A 4,000 YEAR RECORD OF LONG ISLAND SOUND ENVIRONMENTS OBSERVED THROUGH XRF-CORE SCANNING

Many estuaries, including Long island Sound (LIS) have seen major environmental changes over the last millennia. Commonly these changes have been influenced by increases in human population along the coasts, and the direct or indirect effects of this growth on the coastal environment. These effects include changes in aquatic food extraction, contaminant and nutrient input, increased fresh-water run-off through changes in land use, and the release of effluent from wastewater treatment plants. As there is no written history available for most of this time period, we must rely on the sediment record to evaluate environmental changes and their impact on biota over time. For this study we used sediment cores representing different hypoxic regimes in western and central LIS, dated using Hg-pollution profiles, ²¹⁰Pb - ¹³⁷Cs, and ¹⁴C, and spanning the past ~2,000 to ~4,000 years. With the use of an Avaatech XRF (X-ray Fluorescence) core scanner with a Rhodium source, we have derived high-resolution records of elemental concentrations to assess variability in sediment composition over the last millennia. XRF-scanners are powerful tools in paleo-environmental analysis because they provide non-destructive and relatively fast analyses of large numbers of data points from very thin (cm to mm) sediment slices, reflecting a high temporal resolution. XRF scanners measure the chemical composition of sediments as element intensities in total counts, which are proportional to the chemical concentrations. We have measured the concentration of major and trace elements (Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Rh, Zn, Br, Rb, Sr, Y, Zr, Mo, Pb, U, Ag, Sn, Te, I and Ba), and calibrated these measurements through traditional XRF analysis (WDXRF, Bruker S4 Pioneer) on discrete, fused beads and dry powder samples in order to calibrate the semi-quantitative XRF-core scanner measurements. We have evaluated the potential to use the elemental variability in sediments from these complex, multi-source estuarine settings as indicators for changes in salinity, oxygenation and biotic productivity over time.