[Lücke] Bündelantrag PASADO-Support 2: Qualitative environmental and climatic reconstruction for the last glacial interglacial cycles in southern Patagonia - the stable isotope record of the ICDP site Laguna Potrok Aike, Argentina (PASADO-Isotope)
German Title: Bündelantrag PASADO-Support 2: Qualitative environmental and climatic reconstruction for the last glacial interglacial cycles in southern Patagonia - the stable isotope record of the ICDP site Laguna Potrok Aike, Argentina (PASADO-Isotope)
Current Status: completed
Main Applicant:Dr. Andreas Lücke
Dr. Jiayun Zhu
The project PASADO-Isotope investigated the sediment archive of the maar lake Laguna Potrok Aike located at a prominent position on the South American continent east of the Andean cordillera in the Patagonian steppe at 52°S. About 100 m of lacustrine sediments were retrieved during an ICDP drilling campaign. The recovered sediment record covers the last Glacial – Interglacial cycle back to c. 50 ky BP. This South American archive bridges the gap between marine and ice-core records and, thus, represents a unique high-resolution record unravelling the role of the high southern latitudes for the global climate development during the last deglaciation. During the last Glacial, environmental conditions in southern Patagonia were characterized by constantly low lacustrine primary productivity and a stable hydrological balance as indicated by low organic content and stable isotopic composition of sedimentary organic matter and reconstructed lake water isotopic composition. Superimposed on this background two prominent periods of increased primary productivity centred around 38.0 und 46.0 ky BP occur contemporaneous with Antarctic warm events indicating a more widespread, potentially hemispheric extension of these climatic amelioration events then previously known. Deglaciation in Patagonia starts at 17.8 ky BP (age model v3.1) with very rapid, almost instantaneous change of ecological indicators namely a rise of δ13CTOC representing a switch in the mode of lacustrine primary productivity towards a highly productive system. The productivity switch is fostered by nutrient input with the disintegration of permafrost in combination with rising temperatures. The response of the lake’s hydrological balance began with a small delay of some hundred years at 17.6 ky BP visible in the Delata 18 O lake corr record and a comparably transient development during the deglaciation explainable by the conservative behavior of a water body. This deglaciation mode is consistent with records of glacier retreat in the Andes, with rapid rise in ocean temperatures and the rise in Antarctic ice-core temperatures. Since the Delta 18 O lake corr record of Laguna Potrok Aike is an expression of the evaporation-to-inflow (E/I) ratio of the lake, the time series is strongly related to wind induced evaporation driven by the strength of the Southern Hemisphere Westerlies (SHW). While during the first phase of the deglaciation from 17.9 ky BP until about 16.0 ky BP the leading drivers for increased evaporation are rapidly increasing temperatures and increasing average wind strength, the rise of air temperature is strongly attenuated afterwards. Thus, after 16.0 ky BP wind driven evaporation takes the leading role for the E/I ratio and rising Delta 18 O lake corr values since 15.0 ky BP are indicative for the increasing strength of the SHW reaching their maximum in the period 13.4 to 11.3 cal. kyr B.P. Our record, thus, supports the hypothesis that stronger SHW played a key role for the last deglaciation via enhancing CO2 release from the deep Southern Ocean by upwelling. Our data would also be consistent with an early onset of strong SHW at 52°S already with the start of the deglaciation around 17.6 ky BP. Lacustrine carbonate proxies indicate that contemporaneous with the wind and temperature driven rise of evaporation during deglaciation the lake level of Laguna Potrok Aike started to decrease and continued to decrease into the early Holocene. The 87 Sr/86 Sr ratios together with the Delta 18 O values of carbonates indicate the lowest lake level of record and, thus, the driest period in southern Patagonia for the period from 9.2 to 7.0 ka cal BP, which is contemporaneous with previously inferred maximum Westerlies strength during that period.