Pliocene deglacial event timelines and the biogeochemical response offshore Wilkes Subglacial Basin, East Antarctica

Rachel A Bertram,David J Wilson,Tina Van De Flierdt,Robert M Mckay,Molly O Patterson,Francisco J Jimenez-Espejo,Carlota Escutia,Grace C Duke,Briar I Taylor-Silva,Christina R Riesselman

doi:10.1016/j.epsl.2018.04.054

Rachel A Bertram, David J Wilson + Show 8 more

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Significantly reduced ice coverage in Greenland and West Antarctica during the warmer-than-present Pliocene could account for ∼10 m of global mean sea level rise. Any sea level increase beyond this would require contributions from the East Antarctic Ice Sheet (EAIS). Previous studies have presented low-resolution geochemical evidence from the geological record, suggesting repeated ice advance and retreat in low-lying areas of the EAIS such as the Wilkes Subglacial Basin. However, the rates and mechanisms of retreat events are less well constrained. Here we present orbitally-resolved marine detrital sediment provenance data, paired with ice-rafted debris and productivity proxies, during three time intervals from the middle to late Pliocene at IODP Site U1361A, offshore of the Wilkes Subglacial Basin. Our new data reveal that Pliocene shifts in sediment provenance were paralleled by increases in marine productivity, while the onset of such changes was marked by peaks in ice-rafted debris mass accumulation rates. The coincidence of sediment provenance and marine productivity change argues against a switch in sediment delivery between ice streams, and instead suggests that deglacial warming triggered increased rates of iceberg calving, followed by inland retreat of the ice margin. Timescales from the onset of deglaciation to an inland retreated ice margin within the Wilkes Subglacial Basin are on the order of several thousand years. This geological evidence corroborates retreat rates determined from ice sheet modeling, and a contribution of ∼3 to 4 m of equivalent sea level rise from one of the most vulnerable areas of the East Antarctic Ice Sheet during interglacial intervals throughout the middle to late Pliocene.

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Ice grounded below sea level in the East Antarctic Ice Sheet (EAIS) has a potential sea level equivalent of ∼19 m (Fretwell et al, 2013)
Provenance tracing of detrital sediment is an effective tool for deciphering ice sheet histories (Licht and Hemming, 2017)
We demonstrate dynamic behavior of the ice margin at the mouth of the Wilkes Subglacial Basin throughout the Pliocene epoch, with ice retreat on timescales of a few thousand years, substantiating findings of recent modeling studies

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Introduction

Ice grounded below sea level in the East Antarctic Ice Sheet (EAIS) has a potential sea level equivalent of ∼19 m (Fretwell et al, 2013). Such ice is predominantly contained within the Aurora Subglacial Basin, the Recovery Basin, and the Wilkes Subglacial Basin (Fig. 1a). Ery Basin may be vulnerable to melting under future environmental conditions (Golledge et al, 2017a). Collapse of marine-based ice in this basin may have important implications for Southern Ocean stratification and temperature, with the potential to amplify melting in other vulnerable regions of the EAIS (Phipps et al, 2016). It is critical to constrain the sensitivity of the Wilkes Subglacial Basin to future, warmer environmental conditions

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