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Lake system response to Caribbean hurricane activity – a calibration study of ostracode (paleo-)biology and geochemistry (Lago Enriquillo, Dominican Republic)

Subject Area Palaeontology
Term from 2020 to 2024
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 428275545
 
Final Report Year 2025

Final Report Abstract

The major goal of the project was the build-up of a stable isotope-based proxy for the reconstruction of paleo-TCs through the integration of ecological and morphological data with geochemical signatures of modern ostracodes from a tropical lake located within the main development region (MDR) of TCs (Lago Enriquillo, Dominican Republic). To achieve these, important aims of the project included the characterization of the modern ostracode fauna, identification of possible seasonal morphological differences, and measurements of stable isotope values of modern ostracode valves of Lake Enriquillo on a seasonal scale (i.e., dry vs. rainy season) together with the understanding of changes in the hydrochemical composition (ions, δ18O, δD, δ13CDIC). The investigation of surface sediments taken in the dry (March) and the rainy (September) season in 2022 at different water depths and areas of the lake showed that the distribution and abundance of ostracodes is temporally and spatially very variable. Ostracodes are restricted to the upper 14 m water depth which is consistent with the extension of an oxygenminimum zone in September. Currently only three species (Cyprideis similis, Thalassocypria cf. sarbui, Perissocytheridea cribrosa) live in the lake. Adults of C. similis are present the entire year with seasonally differentiated (size) morphotypes, while living T. cf. sarbui and P. cribrosa are restricted to March and September, respectively. Water analyses revealed different hydrochemical facies highlighting strong contrast between e.g., lake water and inflows which contribute to a distinct spatial variability. The variation of δ18O and δ13CDIC between the two sampling campaigns was very low. Oxygen and carbon isotope values of modern ostracode valves display differences in the isotopic composition and variation ranges between species. Differences can be explained by different habitat preferences. Similar to the lake water, ostracode reflect a low variability between the seasons. The comparison of modern ostracode δ18O and δ13C signatures with records from mid to late Holocene skeletal carbonates (ostracodes, corals) of single species and colonies, respectively, from the Enriquillo basin reveals a long-term trend of decreasing δ13C and increasing δ18O values. This and the low intra-annual variability show that the lake is buffered against short term (i.e., seasonal or single hydrological extremes) influences. However, lake level changes are assumed to result from delayed recharge of storm related precipitation. As lake level changes are associated with a distinct shift in δ18O, isotopic values of fossil ostracodes will rather represent interannual changes (i.e., phases) of stormrelated precipitation than single events. Verification of this hypothesis was not yet possible as the ostracode record of sediment core which was taken at the deepest part of the northern basin was discontinuous and characterized by a bad preservation. However, two maxima of ostracodes and other organism remains in the lower part of the core indicate two sedimentation events which could result from hydrological extremes caused by e.g., storms.

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