The behaviour of dissolved Cd, Co, Zn, and Pb in North Atlantic near-surface waters (30 degrees N/60 degrees W-60 degrees N/2 degrees W)

In September 1993 (M26) and June/July 1996 (M36), a total of 239 surface sa mples (7 m depth) were collected on two transects across the open Atlantic Ocean (224 samples) and northwest European shelf edge area. We present an o verview of the horizontal variability of dissolved Cd, Co, Zn, and Pb in be tween the northwest and northeast Atlantic Ocean in relation to salinity an d the nutrients. Our data show a preferential incorporation of Cd relative to P in the particulate material of the surface ocean when related to previ ously published parallel measurements on suspended particulate matter from the same cruise. There is a good agreement with results recently estimated from a model by Elderfield and Rickaby (Nature 405 (2000) 305), who predict for the North Atlantic Ocean a best fit for alpha (Cd/P) = [Cd/P](POM)/[Cd /P](SW) of 2.5, whereas the approach of our transect shows a alpha (Cd/P) v alue of 2.6. The Co concentrations of our transects varied from < 5 to 131 pmol kg(-1), with the lowest values in the subtropical gyre. There were pro nounced elevations in the low-salinity ranges of the northwest Atlantic and towards the European shelf. The Co data are decoupled from the Mn distribu tion and support the hypothesis of marginal inputs as the dominant source. Zinc varied from a minimum of <0.07 nmol kg(-1) to a maximum of 1.2 and 4.8 nmol kg-1 in regions influenced by Labrador shelf or European coastal wate rs, respectively. In subtropical and northeast Atlantic waters, the average Zn concentration was 0.16 nmol kg(-1). Zinc concentrations at nearly three quarters of the stations between 40 degreesN and 60 degreesN were <0.1 nmo l kg(-1). This suggests that biological factors control Zn concentrations i n large areas of the North Atlantic surface waters. The Pb data indicated t hat significant differences in concentration between the northwest and nort heast Atlantic surface waters presently (1996) do not exist for this metal. The transects in 1993 and 1996 exhibited Pb concentrations in the northeas t Atlantic surface waters of 30 to 40 pmol kg(-1) about a fifth to a quarte r of the concentrations observed in 1981. This decline is supported by our particle flux measurements in deep waters of the same region. (C) 2001 Else vier Science Ltd. All rights reserved.