Abstract
While Pleistocene glacial-interglacial cycles are commonly associated with strong waxing and waning of Northern Hemisphere ice sheets, the response of the Antarctic ice sheet and regional changes in oceanographic and environmental conditions to Pleistocene climate dynamics remain poorly constrained. We present a reconstruction of sea-ice cover, sea surface temperature and primary productivity off the Ross Sea margin (Adare Basin at the slope of the Drygalski Basin) during the marine isotope stages (MIS) 9 to 5 (350–70 thousands years ago, encompassing Terminations IV to II). Our multiproxy study relies on micropaleontology (diatoms, dinoflagellate cysts, benthic foraminifers), organic and inorganic geochemistry proxies (carbon and nitrogen isotopes, lipid biomarkers, XRF-data), and sedimentology (IRD) obtained from deep-sea core AS05-10. For each glacial-interglacial transition a clear succession of events can be observed: (near-)permanent sea ice cover during glacial stages is followed by ice-shelf break-up with episodic ice-free areas and surface water stratification. Notably, ice-shelf break-up precedes the increase in air temperature as measured in the Vostok ice core for each glacial-interglacial transition. Generally, air temperature over Vostok starts rising once sea-ice cover at site AS05-10 has significantly decreased, becoming seasonal, as indicated by the diatom species composition. This is also reflected by the high diatom productivity and increased water mixing at site AS05-10, which is indicative of its proximity to the Marginal Ice Zone. At the onset of Termination II (MIS6 to 5), high export productivity and dysoxic bottom water conditions occurred, while water temperature increased about 5 °C. During each interglacial spring/summer sea-ice cover is most reduced, and highest productivity occurs. Following each interglacial, the warm and cold fluctuations match the sawtooth character of the temperatures over Vostok. This record illustrates that at the Ross Sea margin, sea surface conditions and (export) productivity were strongly influenced by the natural climate variability of the Pleistocene. In light of this, current global warming may lead to increased ice-shelf break-up, water column stratification and shifts in the position/size of the Marginal Ice Zone with implications for algal species composition and diversity, and for primary productivity.
Highlights
Antarctic sea ice plays a key role in regional polar climate and biology, and global ocean circulation
Core AS05-10 retrieved from the slope between the Drygalski basin and the Adare Basin records the response of the surface water environment to glacial-interglacial variability in the late Pleistocene
Our multiproxy study identified three phases in each glacialinterglacial transition, which reflect the retreat of the seasonal seaice margin and warming of the surface waters
Summary
Antarctic sea ice plays a key role in regional polar climate and biology, and global ocean circulation. The PP within the sea ice ‘seeds’ surface waters upon melting and the entire polar ecosystem depends on the annual cycle of melting and formation of sea ice (Stoecker et al, 2000; Lizotte, 2001; Garrison et al, 2005; Murphy et al, 2017). The lack of a clear trend in recent times makes future Antarctic sea-ice projections highly uncertain (Arzel et al, 2006; Bracegirdle et al, 2008; Bintanja et al, 2015). Sea ice decline will likely act as a positive feedback to current global warming (e.g., Serreze and Barry, 2011; Park et al, 2015; Abe et al, 2016; Haumann et al, 2016; Andry et al, 2017), which increases the relevance of understanding future sea ice conditions
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