Holocene storminess inferred from sediments of two lakes on Adak Island, Alaska

Abstract

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.

Synoptic scale controls on the δ18O in precipitation across Beringia

“…This dipole-like pattern corresponds to the mapped GNIP δ 18 O precip anomalies (Figures 2a and 2b). The 100 year δ 18 O diatom record from Heart Lake is also consistent with other NPIinferred paleorecords from across Beringia, including northwest North American tree ring records (r = 0.66, P < 0.001) [D'Arrigo et al, 2005], Na + concentrations in Mount Logan ice (r = À0.45, P < 0.001) [Osterberg et al, 2014], and the weight abundance of BSi in Heart Lake (r = À0.48, P < 0.01) [Krawiec and Kaufman, 2014].…”

Holocene atmospheric circulation in the central North Pacific: A new terrestrial diatom and δ18O dataset from the Aleutian Islands

“…These pioneering taxa dominate polar to subpolar and mountainous tundra lakes (Lotter and Bigler, 2000;Rühland et al 2003;Hausmann and Pienitz, 2009;Devlin and Finkelstein, 2011) and their presence suggests a relatively short growth season with cool air temperatures (Smol et al 2005;Rühland et al 2008;Hausmann and Pienitz, 2009). Cool/dry conditions at this time are further supported by low concentrations of biogenic silica (BSi) and organic matter (OM) in nearby Andrew Lake (Krawiec and Kaufman, 2014) and the dominance of Salix and Empetrum in northern Adak (Heusser, 1978).…”

“…A reduction in turbulent wind-driven lake mixing at this time may have also been responsible for increased benthic production and a simultaneous expansion of the littoral zone and benthic habitat (Bradbury et al,2002). Increased winter precipitation and subsequent spring snow melt would account for the sedimentation increase at 3.8 ka from 0.2 to 0.8 mm/yr (Krawiec and Kaufman, 2014). This turbidity would have further reduced light penetration into the benthic zone, thereby promoting fragilarioid taxa which thrive under limited light and generally turbid conditions (Lotter and Bigler, 2000;Douglas and Smol, 2010).…”

“…Aulacoseira subarctica, in particular, is abundant in modern lake systems during years with short, warm winters (Gibson et al 2003;Horn et al 2011). Elevated pollen percentages of Cyperaceae and other wetland species in northern Adak also imply warm/wet conditions at this time (Heusser, 1978) and correspond to higher local lake levels prior to 4.0 ka (Krawiec and Kaufman, 2014). Peak d 18 O diatom (33.3‰) suggests maximum Holocene warmth at 7.6 ka, an inference supported by the simultaneous maximum Holocene abundance of the warm water indicator C. occellata (Rühland et al 2008) (Fig.…”

The effect of species on lacustrine δ18 Odiatom and its implications for palaeoenvironmental reconstructions

“…The core was recovered using a percussion corer operated from a floating platform. The core was split, photographed and described (Krawiec, 2013), with 20 samples taken downcore for d 18 O diatom and diatom species analysis. The samples range in age from 8.0 to 1.0k cal a BP based on a best-fit age-depth model constructed using accelerator mass spectrometry 14 C ages and correlated tephra ages from nearby Andrew Lake .…”