IS DOC THE MAIN SOURCE OF ORGANIC-MATTER REMINERALIZATION IN THE OCEAN WATER COLUMN

Recent interpretations of carbon flux data and deep-sea processes have led to a reconsideration of the role of dissolved organic carbon (DOC ) in supporting water column remineralization and other mid-water biog eochemical transformations (Suzuki et al., 1985; Cho and Azam, 1988; K arl et al., 1988; Christensen et al., 1989; Naqvi and Shailaja, 1993). To date, there have been no direct comparisons of particulate carbon flux data with water column metabolic rates. Here, for the first time, particulate carbon flux and respiratory electron transport activity ( from which metabolic CO2 production is derived), have been monitored s imultaneously for one year in the same area of the northwestern Medite rranean Sea. In the aphotic layer (200-1000 m), particulate organic ca rbon (POC) can support only 20% of the overall organic matter reminera lization. Remineralization rates are consistent with recent calculatio ns of DOC exported from the euphotic layer in this area, confirming th e vital importance of DOC in maintaining deep-water metabolism. This f inding would apply to other regions of mesotrophic and oligotrophic pr oduction and thus affect our understanding of carbon recycling in the water column, new production and O-2 utilization.