HR: 1340h
AN: PP33B-0945    [Abstracts]
TI: Radiocarbon ages and biomarker compositions of organic matter in size-fractionated sediments from the Washington Margin
AU: * Uchida, M
EM: uchidama@jamstec.go.jp
AF: Department of Geology and Geophysics, Woods Hole Ocenographic Institution, Oyster pond rd., Woods Hole, MA 02543 United States
AU: * Uchida, M
EM: uchidama@jamstec.go.jp
AF: Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima, Yokosuka, 237-0061 Japan
AU: Eglinton, T I
EM: teglinton@whoi.edu
AF: Department of Marine Chemistry and Geochemistry, Woods Hole Ocenographic Institution, Oyster pond rd., Woods Hole, MA 02543 United States
AU: Hayes, J M
EM: jhayes@whoi.edu
AF: Department of Geology and Geophysics, Woods Hole Ocenographic Institution, Oyster pond rd., Woods Hole, MA 02543 United States
AU: Coppora, L
EM: laurent.coppola@nrm.se
AF: Swedish Museum of Natural History, Frescativaegen 40, Stockholm, 10405 Sweden
AU: Gustafsson, O
EM: orjan.gustafsson@itm.su.se
AF: Stockholm University, Frescativagen 54, Stockholm, 10405
AU: Andersson, P
EM: andersson@nrm.se
AF: Swedish Museum of Natural History, Frescativaegen 40, Stockholm, 10405 Sweden
AB: In order to examine relationships between sources of organic matter, molecular compositions, diagenetic alteration, and particle size in modern marine depositional regimes, seven surface sediments from depths of 70 to 2700 m were collected along an E-W transect from the mouth of the Columbia River, across the Washington continental margin, to the Cascadia Basin in the N.E. Pacific. The sediments were separated by grain size ($>$250, 100-250, 63-100, 38-63 and $<$38 um) and, using SPLITT (split flow thin cell) fractionation for the finest particles, by sinking rate ($>$1 m/d and $<$ 1m/d). This method was recently tested and validated using a variety of natural sediments [1]. Results indicated that many biogeochemical processes governed by particle dynamics could be examined using this approach.Consistent with earlier reports [2], sediments from the Washington shelf are dominated by large particles ($>$250 um) whereas fine particles ($<$38 um) are predominant in slope and Cascadia Basin sediments. With the exception of inner-shelf stations, most TOC resides in the fine fraction and ranges around 1.5-3%. Radiocarbon ages of TOC ranges from 1190 yrs BP to 4320, with older ages distant from the coast. Organic carbon in the finest grain-size fractions is systematically youngest. The more rapidly sinking split ($>$ 1m/d) is younger than the < 1m/d fraction. Stable carbon isotopic measurements on TOC indicate an increase in delta 13C values from the shelf to the Cascadia Basin (from -25 to -22 permil, suggesting a transition from terrestrial to autochthonous marine sources. The results of biomarker composition in grain-size fractions and bulk-phase organic matter will also be presented with those from radiocarbon and in delta13C values fractions. References [1] Coppola, L., Gustafsson, Andersson, P., Larsson, J. and Axelsson, P. (submitted) Limnol. Oceanogr. Methods. [2] Keil, R.G., Tsamakis, E., Fuh, C.B., Giddings, J.C. and Hedges, J.I. (1994) GCA 58, 879-893
DE: 4806 Carbon cycling
DE: 4850 Organic marine chemistry
DE: 4870 Stable isotopes
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting