A balanced nitrogen budget of the surface layer of the southern Ross Sea, Antarctica

To understand marine biogeochemical cycles, it is critical to quantitativel y balance organic matter transformations within the euphotic zone. Such an assessment for nitrogen is difficult because of lateral advection, uncertai nties in individual measurements, the complexity of elemental transformatio ns (including nitrification and denitrification), and the difficulty of col lecting data on appropriate space and time scales. Two cruises were conduct ed to the southern Ross Sea, Antarctica, to understand the time-varying flu xes of nitrogen into its various pools. From these data a balanced inventor y was constructed. Nitrate removal in the upper 200 m was balanced by parti culate and dissolved organic nitrogen production, ammonification, and verti cal flux. In austral spring nearly all (92%) of the new production remained as particulate nitrogen, but this percentage decreased markedly (52%) by m id-summer, when nitrogen regeneration, PN flux, and DON production were 23, 13 and 12% of net production, respectively. The organic matter budget in t his coastal Antarctic site is dominated by particle transformations.