Major Ice Sheet Change in the Weddell Sea Sector of West Antarctica Over the Last 5,000 Years

Abstract

Until recently, little was known about the Weddell Sea sector of the West Antarctic Ice Sheet. In the last 10 years, a variety of expeditions and numerical modelling experiments have improved knowledge of its glaciology, glacial geology and tectonic setting. Two of the sector's largest ice streams rest on a steep reverse‐sloping bed yet, despite being vulnerable to change, satellite observations show contemporary stability. There is clear evidence for major ice sheet reconfiguration in the last few thousand years, however. Knowing precisely how and when the ice sheet has changed in the past would allow us to better understand whether it is now at risk. Two competing hypotheses have been established for this glacial history. In one, the ice sheet retreated and thinned progressively from its Last Glacial Maximum position. Retreat stopped at, or very near, the present position in the Late Holocene. Alternatively, in the Late Holocene, the ice sheet retreated significantly upstream of its present grounding line and then advanced to today's location due to glacial isostatic adjustment and ice shelf and ice rise buttressing. Both hypotheses point to data and theory in their support yet neither has been unequivocally tested or falsified. Here we review geophysical evidence to determine how each hypothesis has been formed, where there are inconsistencies in the respective glacial histories, how they may be tested or reconciled, and what new evidence is required to reach a common model for the Late Holocene ice sheet history of the Weddell Sea sector of West Antarctica.

The Sensitivity of the Antarctic Ice Sheet to a Changing Climate: Past, Present, and Future

“…Conversely, interpretations of reworked foraminifera from marine sediment cores and multibeam analysis imply an ice sheet that was grounded near the continental shelf break until at least 20 kyr BP, and that most grounding line retreat was more gradual and postdates 10 ka (Arndt et al, 2017;Hillenbrand et al, 2014;Hodgson et al, 2018). Review of these two different scenarios by Siegert et al (2019) highlights that geophysical and cosmogenic data remain consistent with either scenario, but clearly indicate that there was a major redirection of ice flow in the Weddell Sea embayment during the mid-Holocene. It was proposed isostatically-driven processes could be invoked to explain either scenario; either through a redirection of subglacial hydrology leading to a change in dynamic ice flow in the mid-Holocene, or through rebound of the seafloor following early Holocene retreat, resulting a the regrounding of the ice shelf and subsequent a readvance of the grounding line in the mid-Holocene (Siegert et al, 2019, and references therein).…”

“…However, further evidence for an Antarctic contribution to MWP-1a from data on land and the continental margin in other regions such as the Weddell Sea (Arndt et al, 2017;Nichols et al, 2019) is absent, and this issue remains a conundrum (Goehring et al, 2019;Hall et al, 2015;Prothro et al, 2020). The large uncertainties in the underpinning sea level constraints (Hibbert et al, 2016(Hibbert et al, , 2018Stanford et al, 2011), and dating of geological material on land and in the ocean (e.g., see discussion of cosmogenic dating in Siegert et al (2019) and radiocarbon dating in Anderson et al (2014)), and the uncertainty around the AIS size, seaward extent, thickness and volume above flotation at the LGM, mean that currently it remains difficult to quantify the exact contribution of AIS melting to the sea level rise recorded during MWP-1a. Ocean forcing was inferred as the key driver of deglacial AIS dynamics, modulated by global atmospheric teleconnections, that decoupled ice sheet elevation and air temperatures in a high resolution ice core near the Weddell Sea, and resulted in rapid thinning of the AIS during the period coinciding with MWP1-a (Fogwill et al, 2017).…”

Glacial-cycle simulations of the Antarctic Ice Sheet with the Parallel Ice Sheet Model (PISM) – Part 2: Parameter ensemble analysis

“…Geothermal heat flux based on airborne magnetic data from Martos et al (2017) is applied to the lower boundary of a bedrock thermal layer of 2 km thickness, which accounts for storage effects of the upper lithosphere and hence estimates the heat flux at the icebedrock interface. Climate boundary conditions are based on mean precipitation from RACMO2.3p2 (van Wessem et al, 2018) and a temperature parameterization based on ERA-Interim reanalysis data (Simmons, 2006) in combination with the empirical positive-degree-day (PDD; e.g., Reeh, 1991) method. Climatic forcing is based on ice-core reconstructions from EPICA Dome C (EDC; Jouzel et al, 2007) and WAIS (West Antarctic Ice Sheet) Divide ice core (WDC; Cuffey et al, 2016) as well as on sea-level reconstructions from the ICE-6G GIA model Peltier, 2015, 2017).…”

Englacial Architecture and Age‐Depth Constraints Across the West Antarctic Ice Sheet

“…The Institute and Möller Ice Streams (IMIS) comprises 50% of the total area of the WAIS that discharges to the Weddell Sea via the Filchner-Ronne Ice Shelf. Although not currently identified as a region of major ice loss by satellite altimetry (Shepherd et al, 2019), several recent studies, in part using IPR-sounded IRHs, have posited that the region has hosted significant ice-dynamical changes since the Last Glacial Maximum and through the Holocene (Bingham et al, 2015;Hillenbrand et al, 2014;Kingslake et al, 2016;Siegert et al, 2013;Siegert et al, 2019;Winter et al, 2015). Under climate change in the latter half of the 21st century a reorganization of ocean currents could increase melting considerably in the Filchner-Ronne Ice Shelf cavity (Hellmer et al, 2012), leading to marine ice sheet instability as the bed upstream of the grounding lines dips steeply upglacier (Ross et al, 2012).…”