DEVELOPING AN INTEGRATED APPROACH IN UNDERSTANDING THE EVOLUTION OF THE HUDSON ESTUARY

A high-resolution salinity record was developed for the lower Hudson Estuary for the past 5,000 yr. from cores 6 to 9 m long obtained from <1 km north of the Tappan Zee to ~5 km south of the NY/NJ state line. An integrated approach was employed to evaluate paleoenvironmental changes using benthic foraminiferal, stable isotope, Sr/Ca ratio, and sedimentological data. Preliminary C-14 dating from shell material indicates a basal age of ~5,000 yr. with the top of the core dated at ~1,000 yr. in the area near the Tappan Zee (Core SD-30). Benthic foraminiferal assemblages were used to estimate salinity changes. Four biofacies were recognized in the cores and were correlated to present day assemblages, which living in the Hudson River have been calibrated to salinity. Elphidium species abundances were also calibrated to salinity. Preliminary results indicate a good agreement between salinity estimates based on benthic foraminiferal studies and Sr/Ca ratios and stable isotopes records obtained from the juvenile shells (first year growth) of the bivalve species Gemma gemma, permitting them to used as salinity proxies. Long-term trends in summertime salinity estimates at SD-30 range from 15 to 25 per mil between 6,270 and 3,338 yr. BP (uncorrected ages), decreasing to generally less than 15 per mil between 2,825 and 1940 yr. BP (uncorrected ages). In contrast, present-day summertime salinities on the flats (4-8 m water depth) in this area typically range from 10 to 13 per mil. Salinities changed at a much higher frequency within the transition period (3,338 and 2,825 yr. BP, uncorrected ages). These higher frequency changes indicate decadal to centennial scale salinity variability, which would be due to climatic (i.e., precipitation) changes. The long-term trend is probably due to sediment filling of the estuary, which would effectuate the migration of the salinity wedge from the estuary flats and into deeper waters. One surprising result is that the change from generally high to low salinities (migration of the salinity wedge) was abrupt (<1 m). This may have important implications for possible sedimentation pattern changes as a result of the migration of the salinity wedge intruding further into the Hudson Estuary due to future sea-level rises.