HR: 0800h
AN: PP31A-1509    [Abstracts]
TI: A 12,000-Year Climatic Record From Biogenic-Silica Oxygen Isotopes in SW Alaska
AU: * Henderson, A C
EM: ahenders@life.uiuc.edu
AF: Department of Plant Biology, University of Illinois, Urbana, IL 61801 United States
AU: Clarke, G H
EM: gclarke@life.uiuc.edu
AF: Department of Plant Biology, University of Illinois, Urbana, IL 61801 United States
AU: Shemesh, A
EM: aldo.shemesh@weizmann.ac.il
AF: Department of Environmental Sciences and Energy Research, Weizmann Institute of Science, Rehovot, 76100 Israel
AU: Hu, F
EM: fshu@life.uiuc.edu
AF: Department of Plant Biology, University of Illinois, Urbana, IL 61801 United States
AU: Hu, F
EM: fshu@life.uiuc.edu
AF: Department of Geology, University of Illinois, Urbana, IL 61801 United States
AB: Oxygen-isotope analysis of lake sediments offers an effective tool for acquiring paleoclimatic records. In non-alkaline or dilute, oligotrophic lakes where carbonate material is absent or rare, the oxygen-isotope composition of diatoms (δ¹⁸O_diat) is an emerging proxy indicator for climatic reconstruction. Here we present the first δ¹⁸O_diat record spanning the Holocene from the North Pacific region. Ongoke Lake (59°15'N, 159°25'W, 400 m a.s.l, 7 m max depth) is a through-flow system, and it is located in southwestern Alaska near sites whose high-resolution records have documented cyclic variation and solar forcing of Holocene climate. The values of modern water samples from Ongoke Lake fall within the range of precipitation δ¹⁸O values that define a local meteoric water line. This pattern implies negligible evaporative flux as a result of the positive moisture balance under the near-coastal climate of the region. The δ¹⁸O_diat record shows a gradual decrease from c. 32 ‰ to 27 ‰ VSMOW since the onset of the Holocene. This 5 ‰ decrease would mean an 8 to 10°C cooling if driven solely by changing mean annual temperature, which is not a plausible scenario. Thus it is likely that the decreasing δ¹⁸O_diat trend partially reflects (1) that the moisture balance became progressively more positive and/or (2) that winter precipitation became progressively more abundant relative to summer precipitation over the Holocene. The δ¹⁸O_diat record and July insolation at 60°N show broad similarities, suggesting a link between SW Alaskan climate and solar forcing during the Holocene. Biogenic silica (BSi) results from the same lake show a Holocene cooling trend similar to that inferred from δ¹⁸O_diat. The BSi record also displays centennial to millennial cycles coincident with solar changes, as well as with atmospheric temperature and ocean circulation in the North Atlantic. However the relationship between δ¹⁸O_diat and BSi at sub-millennial scales remains unclear.
DE: 1600 GLOBAL CHANGE
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 1620 Climate dynamics (0429, 3309)
DE: 1637 Regional climate change
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005