Impact of surface ocean conditions and aerosol provenance on the dissolution of aerosol manganese, cobalt, nickel and lead in seawater

Abstract

Impact of surface ocean conditions and aerosol provenance on the dissolution of aerosol manganese, cobalt, nickel and lead in seawater Fishwick, MP Highlights  Simulated ocean warming, ocean acidification and anoxia had little impact on the dissolution of aerosol Co, Mn, Ni and Pb in surface seawater  Aerosol provenance and chemical speciation exerted the greatest control on Co and Pb dissolution, with combustion-associated processes (indicated by trace metal enrichment factors), enhancing solubility  Linear relationships between enrichment factors and fractional solubility were found, which are useful in estimating solubility of Fe, Co and Pb in global data sets  Size fractionation of seawater leaches showed that aerosol derived dissolved Pb was mostly colloidal (0.02-0.4 μm), dissolved Mn and Co were mostly soluble (< 0.02 μm), and dissolved Ni displayed a mixed size distribution Abstract Atmospheric deposition is an important pathway by which bioactive trace metals are delivered to the surface ocean. The proportions of total aerosol trace metals that dissolve in seawater, and thus become available to biota, are not well constrained and are therefore a key uncertainty when estimating atmospheric fluxes of these elements to surface waters. The aim of this study was to elucidate the main physico-chemical controls on the dissolution of the bioactive trace metals manganese (Mn), cobalt (Co), nickel (Ni) and lead (Pb). To this end, aerosol and surface seawater samples were collected in the Sargasso Sea and subsequently used in sequential seawater leach dissolution experiments to assess the role of aerosol source, seawater temperature, pH, and concentrations of dissolved oxygen and organic ligands, on aerosol trace metal dissolution. Results reveal that changes in key physico-chemical parameters in seawater leaches had little effect on the proportions of Mn, Co, Ni and Pb released from aerosols, although organic ligand amendments impacted the size distribution of aerosol-derived Mn in solution. Conversely, aerosol source and composition had the most significant effect on the dissolution of aerosol Co and Pb, with the most 'anthropogenic' aerosol samples displaying the highest fractional solubilities in seawater (up to 58% for Co and 112% for Pb).Fractional solubilities over the range of samples and conditions tested were in the range of 50-104% for Mn, 29-58% for Co, 40-85% for Ni and 67-112% for Pb.A large proportion (36-100%, median 89%) of the total dMn, dCo, dNi and dPb was mobilised rapidly during the first leaching step (5 min), with less dTM being released in leaches 2 through 4. Furthermore, investigation of the size distribution of the aerosol-derived trace metals in seawater showed that dissolved Pb was mostly colloidal (0.02-0.4 μm), dissolved Mn and Co were mostly soluble (< 0.02 μm), and dissolved Ni displayed a mixed size distribution. Good empirical relationships were observed between enrichment factors for aerosol antimony (Sb) and the fractional solubilities of aerosol Fe, Co and Pb, suggesting t...

Glacial Dust Surpasses Both Volcanic Ash and Desert Dust in Its Iron Fertilization Potential

“…Another difference is the length of contact time, as our measurements represent instantaneous solubilities of source sediments, whereas wet‐deposited aerosols over the ocean likely have experienced a great deal more processing at acidic pH during atmospheric transport (e.g., Chen and Grassian, 2013; Cwiertny et al., 2008; Duce & Tindale, 1991; Jickells et al., 2016; Solmon et al., 2009) as well as sustained contact time with seawater upon deposition. There also may be a contribution of soluble metals from combustion aerosols in open‐ocean locations (Fishwick et al., 2018; Sedwick et al., 2007; Sholkovitz et al., 2012).…”

“…Values are lower than those measured on three GEOTRACES cruises in the North Atlantic, where Cu solubility ranged from ∼1%–50%, with a median of ∼15% (Shelley et al., 2018). It is possible that these higher values reflect the input of anthropogenic aerosols (Fishwick et al., 2018; Sholkovitz et al., 2010).…”

“…Trace elements such as Cu, Cd, and lead (Pb) can be toxic to phytoplankton in high concentrations, and terrestrial aerosols are a recognized source of these metals (Echeveste et al., 2012; Paytan et al., 2009). As with Fe, the presence of anthropogenic aerosols increases the solubility of these trace metals (Fishwick et al., 2018).…”

Does Sea Surface Temperature Affect Solubility of Iron in Mineral Dust? The Gulf of California as a Case Study

“…Although there are recent estimates of FFeS (e.g., Chance et al, 2015; Fishwick et al, 2018; López‐García et al, 2017; Mackey et al, 2015; Ravelo‐Perez et al, 2016; Winton et al, 2015, 2016), their variability is as high as that of the atmospheric dust deposition values reported for the ocean. In fact, values of FFeS found in literature fall within a wide range varying from 0.001% to 95% (Baker & Croot, 2010; Jickells & Spokes, 2001; Mahowald et al, 2005; Sholkovitz et al, 2012).…”

“…In addition to the lack of consensus among experimental methodologies (Sholkovitz et al, 2012) and operational definitions of dissolved Fe (dFe; <0.2 or <0.45 μm), aqueous Fe, colloidal Fe, and particulate Fe (pFe; >0.2 or >0.45 μm) (Meskhidze et al, 2016; Raiswell & Canfield, 2012), the high variability of FFeS is also closely linked to diverse factors acting specifically on the process of solubility of Fe‐bearing dust (Fe‐dust hereafter). For example, if we consider only the geochemical characteristics, the susceptibility of iron to dissolve depends on the dust mineralogical composition (Journet et al, 2008; Shi et al, 2012); which in turn, is associated with the dust provenance (Aguilar‐Islas et al, 2010; Fishwick et al, 2018; Mahowald et al, 2018; Schroth et al, 2009; Séguret et al, 2011). Grain size, concentration, and atmospheric processing of the dust deposited are other factors involved in the process of Fe solubility in the ocean (Baker & Croot, 2010; Baker & Jickells, 2006; Bonnet & Guieu, 2004; Jickells & Spokes, 2001; Mahowald et al, 2018; Paris & Desboeufs, 2013; Shi et al, 2012, 2015).…”