Late Holocene change in climate and atmospheric circulation inferred from geochemical records at Kepler Lake, south-central Alaska

Abstract

Climate records during the last millennium are essential in placing recent anthropogenic-induced climate change into the context of natural climatic variability. However, detailed records are still sparse in Alaska, and these records would help elucidate climate patterns and possible forcing mechanisms. Here we present a multiple-proxy sedimentary record from Kepler Lake in south-central Alaska to reconstruct climatic and environmental changes over the last 800 years. Two short cores (85 and 101 cm long) from this groundwater-fed marl lake provide a detailed stable isotope and sediment lithological record with chronology based on four AMS 14 C dates on terrestrial macrofossils and 210 Pb analysis. The d 18 O values of inorganic calcite (CaCO 3 ) range from -17.0 to -15.7 %, with the highest values during the period of 1450-1850 AD, coeval with the well-documented Little Ice Age (LIA) cold interval in Alaska. The high d 18 O values during the cold LIA are interpreted as reflecting shifts in atmospheric circulation. A weakening of the wintertime Aleutian low pressure system residing over the Gulf of Alaska during the LIA would have resulted in 18 O-enriched winter precipitation as well as a colder and possibly drier winter climate in south-central Alaska. Also, elevated calcite contents of [80 % during the LIA reflect a lowering of lake level and/or enhanced seasonality (warmer summer and colder winter), as calcite precipitation in freshwater lakes is primarily a function of peak summer temperature and water depth. This interpretation is also supported by high d 13 C values, likely reflecting high aquatic productivity or increased residence times of the lake water during lower lake levels. The lower lake levels and warmer summers would have increased evaporative enrichment in 18 O, also contributing to the high d 18 O values during the LIA. Our results indicate that changes in atmospheric circulation were an important component of climate change during the last millennium, exerting strong influence on regional climate in Alaska and the Arctic.

An extended Arctic proxy temperature database for the past 2,000 years

“…The revisions include updating records using more recent published studies from three sites 17–19 17–19 17–19 , and correcting several errors discovered following publication of the PAGES 2k Consortium article. Specifically: Three records were removed because of insufficient evidence that they are sensitive to temperature 20–22 20–22 20–22 . Sections of five records 23–27 23–27 23–27 23–27 23–27 that were interpreted by the authors to violate criterion 5 were removed.…”

“…Three records were removed because of insufficient evidence that they are sensitive to temperature 20–22 20–22 20–22 .…”

Sedimentary response of lake El Tobar, Spain, to climate: lake level changes after the Maunder Minimum

“…Changes in circulation of air masses and the source of rainfall have been shown in some cases to be responsible for higher δ 18 O values (e.g. Gonyo et al ., ), which have been interpreted as decreases in isotopic distillation of air masses. This would correspond to positive values of the North Atlantic Oscillation (NAO) leading to dry periods, and this is the opposite situation of the LIA, where abundant meteoric precipitation would cause increases in the isotopic distillation of air masses.…”

Ice Cores from the St. Elias Mountains, Yukon, Canada: Their Significance for Climate, Atmospheric Composition and Volcanism in the North Pacific Region

“…Possible supporting evidence for changing atmospheric moisture flow regimes in the North Pacific during the Holocene may be found in the δ 18 O of carbonated and siliceous (diatom) sediments from groundwater-fed lakes in southern Yukon (Anderson et al, 2005(Anderson et al, , 2007 and Alaska (Schiff et al, 2009;Gonyo et al, 2012) and in precipitation records from the western interior of Canada (Birks and Edwards, 2009), although the interpretation of these proxies often varies. Fisher et al (2008) hypothesize that the shifts in the moisture flow regime recorded in Mt.…”