Reconstructing past climatic changes using lacustrine sediments from Laguna Comedero, NW Argentina

VIGNONI, P.A.; TJALLINGII, R.; CÓRDOBA, F.; PLESSEN, B.; TORRES, G.; LUPO, L.; BRAUER, A.

Hamburgo

Congreso; 25th Latin-American Colloquium of Geosciences; 2019

German Science Foundation

The present rainfall pattern in the eastern flank of the Central Andes of NW Argentina results from the interplay between topography and moisture transport during the wet season, mainly controlled by the dynamics of the South American Monsoon System (SAMS).This region is sensitive to shifts in the SAMS, as well as the superposition of other large-scale phenomena (e.g., El Niño Southern Oscillation, Pacific Decadal Oscillation) and therefore constitutes a key region for obtaining realistic regional reconstructions of past climate variability. In this sense, the timing and extent of precipitation changes prior to the instrumental period in this area are still largely unknown, preventing a better understanding of the long term drivers of the SAMS and their effects over the Central Andes of NW Argentina. Laguna Comedero is a highly variable shallow lake located in the subtropical forest of the Yungas in the foothill of the Argentine Eastern Cordillera (24º 06" 54.7" S - 65º 29" 7.2" W, 2,035 m asl). A multi-proxy analysis of an 11 m-long sediment record of this lake system provides new data for reconstructing the regional late Holocene climate history in this region of South America. Our results reveal important changes in sedimentation, from detrital brown layers in the lower part of the core to an alternation of gray clastic and black organic rich intervals with abundant plant debris in the upper 3.5 m (Fig. 1). Below this sediment depth TOC and S values are low, in combination with high values of elements indicative of detrital input (e.g. Ti), revealing no variation of detrital sediments and low amounts of organic matter. However, TOC, C/N and S values strongly increase above 3.5 m. TOC values in the upper 3.5 m ranges from 0.1 to 20.5%, while organic C/N atomic ratio reaches values up to 17, suggesting a substantial contribution of terrestrial organic matter in some layers. These intervals also show low Ti and high S and Fe/Al values that together with the presence of Pyrite, indicate periods of reducing conditions at the lake bottom. Changes recorded in Laguna Comedero sediments reveal that the deposition in the lake varied strongly in the upper 3.5 m of the sediment record indicating an important environmental change at the beginning of the last millennium (ca. AD 1,092). Further analysis needs to be done and a detailed chronological framework is still required to reveal the link between these sediment record changes and the past climate and environmental fluctuations for this region. Thus, future results will provide important insights on the past SAMS activity in the eastern slope of the southern Central Andes.