Abstract
Total and soluble trace metal concentrations were determined in atmospheric aerosol and rainwater samples collected during seven cruises in the south-east Atlantic. Back trajectories indicated that the samples all represented remote marine air masses, consistent with climatological expectations. Aerosol trace metal loadings were similar to previous measurements in clean, marine air masses. Median total Fe, Al, Mn, V, Co and Zn concentrations were 206, 346, 5, 3, 0.7 and 11pmolm−3 respectively. Solubility was operationally defined as the fraction extractable using a pH4.7 ammonium acetate leach. Median soluble Fe, Al, Mn, V, Co, Zn, Cu, Ni, Cd and Pb concentrations were 6, 55, 1, 0.7, 0.06, 24, 2, 1, 0.05 and 0.3pmolm−3 respectively. Large ranges in fractional solubility were observed for all elements except Co; median solubility values for Fe, Al and Mn were below 20% while the median for Zn was 74%. Volume weighted mean rainwater concentrations were 704, 792, 32, 10, 3, 686, 25, 0.02, 0.3 and 10nmolL−1 for Fe, Al, Mn, V, Co, Zn, Cu, Ni, Cd and Pb respectively (n=6). Wet deposition fluxes calculated from these values suggest that rain makes a significant contribution to total deposition in the study area for all elements except perhaps Ni.
Highlights
The transport and deposition of atmospheric aerosol is a significant source of trace metals to the surface ocean (Jickells et al, 2005) and, in large areas of the open ocean, may represent the dominant supply route for certain elements (Ussher et al, 2013)
Aerosol and rain trace metal concentrations have been measured in remote marine air masses over the south-east Atlantic Ocean
Total and soluble Fe, Al, Mn and V concentrations were typically similar to those reported previously for comparable air mass types, being low compared to measurements made in the Saharan dust outflow and polluted northern hemisphere (Sections 3.2 and 3.3)
Summary
The transport and deposition of atmospheric aerosol is a significant source of trace metals to the surface ocean (Jickells et al, 2005) and, in large areas of the open ocean, may represent the dominant supply route for certain elements (Ussher et al, 2013). In addition to direct impacts on phytoplankton growth, micronutrient availability may influence functioning of the marine ecosystem via indirect mechanisms, via impacts on nitrogen fixation (Moore et al, 2009, 2013). Another example of an indirect impact is the use of Co by marine prokaryotes in the synthesis of vitamin B12, an exogenous supply of which is required by eukaryotic phytoplankton (Panzeca et al, 2008). Some trace elements present in atmospheric deposition, for example Cu, can be toxic to marine organisms (Paytan et al, 2009; Jordi et al, 2012)
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