Analysis of Marine DOC using a Dry Combustion Method

B. Fry*
Ecosystems Center
Marine Biological Laboratory
Woods Hole, MA 02543

E. T. Peltzer
Marine Chemistry and Geochemistry Department
Woods Hole Oceanographic Institutiton
Woods Hole, MA 02543

C. H. Hopkinson, A. Nolin and L. Redmond
Ecosystems Center
Marine Biological Laboratory
Woods Hole, MA 02543

Marine Chemistry (1996) 54: 191-201.

Received: 25 August 1995.
Accepted: 14 February 1996.
Published: October 1996.

* Current address: Biology Dept, Florida International University, University Park, Miami FL 33199.

ABSTRACT

As part of a continuing effort to verify and improve measurements of marine dissolved organic carbon (DOC), we combusted dried sea salts and adhered organic matter to assay DOC concentrations in representative samples from the Atlantic and Pacific Oceans. Combustions were performed overnight at 580°C in sealed tubes and oxidation of organic materials occurred via a novel mechanism, thermal sulfate reduction:

2 H2SO4 + CH2O -- > CO2 + 2 SO2 + 3 H2O.

Measured DOC concentrations ranged from 43-114 µMC, with the highest values observed in inshore surface samples from Woods Hole Harbor, and the lowest values observed in twelve deep offshore Atlantic and Pacific waters. Stable carbon isotope values determined for all samples were near -22 per mil, consistent with a predominantly marine phytoplankton origin for DOC. A seasonal study in Woods Hole Harbor showed no significant temporal trends in nearshore DOC concentrations. Problems associated with samples storage and contamination during drying steps prevented precise (± 1 µM) DOC concentration determinations; however, an improved drying and measurement system is outlined (Appendix 1) for possible future dry-combustion studies of DOC concentrations.

Acknowledgements

This research was supported by Department of Energy grant DE-FG-92ER61438 and National Science Foundation grant OCE 92-16897 to BF; and NSF grants OCE 91-15201 and OCE 92-03953 with funds provided by the Office of Global Programs, National Oceanic and Atmospheric Administration to ETP. This is contribution number 9172 from the Woods Hole Oceanographic Institution and US-JGOFS contribution number 215.

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