Organic matter in the ocean

Organic matter stores and transfers carbon across the ocean's surface, interior, and sediments, and these processes play a major role in regulating atmospheric CO2 concentrations and governing ecosystem dynamics. Understanding the composition of this carbon is ultimately necessary to determine its sources, transformations, removal, and ecological impacts. This chapter summarizes our current understanding of how the composition (molecular and isotopic) of organic matter relates to its inventory, transformations, and fluxes throughout the ocean as well as the role of organic matter in linking marine ecology, carbon, nutrient, and metal cycling. The present estimates of the inventory of major carbon reservoirs are first discussed along with the major fluxes within and between reservoirs. We then discuss the state of understanding regarding the composition of organic matter, including forms of organic carbon as well as the incorporation of other elements such as nitrogen, phosphorus, sulfur, metals, and halogens which act as important organo-nutrient reservoirs. We present the readers with intriguing new biogeochemical mechanisms that have important implications for organic matter composition and recycling. Finally, we conclude by discussing the predicted changes of organic matter in response to global climate change.