HR: 0800h
AN: PP51A-0188    [Abstracts]
TI: Distribution of clay minerals on the Alaskan margin near Barrow Canyon revealed by Diffuse Spectral Reflectance measurements
AU: Orsburn, C
EM: corsburn@kent.edu
AF: Department of Geology, Kent State University, Kent, OH 44242, United States
AU: * Ortiz, J D
EM: jortiz@kent.edu
AF: Department of Geology, Kent State University, Kent, OH 44242, United States
AU: Polyak, L
EM: polyak.1@osu.edu
AF: Byrd Polar Research Center, Ohio State University, Columbus, OH 43210, United States
AU: Grebmeier, J M
EM: jgrebmei@utk.edu
AF: Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, TN 37996, United States
AU: Darby, D
EM: ddarby@odu.edu
AF: Department of Ocean, Earth, and Atmospheric Sciences, Old Dominion University, Norfolk, VA 23529, United States
AB: Sediment clay mineral assemblages provide an excellent means of assessing the provenance of Arctic sediment due to the variety of sediment transport mechanisms at work and the existence of distinct weathering sources from differing bedrock geology. During HOTRAX Leg 1 aboard the USCG Ice breaker Healy (cruise HLY0501), we collected jumbo piston cores on the Alaskan margin near Barrow Canyon which provide detailed Holocene sedimentary records. Measurements of Diffuse Spectral Reflectance (DSR) were collected at 1cm resolution from the split surface of the cores using a Minolta CM-2600d UV/VIS spectrophotometer (400-700nm wavelength range; 10nm resolution; 3mm spot size). To interpret the resulting downcore records, we present a preliminary study using 28 coretop sediment samples collected by the Shelf-Basin Interaction program in 2004 arrayed in four transects across the shelf near Barrow Canyon. The samples were analyzed using an ASD Labspec Pro FR UV/VIS/NIR spectrometer (250-2500nm wavelength range, 2-10nm resolution; 20mm spot size). Our results indicate that the measurements from the two instruments are offset by constant factors, but can be easily compared. To estimate the clay mineralogy of the cores, we decomposed the matrix of DSR measurements from the coretop and downcore samples using principle component analysis and compared the resulting factor score patterns with mineral diffuse spectral reflectance signatures from known samples measured in our lab or available from version 5 of the USGS Digital Spectral Library. The three leading modes extracted by principle component analysis of the downcore samples are applicable to the coretops. We infer that the first principle component mode relates to smectite, the second to chlorite, and the third to a mixture of illite and goethite (herein referred to as illite - goethite). The geographic and bathymetric trends in the coretop data indicate that (1) the smectite and illite - goethite components both increase with depth and reach greater values in the two western transects than in the two eastern transects closest to the coast and Barrow Canyon, (2) the smectite and illite- goethite components are anticorrelated in the two western transects, but not in the two eastern transects, (3) chlorite decreases with depth and is highest in the two transects closest to Barrow Canyon. These results suggest that the chlorite on the Alaskan margin is transported by nearshore currents from the Bering Straight and then by bottom currents flowing through the Barrow Canyon. Accordingly, we interpret downcore chlorite peaks inferred from DSR measurements in our sediment cores as evidence of times of enhanced input of Pacific water to the Alaskan Margin.
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 4207 Arctic and Antarctic oceanography (9310, 9315)
DE: 4910 Astronomical forcing
DE: 4926 Glacial
DE: 4936 Interglacial
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting