Project Collaborators: Ellen Thomas (forams), Sherri Cooper (diatoms), Mark Altabet (N isotopes), Marilyn Buchholtz tenBrink (metals), Henk Brinkhuis (dynoflagellates) and Francesca Sangiorgio (pollen) Long Island Sound estuary formed according to our 14C data ~10,000 BP, which is in contrast with the commonly held view of initial marine inundation at 15,000 BP (Stone et al). The local native Americans, who settled ~ 12,000 BP, may have witnessed the initial marine inundation of the Sound (LIS - the American Black Sea?). The Sound now has a mean depth of ~30m, and suffers from severe seasonal hypoxia in its western section (WLIS), sediments that are contaminated with heavy metals, a lobster die-off during 1998-1999, and an ecosystem that may be shifting from N-limitation to Si-limitation in certain areas during parts of the year. Sediment cores were dated with 14C, 210Pb-137Cs, and chemical chronostratigraphy. We determined organic carbon and its d13C, total carbon, total nitrogen and its d15N, biogenic silica, forams, diatoms, dynoflagellates, pollen, Hg, Clostridium perfringens spores (sewage input proxy), and measured d18O, d13C and Ca/Mg on Elphidium excavatum. The carbonate data were locally calibrated on living foraminifera and measured water column parameters: Mg/Ca for water temperature; the d18O and d13C with d18O in LIS water and d13C in DIC. We then derived paleotemperature, paleo salinity and paleo hypoxia parameters. The species level foram, diatom and dynoflagellate studies provide insights into changes in water turbidity, eutrophication, and shifts in the food chain. Our results indicate that LIS started to become eutrophied in the early 1800~Rs and that hypoxia may have been common for more than 150 years. The depth zonation in forams disappeared over this period, whereas over the last 30 years Elphidium excavatum (a diatom-eater) is being outcompeted by Ammonia beccari, an omnivorous species, which may go hand in hand with a switch from diatom-dominated primary productivity to dynoflagellate productivity. The eutrophication is indicated by increased amounts of organic carbon and biogenic silica in the core tops covering the last 200 years. The d15N values shifted from ~ +7 to +9 per mille, indicating the enhanced nitrogen input from mammalian waste (humans, livestock). Clostridium perfringens counts show directly the exponentially growing sewage input with the years. The temperature records indicate the presence of the Medieval Warm Period (MWP), Little Ice Age and Modern Global Warming. Significantly, evidence for bottom water hypoxia during the MWP is absent, suggesting that the current hypoxia are largely driven by eutrophication. Mercury pollution profiles indicate that Hg from the hatmaking industry in CT was a significant local Hg source. Wet periods over the last 200 years are signaled in the cores by thin Hg-enriched layers, indicating the remobilization of Hg-contaminated sediment from uplands (~Sreturn of the mad hatters~T). The waters of WLIS have freshened significantly over the last 150 years, most likely as a result of water input from sewage treatment facilities and increased presence of impervious surfaces in the watersheds. The early colonial activities (e.g., the beaver eradication of the 1600~Rs) may show up in the sedimentary records as early mini-eutrophication and sedimentation rate pulses.