Paper No. 6
Presentation Time: 3:35 PM
MICROFOSSIL PROXIES FOR ANTHROPOGENIC ENVIRONMENTAL CHANGES IN LONG ISLAND SOUND
Microfossil records in cores from western and central Long Island Sound (LIS) provide insight in environmental changes over the last millennium. We constructed age models using 137Cs and 210Pb data, combined with dated Hg pollution records and 14C dating for the lower parts of the cores. Pollen analysis shows that anthropogenic marker pollen (e.g., Ambrosia, Plantago, Rumex, and Poaceae) first increased in abundance during colonial land clearance in the 17th century, followed by a second rapid increase in the 19th/20th century. In dinocyst assemblages, the relative abundance of heterotrophic taxa increased in the 19th century, from ~20-30% to ~60-75%. Diatom assemblages show a decrease in diversity coeval with an increase in the centric:pennate (planktonic:benthic) ratio from ~1.5 to ~4.0 in the 19th century. At the same time, the relative abundance and accumulation rates of the diatom-consuming calcareous benthic foraminifer Elphidium excavatum increased, while the species migrated into the deeper parts (>15 m) of Long Island Sound. Terrestrial and marine microfossils thus document the patterns of change in terrestrial vegetation around LIS and in eutrophication within LIS, showing that both became significant by the middle of the 19th century. Strongly increased accumulation rates of organic carbon, nitrogen and biogenic Si occur at the same time as major changes in the fossil records. From the late 1960s on, benthic foraminiferal assemblages in western LIS underwent qualitative assemblage changes: the species E. excavatum, dominant since the sea entered the LIS basin, was replaced by the opportunistic feeder Ammonia parkinsoniana. Possible causes include lower oxygenation, higher temperatures, invasion by a cosmopolitan species, and a change in the phytoplankton community. We propose that severe eutrophication results in high N/Si values in the waters, which cause diatoms to be out-competed by non-silica using primary producers. The omnivorous foraminifer Ammonia may thus have gained an advantage over the diatom consuming Elphidium. Impacts higher up along the food chain may have occurred as well, because such a shift at the lowest level of the food chain can be expected to reverberate throughout the ecosystem.