Developing Geochemical Evidence for Holocene Hydroclimate Variability in the Subtropical Western North Atlantic

Abstract

Caribbean hydroclimate is regulated by large scale ocean-atmospheric factors (e.g., the North Atlantic Subtropical High - NASH), and increased aridity is predicted into the 21st century. Understanding past changes in precipitation can inform future variability and fill in gaps created by temporal limitations of the satellite record, and uncertainty in the scaling of global climate models in the region. Well-preserved sedimentary records in coastal sinkholes and blue holes across the Caribbean archive proxies that can reconstruct precipitation and environmental variability on Holocene timescales. This dissertation comprises two past hydroclimate records, and one modern sinkhole biogeochemistry study from Great Abaco Island, The Bahamas. The first study uses leaf waxes to reconstruct the isotopic composition of rainfall (δ2H) over the last 3000 years, finding more enriched values from ~3000 to 2100 cal yrs BP and ~1700 to 1000 cal yrs BP that could be associated with drier conditions and an expanded NASH. However, within the last ~1000 cal yr BP, the isotopic signatures were influenced by inputs from the adjacent mangrove. The next study presents a record of sea level position, limnology, and hydroclimate variability from ~8300 to 1300 cal yr BP. Sedimentological and leaf wax proxies provide evidence for i) a basal peat deposit as a sea level maximum, ii) consistent accumulation of lacustrine marl within the basin from ~8300 to 1700 cal yr BP, and iii) a wetter mid-Holocene from reconstructed δ2H. The last study explores geochemical signatures of particulate organic matter (POM) in the water column of two stratified coastal sinkholes. The findings provide evidence for biogeochemical processes occurring along physicochemical gradients, which impact POM and the subsequent archived organic matter. The best proxy target candidates for paleo reconstructions include algal-derived biomarker signals produced within the sinkhole that could reflect regional-scale hydroclimate variability.