A 43-ka mineral magnetic record of environmental variations from lacustrine sediments of Schirmacher Oasis, East Antarctica

Abstract

Glacial-interglacial climatic and environmental variations recorded in lake-bed sediments of Schirmacher Oasis (SO), East Antarctica, are rare; limited data exist on the past behavior of the East Antarctic Ice Sheet (EAIS). In this work, we present the mineral magnetic properties of a radiocarbon-dated sediment core, spanning the past 43,000 years, from a land-locked lake L-49 in SO. We also performed Scanning Electron Microscopic-Energy Dispersive X-ray Spectroscopic (SEM-EDS) studies on magnetic extracts to confirm the magnetic mineralogy. The values of magnetic susceptibility (χlf) and saturation isothermal remanent magnetization (SIRM) are relatively low during the Holocene but high during the last glacial period. Sediments of the last glacial period are composed mainly of coarse-grained (multi-domain - MD) magnetite/titanomagnetite (high values of S20 – an MD proxy, low susceptibility of anhysteretic remanent magnetism (χARM)/SIRM ratio values and high S-ratio values) indicating a stronger intensity of physical weathering in the Lake L-49 catchment. The mineralogy is confirmed by SEM-EDS data for magnetic extracts. Principal Component Analysis (PCA) of the data suggests three processes affecting magnetic properties of the lake sediments, i.e., ferrimagnetic input, biogenic processes and aeolian input. During deglaciation, a shift in the magnetic properties is documented: a decrease in χlf values from 18.6 cal ka BP onwards suggests melting of the snow and ice in the catchment thus leading to a significant production of fine-grained iron oxide minerals. At ~12.77 cal ka BP, high values of χlf and S20 ratio indicates cooling which is related to the Antarctic Cold Reversal (ACR). The Early Holocene Climate Optimum is distinctly imprinted in our record as a sudden decrease in χlf values and an increase in magnetic grain size ratio values (indicating finer iron oxide grains), suggesting a rapid thawing of the ice-sheet in response to a warm climate. The Mid-Holocene Hypsithermal (from 5.8 to 3.5 cal ka BP) and Neoglaciation (3.6 cal ka BP onwards) that are evident in this study correspond with reconstructions from lake and marine sediment, and ice-core records from Antarctica.