HR: 1340h
AN: PP23B-1405    [Abstracts]
TI: Tracing the Holocene variations in sea ice/icebergs along the North Iceland shelf
AU: * Chesley, T L
EM: Tara.Chesley@colorado.edu
AF: Univeristy of Colorado and the Institute of Arctic and Alpine Research, Campus Box 450, , Boulder, CO 80309 United States
AU: Moros, M
EM: Matthias.Moros@bjerknes.uib.no
AF: Bjerknes Centre for Climate Research, Allegaten 54, Bergen, 5007 Norway
AU: Andrews, J T
EM: Andrewsj@colorado.edu
AF: Univeristy of Colorado and the Institute of Arctic and Alpine Research, Campus Box 450, , Boulder, CO 80309 United States
AU: Eberle, D D
EM: ddeberl@usgs.gov
AF: U.S. Geological Survey, Suite E-127, 3215 Marine St., Boulder, CO 80303 United States
AB: During severe ice years, sea ice and icebergs drift onto the northern Iceland shelf and have a major impact on the climate of Iceland. Historically there are records of change in the concentration of ice that go back to the Settlement of Iceland $\sim$870AD. This is one of two major routes whereby ice might be brought to sites to the west of the British Isles. Two models of the variations in IRD throughout the Holocene have been proposed. In one the records show a series of peaks and troughs superimposed on an overall decrease in IRD toward the present. In the other, based on East Greenland cores, there is limited IRD during the Holocene until 6 cal ka when IRD increases and it increases throughout the Neoglacial. We use a new tracer which is the Quantitative Phase Analysis (QPA) of XRD scans of the combined sand/silt/clay fractions of marine sediments, which are spiked by ZnO or corundum, ground to a powder, and scanned between 5ø and 65ø two theta. The minimum sample sized is 0.8 g. Quartz is not a naturally occurring mineral on Iceland and we use the weight% of quartz and the quartz/plagioclase weight% ratios as potential tracers of sediment brought to Iceland from sources on East Greenland and around the Arctic Basin. We present 3 data sets: 1) the variations in quartz data from surface samples on the SW to N-central Iceland shelf; 2) downcore variations in Icelandic subglacial and glacial marine sediments; and 3) downcore variations in the mineralogy of Holocene sediments from cores off N Iceland with a particular focus on data from MD99-2269 which spans the last 12 cal ka with a sampling density of around 1 sample every 30-yr. The surface samples show a band of quartz weight% values of 2-6%\ off N Iceland that parallels the observed limits of sea ice in the spring. At sites in the SW, W, and inshore on the northern margins quartz values are <1%\ in the total sediment. In contrast, "native" Icelandic glacial and glacial marine sediments have negligible quartz content of between 0.0 and $<$1.0%\. The Holocene occurrence of quartz in MD99-2269 shows low and variable amounts in the early Holocene but values start to increase 5-6 cal ka and continue to rise throughout the Neoglacial period---in this the quartz data parallel to the coarse ($>$ 2 mm) IRD records from the East Greenland shelf.
DE: 4207 Arctic and Antarctic oceanography
DE: 4219 Continental shelf processes
DE: 4267 Paleoceanography
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting