Spatial and Temporal Variability of Total Organic Carbon
along 140°W in the Equatorial Pacific Ocean in 1992

E. T. Peltzer and N. A. Hayward
Woods Hole Oceanographic Institution, Woods Hole, MA 02543

Deep-Sea Research II (1996) 43: 1155-1180.
Submitted: 3 January 1995.
Revised: 21 July 1995.
Accepted: 6 January 1996.

ABSTRACT

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.

SELECTED FIGURES

TOC distribution during 1992 along 140°W from 12°N to 12°S, 0-600m: 
  1. February   --  R/V Thomas G. Thompson

  2. April      --  NOAAS Malcolm Baldrige

  3. August     --  R/V Thomas G. Thompson

  4. September  --  NOAAS Discoverer

Acknowledgements

This research was supported by National Science Foundation grants OCE 91-15201 and OCE 92-03953 with funds provided by the Office of Global Programs, National Oceanic and Atmospheric Administration. Computer support for data processing and graphics was provided by National Aeronautics and Space Administration grant NAGW-2431 as part of the Earth Observing System Interdisciplinary Science program. This is contribution number 9017 from the Woods Hole Oceanographic Institution and US-JGOFS contribution number 187.

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