GEOCHEMICAL, POLLEN, AND DIATOM-BASED RECONSTRUCTION OF HOLOCENE ENVIRONMENTAL CONDITIONS IN COLOMBIAN COASTAL LAGOONS

The continental plains from the Colombian Caribbean are highly heterogeneous mosaic of ever changing fluvial and terrestrial ecosystems, wetlands, and coastal lagoons. The latter have been formed since at least the Mid-Holocene, via regression-transgression cycles. Lowland sediment records along the Colombian Caribbean are highly sensitive to the interaction of South American Monsoon, the orbital driven ITCZ movements, and other variations of the hydrological cycle in response to solar activity. Additionally, costal sediment records are ideal to describe how major nutrients are affected by changes in climate. The study of Colombian Caribbean coastal sediments opens an opportunity to effectively measure waterbody boundary conditions, their recovery capacities, and overall ecosystem change. Here, we present a diatom, pollen, and geochemical (bSi, TN, Ortho-P and TP, TC, TIC, Chla, nitrogen and carbon isotopes) reconstruction from sediment cores of Ciénaga del Totumo (10°44′40″N, 75°14′29″W) and Ciénaga La Caimanera (9°24'29.68"N, 75°37'43.75"W), both located in Colombia´s central Caribbean. We detected a major change in all geochemical proxies, in sediment of both water bodies, around 4100 - 4700 14C yr BP. This change is also observed on sediment records from other parts of the world. Wetlands with different salinity gradients were abruptly replaced by drier or saltier coastal plains, and the sporadic appearance of lacustrine bodies. Preliminary time series and wave-let analysis of Totumo´s geochemical data yield cycles similar to those registered in radionuclides from Greenland and Antarctica (periods of 50-60, 85, 145, 174, 272, 622, 1024 yrs).