Diatoms as Proxies for Abrupt Events in the Hudson River Estuary

The Hudson River estuary has been subject to many abrupt events throughout its history including hurricanes, droughts and pluvials. Hurricanes in particular are rare, discrete events that if fingerprinted can be used to develop better age models for Hudson River sediments. Proxies use observed physical characteristics or biological assemblages (e.g. diatom and foraminiferal assemblages) as tools to reconstruct past conditions prior to the modern instrumental record. Using a sediment core taken from the Hudson River (CDO2-29A), in New York City, drought and pluvial layers were selected based on Cs-137 dating while hurricane layers were determined from occurrences of tropical to subtropical foraminifera.

Contrary to previous studies (Weaver, 1970, Weiss et al, 1978), more than sixty different diatom species have been identified using a scanning electron microscope (SEM). Cosmopolitan, hurricane and drought assemblages have begun to be identified after observing multiple layers (Table 1). Tropical foraminifera dominated by Globigerinoides ruber pink were also found in a hurricane layer that we infer was deposited during Hurricane Belle in 1976. More diatom abundance analyses and cataloged SEM pictures will provide further insight into these proxies.

Table 1

Diatom Genera and Species	Environment	Clarification
Cyclotella caspia	Planktonic, marine-brackish	Cosmopolitan
Karayevia clevei	Freshwater	Cosmopolitan
Melosira sp	Planktonic, marine	Cosmopolitan
Thalassiosira sp	Marine, brackish	Cosmopolitan
Staurosirella leptostauron	Benthic, freshwater	Cosmopolitan
Actinoptychus senarius	Planktonic or benthic, freshwater to brackish	Hurricane and pluvial layers
Amphora aff. sp	Benthic, marine or freshwater	Hurricane layers only
Nitzschia sp	Benthic, marine or freshwater	Hurricane layers only
Gomphonema sp	Freshwater	Hurricane layers only
Surirella sp	Marine-brackish	Drought layer only
Triceratium sp	Marine	Drought layer only
Other Genera and species	Environment	Clarification
Globigerinoides ruber pink	Tropical	Hurricane layers only
Silicoflagellate sp	Planktonic, marine	Hurricane layers only