DIATOMS AS PROXIES FOR CLIMATE CHANGE IN THE HUDSON RIVER ESTUARY, NEW YORK

Diatoms were used as proxies for past salinity and long-term precipitation changes in the Hudson River Estuary. The penetration of the salt water wedge into the estuary is governed by tidal currents and freshwater runoff. Ratios of freshwater and marine diatoms in sediments give insight to the level of past penetration of the saltwater wedge, providing relative levels of salinity due to changes in precipitation such as droughts. We sampled long-cores (~7m) along a transect extending from Newburgh to Haverstraw, New York and established a chronology from short-lived radioisotopes (137Cs) and radiocarbon. Preliminary results agree with local historical precipitation records correlating high marine diatom abundance with low precipitation, especially for the mid-1960’s where a pronounced drought occurred in the region. Diatom data may show a drier Medieval Warm Period from 1.2 to 0.9 ka, and a slightly wetter Little Ice Age from 0.5 to 0.1 ka. Sedimentation rates at the millennial scale show long-term trends suggesting that the northern parts of the estuary filled their accommodation space relative to bedrock first. The sedimentation rate of the southern cores (Haverstraw, Peekskill) from 5 to 2 ka ranges from 2.2 to .8 mm/year decreasing to near 0 mm/year at the top, due to the filling of accommodation space. In contrast, the sedimentation rate of the northern cores (West Point, Storm King Mountain, Newburgh) is lower (.2 to .6 mm) from 5 to 1 ka suggesting an early filling of accommodation space. At the decadal scale the northern cores have much higher accumulation rates (10 mm/year) reflecting the lack of equilibrium in this part of the estuary due to topography (Hudson Highlands). A sharp increase in salinity for the past fifty years is attributed to anthropogenic causes. Salt spread on the roads to prevent icing may be the source as the salt is washed into the estuary. We plan to continue to use diatoms as proxies for salinity and long-term climate changes for the region as well as evaluate the anthropogenic impact in the estuary.