ENVIRONMENTAL HISTORY OF LONG ISLAND SOUND: THE FORAM POINT OF VIEW

Marty Buzas' work (1965) on Long Island Sound (LIS) foraminifera in grab samples significantly contributes to our understanding of the evolution of this Urban Sea. Dramatic environmental changes occurred since the formation of LIS with sea level rise at the retreat of the last ice sheet and human influence accelerated with European colonization (~1600s CE). Cores from East LIS show oyster beds with foraminifera overlying varved glacial lake beds, marking the marine incursion that we dated at ~10 ka BP. We collected data in sediment from ~10-8.5 ka, and from 4 ka to Recent in a core at <10m water depth near the mouth of the Housatonic River. Multiple cores in mid to west LIS cover the last 1 ka, with grab samples taken 1996 - 2005. Buzas described low-diversity, depth-zoned foraminiferal faunas: diatom-using Elphidium excavatum dominant in shallow waters (3-23 m, mean 15 m), Buccella frigida common at 15-33 m (mean 25 m), and Eggerella advena at 16-39m (mean 29 m). Similar faunas were observed from ~ 10 ka to ~1980 CE, with foraminiferal accumulation rates and relative abundance of E. excavatum increasing ~1800 CE while E. advena started to decline. At ~ 1980 CE Ammonia sp. became dominant in West LIS, then slowly spread Eastwards, a faunal change unique over the last 10 kyr.

We estimated bottom water salinity, temperature, and oxygenation based on Ca/Mg, ∂¹⁸O and ∂¹³C in E. excavatum. Only minor variability was observed from 10 ka to ~1800 CE, but since then the salinity dropped in western LIS, and salinity-corrected ∂¹³C values declined precipitously. Changes in run-off due to land-use changes and wastewater treatment plant effluents may have increased freshwater inputs into LIS, possibly affecting E advena abundance. Influxes of terrestrial organic matter and enhanced marine productivity as a result of eutrophication led to oxidation of organic matter, producing low oxygen levels in bottom waters. Eutrophication initially led to increased diatom productivity, causing an increase in E excavatum. Surprisingly, benthic faunas did not undergo major changes from ~ 1800 CE on in response to lowered oxygen levels and industrial pollution (e.g., higher Hg, Pb, Cu, Zn), but they did change from ~1980 CE on, with dominance of Ammonia starting in western LIS. We can speculate, but not yet explain this recent, profound faunal change.