Position and strength of the Southern Hemispheric Westerlies ? a multiproxy reconstruction from southern Patagonia (Laguna Azul, Argentina).

ZOLITSCHKA, B.; FEY, M.; MAIDANA N. I.; MAYR, C.; HABERZETTL, T.; CORBELLA, H.; OHLENDORF, C.; SCHÄBITZ, F.; JANSSEN, S.; WULF, S.; LÜCKE, A.

Zaragoza

Congreso; 5th Open Science Meeting.; 2017

PAGES

Temperature,precipitation and wind intensity of South America respond to the air-pressuregradient between polar and subtropical latitudes as well as to sea-surfacetemperatures of adjacent oceans, the extent of sea-ice and continental icemasses and to the pathway of the Southern Hemispheric Westerlies (SHW). Theresulting variations of the regional hydrological balance are recorded insediments of closed lakes, like e.g. Laguna Azul. Multiproxyinvestigations of Holocene sediments from Laguna Azul at 52°S in ArgentineanPatagonia document a superior climatic control. Position and strength of SHWcontrol the semiarid conditions in southeastern Patagonia and overprint theontogeny of this lacustrine system. SHW influence local evaporation,precipitation and insolation with impacts on the type of water-columnstratification and lake-level fluctuations. Both lead to internal feedbacks onwave erosion along the lakeshore, algal communities and trophic conditions aswell as authigenic mineral formation. Based onmultiproxy analyses (sedimentology, geochemistry, stable isotopes, pollen,diatoms), we present a detailed radiocarbon-dated environmental reconstructiondocumenting a millennial-scale hydrological variability for the Holocene.According to this multiproxy dataset, lake internal and external processescharacterize hydrological fluctuations. These include influences of theshrinking and expanding littoral zone as well as changes in lacustrineproductivity, salinity and patterns of water circulation. Driest conditions ofthe record correspond to high wind speeds and a low lake level related tohigher salinity that caused an ectogenic meromixis in the lake?s water body.Together with anoxic conditions in the hypolimnion, methanogenesis and highsalinity were recognized for the early Holocene between 10,300 and 8,500 cal.BP. We relate this period to highest SHW intensities occurring at the latitudeof Laguna Azul (52°S). Only during the past two centuries human impact obscuredthe climatic signal, as evidenced by eutrophication, increased precipitation ofauthigenic calcite and spreading of neophytic species like Rumex.