Trace element concentrations, elemental ratios, and enrichment factors observed in aerosol samples collected during the US GEOTRACES eastern Pacific Ocean transect (GP16)

Abstract

Atmospheric deposition is an important source of bioactive trace elements to the open ocean, but observations of this flux are sparse. Atmospheric deposition of aerosol iron is of particular interest as it can play an important role in supporting primary production in the global ocean, yet it represents a key uncertainty that hampers accurate numerical modeling of the marine iron cycle. We report concentrations of atmospheric trace elements from samples collected as part of the 2013 US GEOTRACES GP16 zonal transect of the eastern Pacific Ocean. The cruise transected a relatively dusty region which coincided with the Peruvian upwelling zone before entering the much less dusty region of the subtropical gyre. The aerosol chemical composition and elemental ratios indicate crustal sources for Al, Ti, V, Mn, and Fe while the analyses suggest that Cu, Cd, and Pb originate from anthropogenic emissions.Dry deposition fluxes were calculated by applying characteristic deposition velocities based on the expected particle size associated with each element. Bulk deposition, which includes wet and dry deposition, was calculated using the inventory of 7Be in the upper water column. Soluble aerosol iron flux estimates were compared with vertical iron fluxes within the water column to assess the relative importance of atmospheric deposition to the marine iron cycle in the region. Atmospheric deposition was insignificant relative to the upwelling input of iron in the areas near the continental sources but increased in relative importance seaward of the coastal upwelling zone even as the magnitude of deposition decreased away from the coast.This article is part of a special issue entitled: “Cycles of trace elements and isotopes in the ocean – GEOTRACES and beyond” - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. González.