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Long-term, large-scale perspectives are necessary for understanding climate variability and its effects on ecosystems and cultures. Tree ring records of the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA) have documented major hydroclimatic variability during the last millennium in the American West, but fewer continuous, high-resolution hydroclimate records of the MCA-LIA period are available for eastern North America, particularly during the transition from the MCA to the LIA (ca. A.D. 1250–1400). Diatoms (micro-algae with silica cell walls) in sediment cores from three Adirondack (NY, USA) lakes and a hiatus in a wetland peat deposit in the Adirondack uplands provide novel insights into the late Holocene hydroclimate history of the Northeast. These records demonstrate that two of the region’s most extreme decadal-scale droughts of the last millennium occurred ca. A.D. 1260–1330 and ca. A.D. 1360–1390 during a dry-wet-dry (DWD) oscillation in the Adirondacks that contributed to forest fires and desiccation of wetlands in New York and Maine. The bimodal drying was probably related to more extreme droughts farther west and coincided with major events in Iroquoian and Abenaki cultural history. Although the causes of the DWD oscillation in the Adirondacks remain uncertain, changing sea-surface temperatures and solar variability are likely to have played a role. 

Abstract. Holocene climate reconstructions are useful for understanding the diversefeatures and spatial heterogeneity of past and future climate change. Herewe present a database of western North American Holocene paleoclimaterecords. The database gathers paleoclimate time series from 184 terrestrialand marine sites, including 381 individual proxy records. The records spanat least 4000 of the last 12 000 years (median duration of 10 725 years)and have been screened for resolution, chronologic control, and climatesensitivity. Records were included that reflect temperature, hydroclimate,or circulation features. The database is shared in the machine readableLinked Paleo Data (LiPD) format and includes geochronologic data forgenerating site-level time-uncertain ensembles. This publicly accessible andcurated collection of proxy paleoclimate records will have wide researchapplications, including, for example, investigations of the primary featuresof ocean–atmospheric circulation along the eastern margin of the NorthPacific and the latitudinal response of climate to orbital changes. Thedatabase is available for download at https://doi.org/10.6084/m9.figshare.12863843.v1 (Routson and McKay, 2020).