Exploring the linkage between lacustrine proxy data and instrumental record for reconstructing past hydroclimatic variability in the southern Pampas.

CÓRDOBA, F.; PIOVANO, E.; SYLVESTRE, F.

Mendoza

Congreso; 18th International Sedimentological Congress. ?Sedimentology at the foot of the Andes?; 2010

International Association of Sedimentologists (IAS)

Long-term climate reconstructions are essential to place recent climate and environmental changes into a broader perspective and a larger time- window. In this context, Argentinean Pampean lake systems (Laguna Mar Chiquita 30°S; Laguna Melincué 34°S; Lagunas Encadenadas del Oeste, 36°S) are exceptional sites to record low frequency climate variability over long periods of time (1000?s to 10?s of years). Lake systems respond physically, chemically and biologically in front of hydroclimatic changes (external forcings) which may be registered along the lake sedimentary records. Lagunas Encadenadas del Oeste (LEO), located in the southwestern part of the Argentinean Pampas (36º S - 62º W), are very reactive in front of the recent and past South America Moonsonal System variability. Here we explore the relationship of the proxy record with the last ~100 yrs of instrumental data. The objective of this study is to understand how the hydroclimatic variability trigger lake changes, that in turn, are recorded as distinctive feature in the lake sediments. Thus, selected proxies can be used to perform more reliable climatic reconstructions for periods prior to the beginning of the instrumental record. A multi-set of sedimentary cores from LEO system was dated using 210Pb and analyzed for total nitrogen (TN), total carbon (TC), total organic carbon (TOC), CaCO3, magnetic susceptibility and water content. Several lithological units were defined in the cores based on sedimentary textures and structures, lithology, sediment color, and organic matter content. Comparisons between the proxy data and the homogenized instrumental data were based on linear regression analysis (proxy data: response variable; instrumental data: predictor variables). To synchronize the records, the climatic predictor variables (monthly standardized precipitation anomalies) were smoothed along time applying a 10 or 6-point Low-pass Gaussian filter (10-LGF and 6- LGF, respectively). Linear regression analyses were then used to find the linkage between the proxy data and the climatic forcing. The highest regression coefficients were found when considering smoothed (6-LGF and 10-LGF) Annual precipitation index (API) and Wet precipitation index (WPI) against proxy data. Conversely, there is a lack of significance when Dry precipitation index (DPI) is considered. The correlation with WPI smoothed data (6-LGF and10-LGF) indicate that proxies are capturing the low frequency variability. Some proxies show statistically significant relationship with the instrumental record. For instance, TOC and TN, which are strongly related to the primary productivity, show significant relationship with WPI. Our results highlight the importance of proxy validations and the development of reliable chronologies to reconstruct climate changes beyond the instrumental record. Results point toward the main influence of decadal climate variations on the lake hydrological balances over the Southern Pampean region of Argentina.