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  • 1
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    Modeled Trends in Antarctic Sea Ice Thickness (2014)
    American Meteorological Society
    In:  EPIC3Journal of Climate, American Meteorological Society, 27(10), pp. 3784-3801, ISSN: 0894-8755
    Details
    Publication Date: 2014-05-15
    Description: Unlike the rapid sea ice losses reported in the Arctic, satellite observations show an overall increase in Antarctic sea ice concentration over recent decades. However, observations of decadal trends in Antarctic ice thickness, and hence ice volume, do not currently exist. In this study a model of the Southern Ocean and its sea ice, forced by atmospheric reanalyses, is used to assess 1992–2010 trends in ice thickness and volume. The model successfully reproduces observations of mean ice concentration, thickness, and drift, and decadal trends in ice concentration and drift, imparting some confidence in the hindcasted trends in ice thickness. The model suggests that overall Antarctic sea ice volume has increased by approximately 30 km3 yr−1 (0.4% yr−1) as an equal result of areal expansion (20 × 103 km2 yr−1 or 0.2% yr−1) and thickening (1.5 mm yr−1 or 0.2% yr−1). This ice volume increase is an order of magnitude smaller than the Arctic decrease, and about half the size of the increased freshwater supply from the Antarctic Ice Sheet. Similarly to the observed ice concentration trends, the small overall increase in modeled ice volume is actually the residual of much larger opposing regional trends. Thickness changes near the ice edge follow observed concentration changes, with increasing concentration corresponding to increased thickness. Ice thickness increases are also found in the inner pack in the Amundsen and Weddell Seas, where the model suggests that observed ice-drift trends directed toward the coast have caused dynamical thickening in autumn and winter. Modeled changes are predominantly dynamic in origin in the Pacific sector and thermodynamic elsewhere.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 2
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    Observed propagation of a large rift in the Larsen C ice shelf: rift development and possible consequences for the stability of the ice shelf (2015)
    In:  EPIC3International Symposium on contemporary ice sheet dynamics, Cambridge, UK, 2015-08-16-2015-08-21
    Details
    Publication Date: 2015-10-05
    Description: The Larsen C ice shelf is the most northerly of the remaining major Antarctic Peninsula ice shelves and is vulnerable to changes in both ocean and atmospheric forcing. It is the largest ice shelf in the region and its loss would lead to a significant drawdown of ice from the Antarctic Peninsula ice sheet. There have been observations of widespread thinning, melt ponding in the northern inlets, and a speed-up in ice flow, processes that have all been linked to former ice-shelf collapses. Previous studies have also highlighted the vulnerability of the Larsen C ice shelf to specific potential changes in its geometry, including a retreat from the Bawden and Gipps Ice Rise. Rift tips in the vicinity of Gipps Ice Rise have been observed to align at a suture zone between two flow units within the shelf. Several studies have provided evidence for marine ice in these suture zones, which has been found to act as a weak coupling between flow units with different flow velocities. It has been concluded that this ice inhibits the propagation of rifts because it can accommodate strain in the ice without fracturing further. In a change from the usual pattern, a northwards-propagating rift from Gipps Ice Rise has recently penetrated through the suture zone and is now more than halfway towards calving a large section of the ice shelf. The rate of propagation of this rift accelerated during 2014. When the next major calving event occurs, the Larsen C ice shelf is likely to lose around 10% of its area to reach a new minimum area for the ice shelf. We followed the rift propagation on MODIS and Landsat imagery and used a numerical model to investigate the influence of the future calving event on ice-shelf stability. We find that the ice front is at risk of becoming unstable when the anticipated calving event occurs.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 3
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    The contribution of the Weddell Gyre to the lower limb of the Global Overturning Circulation (2014)
    Wiley
    In:  EPIC3Journal of Geophysical Research: Oceans, Wiley, 119(6), pp. 3357-3377, ISSN: 2169-9291
    Details
    Publication Date: 2014-07-17
    Description: The horizontal and vertical circulation of the Weddell Gyre is diagnosed using a box inverse model constructed with recent hydrographic sections and including mobile sea ice and eddy transports. The gyre is found to convey 42 +/- 8 Sv (1 Sv = 10^6 m3 s–1) across the central Weddell Sea and to intensify to 54 +/- 15 Sv further offshore. This circulation injects 36 +/- 13 TW of heat from the Antarctic Circumpolar Current to the gyre, and exports 51 +/- 23 mSv of freshwater, including 13 +/- 1 mSv as sea ice to the midlatitude Southern Ocean. The gyre’s overturning circulation has an asymmetric double-cell structure, in which 13 +/- 4 Sv of Circumpolar Deep Water (CDW) and relatively light Antarctic Bottom Water (AABW) are transformed into upper-ocean water masses by midgyre upwelling (at a rate of 2 +/- 2 Sv) and into denser AABW by downwelling focussed at the western boundary (8 +/- 2 Sv). The gyre circulation exhibits a substantial throughflow component, by which CDW and AABW enter the gyre from the Indian sector, undergo ventilation and densification within the gyre, and are exported to the South Atlantic across the gyre’s northern rim. The relatively modest net production of AABW in the Weddell Gyre (6 +/- 2 Sv) suggests that the gyre’s prominence in the closure of the lower limb of global oceanic overturning stems largely from the recycling and equatorward export of Indian-sourced AABW.
    Repository Name: EPIC Alfred Wegener Institut
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  • 4
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    Strong Sensitivity of Pine Island Ice-Shelf Melting to Climatic Variability (2014)
    AAAS
    In:  EPIC3Science, AAAS, 343(6167), pp. 174-178, ISSN: 0036-8075
    Details
    Publication Date: 2014-09-22
    Description: Pine Island Glacier has thinned and accelerated over recent decades, significantly contributing to global sea level rise. Increased oceanic melting of its ice shelf is thought to have triggered those changes. Observations and numerical modeling reveal large fluctuations in the ocean heat available in the adjacent bay and enhanced sensitivity of ice shelf melting to water temperatures at intermediate depth, as a seabed ridge blocks the deepest and warmest waters from reaching the thickest ice. Oceanic melting decreased by 50% between January 2010 and 2012, with ocean conditions in 2012 partly attributable to atmospheric forcing associated with a strong La Niña event. Both atmospheric variability and local ice shelf and seabed geometry play fundamental roles in determining the response of the Antarctic Ice Sheet to climate.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 5
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    Experimental design for three interrelated marine ice sheet and ocean model intercomparison projects: MISMIP v. 3 (MISMIP +), ISOMIP v. 2 (ISOMIP +) and MISOMIP v. 1 (MISOMIP1) (2016)
    In:  EPIC3Geoscientific Model Development, 9(7), pp. 2471-2497, ISSN: 1991-9603
    Details
    Publication Date: 2017-06-15
    Repository Name: EPIC Alfred Wegener Institut
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  • 6
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    Observed rift propagation in the Larsen C Ice Shelf and future calving front stability (2015)
    In:  EPIC3Twenty-Second Annual WAIS Workshop, Sylvan Dale Ranch, Loveland, CO, USA, 2015-09-16-2015-09-19
    Details
    Publication Date: 2015-10-05
    Description: The Larsen C Ice Shelf is the most northerly of the remaining major Antarctic Peninsula ice shelves and is vulnerable to changes in both to ocean and atmospheric forcing. It is the largest ice shelf in the region and its loss would lead to a significant drawdown of ice from the Antarctic Peninsula Ice Sheet. There have been observations of widespread thinning, melt ponding in the northern inlets, and, in the northern part, a speed-up in ice flow, all processes which have been linked to former ice shelf collapses. Previous studies have also highlighted the vulnerability of Larsen C Ice Shelf to specific potential changes in its geometry including a retreat from the Bawden and Gipps Ice Rise. In a change from the usual pattern, a northwards-propagating rift from Gipps Ice Rise has recently advanced towards the center of the ice shelf. It is now more than halfway towards calving a large section of the ice shelf and continues to widen. We followed the rift propagation on MODIS and Landsat imagery and, during the austral winter 2015, on Sentinel 1 radar data. Sentinel 1 data was also used to calculate flow velocity fields for the ice shelf. We used a numerical model to investigate the influence of the future calving event on ice shelf stability. To investigate a range of possible outcomes from a future calving event, we assumed two scenarios for the rift trajectory based on its current orientation and direction of propagation. To assess the stability of the future calving front we analyzed the difference between the predicted directions of ice flow and of first principal stress (stress-flow angle). Regions of the shelf exhibiting low stress-flow angles are likely to be more affected by small-scale calving because stresses act to open existing weaknesses. We find that the ice front is at risk of becoming unstable when the anticipated calving event occurs.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 7
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    Modeling of the influence of sea ice cycle and Langmuir circulation on the upper ocean mixed layer depth and freshwater distribution at the West Antarctic Peninsula (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Schultz, C., Doney, S. C., Zhang, W. G., Regan, H., Holland, P., Meredith, M. P., & Stammerjohn, S. Modeling of the influence of sea ice cycle and Langmuir circulation on the upper ocean mixed layer depth and freshwater distribution at the West Antarctic Peninsula. Journal of Geophysical Research: Oceans, 125(8), (2020): e2020JC016109, doi:10.1029/2020JC016109.
    Description: The Southern Ocean is chronically undersampled due to its remoteness, harsh environment, and sea ice cover. Ocean circulation models yield significant insight into key processes and to some extent obviate the dearth of data; however, they often underestimate surface mixed layer depth (MLD), with consequences for surface water‐column temperature, salinity, and nutrient concentration. In this study, a coupled circulation and sea ice model was implemented for the region adjacent to the West Antarctic Peninsula, a climatically sensitive region which has exhibited decadal trends towards higher ocean temperature, shorter sea ice season, and increasing glacial freshwater input, overlain by strong interannual variability. Hindcast simulations were conducted with different air‐ice drag coefficients and Langmuir circulation parameterizations to determine the impact of these factors on MLD. Including Langmuir circulation deepened the surface mixed layer, with the deepening being more pronounced in the shelf and slope regions. Optimal selection of an air‐ice drag coefficient also increased modeled MLD by similar amounts and had a larger impact in improving the reliability of the simulated MLD interannual variability. This study highlights the importance of sea ice volume and redistribution to correctly reproduce the physics of the underlying ocean, and the potential of appropriately parameterizing Langmuir circulation to help correct for biases towards shallow MLD in the Southern Ocean. The model also reproduces observed freshwater patterns in the West Antarctic Peninsula during late summer and suggests that areas of intense summertime sea ice melt can still show net annual freezing due to high sea ice formation during the winter.
    Description: C. Schultz and S. Doney acknowledge support by the U.S. National Science Foundation (grant PLR‐1440435 to the Palmer Long Term Ecological Research program) and support from the University of Virginia. W. G. Zhang acknowledge support by the U.S. National Science Foundation (grant OPP‐1643901). The MITgcm model is an open source model (mitgcm.org). The version used in this study, with added parameterizations and specific configurations, is on C. Schultz’s github (https://github.com/crisoceano/WAP_MITgcm). A copy of the files with specific configurations for this study, the forcing files needed for the simulations, and a copy of the files used for the KPP package are in three separate records on zenodo.org, under DOIs 10.5281/zenodo.3627365, 10.5281/zenodo.3627564, and 10.5281/zenodo.3627742.
    Keywords: West Antarctic Peninsula ; sea ice ; Langmuir circulation ; mixed layer depth ; glacial runoff
    Repository Name: Woods Hole Open Access Server
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  • 8
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    The contribution of the Weddell Gyre to the lower limb of the Global Overturning Circulation (2014)
    John Wiley & Sons
    Details
    Publication Date: 2022-12-22
    Description: Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 119 (2014): 3357–3377, doi:10.1002/2013JC009725.
    Description: The horizontal and vertical circulation of the Weddell Gyre is diagnosed using a box inverse model constructed with recent hydrographic sections and including mobile sea ice and eddy transports. The gyre is found to convey 42 ± 8 Sv (1 Sv = 106 m3 s–1) across the central Weddell Sea and to intensify to 54 ± 15 Sv further offshore. This circulation injects 36 ± 13 TW of heat from the Antarctic Circumpolar Current to the gyre, and exports 51 ± 23 mSv of freshwater, including 13 ± 1 mSv as sea ice to the midlatitude Southern Ocean. The gyre's overturning circulation has an asymmetric double-cell structure, in which 13 ± 4 Sv of Circumpolar Deep Water (CDW) and relatively light Antarctic Bottom Water (AABW) are transformed into upper-ocean water masses by midgyre upwelling (at a rate of 2 ± 2 Sv) and into denser AABW by downwelling focussed at the western boundary (8 ± 2 Sv). The gyre circulation exhibits a substantial throughflow component, by which CDW and AABW enter the gyre from the Indian sector, undergo ventilation and densification within the gyre, and are exported to the South Atlantic across the gyre's northern rim. The relatively modest net production of AABW in the Weddell Gyre (6 ± 2 Sv) suggests that the gyre's prominence in the closure of the lower limb of global oceanic overturning stems largely from the recycling and equatorward export of Indian-sourced AABW.
    Description: The ANDREX project was supported by the National Environmental Research Council (NE/E01366X/1). L.J. also acknowledges financial support from NSF (OCE-1231803).
    Description: 2014-12-05
    Keywords: Weddell Sea ; Southern Ocean ; Meridional overturning circulation ; Oceanography ; Sea ice ; Climate
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 9
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    Ocean-Forced Ice-Shelf Thinning in a Synchronously Coupled Ice-Ocean Model (2018)
    American Geophysical Union
    Details
    Publication Date: 2018-02-01
    Print ISSN: 2169-9275
    Electronic ISSN: 2169-9291
    Topics: Geosciences , Physics
    Published by American Geophysical Union
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  • 10
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    Variability of the Ross Gyre, Southern Ocean: Drivers and Responses Revealed by Satellite Altimetry (2018)
    American Geophysical Union
    Details
    Publication Date: 2018-06-29
    Description: Year-round variability in the Ross Gyre (RG), Antarctica, during 2011–2015, is derived using radar altimetry. The RG is characterized by a bounded recirculating component and a westward throughflow to the south. Two modes of variability of the sea surface height and ocean surface stress curl are revealed. The first represents a large-scale sea surface height change forced by the Antarctic Oscillation. The second represents semiannual variability in gyre area and strength, driven by fluctuations in sea level pressure associated with the Amundsen Sea Low. Variability in the throughflow is also linked to the Amundsen Sea Low. An adequate description of the oceanic circulation is achieved only when sea ice drag is accounted for in the ocean surface stress. The drivers of RG variability elucidated here have significant implications for our understanding of the oceanic forcing of Antarctic Ice Sheet melting and for the downstream propagation of its ocean freshening footprint. ©2018. The Authors.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by American Geophysical Union
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