Particulate organic carbon fluxes: compilation of results from the 1995 US JGOFS Arabian Sea Process Study: By the Arabian Sea Carbon Flux Group

Abstract

Organic carbon fluxes in the Arabian Sea were measured as a function of depth, season and distance from the coast of Oman. We present here a compilation of measurements of primary production, water-column export flux and sediment accumulation of organic carbon over a full annual monsoon cycle on a 1500-km transect from the coast of Oman toward the central Arabian Sea. This represents an integration of measurements spanning one day (primary production) to 1000 yr (sediments) and gives a broad overview of organic carbon removal and remineralization in the highly productive, seasonally varying region of the northern Indian Ocean. Organic carbon fluxes decreased from the surface to the sediments by a factor of 500–10,000, with the largest rates of change in the upper ocean and at the sediment–seawater interface. Organic carbon fluxes generally decreased with distance offshore, with the largest gradient between surface and seafloor being at the offshore station. Sediment accumulation rates of organic carbon differed by a factor of 40 between nearshore and offshore, while primary productivity varied only by a factor of 2. The decrease in carbon flux with depth that occurs between the deepest traps and the sediment becomes a greater proportion of the total loss with increasing distance from shore. Thus, the influence of processes at the sediment–water interface on the proportion of primary productivity preserved in the sediment increases offshore relative to upper water column processes. Carbon fluxes changed greatly with season, with highest fluxes during the Southwest Monsoon. Export fluxes varied more with season than primary productivity or mid-water fluxes.