Atmospheric Deposition Fluxes over the Atlantic Ocean: a GEOTRACES Case Study

15 Atmospheric deposition is an important source of micronutrients to the ocean, but atmospheric deposition fluxes remain poorly constrained in most ocean regions due to the limited number of field observations of wet and dry atmospheric inputs. Here we present the distribution of dissolved aluminium (dAl), as a tracer of atmospheric inputs, in surface waters of the Atlantic Ocean along GEOTRACES sections GA01, GA06, GA08, and GA10. We used the surface mixed layer concentrations of dAl to calculate atmospheric deposition fluxes using a simple steady state model. We have optimized the 20 Al fractional aerosol solubility, dAl residence time within the surface mixed layer and depth of the surface mixed layer for each separate cruise to calculate the atmospheric deposition fluxes. We calculated the lowest deposition fluxes of 0.15 ± 0.1 and 0.27 ± 0.13 g m -2 yr -1 for the South and North Atlantic Ocean (> 40°S and > 40°N), respectively, and highest fluxes of 2.67 ± 1.96 and 3.82 ± 2.72 g m -2 yr -1 for the South East Atlantic and tropical Atlantic Ocean, respectively. Overall, our estimations are comparable to atmospheric dust deposition model estimates and reported field-based atmospheric deposition 25 estimates. We note that our estimates diverge from atmospheric dust deposition model flux estimates in regions influenced by riverine Al inputs and in upwelling regions. As dAl is a key trace element in the GEOTRACES Programme, the approach presented in this study allows calculations of atmospheric deposition fluxes at high spatial resolution for remote ocean regions. . 30 Biogeosciences Discuss., https://doi.org/10.5194/bg-2018-209 Manuscript under review for journal Biogeosciences Discussion started: 7 May 2018 c © Author(s) 2018. CC BY 4.0 License.