system are sparse, but indicate a highly variable flow field both in time and space. Given the importance of the circulation near the shelf break for cross-shelf exchange of heat, it is timely to further improve our knowledge of the ASC system. This study makes use of the global ocean-sea ice model ACCESS-OM2-01 with a 1/10 degree horizontal resolution and describes the spatial and temporal variability of the velocity field. We categorise the modelled ASC into three different regimes, similar to previous works for the associated Antarctic Slope Front: (i) A surface-intensified current found predominantly in East Antarctica, (ii) a bottom-intensified current found downstream of the dense shelf water formation sites in the Ross, Weddell, and Prydz Bay Seas, and (iii) a reversed current found in West Antarctica where the eastward flowing Antarctic Circumpolar Current impinges onto the continental shelf break. We find that the temporal variability of the Antarctic Slope Current varies between the regimes. In the bottom-intensified regions, the variability is set by the timing of the dense shelf water overflows, whereas the surface-intensified flow responds to the sub-monthly variability in the wind field.

Download Full-text

Cross-Slope Observations in the Bellingshausen Sea, Southern Ocean

10.5194/egusphere-egu2020-463 ◽

2020 ◽

Author(s):

Ria Oelerich ◽

Karen J. Heywood ◽

Gillian M. Damerell ◽

Andrew F. Thompson

Keyword(s):

Current System ◽

Amundsen Sea ◽

Ice Shelves ◽

West Antarctic ◽

Bellingshausen Sea ◽

Average Current ◽

Adcp Data ◽

Basal Melting ◽

Antarctic Slope Current ◽

The Antarctic

The Bellingshausen Sea, located between the West Antarctic Peninsula and the Amundsen Sea, is poorly observed, compared with its neighbours. The Antarctic Slope Front (ASF), that rings the continental slope of Antarctica, supports a westward current (the Antarctic Slope Current). The structure and variability of this current affect exchange processes close to Antarctica such as the transport of warm Circumpolar Deep Water onto the Antarctic continental shelf. This water mass is responsible for the transport of heat across the shelf and therefore the basal melting of ice shelves. Due to the lack of observations, it is still unclear if the ASF even exists in the Bellingshausen Sea or if there are other processes moderating the transport of warm water onto the shelf.We present ship-based and glider-based CTD data collected in 2007 and 2019, which in total provide 7 cross-slope sections in the Bellingshausen Sea. Geostrophic velocities are referenced to lowered ADCP data, shipboard ADCP data and the Dive Average Current. Cumulative transports show remarkable differences between the years 2007 and 2019. The sections of 2007 provide cumulative transports of up to 3.5 Sv eastward. In contrast, the sections in 2019 have cumulative transports up to 2 Sv westward. The sections from 2007 and 2019 are in very similar locations, indicating a temporal change rather than a spatial change.We compare the cross-slope sections from the observations with sections from the NEMO 1/12 &#176; model output. A time series of cumulative transports from the model, covering the years from 2000 to 2010, allows us to identify seasonality and interannual variability in this current system.

Download Full-text