Nitrogen and phosphorus budgets of the North Atlantic Ocean and its watershed |
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Authors: | J N Galloway R W Howarth A F Michaels S W Nixon J M Prospero F J Dentener |
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Institution: | (1) Environmental Sciences, University of Virginia, Charlottesville, VA 22903, USA;(2) Ecology and Systematics, Cornell University, Ithaca, NY 14853, USA;(3) Bermuda Biological Station for Research, St. Georges, GE-01 Bermuda;(4) Graduate School of Oceanography, University of Rhode Island, Naragansett, RI 02882, USA;(5) RSMAS, University of Miami, Miami, FL 33149, USA;(6) Department of Airquality, Wageningen, NL 6700 EV Wageningen, The Netherlands |
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Abstract: | Anthropogenic food and energy production extensively mobilize reactive nitrogen (N) in the watershed of the North Atlantic Ocean (NAO). There is wide spread N distribution by both hydrologic and atmospheric processes within the watershed of the NAO, resulting in reactive N accumulation in terrestrial systems. Net denitrification in most estuaries and continental shelves exceeds the amount of N supplied to the shelves by rivers and requires a supply of nitrate from the open ocean. Thus riverine N is only transported to the open ocean in a few areas with the flow from a few major rivers (e.g., Amazon). Atmospheric N deposition to the open ocean has increased and may increase the productivity of the surface ocean. In addition, as a consequence of increased Fe deposition to the open ocean (due in part to anthropogenic processes), the rate of biological N-fixation may have increased resulting in N accumulation in the ocean. Phosphorus (P) is also mobilized by anthropogenic processes (primarily food production). Relative to N, more of the P is transported across the shelf to the open ocean from both estuaries and major rivers. There are several consequences of the increased availability of N and P that are unique to each element. However, the control on primary productivity in both coastal and open ocean ecosystems is dependent on a complex and poorly understood interaction between N and P mobilization and availability. |
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