Most of the organic matter produced in the surface ocean by photoautotrophs is grazed by zooplankton and recycled quickly within the upper ocean by heterotrophic microbes. The small fraction of organic matter that escapes recycling accumulates in the ocean in the dissolved phase. In terms of carbon, the oceanic inventory of the dissolved organic carbon (DOC) has been previously estimated to be 662-700 PgC (Hansell et al., 2009;Hedges, 1992). Previous estimates of the global ocean DOC export production have employed ocean models and range from roughly 20% (Hansell et al., 2009) to 27% (Yamanaka & Tajika, 1997 of the global ocean carbon export production. The potential importance of marine DOC to global climate is indicated by the fact that the marine DOC inventory rivals the atmospheric carbon inventory. Also, carbon export is a key driver of atmospheric pCO 2 . Indeed, some paleoclimate events have been attributed to changes in the marine DOC cycle (Sexton et al., 2011).The marine DOC cycle has been studied for decades, and as yet, our understanding of DOC dynamics is incomplete. DOC is a complex mixture of thousands of compounds that are chemically and structurally diverse and thus poorly characterized (e.g., Hedges et al., 2000;Hertkorn et al., 2006). Radiocarbon ( 14 C) measurements of deep ocean DOC samples indicate ages as old as 6,000 years (Williams & Druffel, 1987). Thus, accumulated DOC has somehow survived global ocean overturning multiple times.There are also aspects of the global distribution of DOC that remain unexplained. Measurements indicate that DOC in the open ocean exists at very low concentrations, typically in the range of 35-80 μmol kg −1 (Figure 1). The concentration is relatively high and variable near the surface and lower and more uniform at depth. It is typically 65-80 μmol kg −1 in the stratified, warm waters of the tropical and subtropical regions. In the subpolar surface waters, where vertical mixing is strong, the DOC concentration is lower and approaches the deep ocean values of 35∼40 μmol kg −1 . The deep ocean DOC concentration was once thought to be uniform (Martin & Fitzwater, 1992), but as Hansell and Carlson (1998) first reported, there is a modest concentration gradient representing a decrease along the path of the meridional overturning circulation from the North Atlantic to the North Pacific by approximately 14 μmol kg −1 . The surface distribution as well as the deep ocean gradient are not well explained in terms of sources and sinks of DOC. In particular, the DOC sinks (e.g., photodegradation, hydrothermal vents) and their rates are poorly understood (Lang et al., 2006;Mopper et al., 1991). In one case, a DOC
