Larsen C Ice Shelf Research Articles

Larsen ice shelf has progressively thinned.

The retreat and collapse of Antarctic Peninsula ice shelves in tandem with a regional atmospheric warming has fueled speculation as to how these events may be related. Satellite radar altimeter measurements show that between 1992 and 2001 the Larsen Ice Shelf lowered by up to 0.27 +/- 0.11 meters per year. The lowering is explained by increased summer melt-water and the loss of basal ice through melting. Enhanced ocean-driven melting may provide a simple link between regional climate warming and the successive disintegration of sections of the Larsen Ice Shelf.

Glacier surge after ice shelf collapse.

The possibility that the West Antarctic Ice Sheet will collapse as a consequence of ice shelf disintegration has been debated for many years. This matter is of concern because such an event would imply a sudden increase in sea level. Evidence is presented here showing drastic dynamic perturbations on former tributary glaciers that fed sections of the Larsen Ice Shelf on the Antarctic Peninsula before its collapse in 1995. Satellite images and airborne surveys allowed unambiguous identification of active surging phases of Boydell, Sjögren, Edgeworth, Bombardier, and Drygalski glaciers. This discovery calls for a reconsideration of former hypotheses about the stabilizing role of ice shelves.

The initial laparoscopic appearance can predict response to combination therapy in hepatitis C

Antarctica is the fifth-largest continent, covering 5.4 million square miles (14 million square km). The average winter temperature in Antarctica is −81°F (−63°C) and has reached −128.6°F (−89.2°C). About 98% of the Antarctic continent is covered by glacial ice that averages about 1.2 miles (1.9 km) in thickness. The total volume of ice in Antarctica is about 6.4 million cubic miles (26.5 million cubic km), comprising about 90% of the world's ice and about 70% of the world's fresh water. The average height of the ice sheet is approximately 10,000 ft above sea level. At its thickest point, the ice is 15,700 ft (4776 m) thick. The East Antarctic Ice Sheet is by far the biggest ice sheet, making up 92% of the total glacial ice, while the West Antarctic Ice Sheet makes up only about 8%.The Steig et al. analysis that all of Antarctica is warming was refuted by O'Donnell et al., who showed that their methodology was badly flawed. Using the same data as Steig et al., but with better technology, they produced a map showing cooling dominating most of the East Antarctic Ice Sheet with warming primarily constrained to the Antarctica Peninsula. Satellite and surface temperature measurements demonstrate that the Steig et al. contention that all of Antarctica is warming is clearly false. Antarctic satellite temperatures show no warming for 37 years. The Southern Ocean around Antarctica has cooled markedly since 2006. Sea ice has increased substantially, especially since 2012. Surface temperatures at 13 stations on or near the Antarctic Peninsula have been cooling sharply since 2006. Ocean temperatures have been plummeting since about 2007, sea ice has reached all-time highs, and temperatures have been cooling since 2000. The Larsen Ice Shelf Station has been cooling at an astonishing rate of 1.8°C per decade (18°C per century) since 1995.The thickness of most of the West Antarctic Ice Sheet is more than 6000 ft (2000 m) and large areas are more than 10,000 ft (3000 m) thick. The importance of ice thickness is that virtually all of the ice sheet is considerably thicker than the depth below sea level to bedrock, so the ice is grounded and will not float. If the West Antarctic Ice Sheet melts away, where the ice is 10,000 ft thick, the land beneath will rebound isostatically several 1000 ft, bringing most of the subglacial bed above sea level.The Pine Island and Thwaites outlet glaciers are only about 30 miles across, so draining 2.2 million km3 of ice through their narrow channels or sending sea water 1000 miles under the ice sheet is not plausible. Studies of subglacial geothermal heat flow show that the area under the Thwaites glacier is unusually high and is the most likely cause of subglacial melting, rather than ocean water. The West Antarctic Ice Sheet is not collapsing, the retreat of these small glaciers is not caused by global warming, and sea level is not going to rise 10 ft.

Antarctic “Larsen B” Ice shelf shatters

The break‐up of a Connecticut‐sized ice shelf on Antarctica in just about a month's time is not cause for alarm in itself, but suggests that some other ice shelves “are closer to the limit than we thought,” according to Ted Scambos, glaciologist with the National Snow and Ice Data Center (NSIDC) at the University of Colorado at Boulder. On 18 March, Scambos and other scientists announced the loss of more than 3,200 square kilometers of the ice shelf, known as “Larsen B,” located on the eastern side of the Antarctic Peninsula. The ice shelf began breaking up in January, and analysis of a 7 March image from NASA's Terra satellite confirmed the disintegration. With this recent event, the 220‐meter‐thick Larsen ice shelf has lost 5,700 square kilometers in the past 5 years, according to NSIDC.

Northern Larsen Ice Shelf, Antarctica: further retreat after collapse

AbstractChanges of Larsen Ice Shelf, Antarctica, and the surrounding glaciers after its collapse in 1995 were investigated using satellite radar imagery, with emphasis on changes in the glaciers which previously nourished the ice shelf north of Seal Nunataks and now calve directly into the sea. The large glaciers retreated several kilometres inland of the previous grounding line. The velocity field of Drygalski Glacier, the largest glacier in this area, was mapped by means of interferograms derived from pairs of European Remote-sensing Satellite synthetic aperture radar images from 1995 and 1999. The main part of the glacier showed a significant acceleration of flow over these 4 years, with an increase of velocity up to three-fold at the terminus. Similar accelerations were observed by means of interferometry on several other grounded glaciers, suggesting that the removal of ice shelves could lead to an effect on eustatic sea level. For Larsen B, the northernmost surviving part of Larsen Ice Shelf, the retreat of the ice front to October 2000 is documented.

Ice dolines on Larsen Ice Shelf, Antarctica

AbstractIce dolines on the Larsen Ice Shelf, Antarctica, are observed to be elongated depressions a few hundred meters across and up to 19 m deep. One-meter resolution imagery is used to quantify these dimensions. Elevation profiles across five dolines are derived by photoclinometry. Landsat and radar imagery is also used to show that dolines can form in a single melt season and persist for years. Dolines occur in clusters and in direct proximity to surface meltwater lakes. Field observations suggest dolines form by collapse into a subsurface cavity. A direct hydraulic connection with the underlying ocean is believed necessary to drain water that would otherwise collect in dolines. A formation hypothesis is discussed consistent with these observations and with energy-and hydrostatic-imbalance considerations.

A new tide model for the Antarctic ice shelves and seas

AbstractWe describe a new tide model for the seas surrounding Antarctica, including the ocean cavities under the floating ice shelves. The model uses data assimilation to improve its fit to available data. Typical peak-to-peak tide ranges on ice shelves are 1–2 m but can exceed 3 m for the Filchner–Ronne and Larsen Ice Shelves in the Weddell Sea. Spring tidal ranges are about twice these values. Model performance is judged relative to the ~5–10 cm accuracy that is needed to fully utilize ice-shelf height data that will be collected with the Geoscience Laser Altimeter System, scheduled to be launched on the Ice, Cloud and land Elevation Satellite in late 2002. The model does not yet achieve this level of accuracy except very near the few high-quality tidal records that have been assimilated into the model. Some improvement in predictive skill is expected from increased sophistication of model physics, but we also require better definition of ice-shelf grounding lines and more accurate water-column thickness data in shelf seas and under the ice shelves. Long-duration tide measurements (bottom pressure gauge or global positioning system) in critical data-sparse areas, particularly near and on the Filchner–Ronne and Ross Ice Shelves and Pine Island Bay, are required to improve the performance of the data-assimilation model.

Long melt seasons on ice shelves of the Antarctic Peninsula: an analysis using satellite-based microwave emission measurements

AbstractWe have examined the record of melt-season duration on the Antarctic Peninsula using two techniques for detecting the presence of a melt signal in microwave-emission time series covering the period 1978–2000. We have obtained similar estimates of melt-season length using the cross-polarized gradient ratio (XPGR) technique and calibrations previously applied in Greenland and a technique which detects the jump in emission caused by melt without using a sensor- and frequency-dependent threshold value. The close correspondence between results from the two techniques on peninsula ice shelves suggests that the XPGR analysis can be used over the length of the time series. The results show that the long melt seasons of 1992/93 and several later years were exceptional occurrences on the northern parts of the Larsen Ice Shelf. These melt seasons were followed by disintegration events, supporting a possible cause-and-effect relationship.

Biogeochemistry of platelet ice: its influence on particle flux under fast ice in the Weddell Sea, Antarctica

An array of four sediment traps and one current meter was deployed under a well-developed platelet layer for 15 days in the Drescher Inlet in the Riiser Larsen ice shelf, in February 1998. Traps were deployed at 10 m (just under the platelet layer), 112 m (above the thermocline), 230 m (below thermocline) and 360 m (close to sea floor). There was a substantial flux of particulate organic material out of the platelet layer, although higher amounts were collected in the traps either side of the thermocline. Material collected was predominantly composed of faecal pellets containing diatom species growing within the platelet layer. The size classes of these pellets suggest they derive from protists grazing rather than from larger metazoans. Sediment trap material was analysed for particulate organic carbon/nitrogen/phosphorus (POC/PON/POP) and δ 13CPOC (carbon isotopic composition of POC). These were compared with organic matter in the overlying platelet layer and the water column. In turn, the biogeochemistry of the platelet layer and water column was investigated and the organic matter characteristics related to inorganic nutrients (nitrate, nitrite, ammonium, silicate, phosphate), dissolved organic carbon/nitrogen (DOC/DON), pH, dissolved inorganic carbon (DIC), oxygen and δ 13 CDIC (carbon isotopic composition dissolved inorganic carbon).

Cruise reveals history of Holocene Larsen Ice Shelf

In May 2000 the U.S. Antarctic Research Vessel Nathaniel B. Palmer braved extensive ice and the frigid temperatures of the Northwest Weddell Sea to penetrate the coastal leads along the Nordenskold Coast (Figures 1–3). The scientific objective of this international endeavor was to understand the natural variability of the Larsen Ice Shelf, the largest of several ice shelves along the northern extremities of the Antarctic Peninsula to have undergone catastrophic decay over recent years (Figure 2) [Vaughan and Doake, 1996; Skvarca et al., 1999].The study sought to determine the history of the Larsen Ice Shelf beyond the limits of our historical observations. Such knowledge is needed in order to assess the potentially unique nature of the current disintegration pattern and to determine the role of regional versus global warming scenarios on the future of the break‐up trend.

Recognition of contour-current influence in mixed contourite-turbidite sequences of the western Weddell Sea, Antarctica

Sedimentary processes and structures across the continental rise in the western Weddell Sea have been investigated using sediment acoustic and multichannel seismic data, integrated with multibeam depth sounding and core investigations. The results show that a network of channels with associated along-channel ridges covers the upper continental slope. The seismic profiles reveal that the channels initially developed as erosive turbidite channels with associated levees on their northern side due to Coriolis force. Later they were partly or fully infilled, probably as a result of decreasing turbidite activity. Now the larger ones exist as erosive turbidite channels of reduced size, whereas the smaller ones are non-erosive channels, their shape being maintained by contour current activity. Drift bodies only developed where slumps caused a distinctive break in slope inclination on the upper continental rise, which served to initiate the growth of a drift body fed by contour currents or by the combined action of turbidites and contourites. The history of sedimentation can be reconstructed tentatively by correlation of seismo-stratigraphic units with the stages of evolution of the drifts on the western side of the Antarctic Peninsula. Three stages can be distinguished in the western Weddell Sea after a pre-drift stage, which is delimited by an erosional unconformity at the top: (1) a growth stage, dominated by turbidites, with occasional occurrence of slumps during its initial phase; (2) during a maintenance stage turbiditiy-current intensity (and presumably sedimentation rate also) decreased, probably as a result of the ice masses retreating from the shelf edge, and sedimentation became increasingly dominated by contour current activity; and (3) a phase of sheeted-sequence formation. A southward decrease in sediment thickness shows that the Larsen Ice Shelf plays an important role in sediment delivery to the western Weddell Sea. This study shows that the western Weddell Sea has some characteristics in common with the southern as well as the northwestern Weddell Sea: contour currents off the Larsen Ice Shelf have been present for a long time, probably since the late Miocene, but during times of high sediment input from the shelves as a result of advancing ice masses a channel-levee system developed and dominated over the contour-current transport of sediment. At times of relatively low sediment input the contour-current transport dominated, leading to the formation of drift deposits on the upper continental rise. Seaward of areas without shelf ice masses the continental rise mainly shows a rough topography with small channels and underdeveloped levees. The results demonstrate that sediment supply is an important, maybe the controlling factor of drift development on the Antarctic continental rise.

Intense nutrient removal in the remote area off Larsen Ice Shelf (Weddell Sea)

Using Weddell Sea data collected during a cruise with “FS Polarstern” in austral summer 1992/1993, depletions of nutrients and TCO2 in the summer surface layer were calculated. The analogous depletion-like properties for temperature (Heat Storage) and salinity were also computed. The latter properties are useful to describe the physical conditions over the time period pertinent to the depletions. For different areas a strong correlation exists of Heat Storage and nutrient/TCO2 depletions, which is caused by a common factor – the period of light availability. Offshore of the Larsen shelf, an area usually inaccessible due to perennial ice cover, high nutrients/TCO2 depletions are achieved over a short period of time, pointing to a rapidly producing biological system. Primary productivity, calculated from the TCO2 depletion, amounts to about 100 mg C m−2 day−1 for the central Weddell Sea, but 570–1140 mg C m−2 day−1 for the offshore Larsen region. These values agree fairly well with the open-ocean Antarctic and other coastal areas, respectively.

Spatial distribution of net surface accumulation on the Antarctic ice sheet

AbstractAn isopleth map showing the spatial distribution of net mass accumulation at the surface on the Antarctic ice sheet, excluding Graham Land, the Larsen Ice Shelf and eastern Palmer Land, is produced based on field data from approximately 2000 sites. A database of accumulation values for 5365 gridpoint locations with 50 km spacing is interpolated from the isopleth map, giving a bulk accumulation of 2151 Gt a–1 and a mean of 159 kg m–2 a–1 for an area of 13.53 × 106 km2. Following the implementation of deflation and ablation adjustments applicable to sectors of the coastal zone, the accumulation values are reduced to 2020 Gt a–1 and 149 kg m–2 a–1. The new accumulation distribution is compared with another recent distribution, which was based on essentially the same field data using different analysis and interpolation criteria. Differences between the distributions are assessed using residuals for the 50 km gridpoint locations and by comparing average accumulation values for 24 drainage systems. The assessment based on residuals indicates that the two distributions show patterns of accumulation that are coherent at the continental scale, a shared attribute underscored by a small mean residual value of 6 kg m–2 a–1 (a difference of <4%). However, the regional assessment based on average accumulation values for the drainage systems shows differences that are larger than the assessment error (>22%) for six systems that collectively comprise approximately 4/10 of the ice-sheet area and 3/10 of the accumulation.

Interferometric analysis of the deformation pattern of the northern Larsen Ice Shelf, Antarctic Peninsula, compared to field measurements and numerical modeling

AbstractThe motion field of the northern Larsen Ice Shelf, Antarctic Peninsula, was analyzed using radar interferometry in combination with field measurements and finite-element model calculations. The ice shelf between Jason Peninsula and Seal Nunataks has been in steady retreat since January 1995. Model calculations suggest that the ice shelf is in a stage of irreversible retreat since the last calving events in summer 1998/99. The interferometric analysis is based on synthetic-aperture radar data of the tandem mission of European remote-sensing satellites ERS-1 and –2 in austral spring 1995. The phase contributions due to tidal motion were estimated from the vertical displacement at those parts of the grounding zone where the horizontal motion is close to zero" in order to separate the vertical and horizontal motion components over the ice shelf. Satellite-derived velocities compare well with the long-term field measurements along a transverse and a longitudinal profile. The real interferograms and synthetic interferograms, calculated from model velocities, show reasonable agreement over the main parts of the ice shelf, but differ in the boundary zones where the details are not resolved by the model.

Climatic trend and the retreat and disintegration of ice shelves on the Antarctic Peninsula: an overview

Observation of the retreat and disintegration of ice shelves around the Antarctic Peninsula during the last three decades and associated changes in air temperature, measured at various meteorological stations on the Antarctic Peninsula, are reviewed. The climatically induced retreat of the northern Larsen Ice Shelf on the east coast and of the Wordie, George VI, and Wilkins ice shelves on the west coast amounted to about 10 000 km2 since the mid-1960s. A summary is presented on the recession history of the Larsen Ice Shelf and on the collapse of those sections north of Robertson Island in early 1995. The area changes were derived from images of various satellites, dating back to a late 1963 image from the recently declassified US Argon space missions. This photograph reveals a previously unknown, minor advance of the northern Larsen Ice Shelf before 1975. During the period of retreat a consistent and pronounced warming trend was observed at the stations on both east and west coasts of the Antarctic Peninsula, but a major cause of the fast retreat and final collapse of the northernmost sections of the Larsen Ice Shelf were several unusually warm summers. Temperature records from the nearby station Marambio show that a positive mean summer temperature was reached for the first time in 1992-93. Recent observations indicate that the process of ice shelf disintegration is proceeding further south on both sides of the Antarctic Peninsula.

Lead pollution in Antarctic surface snow revealed along the route of the International Trans-Antarctic Expedition

AbstractThis paper reports the lead concentration and flux (where accumulation rate is available) along the route of the 1990 International Trans-Antarctic Expedition. The lead concentration in Larsen Ice Shelf and Antarctic Peninsula, the western part of the route, was 7.4 ± 4.1 pg g−1. The lead concentration in East Antarctic snow (South Pole to Mirny station) was 2 3 times higher than that in West Antarctica (Larsen Ice Shelf to South Pole). Taking into account the difference in site conditions, the difference between the above value over this area in 1989 and the value of 6.3 ±3.3 pg g−1 at a site within this area in 1980 (Wolff and Peel, 1985) is not significant. Because the relative contribution of soil dust, volcanoes and the oceans to lead concentration in Antarctica is about 0.5 pg g−1 under modern climatic conditions (Boutron and Patterson, 1987), it is believed that the lead in Antarctic surface snow is dominated by pollution input. The lead-concentration increase from west to east over the trans-Antarctic route suggests that remote Antarctica has been impacted by anthropogenic activities. The lowest lead flux (0.064 ng cn-2 a−1) was on the Antarctic Plateau, mainly reflecting the background global pollution. The mean flux of 0.273 ng cnT2 a−1 in the western part of the route (Larsen Ice Shelf to the Ellsworth Mountains) may result from the pollution input from the Southern Hemisphere. In addition to the influence of global and/or hemispheric pollution, local activities (notably the use of leaded gasolene) appear to have affected the region from Pionerskaya to Mirny.

The Weddell Sea region: an important precipitation channel to the interior of the Antarctic ice sheet as revealed by glaciochemical investigation of surface snow along the longest trans-Antarctic route

AbstractGlaciochemical analysis of surface snow samples, collected along a profile crossing the Antarctic ice sheet from the Larsen Ice Shelf, Antarctic Peninsula, via the Antarctic Plateau through South Pole, Vostok and Komsomolskaya to Mirny station (at the east margin of East Antarctica), shows that the Weddell Sea region is an important channel for air masses to the high plateau of the Antarctic ice sheet (>2000 m a.s.l.). This opinion is supported by the following. (1) The fluxes of sea-salt ions such as Na+, Mg2 + and CF display a decreasing trend from the west to the east of interior Antarctica. In |eneral, as sea-salt aerosols are injected into the atmosphere over the Antarctic ice sheet from the Weddell Sea, large aerosols tend to decrease. For the inland plateau, few large particles of sea-salt aerosol reach the area, and the sea-salt concentration levels are low (2) The high altitude of the East Antarctic plateau, as well as the polar cold high-pressure system, obstruct the intrusive air masses mainly from the South Indian Ocean sector. (3) For the coastal regions of the East Antarctic ice sheet, the elevation rises to 2000 m over a distance from several to several tens of km. High concentrations of sea salt exist in snow in East Antarctica but are limited to a narrow coastal zone. (4) Fluxes of calcium and non-sea-salt sulfate in snow from the interior plateau do not display an eastward-decreasing trend. Since calcium is mainly derived from crustal sources, and nssSO42- is a secondary aerosol, this again confirms that the eastward-declining tendency of sea-salt ions indicates the transfer direction of precipitation vapor.

The motion field of northern Larsen Ice Shelf, Antarctic Peninsula, derived from satellite imagery

AbstractThe motion field of the northern Larsen Ice Shelf, Antarctic Peninsula, was analyzed, based on Landsat data from 1986 to 1989, Earth Resources Satellite (ERS) synthetic aperture radar (SAR) data from 1992 to 1997, and comparative field measurements along three transects. During this period the northern sections of the ice shelf showed steady retreat, which culminated in the disintegration of the two ice-shelf sections north of Seal Nunataks in January 1995. Velocities of these two sections were derived by cross-correlation, using SAR images of 1 year time intervals and Landsat images of 1-3 year intervals. A slight increase of velocity was observed as crevasses and rifts opened before the final disintegration. In addition, an interferometric motion analysis was carried out for the ice shelf around and south of Seal Nunataks, based on an image pair from the ERS-1/2 Tandem Mission in 1995. This analysis reveals a complex pattern of tidal flexure in the grounding zones, as well as rifting and shear zones on the ice shelf. In addition, the motion of the main input glaciers was derived.

34 year satellite time series to monitor characteristics, extent and dynamics of Larsen B Ice Shelf, Antarctic Peninsula

AbstractA variety of data are used to investigate Larsen B, which is at present the northernmost section of the Larsen Ice Shelf, Antarctic Peninsula. Recently declassified U.S. Argon satellite photographs from 1963 Kosmos photographs from 1975, Landsat images from 1986,1988 and 1990, ERS-1/2 synthetic aperture radar images from 1992-97, Radarsat from 1998 and field surveys are used to analyze the areal extent, surface characteristics and dynamic behaviour of this ice-shelf section over more than three decades. Visible and radar imagery together with field observations are used synergistically to describe the ice-shelf morphology, including meltwater features and rifts. In contrast to the retreat of the ice-shelf sections in the north, Larsen B advanced steadily from 1963 to early 1995, when the area decreased significantly due to a major calving event. Analysis of different satellite images indicates that melting is proceeding further south in accordance with the regional warming trend. In addition? fracturing processes and rapid development of new rifts are observed, associated with recent acceleration of ice motion close to the front. All observations predict major calving events for this ice-shelf section in the near future.

On the relation between organic and inorganic carbon in the Weddell Sea

Carbon cycling in the Weddell Sea was investigated during the ANT X/7 cruise with `FS Polarstern' December 1992–January 1993. Samples were taken on a cross section from Kapp Norvegia to Joinville Island, and on a section from the Larsen Ice Shelf to the northeast. The following quantities were measured: total carbon dioxide (TCO 2), fluorescence from humic substances and total organic carbon. The distribution of TCO 2 was strongly positively correlated to the time elapsed since the various water masses were last ventilated. In general, humic substance fluorescence was positively correlated with TCO 2, with the exception of the productive part of the western Weddell Sea, where the correlation was negative in the surface mixed layer. The increased fluorescence at the surface is suggested to be a result of biological production. The distribution of total organic carbon showed less structure, since this quantity includes a particulate component, which is subject to dispersion processes different from those of the dissolved components TCO 2 and humic substances. The mean total organic carbon concentration below the surface mixed layer was 50 μmol l −1. At some stations, a steep TOC maximum around 2000 m depth was observed. This was interpreted to result from mass sinking of phytoplankton blooms. Total organic carbon had a maximum in surface water, and at some stations also a second subsurface maximum. In the Warm Deep Water (WDW), TCO 2 and fluorescence had their maximum values, while total organic carbon tended to be low. In low productivity surface water in the eastern part of the Kapp Norvegia–Joinville Island section, the lowest flourescence was found. Surface water is eventually formed from Warm Deep Water, which had the highest fluorescence values, and therefore it is concluded that humic substances were removed in situ from surface water. In the central area of the Weddell Sea, TCO 2 and fluorescence showed the highest Warm Deep Water maxima, while total organic carbon was low. The Warm Deep Water in this area is part of the so-called Central Intermediate Water which circulates for a long time within the Weddell Gyre. Reduced total organic carbon, which coincides with the most pronounced Central Intermediate Water characteristics, and high TCO 2 can thus both be accounted for by continued degradation of organic matter in this water mass. The associated fluorescence maximum implies that humic substances are also produced during mineralisation. Recently formed bottom water, by contrast, could be seen as patches of low TCO 2, low fluorescence and high total organic carbon along the western slope of the Weddell Sea.