Production of nitrogen gas via anammox and denitrification in intact sediment cores along a continental shelf to slope transect in the North Atlantic

We measured the production of N(2) gas from anammox and denitrification simultaneously in intact sediment cores at six sites along a transect of the continental shelf (50 m) and deeper slope (2000 m) in the North Atlantic. Maximum rates of total N(2) production were measured on the shelf and were largely due to denitrification, with anammox contributing, on average, 33% of this production. On the continental slope, the production of N(2) gas decreased but the proportion due to anammox reached a maximum of 65%. This change in both amount and dominant pathway of N(2) production could be explained largely by the concentration of organic carbon at each site. With increasing carbon the total production of N(2) increased rapidly while the response of anammox was not significant. On the continental slope, total N(2) production fell below 2 mu mol N m(-2) h(-1) and anammox was strongly related (r = 0.95) to denitrification but the relative magnitude of anammox to denitrification (1.65 : 1) suggested that anammox could not be fuelled by NO(2)(-) from denitrification alone. On the shelf, however, where total N(2) production was predominantly greater than 2 mu mol N m(-2) h(-1), no relationship between anammox and denitrification was found and anammox remained constant at 1.4 mu mol N m(-2) h(-1). Despite the constancy and greater availability of NO(3)(-) and lower temperatures on the continental slope, the significance of anammox to the total production of N(2) appears primarily controlled by the overall rate of N(2) production.