Threshold behavior of a marine‐based sector of the East Antarctic Ice Sheet in response to early Pliocene ocean warming

Abstract

We investigate the stability of the East Antarctic Ice Sheet (EAIS) on the Wilkes Land continental margin, Antarctica, utilizing a high-resolution record of ice-rafted debris (IRD) mass accumulation rates (MAR) from Integrated Ocean Drilling Program Site U1359. The relationship between orbital variations in the IRD record and climate drivers was evaluated to capture changes in the dynamics of a marine-based ice sheet in response to early Pliocene warming. Three IRD MAR excursions were observed and confirmed via scanning electron microscope microtextural analysis of sand grains. Time series analysis of the IRD MAR reveals obliquity-paced expansions of the ice sheet to the outer shelf prior to~4.6 Ma. A decline in the obliquity and a transition into a dominant precession response of IRD MAR occur at~4.6 Ma along with a decline in the amplitude of IRD MAR maxima to low background levels between~4.0 and~3.5 Ma. We speculate that as sea surface temperatures began to peak above 3°C during the early Pliocene climatic optimum, the ice shelves thinned, leading to a greater susceptibility to precession-forced summer insolation and the onset of persistent retreat of a marine-based portion of the EAIS.

Quartz grain microtextures illuminate Pliocene periglacial sand fluxes on the Antarctic continental margin

“…The IODP Site U1359 was drilled in 4,003 m water depth within 100 km of the shelf break on the Wilkes Land margin and recovered Pliocene sediments between ca 50 and 150 mbsf (Figure 1). At Site U1359, as part of this study, 110 samples were analysed across the MPWP, and merged with the previously published record of Hansen et al (2015). Pliocene sediments recovered at IODP Site U1359 consist primarily of silty clays and diatomaceous silty clays with dispersed clasts (>2 mm) with up to ca 43% biogenic silica (Hansen et al, 2015).…”

“…Here the transport history of the sand components recovered from Pliocene Antarctic drillcores is evaluated through detailed analyses of terrigenous particle‐size distributions along with scanning electron microscopy (SEM) of quartz grain microtextures. Previous work has shown that high‐resolution records of the abundance of coarse sand recovered from deep‐sea drillcores on the Wilkes Land margin indicate a response to orbital forcing in the obliquity and precession bands (Hansen et al, 2015; Patterson et al, 2014). However, the contribution of the Neogene Antarctic Ice Sheet to global ice volume changes in the precession band is debated (Caballero‐Gill et al, 2019; DeVleesschouwer et al, 2017), warranting investigation of the precise nature of the ice‐rafted sediment fluxes (Gilbert, 1990).…”

“…An existing Pliocene high‐resolution laser particle‐size record (Hansen et al, 2015) from International Ocean Discovery Program (IODP) Site U1359 is extended across the Mid‐Pliocene Warm Period (MPWP) and the relative proportions of the sand fluxes attributed to ice rafting and other sediment transport mechanisms for this deep‐water site are investigated. Furthermore, a baseline for glacially derived material is provided by analyses of discrete intervals of Neogene ice‐proximal diamictites recovered from the ANDRILL Site 2A (AND‐2A) core in the Ross Sea (Fielding et al, 2008).…”

Orbital Forcing of West and East Antarctic Ice Sheets 3.8-3.0 Ma: A Climate Analogue in Weddell Sea ODP Site 697

“…Ma (Lisiecki & Raymo, 2005). Hansen et al (2015) also shows a shift to a dominant precession response of Wilkes Land EAIS IRD at ~4.6 Ma. Other studies of Wilkes Land EAIS marine sediment cores (Patterson et al, 2014) show a dominant periodicity of 40kyrs between 4.3 and 3.5 Ma and transition to precession thereafter.…”

“…During periods of smaller axial tilt, the insolation distribution anomaly decreases between winter and summer, but increases between equatorial and polar latitudes. As a result, warmer winters increase meridional moisture transport and cooler summers minimize seasonal melt back, thus increasing ice sheet surface mass balance (Raymo & Nisancioglu, 2003;Hansen et al, 2015).…”