Modeling the dynamics and export of dissolved organic matter in the Northeastern U.S. continental shelf

Abstract

Continental shelves are believed to play a major role in carbon cycling due to their high productivity. To improve our understanding of carbon dynamics on continental margins, a dissolved organic matter (DOM) model was developed and imbedded within an existing coupled ocean circulation-biogeochemical model of the U.S. East coast. A model simulation with the DOM module was compared with the reference model (without the DOM module) to illustrate the role of DOM dynamics in coastal ocean biogeochemical cycling. Model results reveal that the progressive release of dissolved organic nitrogen (DON) in the ocean’s upper layer during summer increases the regenerated primary production by 30–300%, which, in turn, enhances the dissolved organic carbon (DOC) production mainly from phytoplankton exudation in the upper layer and solubilization of particulate organic matter (POM) deeper in the water column. This analysis suggests that DOM is a necessary component for representing ecosystem functioning and organic fluxes in models because DOM (1) is a major organic pool directly related to primary production, (2) decouples partially the carbon and nitrogen cycles (through carbon excess uptake, POM solubilization and DOM mineralization) and (3) is intimately linked to the residence time of water masses for its distribution and export. The seasonally produced DOC on the shelf can be exported to the open ocean by horizontal transport at comparable rates (1–2 mol C m −2 yr −1) to particulate organic carbon burial in the southern U.S. Mid-Atlantic Bight (MAB).