Abstract
The importance of the atmospheric deposition of biologically essential trace elements, especially iron, is widely recognized, as are the difficulties of accurately quantifying the rates of trace element wet and dry deposition and their fractional solubility. This paper summarizes some of the recent progress in this field, particularly that driven by the GEOTRACES, and other, international research programmes. The utility and limitations of models used to estimate atmospheric deposition flux, for example, from the surface ocean distribution of tracers such as dissolved aluminium, are discussed and a relatively new technique for quantifying atmospheric deposition using the short-lived radionuclide beryllium-7 is highlighted. It is proposed that this field will advance more rapidly by using a multi-tracer approach, and that aerosol deposition models should be ground-truthed against observed aerosol concentration data. It is also important to improve our understanding of the mechanisms and rates that control the fractional solubility of these tracers. Aerosol provenance and chemistry (humidity, acidity and organic ligand characteristics) play important roles in governing tracer solubility. Many of these factors are likely to be influenced by changes in atmospheric composition in the future. Intercalibration exercises for aerosol chemistry and fractional solubility are an essential component of the GEOTRACES programme.This article is part of the themed issue ‘Biological and climatic impacts of ocean trace element chemistry’.
Highlights
A great deal of research activity has focused on addition of material to the ocean across the air–sea interface, because the realizations that iron (Fe) plays a key role as a limiting nutrient for primary productivity or biological nitrogen fixation in large areas of the global ocean [1,2,3] and that the deposition of mineral dust from the atmosphere was a major source of Fe to the remote ocean [4]
This paper aims to highlight recent progress in this field, with a focus on research driven by the international GEOTRACES programme, and identify topics for which further effort is still required
The extent to which anthropogenic emissions contribute to the atmospheric flux to the oceans and their biogeochemical response to that flux is of increasing interest
Summary
A great deal of research activity has focused on addition of material to the ocean across the air–sea interface, because the realizations that iron (Fe) plays a key role as a limiting nutrient for primary productivity or biological nitrogen fixation in large areas of the global ocean [1,2,3] and that the deposition of mineral dust from the atmosphere was a major source of Fe to the remote ocean [4]. This intercomparison demonstrates very dramatically how different methods for measuring aerosol TEI solubility have a significant influence on the dust flux estimates. These bulk deposition velocities from a given region of the ocean can be used to estimate the flux of any other aerosol component, despite the complication that larger mineral dust aerosols may have higher dry deposition velocities and lower rainfall scavenging ratios.
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