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. 2001 Sep 11;98(19):10552-6.
doi: 10.1073/pnas.181333798. Epub 2001 Aug 21.

Pronounced Climatic Variations in Alaska During the Last Two Millennia

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Free PMC article

Pronounced Climatic Variations in Alaska During the Last Two Millennia

F S Hu et al. Proc Natl Acad Sci U S A. .
Free PMC article

Abstract

Paired oxygen-isotopic analyses of abiotic carbonate and benthic-ostracode shells from lake sediments provide a continuous quantitative record of growing-season temperature for the past 2000 years in the northwestern foothills of the Alaska Range. This record reveals three time intervals of comparable warmth: anno Domini (A.D.) 0-300, 850-1200, and post-1800, the latter two of which correspond to the Medieval Climatic Anomaly and climatic amelioration after the end of the Little Ice Age. The Little Ice Age culminated at A.D. 1700, when the climate was approximately 1.7 degrees C colder than at present. A marked climatic cooling also occurred around A.D. 600, coinciding with extensive glacial advances in Alaska. Comparisons of this temperature record with ostracode trace-element ratios (Mg/Ca, Sr/Ca) further suggest that colder periods were wetter and vice versa during the past 2000 years.

Figures

Figure 1
Figure 1
(A) Map showing location of Farewell Lake (FL) in Alaska. (B) Bathymetry of Farewell Lake and coring location.
Figure 2
Figure 2
Age-depth plot of the Farewell Lake core. Dates <150 calibrated year B.P. are based on 210Pb analysis of bulk sediment, and those >150 calibrated year B.P. are based on 14C analysis of Picea needles, Betula seeds, and unidentified twigs. Error bars represent ± 1σ SE.
Figure 3
Figure 3
Climate records for the past 2000 years. These records include gross sediment composition, carbon and oxygen isotopic values, growing-season temperature anomalies, and trace-element ratios. OC, organic carbon; CaCO3, carbonate as calculated from inorganic carbon content; AC, abiotic carbonate (bulk carbonate excluding shells of ostracodes, bivalves, and gastropods); BO, valves of benthic ostracode C. ikpikpukensis; ΔT, growing-season temperature anomaly; VPDB, Vienna Peedee belemnite. The vertical bar in the ΔT plot marks the temperature range of the 20th century, as represented by the uppermost three samples. Open symbols are original data, and lines are three-point moving averages to emphasize overall trends. Calibrated year B.P. is referenced to the year 1950.

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