Long-term records of Antarctic Intermediate Water variability off northern Chile (SE Pacific)

The importance of intermediate water masses in the global ocean circulation and climate systems is being increasingly highlighted in the last years by both paleoceanographic and modelling studies. Particularly, Antarctic Intermediate Water (AAIW) arises as a key player in rapid reorganizations of the Meridional Overturning Circulation and also, most plausibly, in trapping and releasing atmospheric CO2 on glacial-interglacial time scales. Additionally, this water mass provides an active means of connection between processes occurring at high austral latitudes and the rest of the oceans (through the so-called "ocean tunnel"). Hence, understanding the past variability of AAIW and intermediate water mass developments is of high importance. However, at present, few paleoceanographic reconstructions of the characteristics, strength and variability of AAIW on glacial-interglacial time scales exist, partially due to the lack of long, high-resolution sediment sequences at locations under the influence of this water mass. In order to allow long-term paleoceanographic reconstructions (sub-orbital to orbital time scales) in an area sensitive to AAIW variability, long sediment cores were drilled at intermediate water depths off northern Chile (27°S) with the Marum Sea floor drill rig (MeBo) during the Sonne Expedition ChiMeBo in November 2010. Here we show results of paleo-environmental proxy analysis on the ca 60 m long composite of ChiMeBo cores GeoB15016-1 and GeoB15016-2 (27°29,48'S, 71°07,58'W, 956 m). Comparison of X-ray Fluorescence (XRF) core scanner data to nearby records suggest that the sequence almost completely covers the last 1 Ma with moderate to high sedimentation rates of around 5 cm/ka. None of the previously existing South East Pacific records at intermediate water depths, in comparison, reach beyond the last glacial period, while in the South West Pacific the longest intermediate water record reaches 340 ka (Pahnke and Zahn 2005). At 956 m water depth and northward of the main formation area of AAIW today, the benthic stable isotope, grain size and XRF records we will present provide the first paleoceanographic reconstruction of intermediate water variability in the South Pacific covering such a long time period and with a resolution capable of recording rapid climate changes. Emphasis will be placed on both, long-term patterns as well as abrupt climate events.