A sub-decadal record of East Antarctic biological productivity, and ocean-ice interactions over the Holocene from an ultra-expanded continental shelf sediment drift.

In 2010, International Ocean Discovery Programme site U1357 retrieved a 180 m thick sedimentary sequence from the Adélie Land continental shelf, offshore of the East Antarctic Ice Sheet. The core targeted an expanded sediment drift (termed the Adélie Drift) that provides an ultra-high resolution record of Holocene climate variability adjacent to the Mertz Polynya system, one of the largest exporters of sea ice and Antarctic Bottom Water along the East Antarctic margin. Sedimentation at this site is dominated by pelagic biosiliceous sedimentation with accumulation rates averaging ~1.5-2 cm/year, but is heavily influenced by sediment advection by the westward flowing Antarctic Coastal Current. Previously obtained Holocene marine archives have orders of magnitude lower sedimentation rates, and commonly alternate between massive (bioturbated) and laminated diatom ooze, which obscures the ability to resolve high-frequency change at sub-decadal scales. However, U1357B is continuously laminated, and combined with high sedimentation rates, affords an unprecedented opportunity to assess sub-decadal resolution climate and biological responses at the Antarctic oceanic margin. Specifically, this record identifies El Niño Southern Ocean (ENSO) teleconnections that could account for sea-ice variability, nutrient delivery and high productivity bloom events in the coastal polynyas along Adélie Land throughout the Holocene.

Here, we discuss sedimentary processes associated with formation of the Adélie Drift deposit, and how reconstructions of sediment advection through time can be used to identify shifts in current strength through the Holocene. These currents are driven by katabatic and zonal winds, and are a strong influence on biological productivity in the region. Climatic conditions over the last 11,400 years are reconstructed using a range of CT scan images, lipid biomarkers, diatom analysis, and physical/geochemical core properties. Shifting sensitivity of this system to ENSO forcing over centennial to millennial timescales coincide with rapid baseline shifts in climate and sea-ice state, indicating the existence of tipping points along the coastal margin of East Antarctica.