Sedimentary sources of old high molecular weight dissolved organic carbon from the ocean margin benthic nepheloid layer

Journal Article · Tue Feb 01 04:00:00 EST 2000 · Geochimica et Cosmochimica Acta

DOI:https://doi.org/10.1016/S0016-7037(99)00335-X· OSTI ID:20017447

Average {sup 14}C ages of dissolved organic carbon (DOC) in the ocean are 3--6,000 years, and are influenced by old DOC from continental margins. However, sources of DOC from terrestrial, autochthonous, and sedimentary organic carbon seem to be too young to be responsible for the old DOC observed in the ocean. Since colloidal organic carbon (COC, i.e., high molecular weight DOC), which is chemically very similar to that of bulk DOC, can be effectively isolated from seawater using cross-flow ultrafiltration, it can hold clues to sources and pathways of DOC turnover in the ocean. Radiocarbon measurements on COC in the water column and benthic nepheloid layer (BNL) from two continental margin areas (the Middle Atlantic Bight and the Gulf of Mexico) and controlled laboratory experiments were carried out to study sources of old DOC in the ocean margin areas. Vertical distributions of suspended particulate matter (SPM), particulate organic carbon (POC), nitrogen (PON), and DOC in the water column and bottom waters near the sediment-water interface all demonstrate a well developed benthic nepheloid layer in both ocean margin areas. COC from the BNL was much older than COC from the overlying water column. These results, together with strong concentration gradients of SPM, POC, PON, and DOC, suggest a sedimentary source for organic carbon species and possibly for old COC as well in BNL waters. This is confirmed by the results from controlled laboratory experiments. The heterogeneity of {Delta}{sup 14}C signatures in bulk SOC thus points to a preferential release of old organic components from sediment resuspension, which can be the transport mechanism of the old benthic COC observed in ocean margin areas. Old COC from continental margin nepheloid layers may thus be a potential source of old DOC to the deep ocean.

• Research Organization: Texas A and M Univ., Galveston, TX (US)
• Sponsoring Organization: US Department of Energy; US National Science Foundation; Texas Institute of Oceanography
• OSTI ID: 20017447
• Journal Information: Geochimica et Cosmochimica Acta, Journal Name: Geochimica et Cosmochimica Acta Journal Issue: 4 Vol. 64; ISSN GCACAK; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
58 GEOSCIENCES
ATLANTIC OCEAN
BIOGEOCHEMISTRY
CARBON CYCLE
GULF OF MEXICO
ISOTOPE RATIO
MOLECULAR WEIGHT
ORGANIC MATTER
ORIGIN
SEAWATER