INSIGHTS INTO LATEST PALEOCENE PALEOECOLOGICAL CHANGES IN THE NANNOPLANKTON COMMUNITY ACROSS A SHELF TO OPEN-OCEAN TRANSECT (Invited Presentation)

Changing oceanographic conditions pose a threat to the stability of the modern oceans and to the health of the floral and faunal communities that inhabit them. In order to understand how quickly these communities respond to changing conditions in both the nearshore and open- ocean environments, we document how they responded to abrupt environmental perturbations in the latest Paleocene. Calcareous nannoplankton, cosmopolitan and abundant phytoplankton sensitive to changing oceanographic conditions, offer a means to use the reaction of extinct species to past climate change to predict how similar extant species will react in the modern oceans. Latest Paleocene sediments across a shelf to open-ocean transect, including the Maryland Mattawoman Creek Billingsley Road (MCBR-1) and South Dover Bridge (SDB) cores, the New Jersey Bass River (BR) core, and Site DSDP 605 (western North Atlantic Ocean), were examined for calcareous nannofossil content, and statistical analyses were conducted using Detrended Correspondence Analysis (DCA). Axis DCA 1, which is strongly influenced by the species Hornibrookina arca, accounts for 89% of the variance in the original matrix and DCA 2, which accounts for 10% of variance, is largely influenced by Hornibrookina spp. (a group of small forms that include H. weimerae) and Chiasmolithus bidens. A clear correlation between proximity to shoreline and increasing abundance of H. arca is documented across the transect. Hornibrookina arca comprises up to 80% of the assemblage in the proximal MCBR-1 core and 70% in the top meter of SDB, where paleodepths are estimated to be no greater than 120 m. Percent abundance decreases sharply at BR, to only 8% in the top 0.5 m, and is 0% in the distal DSDP 605. Additionally, percent abundance of C. bidens decreases gradually up-section at MCBR-1 and SDB, suggesting a lessening of cold-water influence over time proximal to the shoreline. Shannon Diversity (H) decreases up-section in both MCBR-1 and SDB. The upper meter of section in both MCBR-1 and SDB, however, record a sharp increase in diversity, as does the section at BR where only one meter of section was analyzed. This roughly coincides with a decrease in Hornibrookina spp. and H.arca and possibly represents stabilization of a disrupted environment just prior to the Paleocene-Eocene Thermal Maximum.