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Atmospheric deposition represents a major input for micronutrient trace elements (TEs) to the surface ocean and is often quantified indirectly through measurements of aerosol TE concentrations. Sea spray aerosol (SSA) dominates aerosol mass concentration over much of the global ocean, but few studies have assessed its contribution to aerosol TE loading, which could result in overestimates of "new" TE inputs. Low‐mineral aerosol concentrations measured during the U.S. GEOTRACES Pacific Meridional Transect (GP15; 152°W, 56°N to 20°S), along with concurrent towfish sampling of surface seawater, provided an opportunity to investigate this aspect of TE biogeochemical cycling. Central Pacific Ocean surface seawater Al, V, Mn, Fe, Co, Ni, Cu, Zn, and Pb concentrations were combined with aerosol Na data to calculate a "recycled" SSA contribution to aerosol TE loading. Only vanadium was calculated to have a SSA contribution averaging >1% along the transect (mean of 1.5%). We derive scaling factors from previous studies on TE enrichments in the sea surface microlayer and in freshly produced SSA to assess the broader potential for SSA contributions to aerosol TE loading. Maximum applied scaling factors suggest that SSA could contribute significantly to the aerosol loading of some elements (notably V, Cu, and Pb), while for others (e.g., Fe and Al), SSA contributions largely remained <1%. Our study highlights that a lack of focused measurements of TEs in SSA limits our ability to quantify this component of marine aerosol loading and the associated potential for overestimating new TE inputs from atmospheric deposition. Plain Language Summary: Sea spray aerosol (SSA) generated by breaking waves and bursting bubbles can dominate the particle population in the marine atmosphere. We investigated whether this mechanism could mobilize significant amounts of trace elements (TEs)—nutrient and pollutant elements present in the surface ocean in very low concentrations. Previous studies have suggested that TEs could become enriched on SSA during its formation, relative to their concentrations in seawater, and this could make the process a more significant source for aerosol concentrations of some elements. But for others, the SSA contribution is always likely to be insignificant. Our calculations based on sea salt and TE aerosol concentrations in the atmosphere and dissolved TEs in the surface ocean suggest that SSA does not contribute significantly to total aerosol TE loading, with the possible exception of vanadium, which has relatively higher concentrations in seawater than the other elements considered. This study highlights that this process remains poorly quantified due to limited direct measurements. Key Points: Sea spray aerosol (SSA) concentration was quantified along a meridional Pacific Ocean transect during low mineral aerosol conditionsSea spray‐derived aerosol trace elements (TEs) are negligible unless significant enrichment occurs during formation; only vanadium is >1%SSA contributions to aerosol TEs of >100% calculated by applying enrichments from earlier studies suggests these are not widely applicable [ABSTRACT FROM AUTHOR]

Samples for organic copper (Cu)-binding ligand characterization were collected along the 2013 U.S. GEOTRACES Pacific (GP16) cruise transect from Peru to Tahiti. Full depth profiles of Cu speciation were collected across a dynamic range in oceanographic conditions including a highly productive coastal region, an oxygen deficient zone, a high nutrient low chlorophyll (HNLC) region, an oligotrophic region and a hydrothermal vent plume. Surface waters from Peru to Tahiti exhibited elevated dissolved Cu and ligand concentrations near Peru and then decreased in concentration (< 1 nM) offshore toward the oligotrophic waters. There was also an apparent shelf sediment source of strong Cu-binding ligands near the coast of Peru. Throughout most of the transect dissolved Cu and ligand concentrations were lower in the upper waters and increased with depth, with the highest concentrations near the ocean bottom. The hydrothermal vent sampled during the cruise did not seem to be a source for dissolved Cu but there was a slight elevation of Cu-binding ligands at the vent site. Similar vertical patterns in Cu-binding ligands were seen in both the GP16 dataset and the North Atlantic GEOTRACES (GA03) cruise, with notable differences in deep waters of the Pacific. The older water masses of the Pacific were highlighted by higher concentrations of dissolved Cu, Cu-binding ligands, and the free Cu ion (Cu2+) relative to the deep Atlantic. Excess Cu ligands in both GP16 and GA03 point to a possible fraction of Cu accumulating in the deep Pacific that is inert to ligand exchange, suggesting older waters might contain a high fraction of unreactive Cu. • Strong copper-binding ligands detected near the shelf of Peru. • Offshore oligotrophic waters found to have lowest dissolved copper and copper-binding ligand concentrations • Comparison of copper speciation data between the Atlantic (GA03) and Pacific (GP16) U.S. GEOTRACES transects • Evidence for exchange-inert dissolved copper fraction accumulating in older Pacific deep waters [ABSTRACT FROM AUTHOR]

Most of the lead (Pb) in today's ocean is from human activities, although natural sources contribute small amounts of Pb that are usually masked by massive anthropogenic emissions. In the U.S. GEOTRACES East Pacific Section (GP16), anthropogenic Pb is observed throughout the water column, and as seen elsewhere in the Pacific, Pb concentrations are highest in the upper hundreds of meters of the ocean and generally decrease with depth. Thermocline Pb concentrations are higher in the eastern portion of the section near the South American coast, decreasing with distance from the South American continent, as previously reported for redox sensitive trace elements (e.g., Mn). High precision Pb isotope ratios show that there has been a change over the past few decades in the source of Pb in the westernmost upper waters, shifting from an American-Australian type Pb intermixture to a Chinese-American-type Pb intermixture. Although it is known from the study of hydrothermal solutions and sediments that there is a large primary Pb flux from high temperature ridge crest hydrothermal springs, most of this Pb precipitates near the hydrothermal vents and very little escapes into the open water column. In fact, hydrothermal ferromanganese oxyhydroxides precipitated from the hot spring emissions strip anthropogenic Pb out of the water column, resulting in the lowest Pb concentrations ever observed in the ocean (a few tenths of a picomole/kg) in the high 3He-plume to the west of the East Pacific Rise. Deeper waters have similarly low Pb concentrations, probably as a result of the sinking veil of hydrothermal-source ferromanganese oxyhydroxides. Core top sediments from this section and previous work show clear evidence of less-radiogenic Mid Ocean Ridge Basalt (MORB) Pb distinct from the crustal and anthropogenic Pb seen in non-ridge crest sediments, specifically, low values of 206Pb/207Pb (1.189), 208Pb/207Pb (2.449), and 206Pb/204Pb (18.42), compared to ~1.195, ~2.475, and ~ 18.75 respectively for the non- hydrothermal sediments. Near bottom dissolved (<0.2 μm filter) water column Pb (with concentrations <2 pmol kg−1) at the ridge crest and in the near-downstream neutrally-buoyant hydrothermal plume show 206Pb/207Pb - 208Pb/206Pb trends that are lower than observed throughout the rest of the water column and fall within the mixing end- member isotope ratios of less radiogenic MORB and more radiogenic anthropogenic Pb sources. Thus there is a very small leakage (~1%) of primary high temperature hydrothermal Pb into the water column. But at the westernmost station (36), which shows a diluted continuation of the 3He, manganese (Mn), and iron (Fe) plume from 2200 to 2700 m, the >2200 m Pb isotope ratios deeper than 2000 m return to the non-hydrothermal ratios with no remaining detectable MORB. • In GT Section GP16, anthropogenic Pb is observed throughout the water column, as seen throughout the Pacific. • Pb isotope ratios show a recent change in the source of Pb in the westernmost upper waters. • Hydrothermal FeMn oxyhydroxides strip anthropogenic Pb and most hydrothermal Pb emissions out of the water column. • There is a very small (~1%) leakage of primary high temperature hydrothermal MORB-derived Pb into the water column. [ABSTRACT FROM AUTHOR]

Trace element (TE) fluxes and their residence times (Fe, Mn, Cu, Pb, Cd, and V) within the surface ocean were determined along the GEOTRACES East Pacific Zonal Transect (GP16/EPZT) and found to reflect the diverse physical and geochemical conditions encountered across the track. The TE flux from atmospheric deposition, vertical mixing, and upwelling into the mixed layer and into the particle production zone (PPZ) along the GEOTRACES EPZT transect were evaluated with 7Be-based methods developed in earlier works. A horizontal input flux is driven from east to west by the South Equatorial Current (SEC), and estimated advection velocities were applied to horizontal gradients in the distributions of several TEs to approximate this term. There is a minimum in atmospheric deposition in the central gyre, with higher fluxes to the east due to large near-shore aerosol TE loadings, and higher to the west due to greater precipitation-driven deposition velocities (V b). The 7Be-derived vertical diffusion (K z) values range from 2.5 to 39 m2/d (0.29 × 10−4 to 4.5 × 10−4 m2/s) with higher values generally within the nearshore upwelling region and the lowest values within the stratified central gyre. Manganese displayed a well-defined gradient extending from the nearshore stations into the central gyre such that the advective term is a major component of the total input flux, particularly within the central gyre. Relative to other inputs the atmospheric input of soluble Mn is only of minor importance. Unlike Mn, there is no discernable horizontal gradient in the dissolved Fe data and therefore, there is no horizontal component of flux. Nearshore removal processes are more intense for dissolved Fe than for dissolved Mn and as a result, dissolved Mn remains elevated much farther offshore than does dissolved Fe. For the stratified mid-ocean gyre stations, the total input of Fe from all sources is relatively small compared to the inshore stations, and atmospheric deposition becomes the dominant mode of input. Aerosol Fe solubility determined by a 25% acetic acid leach with hydroxylamine hydrochloride was much greater than that derived from a leach using ultra-pure deionized water. This led to significant differences in the residence time of Fe calculated for the mid-ocean gyre using these different solubilities. Generally, each element displays relatively short (weeks–months) residence times within the nearshore region of robust upwelling, reflecting large input terms and rapid removal. Moving offshore, total input fluxes decrease and the residence times of the TEs increase markedly until the western edge of the transect. There, relaxation of ocean stratification permits greater upward turbulent flux and greater rainfall leads to greater atmospheric input of TEs. • Trace element fluxes to the surface ocean were determined along the GEOTRACES EPZT. • Trace element residence times in the surface ocean were determined along the transect. • Trace element properties reflected diverse physical and geochemical conditions. [ABSTRACT FROM AUTHOR]