Abstract
Oceanic dissolved organic carbon (DOC) is, at 662 ± 32 petagrams of carbon (Pg C), one of Earth's major, exchangeable carbon reservoirs. With its large inventory and biologic turnover, the pool has been invoked as a principal source/sink of atmospheric CO
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driving paleoclimate variations. Controls on past source/sink functions remain unknown, but insights can be gleaned from the modern ocean. Here, we find that new nutrients introduced to the euphotic zone exert a fundamental and predictable control on the net production of DOC, in turn playing a large part in determining the surface distribution and concentrations of the pool. Climate-driven changes in surface ocean renewal of nutrients will ultimately control the source term, dictating the inventory of carbon residing in marine DOC.
The inventories of carbon residing in organic matter dissolved in the ocean [dissolved organic carbon (DOC)] and in the atmosphere as CO
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are of the same order of magnitude, such that small changes in the DOC pool could have important consequences in atmospheric carbon and thus climate. DOC in the global ocean is largely formed in the sunlit euphotic zone, but identifying predictable controls on that production is an important yet unrealized goal. Here, we use a testable and causative correlation between the net production of DOC and the consumption of new nutrients in the euphotic zone of the Atlantic Ocean. We demonstrate that new nutrients introduced to the euphotic zone by upwelling in divergence zones and by winter convective overturn of the water column, and the primary production associated with those nutrients, are the ultimate driver of DOC distributions across the Atlantic basins. As new nutrient input will change with a changing climate, the role of DOC in the ocean’s biological pump should likewise be impacted.
