Export flux of carbon at the equator during the EqPac time-series cruises estimated from super(2) super(3) super(4) Th measurements

Distributions of super(2) super(3) super(4) Th were determined in three particle-size classes (>53, 1-53 and 0.7-1.0 mu m) and in filtered seawater during each of the two time-series cruises of the U.S. JGOFS Process Study in the equatorial Pacific. Four vertical profiles were measured on the equ...

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Published in:Deep-sea research. Part II, Topical studies in oceanography Topical studies in oceanography, 1996-01, Vol.43 (4-6), p.1133-1153
Main Authors: Bacon, M P, Cochran, J K, Hirschberg, D, Hammar, T R, Fleer, A P
Format: Article
Language:English
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Summary:Distributions of super(2) super(3) super(4) Th were determined in three particle-size classes (>53, 1-53 and 0.7-1.0 mu m) and in filtered seawater during each of the two time-series cruises of the U.S. JGOFS Process Study in the equatorial Pacific. Four vertical profiles were measured on the equator at 140 degrees W from the sea surface to 400 m depth between 24 March and 9 April 1992 (Time-series I) and again between 3 and 18 October 1992 (Time-series II). In addition, both organic and inorganic carbon were measured in each of the particle fractions. The results were used with a one-dimensional model, which includes the equatorial upwelling, to estimate the flux of particulate carbon sinking out of the surface layer. The flux of particulate organic carbon (POC) at the base of the euphotic zone (0.1% light level, 120 m depth) was estimated to average 1.9 mmol m super(-) super(2) day super(-) super(1) during El Nino (Time-series I) and 2.4 mmol m super(-) super(2) day super(-) super(1) during the cold period that followed (Time-series II). These values amount to only similar to 2% of the primary production measured during each of the same periods and are insufficient to balance the new production, estimated previously to be similar to 17% of primary production. These results are consistent with the hypothesis that the major part of the new production is removed from the region by advection in the form of dissolved organic matter. The POC flux profile indicates a net remineralization below the 1% light level (80 m depth) such that the flux reaching 200 m depth has been reduced by similar to 55%, giving a remineralization length scale of similar to 155 m. For particulate inorganic (carbonate) carbon the flux at 200 m averaged 0.54 mmol m super(-) super(2) day super(-) super(1) during Time-series I and 0.71 mmol m super(-) super(2) day super(-) super(1) during Time-series II, very similar to the fluxes reported in deep sediment traps deployed at the same time. Estimates of the average large-particle sinking velocity give values
ISSN:0967-0645