ANALYSIS OF TOTAL AND ORGANIC-CARBON AND TOTAL NITROGEN IN SETTLING OCEANIC PARTICLES AND A MARINE SEDIMENT - AN INTERLABORATORY COMPARISON

10 laboratories, using their routine methods, collaborated in a compar ison of analyses of total carbon, nitrogen and organic carbon in a sin gle sample of marine sediment and a pooled sample of settling particul ate material collected by sediment trap. The standard error of the mea ns from all individual laboratories was +/-3% of the mean for all tota l carbon results, and for total nitrogen in the marine sediment, but w as +/-7% of the mean for total nitrogen in the sediment trap material. Larger errors (+/-8% of the mean) were found for organic carbon resul ts from both the marine sediment and the sediment trap material, with a range of results (expressed as a percentage of the untreated dry wei ght) for the sediment trap sample analyzed here of 5.60-8.03%. When th is range is compared with that of particulate organic carbon concentra tion in sediment trap material obtained by different workers at variou s deep ocean sites (2.4-10.2%) [Wefer, G., 1989. Particle flux in the ocean: Effects of episodic production, in: W.H. Berger, V.S. Smetacek, G. Wefer (Eds.), Productivity of the Ocean: Present and Past, John Wi ley & Sons, pp, 139-154.] it is apparent that a large proportion of th e observed oceanic variability could be accounted for by difference in analytical technique. We suggest that the problem stems from the diff iculty of accurate separation of the organic and inorganic phases and discuss the inaccuracies involved in the separation. We present eviden ce that the range of results is partly due to either volatilisation of organic carbon during acid treatment, or incomplete removal of organi c matter during thermal treatment. Lf results from different laborator ies are to be compared, as is presently required for basin scale and g lobal studies of ocean carbon cycling and budgets, there is clearly a need for suitable reference materials, rigorous intercalibration and t echnique development. (C) 1998 Elsevier Science B.V.