Biogeochemical cycling of Particulate Organic Matter within two stratified coastal sinkholes
Abstract
Sinkholes and blue holes are formed by the dissolution of carbonate rock and represent local sediment traps within coastal karst platforms. These basins are connected to the coastal aquifer and are often hydrographically stratified into three constituent layers (a meteoric water layer on top, a mixing zone, and anoxic saline layer at the base). Such stratification promotes excellent sedimentary preservation for paleoenvironmental/paleoclimatic reconstructions (e.g. landscape, climate, hurricane frequency), and recovered sedimentary cores in the Caribbean represent up to 50,000 years of laminated, accumulated sediment. A major contributor to the sedimentary organic matter preserved within sinkhole basins can be authigenic production within the meteoric lens, depending on changes in basin hydrography. However, we do not fully understand the modern biogeochemical interactions in the lower layers that likely drive variability in the composition of Particulate Organic Matter (POM) that is being produced, transformed, and eventually preserved as sedimentary OM. Mapping this variability within karst basins will not only give insight into hydrologic processes and eventual OM preservation, but it will allow us to explore the sources and fate of POM that can be discharged into the coastal ocean.
Here, we will present a comparative study of the modern hydrologic data (salinity, temperature, dissolved oxygen, pH, d2H and d18O of water), and d13C, d15N, C:N, and preliminary sequenced DNA results of POM collected along depth profiles within two distinct sinkhole basins on Abaco Island, northern Bahamas. Initial results reveal that pigments of POM change with depth and stratification, with POM concentrations being highest within the mixing zone (~30 mg/L). d13CPOM values range from -36 to -30‰ and -28 to -22‰ within each basin respectively, suggesting shifts in the origin of accumulated POM that align with changes in hydrography. Through further constraining modern water column processes in two stratified basins, we can improve our understanding of coastal carbon dynamics within karst platforms, and our ability to interpret OM source shifts within similar systems for paleoenvironmental reconstructions.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMGC050..05T
- Keywords:
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- 0439 Ecosystems;
- structure and dynamics;
- BIOGEOSCIENCES;
- 1615 Biogeochemical cycles;
- processes;
- and modeling;
- GLOBAL CHANGE;
- 1817 Extreme events;
- HYDROLOGY;
- 4217 Coastal processes;
- OCEANOGRAPHY: GENERAL