Ice retreat in Wilkes Basin of East Antarctica during a warm interglacial

Abstract

Efforts to improve sea level forecasting on a warming planet have focused on determining the temperature, sea level and extent of polar ice sheets during Earth's past interglacial warm periods 1-3. At ~400 thousand years before present, during the interglacial period known as Marine Isotopic Stage 11 (MIS 11), the Earth, globally was 1-2°C warmer 2 and sea level was 6-13m 1,3 higher. Sea level estimates in excess of ~10m, however, have been discounted as these require contribution from the East Antarctic Ice Sheet 3 , which has been argued to have remained stable at MIS 11 and for millions of years prior 4,5. Here, we show how the evolution of 234 U enrichment within subglacial waters of East Antarctica records the ice sheet response to MIS 11 warming. Within the Wilkes Basin, subglacial chemical precipitates of opal and calcite record the accumulation of 234 U, the product of rock-water contact within an isolated subglacial reservoir, up to 20 times higher than marine waters. The timescales of 234 U enrichment place the inception of this reservoir to MIS 11. Informed by the observed 234 U cycling in the Laurentide ice sheet, where 234 U accumulated during periods of ice stability 6 and was purged in response to deglaciation 7 , we interpret our East Antarctic dataset to record ice loss within the Wilkes Basin at MIS 11. The 234 U ingrowth within the Wilkes Basin is shared by the McMurdo Dry Valley brines 8-10 , supporting 11 brine origination beneath the adjacent East Antarctic ice sheet. The requirement that brine salts 10 and bacteria 12 are from marine waters implies that MIS 11 ice loss was coupled with marine flooding. Collectively these data indicate that during one of the warmest Pleistocene interglacials, the ice sheet margin at the Wilkes Basin retreated to the proximity of the precipitate location, ~700km inland from the current position, which assuming current ice volumes, would contribute ~3-4m 13 to global seas.

A new sea-level record for the Neogene/Quaternary boundary reveals transition to a more stable East Antarctic Ice Sheet

“…These calculated sea-level highstands imply a retreat of all marine-based sectors of the EAIS, which presently store ice equivalent to ∼19 msle (26). This observation is broadly consistent with 1) three-dimensional ice-sheet model results (55) showing that a retreat of almost all marine-based ice of the EAIS is plausible under pCO 2 conditions of 400 ppmv and 2) geological evidence (19,20) S3 for details): As sampling resolution increases, the amplitude of the recovered signal increases (coefficient = −0.16261, SE = 0.04559, P < 0.01) with no detectable difference between MIS 101 and MIS 100 (coefficient = 0.11128, SE = 0.06448, P > 0.05), which explains 30.4% of data variability.…”

“…The structure of the benthic oxygen isotope composite suggests that this stability endured for most of the Quaternary until the "super-interglacials" of the late Pleistocene, for example MIS 11 and 5 (Fig. 1A), for which retreat has already been proposed based on independent lines of evidence (19,20) (Fig. 2).…”

“…The latter records (20) also indicate EAIS retreat during the last interglacial MIS 5e (∼120 ka). Melting of the EAIS as inferred in the late Quaternary was likely driven by oceanatmosphere warming around Antarctica and grounding-line retreat in response to ice-ocean interactions (19,20).…”

“…2) imply EAIS melting during the Quaternary "super-interglacials" of Marine Isotope Stage (MIS) 11 (∼400 ka) and 31 (∼1.07 Ma) under relatively low pCO 2 conditions. Supporting evidence for EAIS retreat during the most recent "super-interglacial" MIS 11 comes from isotope measurements in mineral deposits recording past changes in subglacial East Antarctic waters (19), as well as records of ice-rafted debris (IRD) and detrital sediment neodymium isotopes from offshore the Wilkes Subglacial Basin (20). The latter records (20) also indicate EAIS retreat during the last interglacial MIS 5e (∼120 ka).…”

Rapid postglacial rebound amplifies global sea level rise following West Antarctic Ice Sheet collapse

“…An accurate treatment of the signal in sea level modeling of the LIG requires not only that the exposure of marine-based sectors be included in the modeling ( 9 – 12 , 18 ) but also that areas of low viscosity in the shallow mantle beneath much of WAIS be accounted for. These conclusions also hold for previous interglacials in which marine-based sectors of the AIS destabilized ( 53 ), including those in EAIS.…”