Ostracode Geochemical Record of Holocene Climatic Change and Implications for Vegetational Response in the Northwestern Alaska Range

摘要: Abstract Trace-element analysis of the calcareous shells ostracodes in a sediment core from Farewell Lake provides first limno-geochemical record for climatic reconstructions Alaska. When compared with pollen data same site, this offers new insights into controls over vegetation dynamics during Holocene. The low Mg/Ca ratios and high Sr/Ca suggest that relatively cold dry climate prevailed region between 11,000 9000 yr B.P. (uncalibrated14C ages are used throughout paper). This result contrasts previous interpretations thermal maximum at time, corresponding to widespread establishment ofPopuluswoodland/forest. trace-element suggests, instead, warmest period early Holocene was 8500 8000 decline ofPopulus.Marked decreases major increase effective moisture around 6500 B.P., which coincided ofPiceaboreal forests region. change probably much Alaska adjacent Canada might have induced rapid spread ofAlnusand shift fromPicea glaucatoP. marianadominance across Our geochemical also suggests late-Holocene history more complex than previously thought on basis palynological studies. According record, growing-season temperatures increased 6000–4500 decreased 4500–1500 fluctuations afterward. After 6000 stratigraphic changes percentages ofPiceaappear be positively related those Mg/Ca. relationship implies once threshold crossed ofPiceaforests temperature primary control ofPiceapopulation density.