Sedimentological facies characterization of Pliocene key interglacial-glacial intervals, IODP site 1361A, East Antarctic Wilkes Land margin

Marine sediment cores containing a unique Pliocene paleoenvironmental record were collected from the East Antarctic Wilkes Land continental rise by the IODP Expedition 318 at Site U1361 (Escutia et al., 2011). Site U1361 is located in front of the Wilkes Subglacial Basin (WSB) were, today, the East Antarctic Ice Sheet (EAIS) is grounded below sea level (marine-based) and therefore more vulnerable to climate changes.

We have conducted a facies analysis using shipboard measurements taken during Expedition 318 (i.e., physical properties data such as density (GRA) and magnetic susceptibility (MST) and high-resolution digital images), complemented with continuous elemental geochemical analyses. In addition, we have conducted high-resolution siliceous microfossil analyses to characterize past “warmer-than-present” intervals during the Pliocene warm period (~ 3-5 Ma) and their terminations recorded in site U1361 between ~ 73 to 123 mbsf. Our study is complemented by a pilot high-resolution detailed work on siliceous microfossils conducted from 3.69 to y 3.56 Ma that captures changes in sea ice cover and oceanic conditions (Armbrecht et al., 2018).

Preliminary analyses show that sediments consist of alternating intervals of interglacial diatom-rich/bearing silty clay with dispersed clasts that are ~ 0.5 to 8 m thick, and glacial sparsely laminated bioturbated clays with occasionally dispersed clasts.  In general, interglacial sediments is characterized by lower density, higher MST values, lower Mn/Ti and Fe/Ti ratios, and high Ca/Al, Si/Al, and Ba/Al ratios. Bioturbated clay with any dispersed clasts has a marked opposite trend (i.e., higher density, lower MST values, lower Ca/Al, Si/Al, and Ba/Al ratios and higher Mn/Ti and Fe/Ti ratios). This changes in lithology, physical properties and geochemical composition record significant changes in paleoenvironmental conditions. However, each glacial/interglacial (and vice versa) period exhibit specific characteristics and diatom associations pointing to different sea ice conditions during the selected Pliocene intervalsthat can be indirectly linked to ice-sheet dynamics in the Wilkes Subglacial Basin. The results of this study are relevant in order to understand the response of the EAIS dynamics and marine biota to an increase of the ocean surface temperatures during the transition from atmospheric CO₂ concentrations similar to pre-industrial to concentrations close to present values (410 ppm).

This work has been conducted in the frame of projects H2020-MSCA-IF-2018-ANTICE-841980/CTM2017-89711-C2-1-P and is a contribution to the SCAR INSTANT Program.

Escutia, C. et al., 2011 doi:10.2204/​iodp.proc.318.105.2011

Armbrecht et al., 2018. doi:10.1016/j.marmicro.2017.10.008