More information on: http://www.whoi.edu/people/sbertrand
My Ph-D thesis (partly in french) can be downloaded here: ftp://ftp.whoi.edu/pub/users/sbertrand/These_Seb_02-2005.pdf

Several recent studies have demonstrated that climate records from Antarctic ice cores are clearly asynchronous with the rapid changes of the Northern Hemisphere. However, paleoclimate data from the rest of the Southern Hemisphere yield conflicting interpretations of interhemispheric synchrony/asynchrony of the climate system. In order to better constrain the paleoclimate history of southern South America since the Last Glacial Maximum, we investigated the sedimentary record of Lago Puyehue, located at the northern boundary of the southern westerly wind belt in South-central Chile (40°S), by a multi-proxy analysis of sediment cores collected in the framework of the OSTC ENSO-Chile project in 2002.

In Lago Puyehue (164 km², 40°S, elevation 185 m), we first investigated the recent (600 yrs) sedimentation at PU-II coring site, which is characterized by finely laminated sediments, with only small disturbances due to volcanic and seismic activities. Our objectives were to (1) test different measurement techniques for density, organic matter and biogenic silica contents, and (2) reconstruct regional climate changes during the last 600 years. Several proxies were measured: grain-size, magnetic susceptibility, major elements geochemistry, biogenic silica concentration and organic matter content and properties (C/N, d13C). These were used to reconstruct paleo-precipitation and paleo-productivity changes around 40°S. The results demonstrate that during the last 600 years, the highest terrigenous mass accumulation rates occur between AD 1490 and AD 1700. This is probably due to higher precipitation in the Andes during the first part of the European Little Ice Age (LIA). This work therefore supports the fact that the LIA is a global event, not only restricted to the Northern Hemisphere.

The most relevant paleoclimate proxies have then been selected and applied to a 11 m long core from the same coring site, which covers the last 18,000 yrs. The results evidence that the sediment grain-size is highly correlated with its biogenic content and can be used as a proxy for lake paleoproductivity. On the other hand, the magnetic susceptibility signal is highly correlated with the aluminium and titanium concentrations and can be used as a proxy for the terrigenous supply. Temporal variations of sediment composition demonstrate that, since the Last Glacial Maximum, the Chilean Lake District was characterized by three abrupt climate changes superimposed on a long term climate evolution. These rapid climate changes are: (1) the end of the Last Glacial Maximum at 17,300 cal. yr. BP; (2) a 13,100-12,300 cal. yr. BP cold event, ending rapidly and interpreted as the local counterpart of the European Younger Dryas, and (3) a 3400-2900 cal. yr. BP climatic instability probably due to low solar activity. The timing of the 13,100-12,300 cold event is compared with similar records in both hemispheres and demonstrates that this Southern Hemisphere climate change leads the Northern Hemisphere Younger Dryas cold period by 500 to 1000 years.

The sedimentary record of Lago Icalma (11.65 km², 38°S, elevation 1140 m) is rather different. It is strongly disturbed by seismic and volcanic events and it has been used to reconstruct the seismic activity in the South-central Andes during the last 8000 years. See the pdf version of my PhD thesis for more details.