Antarctic Peninsula Ice Shelves Research Articles

Characteristics of Surface “Melt Potential” over Antarctic Ice Shelves based on Regional Atmospheric Model Simulations of Summer Air Temperature Extremes from 1979/80 to 2018/19

Abstract We calculate a regional surface “melt potential” index (MPI) over Antarctic ice shelves that describes the frequency (MPI-freq; %) and intensity (MPI-int; K) of daily maximum summer temperatures exceeding a melt threshold of 273.15 K. This is used to determine which ice shelves are vulnerable to melt-induced hydrofracture and is calculated using near-surface temperature output for each summer from 1979/80 to 2018/19 from two high-resolution regional atmospheric model hindcasts (using the MetUM and HIRHAM5). MPI is highest for Antarctic Peninsula ice shelves (MPI-freq 23%–35%, MPI-int 1.2–2.1 K), lowest (2%–3%, <0 K) for the Ronne–Filchner and Ross ice shelves, and around 10%–24% and 0.6–1.7 K for the other West and East Antarctic ice shelves. Hotspots of MPI are apparent over many ice shelves, and they also show a decreasing trend in MPI-freq. The regional circulation patterns associated with high MPI values over West and East Antarctic ice shelves are remarkably consistent for their respective region but tied to different large-scale climate forcings. The West Antarctic circulation resembles the central Pacific El Niño pattern with a stationary Rossby wave and a strong anticyclone over the high-latitude South Pacific. By contrast, the East Antarctic circulation comprises a zonally symmetric negative Southern Annular Mode pattern with a strong regional anticyclone on the plateau and enhanced coastal easterlies/weakened Southern Ocean westerlies. Values of MPI are 3–4 times larger for a lower temperature/melt threshold of 271.15 K used in a sensitivity test, as melting can occur at temperatures lower than 273.15 K depending on snowpack properties.

High-resolution spatio-temporal analysis of snowmelt over Antarctic Peninsula ice shelves from 2015 to 2021 using SAR images

ABSTRACT Ice shelves play an essential role in the dynamics of the Antarctic ice sheet. The surface meltwater is important, as it can irreversibly weaken ice shelves by exerting additional hydrostatic pressure. Therefore, high-resolution snowmelt products are urgently needed to accurately analyze melting patterns of ice shelves and further estimate mass loss. In this study, a new high-resolution (40 m) snowmelt dataset over all of the Antarctic Peninsula ice shelves larger than 100 km was developed based on the modified snowmelt detection framework by using a co-orbit normalization method. The dataset provides detailed snowmelt information on each ice shelf, including the image coverage, melting area and melting ratio every 5 days. The melting patterns of three typical ice shelves (George VI, Wilkins and Larsen C Ice Shelves) and the spatio-temporal melting distribution of the Antarctic Peninsula (AP) were further analyzed. The snowmelt information indicates that both the extent and duration of snowmelt have been increasing in the Antarctic Peninsula from 2015 to 2021, and we found that the snowmelt on the Antarctic Peninsula showed a spatial pattern of significantly intense snowmelt on the western side. We believe this study will provide essential data for ice shelf investigation to support other fields of polar research.

Changes in area, flow speed and structure of southwest Antarctic Peninsula ice shelves in the 21st century

Abstract Since the mid-20th century, ice shelves around the Antarctic Peninsula have declined in extent and thickness, and some have shown signs of structural instability. Here, using satellite imagery from 1999/2000 to 2019/20 (Landsat 7 and 8, Sentinel-2 and ASTER), we measure areal changes, calculate surface flow speeds, and quantify structural changes of Bach, Stange and George VI ice shelves, located in the southwest Antarctic Peninsula. We recorded a total area loss of 797.5 km2 from 2009/10 to 2019/20, though spatial and temporal patterns varied at individual ice fronts. Flow speeds remained largely stable over the observation periods, but notable acceleration was calculated for Bach Ice Shelf, and at the northern and southern extents of George VI Ice Shelf. Open fractures widened and lengthened between 2009/10 and 2019/20 on all three ice shelves. We conclude that Stange Ice Shelf is stable, and not under any immediate threat of enhanced recession. Continued ice-mass loss and consequential speed up of George VI South may cause further fracturing and destabilisation in the coming decades. Of more immediate concern are the glaciological changes noted for Bach Ice Shelf and George VI North; substantial areas of stabilising ice have already, or will soon be removed, that may lead to enhanced recession within the next decade.

Seasonal evolution of Antarctic supraglacial lakes in 2015–2021 and links to environmental controls

Abstract. Supraglacial meltwater accumulation on ice shelves may have important implications for future sea level rise. Despite recent progress in the understanding of Antarctic surface hydrology, potential influences on ice shelf stability as well as links to environmental drivers remain poorly constrained. In this study, we employ state-of-the-art machine learning on Sentinel-1 synthetic aperture radar (SAR) and optical Sentinel-2 satellite imagery to provide new insight into the inter-annual and intra-annual evolution of surface hydrological features across six major Antarctic Peninsula and East Antarctic ice shelves. For the first time, we produce a high-resolution record of supraglacial lake extent dynamics for the period 2015–2021 at unprecedented 10 m spatial resolution and bi-weekly temporal scale. Through synergetic use of optical and SAR data, we obtain a more complete mapping record also enabling the delineation of buried lakes. Our results for Antarctic Peninsula ice shelves reveal below-average meltwater ponding during most of melting seasons 2015–2018 and above-average meltwater ponding throughout summer 2019–2020 and early 2020–2021 considering years 2015–2021 as a reference period. Meltwater ponding on investigated East Antarctic ice shelves was far more variable, with above-average lake extents during most 2016–2019 melting seasons and below-average lake extents during 2020–2021, considering the reference interval 2016–2021. This study is the first to investigate relationships with climate drivers both spatially and temporally including time lag analysis. The results indicate that supraglacial lake formation in 2015–2021 is coupled to the complex interplay of local, regional and large-scale environmental drivers with similar driving factors over both ice sheet regions. In particular, varying air temperature, solar radiation and wind conditions influenced supraglacial lake formation over all six ice shelves despite strong local to regional discrepancies, as revealed through pixel-based correlation analysis. Furthermore, regional climatic conditions were shown to be influenced by Southern Hemisphere atmospheric modes showing large-scale impacts on the spatio-temporal evolution of supraglacial lakes as well as on above- or below-average meltwater ponding with respect to the period 2015–2021. Finally, the local glaciological setting, including melt–albedo feedbacks and the firn air content, was revealed to strongly influence supraglacial lake distribution. Recent increases in Antarctic Peninsula surface ponding point towards a further reduction in the firn air content, implying an increased risk for ponding and hydrofracture. In addition, lateral meltwater transport was observed over both Antarctic regions with similar implications for future ice shelf stability.

Spatial variability and regional trends of Antarctic ice shelf surface melt duration over 1979–2020 derived from passive microwave data

AbstractPassive microwave satellite observations are used to identify the presence of surface meltwater across Antarctica at daily intervals from July 1979 to June 2020, with a focus on ice shelves. Antarctic Peninsula ice shelves have the highest number of annual days of melt, with a maximum of 89 days. Over the entire time period, there are few significant linear trends in days of melt per year. High melt years can be split into two distinct categories, those with high melt days in Dronning Maud Land and Wilkes Land, and those with high melt days in the Antarctic Peninsula and the Bellingshausen Sea sector of West Antarctica. The first pattern coincides with significant negative correlations between melt days and spring and summer Southern Annular Mode. Both patterns also form the primary modes of spatial and annual variability in the dataset observed by Principal Component Analysis. Areas experiencing extended melt for the first time in years tend to show large decreases in subsequent winter microwave emissions due to structural changes in the firn. We use this to identify the impact of novel melt events, particularly over the austral summers of 1991/92 and 2015/16 on the Ross Ice Shelf.

Evaluation of passive microwave melt detection methods on Antarctic Peninsula ice shelves using time series of Sentinel-1 SAR

Passive microwave datasets have been used to quantify the extent and duration of surface melt in Greenland and Antarctica from 1978 on with daily and near-daily intervals. These results have important implications for climate analysis and may help evaluate ice shelf stability. However, the accuracy of passive microwave methods used to detect melt is difficult to quantify, especially on the Antarctic Peninsula. Here four different melt detection methods are employed, including a new formulation of a statistical analysis of brightness temperature time series using a K-means clustering algorithm. Strikingly, two of the most widely used passive microwave melt detection methods are found to vary by 48% mean days of melt per year across six different locations on the Larsen C, Wilkins, and George VI Ice Shelves. In the absence of ground truth observations, time series of Sentinel-1 SAR observations from 2016 on provide a comparison dataset. In topographically flat regions where surface melt is spatially uniform, the passive microwave melt detection method based on a K-means analysis and the cross-polarization gradient ratio method demonstrate the highest agreement and correlation with active radar melt detection methods. One issue which has plagued passive microwave analysis is its coarse spatial resolution. High resolution SAR images are able to demonstrate and quantify the spatial variability of melt within individual passive microwave pixels. Melt is shown to be suitably uniform in space for passive microwave applications at the study sites on Antarctic Peninsula ice shelves, but not so in other regions of the Antarctic Peninsula. Spatial heterogeneity of surface melt on the sub-pixel scale is often related to varying surface topography.

Summertime cloud phase strongly influences surface melting on the Larsen C ice shelf, Antarctica

AbstractSurface melting on Antarctic Peninsula ice shelves can influence ice shelf mass balance, and consequently sea level rise. We show that summertime cloud phase on the Larsen C ice shelf on the Antarctic Peninsula strongly influences the amount of radiation received at the surface and can determine whether or not melting occurs. While previous work has separately evaluated cloud phase and the surface energy balance (SEB) during summertime over Larsen C, no previous studies have examined this relationship quantitatively. Furthermore, regional climate models frequently produce surface radiation biases related to cloud ice and liquid water content. This study uses a high‐resolution regional configuration of the UK Met Office Unified Model (MetUM) to assess the influence of cloud ice and liquid properties on the SEB, and consequently melting, over the Larsen C ice shelf. Results from a case‐study show that simulations producing a vertical cloud phase structure more comparable to aircraft observations exhibit smaller surface radiative biases. A configuration of the MetUM adapted to improve the simulation of cloud phase reproduces the observed surface melt most closely. During a five‐week simulation of summertime conditions, model melt biases are reduced to <2 W·m−2: a four‐fold improvement on a previous study that used default MetUM settings. This demonstrates the importance of cloud phase in determining summertime melt rates on Larsen C.

Quantifying vulnerability of Antarctic ice shelves to hydrofracture using microwave scattering properties

Recent ice shelf disintegrations on the Antarctic Peninsula and subsequent increases in ice sheet mass loss have highlighted the importance of tracking ice shelf stability with respect to surface melt ponding and hydrofracture. In this study, we use active microwave scatterometry in time-series to estimate melt season duration, and winter backscatter levels as a proxy for relative concentration of refrozen ice lenses in Antarctic ice shelf firn. We demonstrate a physical relationship between melt days and firn/ice backscatter using scatterometry and field data from Greenland, and apply the observed relationship to derive and map a vulnerability index for Antarctica's ice shelves. The index reveals that some remaining Antarctic Peninsula ice shelves have already reached a firn state that is vulnerable to hydrofracture. We also show that the progression of an ice shelf towards vulnerability is affected by many factors, such as surface mass balance, internal stresses, and ice shelf geometry.

Oceanographic influences on the stability of the Cosgrove Ice Shelf, Antarctica

Ferrero Bay, located in eastern Pine Island Bay (PIB) of the Amundsen Sea Embayment, is one of the largest and southernmost fjords yet studied in Antarctica. High-resolution multibeam swath bathymetric data, chirp sonar sub-bottom profiles, and three Kasten cores were collected in Ferrero Bay during the IB Oden Southern Ocean 2009–2010 cruise (OSO0910). Core KC-15 from the inner bay yielded two carbonate ages providing a minimum age for ice sheet recession from this sector of PIB by ~11 cal. kyr BP. In total, seven additional acid insoluble organic (AIO) fraction radiocarbon ages provide a linear age model with an R2 of 0.99. Variations in magnetic susceptibility, grain size, total organic carbon (TOC) and nitrogen, diatom abundance, and foraminiferal assemblage and abundance are used to interpret glacial history and paleoceanographic conditions. Grounding line retreat was characterized by advection of planktic foraminifera beneath an ice shelf that may have extended across the middle continental shelf. Following initial deglaciation, the Cosgrove Ice Shelf covered Ferrero Bay, and productivity was virtually absent during the mid-Holocene, while benthic foraminifera indicate periodic incursion of warm Circumpolar Deep Water. The ice shelf persisted until 2.3 cal. kyr BP, when TOC and diatom abundance increased as the bay opened and coastal areas deglaciated. Abundant diatoms demonstrate open marine conditions and seasonal sea ice during the recent open water phase, while high benthic foraminiferal abundance indicates active benthos. The retreat of the Cosgrove Ice Shelf was out of phase with Antarctic Peninsula ice shelves and ice-core proxy temperatures, implying that it did not respond to Holocene climate events but rather to the influence of Circumpolar Deep Water and possibly to internal glacial dynamics.

Meltwater produced by wind–albedo interaction stored in an East Antarctic ice shelf

Surface melt has been tied to the collapse of Antarctic Peninsula ice shelves. This study illustrates that warmer temperatures associated with katabatic winds drive similar processes in an East Antarctic ice shelf, highlighting vulnerability to disintegration.

Divergent trajectories of Antarctic surface melt under two twenty-first-century climate scenarios

Ice shelves modulate Antarctica’s contributions to sea-level rise. Regional-climate-model simulations and observations suggest historical ice melt intensification before collapse of Antarctic peninsula shelves, and project future melt evolution. Ice shelves modulate Antarctic contributions to sea-level rise1 and thereby represent a critical, climate-sensitive interface between the Antarctic ice sheet and the global ocean. Following rapid atmospheric warming over the past decades2,3, Antarctic Peninsula ice shelves have progressively retreated4, at times catastrophically5. This decay supports hypotheses of thermal limits of viability for ice shelves via surface melt forcing3,5,6. Here we use a polar-adapted regional climate model7 and satellite observations8 to quantify the nonlinear relationship between surface melting and summer air temperature. Combining observations and multimodel simulations, we examine melt evolution and intensification before observed ice shelf collapse on the Antarctic Peninsula. We then assess the twenty-first-century evolution of surface melt across Antarctica under intermediate and high emissions climate scenarios. Our projections reveal a scenario-independent doubling of Antarctic-wide melt by 2050. Between 2050 and 2100, however, significant divergence in melt occurs between the two climate scenarios. Under the high emissions pathway by 2100, melt on several ice shelves approaches or surpasses intensities that have historically been associated with ice shelf collapse, at least on the northeast Antarctic Peninsula.

Firn air depletion as a precursor of Antarctic ice-shelf collapse

AbstractSince the 1970s, the sudden, rapid collapse of 20% of ice shelves on the Antarctic Peninsula has led to large-scale thinning and acceleration of its tributary glaciers. The leading hypothesis for the collapse of most of these ice shelves is the process of hydrofracturing, whereby a water-filled crevasse is opened by the hydrostatic pressure acting at the crevasse tip. This process has been linked to observed atmospheric warming through the increased supply of meltwater. Importantly, the low-density firn layer near the ice-shelf surface, providing a porous medium in which meltwater can percolate and refreeze, has to be filled in with refrozen meltwater first, before hydrofracturing can occur at all. Here we build upon this notion of firn air depletion as a precursor of ice-shelf collapse, by using a firn model to show that pore space was depleted in the firn layer on former ice shelves, which enabled their collapse due to hydrofracturing. Two climate scenario runs with the same model indicate that during the 21st century most Antarctic Peninsula ice shelves, and some minor ice shelves elsewhere, are more likely to become susceptible to collapse following firn air depletion. If warming continues into the 22nd century, similar depletion will become widespread on ice shelves around East Antarctica. Our model further suggests that a projected increase in snowfall will protect the Ross and Filchner–Ronne Ice Shelves from hydrofracturing in the coming two centuries.

The structural glaciology of southwest Antarctic Peninsula Ice Shelves (ca. 2010)

The Antarctic Peninsula has recently seen a rapid breakup of its peripheral ice shelves, attributed to atmospheric and oceanic warming in the region. Previous work has illustrated that the final breakup mechanisms are often controlled by the structural glaciology of the ice shelf, and thus understanding the structure of the remaining ‘stable’ ice shelves is of fundamental importance to assess their future response to continued environmental changes. The accompanying map presents the structural glaciology of Bach, George VI and Stange Ice Shelves in the southwest Antarctic Peninsula, from ca. 2010, with a description of each feature presented here.

Thirty years of elevation change on Antarctic Peninsula ice shelves from multimission satellite radar altimetry

We use data acquired between 1978 and 2008 by four satellite radar altimeter missions (Seasat, ERS‐1, ERS‐2 and Envisat) to determine multidecadal elevation change rates (dhi/dt) for six major Antarctic Peninsula (AP) ice shelves. In areas covered by the Seasat orbit (to 72.16°S), regional‐averaged 30‐year trends were negative (surface lowering), with rates between −0.03 and −0.16 m a−1. Surface lowering preceded the start of near‐continuous radar altimeter operations that began with ERS‐1 in 1992. The average rate of lowering for the first 14 years of the period was typically smaller than the 30‐year average; the exception was the southern Wilkins Ice Shelf, which experienced negligible lowering between 2000 and 2008, when a series of large calving events began. Analyses of the continuous ERS/Envisat time series (to 81.5°) for 1992–2008 reveal a period of strong negative dhi/dt on most ice shelves between 1992 and 1995. Based on prior studies of regional atmospheric and oceanic conditions, we hypothesize that the observed elevation changes on Larsen C Ice Shelf are driven primarily by firn compaction while the western AP ice shelves are responding to changes in both surface mass balance and basal melt rates. Our time series also show that large changes in dhi/dt can occur on interannual time scales, reinforcing the importance of long time series altimetry to separate long‐term trends associated with climate change from interannual to interdecadal natural variability.

Oceanic controls on the mass balance of Wilkins Ice Shelf, Antarctica

Several Antarctic Peninsula (AP) ice shelves have lost significant fractions of their volume over the past decades, coincident with rapid regional climate change. Wilkins Ice Shelf (WIS), on the western side of the AP, is the most recent, experiencing a sequence of large calving events in 2008 and 2009. We analyze the mass balance for WIS for the period 1992−2008 and find that the averaged rate of ice‐shelf thinning was ∼0.8 m a−1, driven by a mean basal melt rate of 〈wb〉 = 1.3 ± 0.4 m a−1. Interannual variability was large, associated with changes in both surface mass accumulation and 〈wb〉. Basal melt rate declined significantly around 2000 from 1.8 ± 0.4 m a−1 for 1992–2000 to ∼0.75 ± 0.55 m a−1for 2001–2008; the latter value corresponding to approximately steady‐state ice‐shelf mass. Observations of ocean temperatureT obtained during 2007–2009 by instrumented seals reveal a cold, deep halo of Winter Water (WW; T ≈ −1.6°C) surrounding WIS. The base of the WW in the halo is ∼170 m, approximately the mean ice draft for WIS. We hypothesize that the transition in 〈wb〉 in 2000 was caused by a small perturbation (∼10–20 m) in the relative depths of the ice base and the bottom of the WW layer in the halo. We conclude that basal melting of thin ice shelves like WIS is very sensitive to upper‐ocean and coastal processes that act on shorter time and space scales than those affecting basal melting of thicker West Antarctic ice shelves such as George VI and Pine Island Glacier.

Geological constraints on glacio-isostatic adjustment models of relative sea-level change during deglaciation of Prince Gustav Channel, Antarctic Peninsula

The recent disintegration of Antarctic Peninsula ice shelves, and the associated accelerated discharge and retreat of continental glaciers, has highlighted the necessity of quantifying the current rate of Antarctic ice mass loss and the regional contributions to future sea-level rise. Observations of present day ice mass change need to be corrected for ongoing glacial isostatic adjustment, a process which must be constrained by geological data. However, there are relatively little geological data on the geometry, volume and melt history of the Antarctic Peninsula Ice Sheet (APIS) after Termination 1, and during the Holocene so the glacial isostatic correction remains poorly constrained. To address this we provide field constraints on the timing and rate of APIS deglaciation, and changes in relative sea-level (RSL) for the north-eastern Antarctic Peninsula based on geomorphological evidence of former marine limits, and radiocarbon-dated marine-freshwater transitions from a series of isolation basins at different altitudes on Beak Island. Relative sea-level fell from a maximum of c. 15 m above present at c. 8000 cal yr BP, at a rate of 3.91 mm yr −1 declining to c. 2.11 mm yr −1 between c. 6900–2900 cal yr BP, 1.63 mm yr −1 between c. 2900–1800 cal yr BP, and finally to 0.29 mm yr −1 during the last c. 1800 years. The new Beak Island RSL curve improves the spatial coverage of RSL data in the Antarctic. It is in broad agreement with some glacio-isostatic adjustment models applied to this location, and with work undertaken elsewhere on the Antarctic Peninsula. These geological and RSL constraints from Beak Island imply significant thinning of the north-eastern APIS by the early Holocene. Further, they provide key data for the glacial isostatic correction required by satellite-derived gravity measurements of contemporary ice mass loss, which can be used to better assess the future contribution of the APIS to rising sea-levels.

Acceleration and spatial rheology of Larsen C Ice Shelf, Antarctic Peninsula

The disintegration of several Antarctic Peninsula ice shelves has focused attention on the state of the Larsen C Ice Shelf. Here, we use satellite observations to map ice shelf speed from the years 2000, 2006 and 2008 and apply inverse modeling to examine the spatial pattern of ice‐shelf stiffness. Results show that the northern half of the ice shelf has been accelerating since 2000, speeding up by 15% between 2000 and 2006 alone. The distribution of ice stiffness exhibits large spatial variations that we link to tributary glacier flow and fractures. Our results reveal that ice down‐flow from promontories is consistently softer, with the exception of Churchill Peninsula where we infer a stabilizing role for marine ice. We conclude that although Larsen C is not facing imminent collapse, it is undergoing significant change in the form of flow acceleration that is spatially related to thinning and fracture.

Ice-stream retreat and ice-shelf history in Marguerite Trough, Antarctic Peninsula: Sedimentological and foraminiferal signatures

Research Article| May 01, 2011 Ice-stream retreat and ice-shelf history in Marguerite Trough, Antarctic Peninsula: Sedimentological and foraminiferal signatures Aoibheann A. Kilfeather; Aoibheann A. Kilfeather † 1Department of Geography, Durham University, Science Site, South Road, Durham, DH1 3LE, UK †E-mail: a.a.kilfeather@durham.ac.uk Search for other works by this author on: GSW Google Scholar Colm Ó Cofaigh; Colm Ó Cofaigh 1Department of Geography, Durham University, Science Site, South Road, Durham, DH1 3LE, UK Search for other works by this author on: GSW Google Scholar Jerry M. Lloyd; Jerry M. Lloyd 1Department of Geography, Durham University, Science Site, South Road, Durham, DH1 3LE, UK Search for other works by this author on: GSW Google Scholar Julian A. Dowdeswell; Julian A. Dowdeswell 2Scott Polar Research Institute, University of Cambridge, Cambridge, CB2 1ER, UK Search for other works by this author on: GSW Google Scholar Sheng Xu; Sheng Xu 3Scottish Universities Environmental Research Centre, Scottish Enterprise Technology Park, East Kilbride, G75 0QF, UK Search for other works by this author on: GSW Google Scholar Steven G. Moreton Steven G. Moreton 4NERC Radiocarbon Facility (Environment), Scottish Enterprise Technology Park, Rankine Avenue, East Kilbride, Glasgow, G75 0QF, UK Search for other works by this author on: GSW Google Scholar Author and Article Information Aoibheann A. Kilfeather † 1Department of Geography, Durham University, Science Site, South Road, Durham, DH1 3LE, UK Colm Ó Cofaigh 1Department of Geography, Durham University, Science Site, South Road, Durham, DH1 3LE, UK Jerry M. Lloyd 1Department of Geography, Durham University, Science Site, South Road, Durham, DH1 3LE, UK Julian A. Dowdeswell 2Scott Polar Research Institute, University of Cambridge, Cambridge, CB2 1ER, UK Sheng Xu 3Scottish Universities Environmental Research Centre, Scottish Enterprise Technology Park, East Kilbride, G75 0QF, UK Steven G. Moreton 4NERC Radiocarbon Facility (Environment), Scottish Enterprise Technology Park, Rankine Avenue, East Kilbride, Glasgow, G75 0QF, UK †E-mail: a.a.kilfeather@durham.ac.uk Publisher: Geological Society of America Received: 25 Feb 2010 Revision Received: 02 Jul 2010 Accepted: 08 Jul 2010 First Online: 08 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 © 2011 Geological Society of America GSA Bulletin (2011) 123 (5-6): 997–1015. https://doi.org/10.1130/B30282.1 Article history Received: 25 Feb 2010 Revision Received: 02 Jul 2010 Accepted: 08 Jul 2010 First Online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Aoibheann A. Kilfeather, Colm Ó Cofaigh, Jerry M. Lloyd, Julian A. Dowdeswell, Sheng Xu, Steven G. Moreton; Ice-stream retreat and ice-shelf history in Marguerite Trough, Antarctic Peninsula: Sedimentological and foraminiferal signatures. GSA Bulletin 2011;; 123 (5-6): 997–1015. doi: https://doi.org/10.1130/B30282.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The timing, nature, and causes of grounded ice-sheet retreat following the Last Glacial Maximum (LGM) in Marguerite Trough, west Antarctic Peninsula, and subsequent early Holocene ice-shelf decay, are presented in this paper. We use sedimentological, foraminiferal, geotechnical, and accelerator mass spectrometer (AMS) radiocarbon data from marine cores from the mid-continental shelf, together with previously published AMS dates, to establish a sedimentological and chronological model.Initial ice-sheet retreat through the outer- and mid-shelf sectors of Marguerite Trough was under way by ca. 14 ka B.P., was rapid, and coincided with the sea-level rise of meltwater pulse 1a. An ice shelf formed during this retreat, and fine-grained, laminated muds reflecting meltwater-derived suspension settling and/or tidal pumping were deposited. During this time the ice sheet remained grounded on the inner shelf.Ice-shelf breakup and retreat of the calving front, from ca. 13.2 to 12.5 ka B.P., was slow (∼100 m a−1) across the outer- and mid-shelf, with calving bay conditions remaining for at least 3.5 ka. We interpret this ice-shelf decay to have been driven by an incursion of Weddell Sea Transitional Water onto the shelf. In contrast, grounding-line and ice-shelf retreat in the inner bay occurred from ca. 9.3 ka B.P. and was driven by Circumpolar Warm Deep Water encroaching onto the continental shelf. At this time the mid-shelf was an open-marine environment characterized by hemipelagic deposition. These findings highlight the importance of oceanographic controls in the breakup of Antarctic Peninsula ice shelves during the Holocene. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Persistent iceberg groundings in the western Weddell Sea, Antarctica

We use the time-average of a series of satellite synthetic aperture radar (SAR) images from 2005 to 2007 to identify grounded icebergs in the western Weddell Sea. Satellite laser altimetry along repeated ground tracks confirms that regions of high mean backscatter are associated with stationary, tabular icebergs. The altimeter data also provide iceberg freeboard, from which we infer maximum ice draft assuming the lightly-grounded limit and a two-layer density model consistent with a source at Filchner–Ronne Ice Shelf. The maximum iceberg draft agrees very well with the ocean depth at a point where the bathymetry is well constrained by ship soundings. However, for an extensive region near 71°S, south of Larsen C Ice Shelf, the maximum grounding depth for several icebergs reveals the ocean to be locally more than 200 m shallower than in bathymetry products. This previously uncharted bank is expected to have a profound effect on the northward flow of the western Weddell Gyre and the cross-slope transport of offshore warm deep water towards the eastern Antarctic Peninsula ice shelves. Passive microwave data also show that sea-ice concentration is reduced in the vicinity of this group of grounded icebergs, indicating an iceberg influence on ocean/atmosphere heat and freshwater exchanges.

Examining Holocene stability of Antarctic Peninsula ice shelves

Temperatures on the Antarctic Peninsula are increasing at a rate of 3.4°C per century, more than five times the global mean. At the same time, the region's ice shelves have retreated and collapsed, with an area of more than 14,000 square kilometers disappearing within the past two decades. Ice shelf retreat has followed the southward migration of the −9°C mean annual isotherm, referred to as the ‘climatic limit of ice shelf stability’ (Figure 1).Thus, present‐day ice shelf retreats on the Antarctic Peninsula have been linked to increased atmospheric temperature [Vaughan et al., 2003].