Stability Of West Antarctic Ice Sheet Research Articles

Abrupt Holocene ice loss due to thinning and ungrounding in the Weddell Sea Embayment

The extent of grounded ice and buttressing by the Ronne Ice Shelf, which provides resistance to the outflow of ice streams, moderate West Antarctic Ice Sheet stability. During the Last Glacial Maximum, the ice sheet advanced and was grounded near the Weddell Sea continental shelf break. The timing of subsequent ice sheet retreat and the relative roles of ice shelf buttressing and grounding line changes remain unresolved. Here we use an ice core record from grounded ice at Skytrain Ice Rise to constrain the timing and speed of early Holocene ice sheet retreat. Measured δ18O and total air content suggest that the surface elevation of Skytrain Ice Rise decreased by about 450 m between 8.2 and 8.0 kyr before 1950 ce (±0.13 kyr). We attribute this elevation change to dynamic thinning due to flow changes induced by the ungrounding of ice in the area. Ice core sodium concentrations suggest that the ice front of this ungrounded ice shelf then retreated about 270 km (±30 km) from 7.7 to 7.3 kyr before 1950 ce. These centennial-scale changes demonstrate how quickly ice mass can be lost from the West Antarctic Ice Sheet due to changes in grounded ice without extensive ice shelf calving. Our findings both support and temporally constrain ice sheet models that exhibit rapid ice loss in the Weddell Sea sector in the early Holocene.

Enhanced moisture delivery into Victoria Land, East Antarctica, during the early Last Interglacial: implications for West Antarctic Ice Sheet stability

Abstract. The S27 ice core, drilled in the Allan Hills Blue Ice Area of East Antarctica, is located in southern Victoria Land, ∼80 km away from the present-day northern edge of the Ross Ice Shelf. Here, we utilize the reconstructed accumulation rate of S27 covering the Last Interglacial (LIG) period between 129 ka and 116 ka (where ka indicates thousands of years before present) to infer moisture transport into the region. The accumulation rate is based on the ice-age–gas-age differences calculated from the ice chronology, which is constrained by the stable water isotopes of the ice, and an improved gas chronology based on measurements of oxygen isotopes of O2 in the trapped gases. The peak accumulation rate in S27 occurred at 128.2 ka, near the peak LIG warming in Antarctica. Even the most conservative estimate yields an order-of-magnitude increase in the accumulation rate during the LIG maximum, whereas other Antarctic ice cores are typically characterized by a glacial–interglacial difference of a factor of 2 to 3. While part of the increase in S27 accumulation rates must originate from changes in the large-scale atmospheric circulation, additional mechanisms are needed to explain the large changes. We hypothesize that the exceptionally high snow accumulation recorded in S27 reflects open-ocean conditions in the Ross Sea, created by reduced sea ice extent and increased polynya size and perhaps by a southward retreat of the Ross Ice Shelf relative to its present-day position near the onset of the LIG. The proposed ice shelf retreat would also be compatible with a sea-level high stand around 129 ka significantly sourced from West Antarctica. The peak in S27 accumulation rates is transient, suggesting that if the Ross Ice Shelf had indeed retreated during the early LIG, it would have re-advanced by 125 ka.

On the influence of post-LGM ice shelf loss and grounding zone sedimentation on West Antarctic ice sheet stability

The Whales Deep Basin in eastern Ross Sea was occupied by the paleo-Bindschadler Ice Stream during the Last Glacial Maximum (LGM). Previous studies showed that megascale glacial lineations (MSGLs) extend to the continental shelf edge. In a landward direction, these lineations are buried by an overlapping stack of backstepped grounding zone wedges (GZWs). The constraints require that the West Antarctic Ice Sheet (WAIS) grounded at least seven times within 60km of the shelf edge but the morphological relationships in the Whales Deep Basin cannot be used to uniquely reveal the magnitudes of either grounding line and/or calving front retreat and re-advance between the successive groundings. Here we show a new regional transect of cores from the basin which demonstrates that there were no major back and forth oscillations of either the grounding line or calving front during the overall retreat of grounded and floating ice. Instead, the new sedimentologic data show that a small ice shelf formed as the grounding line retreated from the shelf edge and backstepped over the outer continental shelf. An event bed records breakup of the ice shelf that covered the outer shelf. The stratal relationships indicate that the ice-shelf collapse occurred during the fourth grounding and that the grounding line remained on the outer continental shelf for three additional groundings. We infer that accelerated ice stream flow (due to loss of buttressing) increased sediment flux to the grounding line and thinned the WAIS at the grounding line. Following the seventh grounding, thinning contributed to an abrupt 200km retreat of the grounding line to the middle continental shelf and a large ice shelf re-formed over the middle continental shelf. A series of small-scale moraine ridges formed as the grounding line shifted south towards Roosevelt Island. The facies relationships on the middle continental shelf indicate that the calving front then shifted abruptly to its modern position. The ground-truth of the seafloor geomorphology presented here is important because it is a necessary framework for constraining retreat chronology for a central part of the WAIS that was not influenced by East Antarctic Ice Sheet overflow.

Ice sheets viewed from the ocean: the contribution of marine science to understanding modern and past ice sheets

Over the last two decades, marine science, aided by technological advances in sediment coring, geophysical imaging and remotely operated submersibles, has played a major role in the investigation of contemporary and former ice sheets. Notable advances have been achieved with respect to reconstructing the extent and flow dynamics of the large polar ice sheets and their mid-latitude counterparts during the Quaternary from marine geophysical and geological records of landforms and sediments on glacier-influenced continental margins. Investigations of the deep-sea ice-rafted debris record have demonstrated that catastrophic collapse of large (10(5)-10(6) km(2)) ice-sheet drainage basins occurred on millennial and shorter time scales and had a major influence on oceanography. In the last few years, increasing emphasis has been placed on understanding physical processes at the ice-ocean interface, particularly at the grounding line, and on determining how these processes affect ice-sheet stability. This remains a major challenge, however, owing to the logistical constraints imposed by working in ice-infested polar waters and ice-shelf cavities. Furthermore, despite advances in reconstructing the Quaternary history of mid- and high-latitude ice sheets, major unanswered questions remain regarding West Antarctic ice-sheet stability, and the long-term offshore history of the East Antarctic and Greenland ice sheets remains poorly constrained. While these are major research frontiers in glaciology, and ones in which marine science has a pivotal role to play, realizing such future advances will require an integrated collaborative approach between oceanographers, glaciologists, marine geologists and numerical modellers.

The Mid‐Brunhes Event and West Antarctic ice sheet stability

AbstractThe complex cyclical nature of Pleistocene climate, driven by the evolving orbital configuration of the Earth, is well known but not well understood. A major climatic transition took place at the Mid‐Brunhes Event (MBE), ca. 430 ka ago after which the amplitude of the ca.100 ka climate oscillations increased, with substantially warmer interglacials, including periods warmer than present. Recent modelling has indicated that while the timing of these warmer‐than‐present transient (WPT) events is consistent with southern warming due to a deglaciation‐forced slowdown of the Atlantic Meridional Overturning Circulation, the magnitude of warming requires a local amplification, for which a candidate is the feedback of significant West Antarctic Ice Sheet (WAIS) retreat. We here extend this argument, based on the absence of WPTs in the early ice core record (450–800 ka ago), to hypothesize that the MBE could be a manifestation of decreased WAIS stability, triggered by ongoing subglacial erosion. Copyright © 2011 John Wiley & Sons, Ltd.

Ice‐dynamical constraints on the existence and impact of subglacial volcanism on West Antarctic ice sheet stability

Subglacial volcanism in West Antarctica may play a crucial role in the dynamics and stability of the West Antarctic Ice Sheet (WAIS). Evidence supporting the existence of an individual subglacial volcanic center (Mt. Casertz) in the upper catchments of Whillans and Kamb Ice Stream (WIS and KIS), comes from a comparison of ice sheet modeling results with measured ice velocities. Lubrication of an area, which otherwise should be frozen to its bed, is best explained by basal melt water generated in the vicinity of Mt. Casertz. The estimated melt water production of Mt. Casertz corresponds to ∼8 % of the total melt water production in the two catchments. This would be sufficient to offset basal freezing in the dormant KIS, relubricating its bed and potentially causing a restart. Near future volcanic activity changes are speculative, but would have far reaching implications on the dynamics and stability of the WAIS requiring further investigation.