HR: 15:11h
AN: OS43B-06    [Abstracts]
TI: Constraints on the Origin of Sedimentary Organic Carbon in the Beaufort Sea from Coupled Molecular ¹³C and ¹⁴C Measurements
AU: * Drenzek, N
EM: ndrenzek@whoi.edu
AF: Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, 266 Woods Hole Road, Woods Hole, MA 02543 United States
AU: Montlucon, D
EM: dmontlucon@whoi.edu
AF: Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, 266 Woods Hole Road, Woods Hole, MA 02543 United States
AU: Yunker, M
EM: Mark-Yunker@telus.net
AF: Institute of Ocean Sciences, 7137 Wallace Drive, Brentwood Bay, BC V8M 1G9 Canada
AU: Macdonald, R
EM: MacdonaldRob@pac.dfo-mpo.gc.ca
AF: Department of Fisheries and Oceans, Institute of Ocean Sciences, P.O. Box 6000, Sidney, BC V8L 4B2 Canada
AU: Eglinton, T
EM: teglinton@whoi.edu
AF: Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, 266 Woods Hole Road, Woods Hole, MA 02543 United States
AB: The type and flux of organic carbon (OC) delivered from the continents to the sea can both influence, and be influenced by, climate change on regional and global scales. In order to develop a more complete view of OC delivery in the climatically sensitive Arctic region, we measured the stable carbon and radiocarbon isotopic signatures of individual lipid biomarkers and products of kerogen pyrolysis from the surficial sediments of several sites on the Mackenzie Shelf and adjacent slope of the Beaufort Sea. Even carbon numbered fatty acids exhibit a trend of increasing radiocarbon age with increasing chain length, from modern values for shorter homologues (nC₁₈ or below) to several thousand years old for their longer counterparts (nC₂₄ or greater). Such depleted Δ¹⁴C values for longer-chain fatty acids likely reflect supply of vascular plant OC that has been `pre-' on the continents for several millennia prior to delivery to the Beaufort Sea. Their concomitant stable carbon isotopic compositions support a C3 land plant source. The molecular distributions and corresponding δ<sup>13</sup>C and Δ<sup>14</sup>C signatures of solvent-extractable alkanes point to at least two sources: higher plant leaf waxes and a <sup>14</sup>C-`dead' component likely derived from erosion of organic-rich sedimentary rocks exposed within the Mackenzie River drainage basin. The stable carbon and radiocarbon compositions of straight chain n-hydrocarbon pyrolysis products from the corresponding demineralized sediments suggest their vascular plant-derived precursor structures also spent several millennia in continental reservoirs before being delivered to the Beaufort Sea. On a bulk level, the trend in sedimentary organic carbon contents, C/N ratios, and δ¹³C values point to an overall decrease in the terrigenous input (mainly from the Mackenzie river) with distance offshore, whereas bulk Δ¹⁴C measurements exhibit no trend suggesting a somewhat constant pre-aged component. A dual molecular isotopic mass balance approach based on the lipid δ¹³ C and Δ¹⁴C signatures is used to construct a budget of terrestrial, marine, and petrogenic OC burial on the shelf. Results indicate that 40-50% of the carbon currently being buried in the Beaufort Sea is derived from the weathering of ancient sedimentary rock. The balance is composed of marine and terrestrial input, supporting the qualitative description of OC sources given by the bulk and molecular patterns above. This suggests that mass balances utilizing the δ¹³C and Δ¹⁴C signatures of biomarkers as endmembers can be used to quantitatively deconvolve multiple sources of organic carbon in marine sediments.
DE: 1050 Marine geochemistry (4835, 4845, 4850)
DE: 1055 Organic and biogenic geochemistry
DE: 4806 Carbon cycling (0428)
DE: 4850 Marine organic chemistry (0470, 1050)
SC: Ocean Sciences [OS]
MN: Fall Meeting 2005