Paleoceanographic reconstruction of the Antarctic Intermediate Water in the South East Pacific throughout the last 1 Ma

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The importance of intermediate waters for the global ocean circulation and climate is being increasingly highlighted in the scientific community in recent decades. Particularly, Antarctic Intermediate Water (AAIW) as the most widespread intermediate water mass worldwide arises as a key component in transferring CO2 from atmospheric to marine reservoirs and vice versa, as a key player in rapid reorganizations of the meridional overturning circulation, and furthermore it provides a means of connection between processes occurring at high austral latitudes and the rest of the oceans. Despite its role in a number of oceanic and climatic processes, paleoceanographic reconstructions of the AAIW needed to assess its role within these processes under a range of forcing conditions are scarce. This is partly due to the lack of long, continuous sedimentary sequences at intermediate depths. This project aims to fill in this gap by exploiting two sediment cores from the Chilean margin, i.e. close to the main area of formation of the AAIW nowadays. The short gravity core GeoB3359-3 (~3.8 m) is collected from todays core of the AAIW close to its formation site, a setting plausibly accounting also for the last glacial period. The long MeBo core GeoB15020 (~78 m) has been retrieved from the upper boundary and northernmost reaches of the AAIW today. Probably it was under an even stronger influence of this water mass during the past 12 glacial periods. We propose to perform stable isotope and trace element analyses in benthic foraminifera (i) to reconstruct changes in the type characteristics of the AAIW from 24 to 7 ka before present (GeoB3359-3), (ii) to define the geometry and northward spreading of the AAIW during the last ~1 Ma (GeoB15020), (iii) to relate changes in the spreading of this water mass to shifts in its production rate, and (iv) to assess the long-term evolution of the AAIW during the last ~1 Ma, potentially covering the Mid Pleistocene Transition (GeoB15020). As there are no comparable archives available, this set of records will become the most complete and extensive reconstruction of the evolution of the AAIW.