Pollen and climate dataset at Southern Patagonia: evaluating weaknesses and strengths for quantitative palaeoclimatic reconstructions

TONELLO, M.S; MANCINI, M.V; DE PORRAS, M.E.; BAMONTE, F.P.; SOTTILE, G.D.

Valdivia

Simposio; II Internationalnal Symposium "Reconstructing Climate Variations in South America and the Antarctic Peninsula over the last 2000 years"; 2010

LOTRED-SA iniciativa PAGES

One of the important advances in pollen-based climate reconstructions has been the increase of efforts to improve the statistical precision of pollenbased reconstruction models. In this sense, pollen and climate dataset evaluations are presented for southern Patagonia. The original pollen dataset consisted of 221 georeferenced surface soil samples uniformly distributed between 46°-52°S and 67°-73°W and included 81 pollen types. Manual procedures and graphical tools were used to identify duplicate samples and/or to evaluate taxonomic consistency in the pollen identifications. This quality assessment led to the bestPollen dataset (bPD) that includes 155 samples and 57 pollen types. A further selection consisted of eliminating samples from over-represented vegetation units, generating a minimalPollen dataset (mPD) of 87 samples and 43 pollen types. Climate data were compared between instrumental data and different Global Climate databases in order to accurately represent modern climatic features. Some data overestimated precipitation values (50-240 mm) at locations close the Andes, while underestimated values (50-100 mm) are registered at coastal stations. Temperature estimations did not reveal significant differences between databases, and generally showed good agreement with the instrumental data. Calibration models for annual precipitation (Pann) as well as annual (Tann), July (Tjul) and January (Tjan) temperature were elaborated based on bPD and mPD, applying a transfer function (WA-PLS) and the Modern Analog Technique (MAT). The results of cross-validation (r2, RMSEP, MaxBias) demonstrated that MAT models performed slightly better than WA-PLS models although there were no significant differences based on using bPD or mPD. The models presented a good inference power to estimate Pann and Tjan, but moderate and poor success at estimating Tann and Tjul, respectively. In order to validate the calibration models potential, Pann and Tjan were reconstructed from two fossil pollen records of the Late Holocene, providing therefore key information on past regional climate variability at southern Patagonia.