The environmental signal of lake sediments in Mesoamerica: Modern pollen and geochemical composition

Résumé fourni par la source

Lake sediment composition depends on the environmental context where sediments are produced, transported, and deposited. Factors involved in sedimentary processes imprint specific signatures on sediments, thus providing evidence on the environmental context at the time of deposition. The interaction of the involved factors and processes, however, results in complex signals that in some instances are difficult to interpret. Here, we explore and quantify the relationships between commonly analyzed attributes of lake sediments and the geological, climatic, and ecological context of the corresponding catchment basins. For this purpose, we analyzed the geochemical composition and modern pollen spectra of 132 lakes, and characterized each locality in terms of climate, topography, vegetation cover, geology, and human activities in the catchment basin. The studied lakes included areas of Mexico, Guatemala, Belize, Honduras, and El Salvador, thus encompassing Mesoamerica, a culturally defined region. Multivariate statistics and regression techniques were used to assess the quantitative relationships between environmental and sedimentary variability. According to our results, the inorganic sediment chemistry is strongly influenced by basin geology, reflecting the contrasting nature of karstic versus other sediments. Conversely, the organic components are likely controlled by local factors, such as lake trophic status. Pollen assemblages reflect the regional biogeographic gradient from temperate to tropical vegetation with a strong modulation by topographic and climatic gradients. Our study confirms that whereas pollen spectra reflect regional conditions, sediment geochemistry captures local variability, highlighting the importance of a multiproxy approach for conducting paleoenvironmental reconstructions.

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