NSF Award Abstract - #0223509

AWSFL008-DS3

Coastal Zone Control of Interacting C-N-P Cycles Under Global Change

Abstract

Abstract

The area of the global coastal zone, approximated by the continental shelves, is about 7% of the surface area of the ocean, and its volume is about 9% of the volume of the surface ocean layer (3 x 10 km). Despite its relatively small size, up to 20% of total oceanic biological production occurs there, at least 80% of the mass of terrigenous materials reaching the ocean is deposited there, and 30 to 50% of total carbonate and 80% of total organic carbon accumulation in the ocean occur in the coastal zone. In addition, coastal zone environments are being heavily impacted, disproportionately more than the much larger area of the open ocean, by modifications of the biogeochemical dynamics and cycles of carbon (C), nitrogen (N), and phosphorus (P), three of six of the major life-essential elements (the other three being sulfur, oxygen, and hydrogen). The coastal zone is strongly affected by the environmental biogeochemical changes occurring in its neighboring domains of land, ocean, sediments, and atmosphere. Because of both climatic change and human-induced forcings on the environment, it is this region of the ocean that is most susceptible to anthropogenic fluxes of materials and changes in water quality, organic productivity, and biodiversity. Until very recently, little attention has been paid to the coastal zone on a global scale and its role in the global C-N-P biogeochemical cycles that are important to life on land and in the oceans. In this proposal we address a fundamental scientific problem that is also of substantial concern to the human society: the recent past, present, and near future behavior of the coupled C-N-P biogeochemical cycles in the coastal marine zone that are influenced by climatic change and human activities. The time scale of our research is decades to centuries, including the past 300 years of increasing human perturbations and about a century of the future, as based on current projections of the magnitudes of the perturbations. To accomplish our goals, we employ a modeling methodology developed by us under previous NSF support to analyze environmental change in the global system of four do-mains: land, ocean, sediments, and atmosphere. We deal with the following research issues: (a) the changing roles of nutrient N and P fluxes to the coastal zone from land and from the open ocean as drivers of organic productivity and the carbon cycle in general; (b) the changing state of organic carbon metabolism in the coastal zone, and the release or uptake of atmospheric carbon dioxide by coastal waters, as controlled by the production and storage of organic and inorganic carbon (CaCO3 ) in the coastal zone; (c) the effect of rising atmospheric CO2 concentrations on the organic and inor-ganic C-N-P cycles in the coastal zone, and (d) the effects of possible changes in the thermohaline circulation of the ocean and in coastal oceanic circulation (upwelling and onwelling) on the C-N-P cycles in the coastal margin and their linkages to the land, atmosphere, sediments, and open ocean. We expect our results to show to what extent the coupling between the C-N-P cycles and increased nutrient inputs from changes in the land domain have been responsible for the biogeochemical dynamics of the coastal zone from the recent past to the present. We also expect our results to show that the projected trends of environmental change on land, changes in the magnitude of thermohaline circulation and coastal upwelling, and global climate are likely to make the coastal zone a more active and quantitatively important site in the transfer of materials between it and the domains of land, atmosphere, and sediments and sub-domain of open ocean in the future. This tentative conclusion has important implications to the biogeochemical state of the coastal zone relative to the human population that depends on it.