The abundance of sedimentary organic material from two lakes was used to infer past Holocene storminess on Adak Island where frequent storms generate abundant rainfall and extensive cloud cover. Andrew and Heart Lakes are located 10 km apart; their contrasting physical characteristics cause the sedimentary organic matter to respond differently to storms. Their records were synchronized using correlated tephra beds. Sedimentation rates increased between 4.0 and 3.5 ka in both lakes. Over the instrumental period, Andrew Lake biogenic-silica content (BSi) is most strongly correlated with winter sunlight availability, which influences photosynthetic production, and river input, which influences the dilution of BSi by mineral matter. Heart Lake BSi is likely affected by wind-driven remobilization of sediment, as suggested by correlations among BSi, the North Pacific Index, and winter storminess. The results indicate relatively stormy conditions from 9.6 to 4.0 ka, followed by drying between 4.0 and 2.7 ka, with the driest conditions from 2.7 to 1.5 ka. The stormiest period was between AD 500 and 1200, then drying from 1150 to 1500 and more variable until 1850. This record of Holocene storminess fills a major gap at the center of action for North Pacific wintertime climate.
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Fluctuations in the abundance of organic material reflect wet and stormy versus drier periods differently for the two lakes. At Andrew Lake, BSi and inferred chlorophyll- a reflects changes in the abundance of organic material in response to sunlight availability and mineral-matter dilution. The same proxies at Heart Lake show evidence for the effects of storm-wind-induced sediment remobilization. This interpretation is supported by the strong downcore relation between BSi and inferred chlorophyll- a at Andrew Lake, and by the reworked vegetation macrofossils in 14 C-dated samples from Heart Lake ( Krawiec et al., 2013 ).
The U.S. Fish and Wildlife Service , Alaska Maritime Natural Wildlife Refuge and CH2M Hill Polar Services provided logistical support for fieldwork on Adak Island. R.S. Anderson provided insights into the vegetation history based on his pollen analysis of Heart Lake sediment. We thank Caleb Schiff, Yarrow Axford, and David Vaillencourt for help with coring and Katherine Cooper and the staff at the University of Minnesota Limnological Research Center for assistance in the laboratory. Caleb Schiff conducted initial analysis of the 2009 surface cores and David Vaillencourt generated the age model for Andrew Lake. The National Science Foundation Award EAR-0823522 funded this study.
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- Adak Island
- Biogenic silica
- Holocene storminess
- Inferred chlorophyll-a
- Lake sediments
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