HR: 1340h
AN: PP33B-1564    [Abstracts]
TI: Diatoms as Proxies for a Fluctuating Ice Cap Margin, Hvitarvatn, Iceland
AU: * Black, J L
EM: jblack@colorado.edu
AF: INSTAAR and Geological Sciences, University of Colorado, 1560 30th St., UCB 450, Boulder, CO 80309-0450 United States
AU: Miller, G H
EM: gmiller@colorado.edu
AF: INSTAAR and Geological Sciences, University of Colorado, 1560 30th St., UCB 450, Boulder, CO 80309-0450 United States
AU: Geirsdottir, A
EM: age@hi.is
AF: Department of Geosciences, Science Institute, University of Iceland, Dunhaga 3, Reykjavik, 107 Iceland
AB: There are no complete records of terrestrial environmental change for the Holocene (11,000yrs) in Iceland and the status of Icelandic glaciers in the early Holocene remains unclear. It is not even known whether Iceland's large ice caps disappeared in the early Holocene, and if they did, when they re-grew. Icelandic lakes are particularly well suited to address these uncertainties as: 1) Glacial erosion and soft bedrock result in high lacustrine sedimentation rates, 2) Diagnostic tephras aid the geochronology, 3) Iceland's sensitivity to changes in North Atlantic circulation should produce clear signals in key environmental proxies (diatoms) preserved in lacustrine sequences, and 4) Ice-cap profiles are relatively flat so small changes in the equilibrium line altitude result in large changes in accumulation area. Hence, large changes in ice-sheet margins during the Holocene will impact sedimentation in glacier-dominated lakes and the diatom assemblages at those times. Hvitarvatn is a glacier dominated lake located on the eastern margin of Langjokull Ice Cap in central-western Iceland. The uppermost Hvitarvatn sediments reflect a glacially dominated system with planktonic, silica-demanding diatom taxa that suggest a high dissolved silica and turbid water environment consistent with high fluxes of glacial flour. Below this are Neoglacial sediments deposited when Langjokull was active, but outlet glaciers were not in contact with Hvitarvatn. The diatom assemblage here shows a small increase in abundance, but is still dominated by planktic, silica-demanding taxa. A distinct shift in lake conditions is reflected in the lowermost sediments, composed of predominantly benthic diatoms and deposited in clear water conditions with long growing seasons likely found in an environment with warmer summers than present and with no glacial erosion. Langjokull must have disappeared in the early Holocene for such a diverse, benthic dominated diatom assemblage to flourish.
DE: 1605 Abrupt/rapid climate change (4901, 8408)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005