Reconstructing Late-Glacial and Holocene climate change in the southern hemisphere from a South Chilean Lake Transect (CHILT) (FWOAL519)

OBJECTIVES The objective of the CHILT project is to reconstruct Late-Glacial and Holocene climate variations that are recorded in lake sediment records along a N-S transect through the southwestern part of South America, from the Chilean Lake District (39°S) in the north to Patagonia (53°S) in the south. This part of South America is particularly well suited to produce valuable paleoclimate records for the study of spatial and temporal patterns in climate variability in the southern hemisphere. It is the only landmass extending this far South, which allows comparing continental records from southern medium to high latitudes to those from Antarctica and the sub- Antarctic islands, but also with those from lower latitudes. The continuous distribution of large lakes across a wide latitudinal belt (i.e. 40-55°S, more or less coincident with the natural northern and southern boundaries of the "Southern Polar Front") makes the region particularly interesting for the proposed study (e.g. Sugden et al., 2005; Sterken et al., 2008). Two specific objectives will be addressed: - Objective 1: To gain a bettter understanding of the deglaciation history of southern South America. Additional paleoclimate reconstructions and geological field data are required to test and improve a recently developed model for the deglaciation of the Patagonian Ice Sheet (Hulton et al., 2002), as many uncertainties remain regarding the exact timing, speed and mode of retreat of this ice sheet (e.g. Lowell et al., 1995; McCulloch & Davies, 2001; Bentley, 1997). The model, in particular, suggests a highly instable icesheet behaviour in the area north of 43°S, but this is not conclusively supported by the existing empirical data. Considerable disagreement exists, for example, between the sparse, continuous marine and lacustrine records from the area and the more widespread, but discontinuous terrestrial records (De Batist et al., 2008). CHILT will better document the mode and timing of retreat of the Patagonian Ice Sheet from the region between 39 and 53°S, by means of a series of detailed reflection seismic studies and a multiproxy analysis of long sediment cores from lakes that have adequately recorded the deglaciation. - Objective 2: To study the temporal and spatial variability of rapid climate fluctuations that occurred during the transition between the Late-Glacial and the Holocene. In recent years, the international paleoclimate community has paid considerable attention to the possible link between the Antarctic Cold Reversal (ACR) and the Younger Dryas Cold Reversal (YDCR), during the transition from the Last Glacial Maximum (LGM) to the Holocene. The YDCR (~11.6-12.9 ka) has been very well documented in several paleoclimate records in the northern hemisphere (e.g. Stuiver et al., 1995) and is often regarded to have had a global impact (Barrows et al., 2007). The ACR (~12.5-14.5 ka) was recorded in a number of Antarctic ice cores as a cold phase that temporarily interrupted the gradual postglacial warming. The ACR clearly precedes the YDCR, which suggests that the YDCR could have been caused in response to the ACR and that it therefore did not have a global, synchronous expression at all. In Patagonia (55°S), a glacial re-advance at 12.1-15.3 ka was documented by McCulloch & Davies (2001), more or less coeval with the ACR. Further to the north (41°S), Hajdas et al. (2003) recently detected the "Huelmo-Mascardi cold/wet event" (~12.0-13.4 ka), which seems to have occurred exactly in between the ACR and YDCR. A recent multiproxy analysis of a sediment core from Lago Puyehue (~41°S) confirmed the existence and timing of this climate fluctuation in this region (Bertrand et al., 2008; Boës & Fagel, 2008b). These recent observations seem to support the hypothesis of a propagation of Antarctic climate signals towards the north, across a transition zone in the southern medium to high latitudes. However, considerable uncertainties still remain regarding the exact extent, timing and duration of this Late-Glacial climate fluctuation (Sugden et al., 2005). Why has it apparently not been detected in marine (40°S, ODP site 1233; Lamy et al., 2004) and in many of the terrestrial (44°S, Bennett et al., 2000) records from the same area? Does the Huelmo-Mascardi event mark a return to colder or to more humid conditions? What does it tell us about the underlying processes by which different climate systems interact. CHILT will try to significantly reduce the uncertainties regarding this Late-Glacial climate fluctuation by producing three welldated, high-resolution reconstructions of temperature and precipitation for the period of ~9.0-16.0 ka, based on a quantitative multiproxy analysis of long sediment cores from lakes located along a latitudinal transect through the region (39-53°S).

Keywords:paleoclimate, Lake sediments, Stable isotopes

Disciplines:Mathematical sciences and statistics, History and archaeology, Biological sciences, Earth sciences, Chemical sciences