Southern Ocean sediment records reveal future scenarios of the circum-Antarctic frontal system

The Southern Ocean (SO) and Antarctica are intrinsic to the Earth´s climate system. While the oceanic firewall of the Antarctic Circumpolar Current (ACC) frontal system is presently mitigating ocean warming and enhancing ice-sheet stability in Antarctica, it is beginning to weaken and its future is uncertain. With few exceptions, instrumental and satellite-based climate records in the SO and Antarctica do not exceed the past 50 years and are thus too short to place the recent anthropogenic global warming-induced SO changes in the context of natural climate variability.

It has long been recognized that the distribution of biogenic and terrigenous sediments in the SO closely reflects the meridional character of the ACC, which critically links the climatic gradients between glaciated Antarctica and the subtropics (e.g., Diekmann, 2007; Keany & Kennet, 1972). The most prominent SO sedimentation pattern is the circumpolar occurrence of diatomaceous oozes, formed of the amorphous opaline silica (Si) remains of marine micro algae. This so-called opal belt (Lisitzin, 1971) is the largest sink of biogenic Si in the world ocean (Chase et al., 2015). Opal contents in the SO are maximal in the vicinity of the Polar Front and decrease towards Antarctica, the latter being largely controlled by increasing sea-ice cover (Chase et al., 2015). Today, the opal belt in the Polar Frontal Zone roughly corresponds to the modern oceanic firewall, i.e. the limit between substantial surface ocean warming to the north and dampened surface warming to the south. North of the Subantarctic Front, an abrupt shift occurs to predominantly calcareous  sediments, composed of carbonate skeletal remains built by planktic and benthic foraminifera and marine algae (coccolithophorids). 

We assess past changes in sediment budgets across the ACC fronts, and assess four-dimensional variations of ACC circulation across different climate states. This is done through sediment echosounder records, calibrated with down-core sediment records along the cross-frontal transects. These data allow to obtain geographically extensive estimates of changes in the position and latitudinal distribution of major oceanic sediment types occurring at the SO firewall.

At the present stage, we focus on ACC fluctuations and frontal shifts on cross frontal transects from selected regions in SW Pacific SO domain, where previous expeditions provide sediment echosounder profiles and sediment cores. However, future research requires the integration of additional core material, and a denser grid of sediment echosounder data in different SO sectors in order to capture expected zonal heterogeneities of ACC strength changes and frontal shifts on a hemispheric scale. For this purpose, substantial coordination efforts and collaboration with international partners is required.

Diekmann B (2007) Sedimentary patterns in the late Quaternary Southern Ocean. Deep Sea Research Part

Keany J, Kennett JP (1972) Pliocene-early Pleistocene paleoclimatic history recorded in Antarctic-Subantarctic deep-sea cores. Deep Sea Research and Oceanographic Abstracts, 19(8):529–548. 

Lisitzin AP (1971) Distribution of siliceous microfossils in suspension and in bottom sediments, in The Micropaleontology of Oceans, edited by B. M. Funnell and W. R. Reidel, pp. 173–195, Cambridge Univ. Press.

Chase Z, Kohfeld KE, Matsumoto K (2015) Controls on biogenic silica burial in the Southern Ocean. Glob. Biogeochem. Cycles 29:1599-1616.