Spatial variability of particle associated trace elements in near-surface waters of the North Atlantic (30°N/60°W to 60°N/2°W), derived by large volume sampling

Abstract

On a transect between the northwest and northeast Atlantic Ocean (30°N/60°W to 60°N/2°W) suspended particulate material (SPM) in 24 near-surface water samples (4–22 m 3 ) was collected by using a large volume centrifuge system. The samples were analysed for Al, Cd, Co, Cu, Fe, Mn, Ni, Pb, Ti, Zn, POC/PON, Opal and CaCO 3 . The SPM concentrations varied between 32 and 447 mg m −3 , with two maxima in the open ocean. Its composition was mainly controlled by biological production, the different water masses of the North Atlantic current system, and by the atmospheric dust deposition, particularly in the trade wind area off Africa. The average bulk composition of the collected material (on the dry weight basis) consisted of 33±4% POC, 14.3±7.9% CaCO 3 and 4.4±2.7% Opal. In two-thirds of the samples, the lithogenic fraction was found to be <5%. The average (±1 standard deviation) trace element concentrations (with one shelf sample excluded) were 3.9±4.0 for Al, 1.0±1.4 Fe, 0.07±0.04 Mn, 0.10±0.11 Ti (nmol l −1 ), and 17.6±15.2 for Cd, 8.1±4.6 Co, 130±240 Cu, 35±27 Ni, 5.1±8.8 Pb and 63±49 Zn (pmol l −1 ). The trace element contents of selected `biogenic samples' (numbers 15–23) are in good agreement with data of open-ocean plankton . For this data set, an approximate Redfield-type composition of C:N: P :Fe:Zn,Mn:Ni:Cd:Cu:Co:Pb=180:23: 1 :0.005:0.002:0.001:0.0005:0.0004:0.0002:0.00004 was estimated. We found the molar Fe:C ratio of 2.6×10 −5 in our `biogenic samples' close to reported mean physiological Fe requirement of plankton organisms. From our findings, however, it cannot be decided if Fe is a limiting element in the study area or not.