Atmospheric circulation patterns in the Southern Ocean during the Holocene
To obtain a global picture of the Earth’s past climate variability and its causes, numerous and geographically well dispersed proxy records are indispensable. In certain areas such as the North Atlantic region proxy-records are well represented but this is not yet the case for the mid and high latitudes of the Southern Hemisphere. However, recently it became clear that the Southern Ocean played a crucial role in past global climate history. The interplay between one of the most vigorous ocean currents on Earth, the Antarctic Circumpolar Current, and the Southern Hemisphere westerly wind belt (SHW) had an important influence on atmospheric CO2 concentrations for example during the last glacial-interglacial transition. Also during the Holocene, shifting SHW might have had an influence on climate variability. It is therefore highly needed to obtain sound reconstructions of past SHW variability both in time and space. Most SHW proxy-records are originating from South America and in a lesser extent from New Zealand, covering a restricted area in the vast Southern Ocean. Up to today, the South Indian Ocean remains a blank spot.
We intend to fill the gap by reconstructing past Holocene climate variability with a focus on potential intensification/latitudinal shifts of the SHW belt in the Indian Ocean sector of the Southern Ocean.
A prerequisite for reconstructing changes in SHW, currently situated between 35° to 60° S, is the availability of terrestrial records that (i) mainly reflect atmospheric conditions and (ii) are situated on a latitudinal transect covering the wind belt. Therefore, we sampled a unique set of terrestrial records from three islands that are located on a latitudinal transect going from Iles Kerguelen (49° S) in the core of the wind belt, over Iles Crozet (46° S) to Ile Amsterdam (37° S) at its northern edge. Peat archives from these islands, mainly depending on the atmosphere for their water balance, are studied to reconstruct past SHW intensity variability at each latitude using proxy-methods reflecting humidity/precipitation changes (e.g. testate amoebae, plant macrofossils, the preservation of the peat, biogenic silica) and wind intensity changes (e.g. exotic long distance pollen content, aeolian sand influx). High resolution 14C chronologies of the peat records allows integrating the South Indian island proxy-records resulting in a sound reconstruction of SHW variability in this sector that in turn can be compared to SHW reconstructions in the Atlantic and Pacific sectors of the Southern Ocean as well as to other climate archives such as Antarctic ice cores.
The research in the Indian Ocean is part of the larger ongoing Swedish-French collaboration project “Deciphering the role of the Southern Ocean in the global climate system” between the Geology Department, LU and the LSCE (Laboratoire des Sciences du Climat et de l’Environnement, Gif-sur-Yvette, France). The major aims of the Swedish-French collaboration are (i) documenting the Southern Ocean climate behaviour along three latitudinal transects (c. 40°-55° S), in the Atlantic, Indian and Pacific sectors with terrestrial (LU) as well as marine records (LSCE) for the last 20000 years - the last glacial-interglacial transition and the Holocene and (ii) comparing our proxy based climate records with model simulations to better understand the mechanisms behind the climate events during this period.