Magneto-biostratigraphic age models for Pleistocene sedimentary records from the Ross Sea

Abstract

The Ross Sea is one of the major sites of formation for Antarctic Bottom Water (AABW), a key component of the global ocean overturning circulation. However, there is currently a lack of high quality stratigraphic records documenting how this water mass flows from the continental shelf into the abyssal ocean, and specifically how this pathway is affected by changes in ice sheet cover on the Ross Sea continental shelf through Pleistocene glacial-interglacial cycles. Over the course of two expeditions in 2015 and 2016, a suite of cores from the upper continental slope to the abyssal plain was obtained by the Korea Polar Research Institute from the R/V Araon. The age of these cores ranges from Holocene to the latest Pliocene, and they hold the potential to document a source-to-sink record of AABW transfer into the abyssal Pacific Ocean. The cores are located in regions with distinct differences in bottom water energy, with high-energy cascading water masses on the upper slope creating the potential for erosional hiatuses, passing downslope into a lower energy setting. To decipher the complex environmental records and allow core-to-core correlation, robust chronostratigraphies are essential. Here, we present age models for four of these cores, based on correlation between their magnetostratigraphy and the geomagnetic polarity timescale, resulting in sedimentation rates between 1.5 cm/ky and 0.5 cm/ky. Rock magnetic data indicate the remanence is carried by magnetite with an almost ubiquitous contribution of high coercivity fraction that is not demagnetised by 100 mT. We demonstrate that a reliable magnetostratigraphy is established for each of these cores, and magnetic properties can be used to identify potential hiatuses in the cores and as a proxy for sedimentary grain-size.