Benthic denitrification and nitrogen cycling at the slope and rise of the NW European Continental Margin (Goban Spur)

The rate of benthic denitrification in slope and rise sediments of a transe ct across the N.W. European Continental Margin (Goban Spur) was evaluated f rom 31 pore water nitrate profiles obtained during six cruises between May and October. All profiles had well separated zones of nitrification and den itrification. High near-surface nitrate concentrations prevented the influx of nitrate from the bottom water. The denitrification rates obtained from steady-state-modelling ranged from 0.13 to 2.56 mu mol N cm(-2) y(-1) and s howed an exponential increase both with decreasing water depth and with inc reasing rate of organic carbon degradation. Denitrification rates in a near by canyon, which did not follow these relationships, were estimated to be m uch higher as a result of erosion and redistribution of organic matter. Den itrification at the Goban Spur slope and rise is much lower than previously reported for similar environments in the Pacific resulting predominantly f rom the different oxygen and nitrate concentrations in the bottom water. A weighted average for the whole slope and rise sediment system shows that 17 % of the particulate organic nitrogen input (8.93 mu mol N cm(-2) y(-1)) is denitrified and only 1% is buried, the rest being released as nitrate. Alt hough being ten times higher compared with basin sediments, denitrification on the slope and rise is several times lower than on the adjacent shelf. ( C) 1998 Elsevier Science Ltd. All rights reserved.