Deep-Sea Research II (1996) 43: 1155-1180.
Submitted: 3 January 1995.
Revised: 21 July 1995.
Accepted: 6 January 1996.
Total organic carbon (TOC) was analyzed on four transects along 140°W in 1992 using a high temperature combustion / discrete injection (HTC/DI) analyzer. For two of the transects, the analyses were conducted on-board ship. Mixed-layer concentrations of organic carbon varied from about 80 µMC at either end of the transect (12°N and 12°S) to about 60 µMC at the equator. Total organic carbon concentrations decreased rapidly below the mixed-layer to about 38-40 µMC at 1000 m across the transect. Little variation was observed below this depth; deep water concentrations below 2000 m were virtually monotonic at about 36 µMC. Repeat measurements made on subsequent cruises consistently found the same concentrations at 1000 m or deeper but substantial variations were observed in the mixed-layer and the upper water column above 400 m depth.
Linear mixing models of total organic carbon versus sigma-theta exhibited zones of organic carbon formation and consumption. TOC was found to be inversely correlated with apparent oxygen utilization (AOU) in the region between the mixed-layer and the oxygen minimum. In the mixed-layer, TOC concentrations varied seasonally. Part of the variations in TOC at the equator were driven by changes in the upwelling rate in response to variations in physical forcing related to an El Niño and to the passage of tropical instability waves. TOC export fluxes, calculated from simple box models, averaged 8 ± 4 mmol C / m² · day at the equator and also varied seasonally. These export fluxes account for 50-75% of the total carbon deficit and are consistent with other estimates and model predictions.