Isotopic evidence for the contemporary origin of high-molecular weight organic matter in oceanic environments

Details Isotopic evidence for the contemporary origin of high-molecular weight organic matter in oceanic environments Isotopic evidence for the contemporary origin of high-molecular weight organic matter in oceanic environments

Feb 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995gecoa..59..625s&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 59, Issue 3, pp.625-631

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Scientific paper

Previous work has suggested that apparent old 14 C ages for oceanic DOC are the result of mixing of different organic carbon fractions. This report provides direct evidence for a contemporary 14 C age of a high-molecular-weight (HMW) fraction of colloidal organic carbon ( 10 kD). Colloidal organic matter, COM 10 (from 10 kDaltons (kD) to 0.2 m), isolated from the upper water column of the Gulf of Mexico and the Middle Atlantic Bight (MAB) region, generally has a contemporary age (i.e., younger than a few decades), while COM 1 (from 1 kD to 0.2 m), is apparently old: 380-4500 y P. Thus, BMW COM 10 (3-5% of DOC) from the upper water column is derived from living particulate organic matter (POM) and cycles rapidly, while a significant fraction of low-molecular-weight ( 1 kD) DOM is likely more refractory, and cycles on much longer time scales. The presence of pigment biomarker compounds in COM 1 from the upper water column points to selected phytoplankton species as one of the sources of COM. Terrestrial carbon as another source of COM is suggested from the inverse correlation between 14 C and 13 C values, as well as the increasing 13 C values with increasing salinity. 234 Th-derived turnover times of COM 10 and COM 1 from both the Gulf of Mexico and MAB are consistently short, 1-20 and 3-30 days, respectively. These short residence times support the hypothesis that 14 C ages of colloidal fractions of DOC are the result of COM fractions being a mixture of several endmembers with fast and slow turnover rates.

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