Climate change evidences from the end of the Little Ice Age to the Current Warm Period registered by Melincué Lake (Northern Pampas, Argentina)

Abstract

Geochemical, sedimentological, historical and instrumental information from Melincué Lake (33° 43?S /61°28? W) was analyzed in order to reconstruct main hydro-climatic changes along the Pampean region, considering the end of theLittle Ice Age (LIA) and the Current Warm Period (CWP) climatic phases. Elemental X-ray fluorescence determinations were performed on a dated short core extracted from the deepest part of the lake. Chemical (Ca, Sr, Al, K, Si, Ti and Fe) variation was analyzed along with physical (magnetic susceptibility, dry bulk density and medium particle size) and mineralogical proxies, as well as carbon and nitrogen contents (organic and inorganic carbon and organic nitrogen). Multicomponent statistical analyses allowed the identification of the main environmental processes ruling sedimentation, which included carbonate precipitation, detrital input and primary productivity. Homogeneous, carbonate-rich, detrital-rich and organic matter-poor deposits reflect very shallow and ephemeral lake conditions during the last years of the LIA period. Very low sedimentation rates and the presence of discontinuities in the sedimentary record pointed to episodes of extensive lake shrinkages and probable lake-floor subaerial exposures. Bedded and laminated organic-rich muds accumulated in perennial lake conditions after ca. AD 1880 reveal an important environmental change concurrent with the onset of the Current Warm Period. The contrast of sediment composition and lithological characteristics with the instrumental record of the CWP allowed us to consider the development of a shallow saline-lake system, enhanced detrital input and carbonate precipitation during dry periods. In turn, higher lake levels, and thus more diluted lake-waters during wetter periods, resulted in enhanced organic lake productivity and lower carbonate precipitation. The comparison of the paleolimnological reconstruction from Melincué Lake to different hydrological and paleoclimatic records (i.e. limnimetric measurements and ocean temperature changes) suggests that the moisture variation registered between the LIA and the CWP was consistent with (and likely forced by) large-scale climatic oscillations. The present study provides new evidences to evaluate the climate and environmental changes in central Argentina related to the dynamics of the South American Monsoon systemduring the last five centuries.