Holocene relative sea-level change in the Pine Island-Thwaites Glacier region of West Antarctica

Abstract:

Here, we present the first Holocene relative sea-level (RSL) record for the Pine Island Bay region (PIB) of the Amundsen Sea Embayment (ASE) constructed from more than 70 radiocarbon dates of shells and penguin bones collected from raised marine beaches on three distinct island chains. Reconstructions of RSL allow assessment of past ice-volume fluctuations, provide boundary conditions for geophysical model simulations and provide information on deglacial history. This is important because the West Antarctic Ice Sheet (WAIS) has retreated and thinned at accelerated rates over the past three decades in the ASE sector, and this trend is predicted to continue in the coming centuries. Mass loss of the largest glacier in the ASE, Thwaites Glacier (TG), is of particular concern, because it is hypothesized to be on the verge of runaway retreat. If TG were to collapse, much of the WAIS would be susceptible to the same fate, with the potential for as much as 3.3 m of global sea-level rise. Our results suggest uninterrupted glacial isostatic rebound since 4.3 kyr BP with no evidence of retreat and subsequent readvance of glaciers in the PIB region during the late Holocene. One date from a reworked shell suggests a minimum age of 10.7 kyr BP for retreat of grounded ice from the embayment, which agrees well with marine records from the region. The remaining ages from sites as much as 27 m above sea level (close to the inferred marine limit) constrain an exponential RSL curve that extends from 4.3 kyr BP to present. Our results show that the PIB region experienced 5 - 10 mm/yr of RSL change since the mid Holocene. In contrast, current bedrock uplift rates in the ASE range between 15 - 41 mm/yr. Although RSL accounts for multiple factors including bedrock uplift, the difference between modern rates and Holocene RSL change suggests that an elastic response of the lithosphere is contributing to increased isostatic adjustment at present due to recent, rapid ice-mass loss in the ASE.