HR: 0800h
AN: PP51A-0179    [Abstracts]
TI: Luminescence From Sediment Within the sea ice of the Arctic Ocean
AU: * Berger, G W
EM: glenn.berger@dri.edu
AF: Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512-1095, United States
AB: During the trans-Arctic Ocean HOTRAX'05 expeditions dirty sea ice was collected for luminescence tests at 4 sites from north of Alaska to near the North Pole. Samples were shielded from daylight during collection to permit laboratory analyses of the light-sensitive luminescence from quartz and feldspar grains within these clayey silts and silty clays. Most of the sediment preserved in Arctic Ocean bottom cores is first carried by sea ice. Accurate luminescence dating of bottom cores requires daylight exposure of siliciclastic grains before burial. Therefore, tests for the presence and nature of luminescence within dirty sea ice were carried out. These tests included dual-wavelength TL (thermoluminescence) optical bleaching, multi-aliquot IRSL (infrared-stimulated- luminescence) experiments, and single-aliquot IR (for feldspar response) and post-IR B-PSL (blue-photon- stimulated-luminescence) (for quartz response) experiments. All tests were performed on polymineral 4-11 micron diameter grains. The TL bleaching tests indicate that the TL clock was effectively zeroed for the two samples from the western ocean, but only partly zeroed for the two samples from the central ocean. This variation within TL data is enhanced by use of the more sensitive PSL methods. Apparent ages range among the 4 samples from ca. 400 yr to 1300 yr using a long-bleach IRSL procedure, but are effectively zero using a short-bleach procedure. Age estimates from single-aliquot tests range analogously from ca. 200 yr to 7 kyr using the conventional late- subtraction procedure, but are effectively zero using the early-subtraction method. Therefore relict ages near zero can be measured for sea-ice sediment using appropriate procedures. Thus, the much larger luminescence apparent ages (several kyr) measured (Berger, 2006, Quat. Sci. Rev., v25, p2529) in core tops from across the Arctic Ocean must manifest bottom-current reworking processes (mixing of ‘old' and ‘young' grains in darkness).
DE: 0750 Sea ice (4540)
DE: 1105 Quaternary geochronology
DE: 4558 Sediment transport (1862)
DE: 4863 Sedimentation (1861)
DE: 9315 Arctic region (0718, 4207)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting