A. Camerlenghi¹, L. Sagnotti², R.G. Lucchi¹, M. Rebesco¹, and P. Macri'²

¹Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS), Borgo Grotta Gigante 42/c, 34010 Sgonico (Trieste) Italy
²Istituto Nazionale di Geofisica e di Vulcanologia (INGV), Via di Vigna Murata, 605, 00143 - Roma, Italy acamerlenghi@ogs.trieste.it

On the Pacific margin of the Antarctic Peninsula there were rapid climatic oscillations during the last glacial period that affected the textural, compositional and rock magnetic records of fine grained hemipelagic sediments. Such records are preserved in sediment drifts on the upper continental rise, produced by the interaction of weak along-slope bottom water flows with sediment entrained from turbidity currents, biogenic settling, ice rafted debris (IRD) and turbid plumes. We summarise the results of the SEDANO (SEdiment Drifts of the ANtarctic Offshore) Project, which selected sediment drift 7 on the Pacific margin of the Antarctic Peninsula as the focus of the geophysical and geological investigations. This drift is included in one of four main glacial depositional systems developed since middle Miocene.

Each system is composed by: 1) a prograding wedge between major glacial troughs on the outer shelf; 2) one or more sediment drifts separated by deep-sea channel systems on the upper continental rise. Trough-mouth fans and submarine canyons are missing along this margin. The spatial arrangement of the depositional elements is inferred to be controlled by the shear strength of the sediment deposited by ice flows conveyed by an elongated structural high.

Analysis of cores allows correlation up to 200 km and identification of up to 4 glacial and interglacial cycles. Modest grain-size variations within the very fine-grained surface drift sediments suggest minor changes in the bottom water regime both in term of space and time. Conversely, a coarsening outward trend observed in the sediment from the adjacent deep-sea channel with presence of gravel-sized turbidites at 250 km form the continental slope suggests the high efficiency of this depositional system. Glacial and interglacial cycles are reflected by variations in the clay mineral assemblage that represent different supply processes and provenance areas. Based on X-ray sedimentological facies, grain size, clay mineral assemblage and biostratigrpahy, we have identified 4 climatic stages (glacial, interglacial and transitional stages) Through an analysis of the paleomagnetism and environmental magnetism on three cores, we have identified sharp coercivity minima during the last glacial period that correlate to the major rapid cooling events of the northern Atlantic (Heinrich layers). We link these changes to a variable input of detrital organic matter, controlled by past sea-ice extent, induced by cooling events. These rapid changes during the last glacial period (presumably modulated by sea ice dynamics) can be correlated to other local Southern Ocean paleoclimatic proxies and were almost coeval to the major cooling events in the northern Atlantic that resulted in the deposition of the characteristic Heinrich layers, suggesting that they roughly timed with millennial scale climate events that occur globally. Our findings therefore support previous observations of the influence of millennial time scale changes in North Atlantic thermohaline circulation on the oceanography of the Southern Ocean. Though, the ultimate causes of our proposed increase of sea ice extension correlative to the Heirich events are yet to be identified.