Was a carbon balance measured in the equatorial Pacific during JGOFS?

The likelihood that the carbon fluxes measured as part of the US-JGOFS field program in the equatorial Pacific ocean (EqPac) during 1992 yielded a balanced carbon budget for the surface ocean was determined. The major carbon fluxes incorporated into a surface carbon budget were: new production, particulate organic carbon (POC) and dissolved organic carbon (DOC) export, CaCO(3) export, CO(2) gas evasion, dissolved inorganic carbon (DIC) supply, and the time rate of charge. The ratio of the measured concentration gradients of DOC and DIC provided a constraint on the ratio of POC/DOC export. Uncertainties of +/-30-50% for individual carbon flux measurements reduce the likelihood that a carbon balance can be measured during a JGOFS process-type study. As a benchmark, carbon fluxes were prescribed to yield a hypothetical surface carbon budget that was, on average, balanced. Given the typical errors in the individual carbon fluxes, however, there was only about a 30% chance that this hypothetical budget could be measured to be balanced to +/- 50%. Using this benchmark, it was determined that there was a similar to 95% chance that the carbon flux measurements yielded a surface DIC budget balanced (to +/- 50%) during El Nino conditions in boreal spring 1992, when the total organic carbon export rate was similar to 5 mmol C m(-2) day(-1) and the POC export was similar to 3 mmol C m(-2) day(-1). In boreal fall 1992, during cold period conditions, there was a similar to 70% chance that the surface carbon DIC budget was balanced when the total organic carbon export rate was similar to 20 mmol C m(-2) day(-1) and export was similar to 13 mmol C m(-2) day(-1). The DOC to DIC concentration gradient ratio of similar to 0.15, measured in depth profiles down to 100 m and in surface waters, was used as an important constraint that most ( > 70%) of the organic carbon exported from the euphotic zone was POC rather than DOG. If a balanced surface DIC budget was used to lest the compatibility of individual carbon fluxes measured during EqPac, then a three-to four-fold increase in total and particulate organic carbon export between spring and fall is indicated. This increase was not reflected in the POC loss rates measured by drifting sediment trap collections or estimated by (234)Th deficiencies coupled with the C/Th measured on suspended particles. (C) 1998 Elsevier Science Ltd. All rights reserved.