Hydrography and local sources of dissolved trace metals Mn, Ni, Cu, and Cd in the northeast Atlantic Ocean

Vertical profiles of dissolved Ni and Cd in the northeast Atlantic Ocean are dominated by conservative mixing of North Atlantic Deep Water and Antarctic Bottom Water. Local regenerative input of Ni and Cd is restricted to thermocline waters. In deep waters Cu is affected by mixing of water masses, but input from the sediment is also important. The North Atlantic Deep Water (NADW) contains 3.5-4.0 nM Ni, 1.2-2.0 nM Cu, 200-240 pM Cd and has a Cd/PO4 ratio of 180-220 pmol/mu mol. The bottom waters (Lower Deep Water, LDW) are a mixture of 69% NADW and 31% Antarctic Bottom Water (AABW). The LDW contains 4.9 +/- 0.6 nM Ni, 2.47 +/- 0.56 nM Cu, 315 +/- 30 pM Cd and has a Cd/PO4 ratio of 216 +/- 0.14 pmol/mu mol. For Cd and Ni the bottom water (LDW) values are consistent with conservative mixing of NADW and AABW, for Cu an excess is ascribed to additional benthic input. Local sources and sinks dominate the dissolved Mn distribution. The deep water concentration of Mn varies between 0.2 and 0.5 nM and is not related to the presence of watermasses. (C) 1997 Elsevier Science B.V.