RECONSTRUCTING THE HISTORY OF ANOXIA AND CLIMATE CHANGE IN LAGUNA ENCANTADA IN CHETUMAL, MEXICO

Lakes are sensitive to changes in temperature and oxygen. Dissolved oxygen is less soluble in warmer water, so anoxia (lack of oxygen) is expected to become more widespread as surface temperatures rise in response to increased anthropogenic carbon dioxide. Problems associated with anoxia include harmful algal blooms, fish kills, and decreased water quality. Understudied tropical lakes like Laguna Encantada tend to be less prone to mixing and are located in remote areas, making the pristine lakes ideal for studying anoxia. There are relatively few reliable methods for determining how oxygen concentrations have changed with time in lakes. One aim of this study is to adapt the reactive iron proxy method to track freshwater anoxia. In a warming world where anoxia can become more common, reconstructions of climate and anoxic conditions from biogeochemical alterations of lake sediment can provide insight into how climate change can impact society. A 4.5 meter sediment core was collected from Laguna Encantada. Based on lithology, 3 distinct units were identified from the bottom to the top of the core. Laminations of carbonates and organic matter at the bottom of the core (Unit 1) transition (Unit 2) into massive bedding emplaced by rapid deposition (Unit 3). The C/S ratios indicate an initial marine influence in Unit 1 that transitioned (Unit 2) to lacustrine conditions in Unit 3. Total iron and aluminum concentrations are similar with overall decrease towards younger sediment, suggesting iron is controlled by detrital input. Reactive iron extractions are ongoing; these data are expected to provide constraints on past oxygen conditions. Stable isotopes of carbon, nitrogen, and sulfur will also be analyzed and could correlate with Mayan settlement history in the Yucatan. This research can give insight into future conditions as climate change continues and implications on the consequences on freshwater systems and agriculture.