THE EFFECT OF RATE OF TEMPERATURE AND SEA LEVEL CHANGE ON FORAMINIFERAL SPECIES DIVERSITY

Marine sedimentary deposits on the Atlantic Coastal Plain record paleoecologic data from Paleogene and Neogene climate intervals when sea level and sea surface temperature (SST) were higher than at present. In order to understand the impact on the shallow water habitat of not just the magnitude of change but also the rate of change, we compared SST and sea level data to foraminiferal species diversity metrics from paleoclimate intervals recorded in cores and outcrops in Maryland and Virginia to predict how modern diversity may be affected in the near future. We assessed foraminiferal diversity across climate events of a range of magnitudes and durations, superimposed on different background climate states: the Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma), a short and rapid warm peak during a greenhouse climate, the Miocene Climatic Optimum (~16.9-14.7 Ma), a longer warm interval at the peak of a greenhouse climate, the Middle Miocene Climate Transition (~14.7-13.8 Ma), representing slow and punctuated global cooling, and the mid-Piacenzian Warm Period (~3.3-3.0 Ma), a warm period during overall global cooling. PETM data from the South Dover Bridge sediment core from southeastern Maryland include benthic and planktic foraminiferal assemblages, sea level and SST estimates, and the duration of two carbon isotope excursions (CIEs) that signify environmental perturbations. Sea level rose twice as fast during the larger CIE and for more than twice as long with three times the total change compared to the smaller CIE. Rate of SST rise was similar for both CIEs, but that rate continued for twice as long during the larger CIE. Interestingly, while benthic diversity decreased across the PETM, planktic diversity increased due to the addition of excursion taxa. Both benthic and planktic assemblages were more affected by the larger CIE, indicating the importance of the duration of the event. Results from similar analyses of the Middle Miocene BG&E core (southeastern Maryland) and Piacenzian cores and outcrops (southeastern Virginia) will be presented. This research provides a preliminary indication of foraminiferal diversity changes to be expected in the near future under the current rate of rising temperatures and sea level.