Biogeochemistry of Fe and other trace elements (Al, Co, Ni) in the upper Atlantic Ocean

Iron and other trace metals (Al, Co, Ni) were measured through the upper water column during two north-south transects of the Atlantic Ocean (approximately 50°N-50°S), from the United Kingdom (UK) to the Falkland Islands (September/October 1996) and from South Africa to the UK (May/June 1998). Total dissolvable iron (TD-Fe) concentrations in the surface layers (<200 m) of the open Atlantic Ocean averaged 0.95±0.67 nM (n = 142) during the 1996 cruise and 1.08±0.59 nM (n = 160) during the 1998 cruise, with increased values in shelf waters at both extremes of the transects. Iron enrichments, fingerprinted via correlation with other trace metals, macronutrients and hydrography, correlated well with dry aerosol deposition off the west African continent and wet deposition in the Inter-Tropical Convergence Zone (ITCZ), with levels > 2.2 nM observed in surface waters in these regions. Benthic fluxes provided a significant amount of Fe (2-38 nM) to the base of the water column in Coastal zones. In addition, samples collected from one Atlantic Meridional Transect (AMT) expedition were re-analysed after a 16 month acidification period and showed significant increases over shipboard analyses (average values increasing to 2.26±1.50nM), indicating the extended release of Fe from leachable particulate material in the stored samples. Detailed profiling through the euphotic zone revealed TD-Fe distributions that exhibited strong relationships with biological uptake, regeneration and water column hydrography. In equatorial and tropical North Atlantic waters, trace elemental distributions showed evidence of recent atmospheric deposition through a history of stratified mixed layers. © 2002 Elsevier Science Ltd. All rights reserved.