Sedimentary organic matter preservation: A test for selective degradation under oxic conditions

Journal Article · Thu Jul 01 04:00:00 EDT 1999 · American Journal of Science

DOI:https://doi.org/10.2475/ajs.299.7-9.529· OSTI ID:20006251

Hedges, J I; Hu, F S; Devol, A H; Hartnett, H E; Tsamakis, E; Kei, R G

The authors report here a test of the hypothesis that the extent of organic matter preservation in continental margin sediments is controlled by the average period accumulating particles reside in oxic porewater immediately beneath the water/sediment interface. Oxygen penetration depths, organic element compositions, and mineral surface areas were determined for 16 sediment cores collected along an offshore transect across the Washington continental shelf, slope, and adjacent Cascadia Basin. Individual amino acid, sugar, and pollen distributions were analyzed for a 11 to 12 cm horizon from each core, and {sup 14}C-based sediment accumulation rates and stable carbon isotope compositions were determined from depth profiles within a subset of six cores from representative sites. Sediment accumulation rates decreased, and dissolved O{sub 2} penetration depths increased offshore along the sampling transect. As a result, oxygen exposure times (OET) increased seaward from decades (mid-shelf and upper slope) to more than a thousand years (outer Cascadia Basin). Organic contents and compositions were essentially constant within individual sediment cores but varied consistently with location. In particular, organic carbon/surface area ratios decreased progressively offshore and with increasing OET. Three independent compositional parameters demonstrated that the remnant organic matter in farther offshore sediments is more degraded. Both concentration and compositional patterns indicated that sedimentary organic matter exhibits a distinct and reproducible oxic effect. OET helps integrate and explain organic matter preservation in accumulating continental margin sediments and hence provides a useful tool for assessing transfer of organic matter from the biosphere to the geosphere.

• Research Organization: Univ. of Washington, Seattle, WA (US)
• OSTI ID: 20006251
• Journal Information: American Journal of Science, Journal Name: American Journal of Science Journal Issue: 7-9 Vol. 299; ISSN AJSCAP; ISSN 0002-9599
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
58 GEOSCIENCES
BIODEGRADATION
CARBON CYCLE
CONTINENTAL MARGIN
ECOLOGICAL CONCENTRATION
GEOCHEMISTRY
GEOLOGIC HISTORY
ORGANIC MATTER
OXYGEN