Diatom responses to late Pleistocene and Holocene climate and ecosystem change on the Rensselaer Plateau of eastern New York state, U.S.A

Diatoms extracted from two lacustrine sediment cores from the Rensselaer Plateau of eastern New York state (USA) reveal patterns of considerable late Pleistocene and Holocene climate variability associated with droughts possibly linked to Laurentide ice sheet meltwater releases that caused changes in the Atlantic Meridional Overturning Circulation or solar forcing of North Atlantic sea surface temperatures. Samples were taken from Dyken and Shaver Ponds, glacial kettle lakes that contain sediment records extending to > 13.3 and > 11.5 cal kyr BP, respectively. The species assemblages in the sediments of both ponds are typical of low alkalinity lakes of the northeastern United States. The most common taxa include several members of the genus Aulacoseira, Asterionella ralfsii var. americana, Tabellaria fenestrata, Discostella stelligera, and Lindavia intermedia, although over 250 different taxa were encountered. Several changes in the diatom flora coincide with changes in forest composition as determined from paired pollen and plant macrofossil studies and suggest climate disruptions at ~ 10.6, ~ 9.2, ~ 8.2, and ~ 6.1 cal kyr BP. The last of these events precedes the classical hemlock (Tsuga) decline in the US Northeast that began at ~ 5.5 cal kyr BP and is notable in the sudden appearance of the diatom Lindavia rossii in Shaver Pond. This species shows repeated oscillations throughout the period of the decline and suggests that climate became much drier during the middle Holocene, shifting the hydrologic balance of the lake toward greater importance of alkaline groundwater inflow. Additional features of the Rensselaer Plateau diatom records reveal evidence of Younger Dryas cooling that created tree canopy gaps and made way for nitrogen-fixing alders (increase in diatom taxa that respond to nutrient enrichment) and response of both lakes to late Holocene neoglacial cooling (increase in acidophilic and dystrophic taxa as boreal conifers regained prominence).