NITROGEN AND PHOSPHORUS BUDGETS OF THE NORTH-ATLANTIC OCEAN AND ITS WATERSHED

Anthropogenic food and energy production extensively mobilize reactive nitrogen (N) in the watershed of the North Atlantic Ocean (NAO). Ther e is wide spread N distribution by both hydrologic and atmospheric pro cesses within the watershed of the NAO, resulting in reactive N accumu lation in terrestrial systems. Net denitrification in most estuaries a nd 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 t he flow from a few major rivers (e.g., Amazon). Atmospheric N depositi on to the open ocean has increased and may increase the productivity o f the surface ocean. In addition, as a consequence of increased Fe dep osition to the open ocean (due in part to anthropogenic processes), th e rate of biological N-fixation may have increased resulting in N accu mulation in the ocean. Phosphorus (P) is also mobilized by anthropogen ic 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 ava ilability of N and P that are unique to each element. However, the con trol 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.