Testing the stratigraphic and paleoenvironmental resolution of sediment drifts off West Antarctica for IODP drilling

Lead Research Organisation: University of Cambridge
Department Name: Earth Sciences


There is intense scientific and public interest in the potential response of the Antarctic Peninsula and West Antarctica ice sheets to global warming. Recent observations suggest that this region is undergoing rapid changes including warming, ice-shelf disintegration, ice-sheet thinning and retreat. These recent changes need to be considered in a longer geological context by studying marine sediments proximal to the West Antarctic and Antarctic Peninsula Ice-Sheets. Toward this end, we have submitted and IODP proposal, currently awaiting scheduling, to drill a serie of sites on sediment drifts located in the Bellinghausen Sea (Pacific Ocean). Imprecise chronological control, due in large part to lack of foraminiferal carbonate for isotopic analysis, has stymied paleoceanographic interpretations of sediment cores from the Southern ocean. In preparation for the anticipated IODP expedition, we propose a 'proof-of-concept' study to apply the main paleoceanographic and stratigraphic methods to be employed in the study of the long sequences to be recovered by IODP. We will study piston core PC466 taken at one of the proposed IODP Sites (Pen-1), It was recovered at a water depth of 2400m on a sediment drift on the continental rise in the Bellinghausen Sea (64S, 69W ) by the British Antarctic Survey on RRS James Clark Ross. This short sedimentary record of 10.5 meters spans the last glacial period (~70,000 years) with high sedimentation rates and exhibiting distinct millennial-scale variability in both elemental composition (XRF) and magnetic susceptibility. Our goals for core PC-466 are three-fold. 1) Develop an accurate age model that can be used for stratigraphic correlation to other marine sediment cores and polar ice cores in both hemispheres. 2) Study the advance and retreat of ice sheets using ice-rafted detritus. 3) Reconstruct surface water conditions (temperature, salinity, carbonate-ion concentration, and sea ice). If we are successful in demonstrating that it is possible to apply traditional stratigraphic and paleoceanographic tools to the last glacial period of core PC-466, (a time period that paleoclimatologists and paleoceanographers know best), then we can be reasonably confident that such approaches will work for thousands of meters of record envisaged by proposal-732 and covering the last several million years.


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Vautravers M (2013) Palaeoenvironmental records from the West Antarctic Peninsula drift sediments over the last 75 ka in Geological Society, London, Special Publications

Description Proposal IODP Full-732 to drill sediment drifts off the Antarctic Peninsula and West

Antarctica is awaiting scheduling by the IODP Operations Task Force. In preparation for the expedition, we studied a piston core located at one of the proposed IODP sites to evaluate the
challenges posed by stratigraphy and paleoceanographic proxies in the Antarctic environment. We sought to evaluate whether cores from sediment drifts off West Antarctica could be used to develop reliable age models and palaeoclimatic records. This 'proof ofconcept' study was conducted on piston core JR179-PC-466, at the same location as one of the proposed IODP drill sites. This 10.45-m long core is dominated by glaciomarine terrigenous sediments with <1 weight% calcium carbonate. Despite the very low abundance of carbonate, shells of planktonic foraminifera were sufficient for stable isotope analysis in 2/3 of the samples examined. Despite gaps in oxygen isotope record, it was possible to recognize glacial-interglacial periods. The core stratigraphy was then established using oxygen isotopes and by correlating relative palaeomagnetic intensity (RPI) with a stacked reference curve. The core spans the last 75 ka with average sedimentation rates between ~4 and 25 cm kyr-1. Radiocarbon dating is difficult as only two samples of more than 300 examined contained enough foraminifera for this purpose.

Planktonic foraminifera abundances fluctuate between 0 and 30 individuals per gram, with lowest abundances during Marine Isotope Stage (MIS) 2 and 4. Planktonic foraminifera are
present during the Holocene, but more abundant during MIS3 owing to less dilution by terrigenous sediment and/or better carbonate preservation. The oxygen isotope record does not vary significantly during MIS3 and is not confounded by local influences such as sea-ice or melt water, and captures environmental changes of regional significance. The lack of very
low planktonic _18O values during MIS3 argues against large input of fresh water from melting of the Antarctic Peninsula Ice Sheet (APIS). During MIS 3, foraminifer abundance peaks correlate with warmings in Antarctic as expressed in the d18O record of the EDML ice core. These periods mark times of exceptionally good carbonate preservation during MIS3.

Estimating sea-ice cover using diagnostic diatom and radiolarian species in smear slides proved difficult because of the low abundance and poor preservation of siliceous microfossils at the core site. However, we counted a juvenile morphotype of N. pachyderma (s) that provides evidence for changing sea-ice cover. The core site was under permanent sea-ice conditions during MIS2 with episodic seasonally open conditions during MIS3. The abundance of IRD (>355 mm) is greatest during the last deglaciation between ~19 and 11 ka, as sea level rise destabilized the WAIS and APIS that had advanced onto the shelf during the lowstand of the last glacial maximum (LGM).

Our results demonstrated it is possible to produce a stratigraphy and infer palaeoceanographic changes from a sediment drift core taken in ~2000 m of water off west Antarctica. The west
Antarctic sediment drifts thereby offer an attractive target for drilling by the Integrated Ocean Drilling Program (IODP) to obtain long records of palaeoenvironmental change at high temporal resolution in a climatically sensitive region.
Exploitation Route The project demonstrated proof of concept that will be applied to IODP drilling of sediment drifts near the Antarctic Peninsula. The research cruise is awaiting scheduing.
Sectors Environment

Description The project demonstrated proof of concept that will be applied to IODP drilling of sediment drifts near the Antarctic Peninsula. The research cruise is awaiting scheduing.
First Year Of Impact 2013
Sector Environment