Abstract
The Holocene is characterised by millennial-scale climatic and oceanic fluctuations superimposed on an orbitally-paced warming trend. In Antarctica, spatial heterogeneity in these fluctuations result in local and regional variations in ice-shelf behaviour and environmental conditions. The timing of ice-retreat within the Ross Sea has been regionally constrained. However, disparities in deglacial timing between marine and terrestrial records remains unresolved in the southwest (SW) Ross Sea, but is likely to arise from challenges associated with dating marine sediments. Following deglaciation, there are limited constraints on oceanographic and climatic conditions during Holocene warming, and the subsequent impacts on sea-ice extent and primary productivity.
We present a new multi-site reconstruction of deglacial ice-retreat timing and Holocene sea-ice extent and primary production from four Holocene marine sedimentary records. These cores were collected from the SW Ross Sea during the 2015 Araon Cruise ANA05B, and are located offshore of Mawson Glacier (GC78), Granite Harbour (GC80), north and northeast of Ross Island (GC72 and GC71 respectively). Cores are up to 4.5 m long and contain a basal ice-associated facies overlain by diatom ooze. Core-to-core correlation is achieved through ramped pyrolysis 14C chronology, reservoir-corrected using 210Pb dating. It is a unique chronological approach to this region, whereby a local reservoir age of 1999 72 years has been generated. Results reconcile deglacial timing differences between published onshore and offshore records, and show there was rapid and sustained retreat in the SW Ross Sea from 6.5-5 ka possibly in response to a poleward shift in westerly winds and incursions of warm C ircumpolar Deep Water (CDW) onto the Ross Sea continental shelf.
To reconstruct the post-glacial environment, we utilize geochemical proxies for gross diatom abundance, nutrient utilization and water stratification (wt.% BSi, d13C, d15N), and diatom assemblages for sea-ice extent and duration. Millennial-centennial scale trends appear to be strongly influenced by internal climate modes of the El Niño Southern Oscillation (ENSO) and the Southern Annular Mode (SAM). Of particular interest is a d13C excursion (up to -30‰) in GC72, GC78 and GC80. This excursion corresponds to a high abundance of Corethron spp. and/or Chaetoceros spp. that reflects a transient lateral expansion of the Ross Sea Polynya during the Little Ice Age.