Holocene tephrochronology and storminess inferred from two lakes on Adak Island, Alaska

The central Aleutian Islands are located in a center of action for wintertime climate and North Pacific storm tracks, and they form part of an active volcanic arc. Sediment cores from two lakes on Adak Island were analyzed for primary productivity proxies and tephra correlations between the lakes. This study fills a large data gap in subarctic paleoclimate records and provides improved understanding of the local tephra-fall history.;Core chronologies were based on radiocarbon and short-lived isotopes. Ten tephras were correlated between the lakes based on magnetic susceptibility, grain morphology, and internal stratigraphy (color and grain size). Tephra ties to the Andrew Lake age model identified radiocarbon dates with built-in ages for Heart Lake. Andrew Lake is less prone to older carbon contamination, whereas Heart Lake's shallow platform facilitates remobilization of previously deposited sediments. The composite tephrostratigraphy includes 30 unique tephras deposited over 9600 years. Five were correlated with tephras described in previous studies on Adak Island based on stratigraphic succession, inferred age, and internal stratigraphy.;The abundant preserved biological material, including biogenic silica (BSi), organic matter (OM), and chlorophyll-a, were analyzed to infer past changes in productivity. Sedimentary sequences from both lakes show increased sedimentation rates between 4.0 and 3.0 cal ka, possibly in response to increased eolian input and glaciation in the Andrew Lake catchment. BSi in Andrew Lake seems to respond to sunlight availability and mineral-matter dilution, both associated with storm frequency, whereas BSi in Heart Lake fluctuates less, indicative of remobilization. This is supported by correlations between BSi, the North Pacific Index, and winter storminess during the instrumental period. Although frequent tephra deposition complicates interpretations, wetter-than-average conditions are inferred from 9.6 to 4.0 cal ka and between 500 and 1200 AD. I infer drying trends from 4.0 to 2.7 ka, 1150 to 1500 AD, and 1900 to the present, as well as drier-than-average conditions from 2.7 ka to 500 AD. This study demonstrates that proxies analyzed in two different lakes respond differently to the same hydroclimate changes.