The biogeochemistry of particulate trace elements and isotopes in the North Atlantic Ocean
Barrett, Pamela Meade
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The distributions and bioavailability of trace metals and their isotopes are strongly controlled by partitioning between the dissolved phase and suspended and sinking biotic and abiotic particles. This work presents new particulate trace element data from CLIVAR section A16N in the North Atlantic collected during two occupations in 2003 and 2013. ED-XRF methods were adapted for trace element analysis of marine suspended particulate matter at sub-nanomolar concentrations. Paired analyses of particulate Al, P, Ca, V, Mn, Fe, Ni, Cu, Zn, and Pb concentrations using samples collected from the upper water column in the Atlantic and Pacific Oceans show that ED-XRF and HR ICP-MS methods produce comparable data for many trace elements of oceanographic interest. By quantifying changes in the concentrations of subsurface particulate Al and Fe and mixed-layer dissolved Al in the equatorial North Atlantic, we estimate dust deposition to surface waters in the eastern North Atlantic increased by approximately 15% between 2003 and 2013. Increased concentrations of dissolved Al in subtropical mode waters suggest that dust deposition may have also increased in the western basin. Particulate calcium distributions and total alkalinity measurements along A16N in 2003 and 2013 were used to estimate shallow-water carbonate dissolution. In the tropical North Atlantic, water masses at intermediate depths were undersaturated with respect to aragonite. Carbonate dissolution rates were estimated to be 0.7–0.9 mmol m−2 d−1, indicating this region is a hotspot for shallow carbonate dissolution in the Atlantic basin. Finally, the enriched δ65Cu of particulate matter samples suggests that adsorptive and passive scavenging processes likely dominate the fractionation of Cu stable isotopes in the upper ocean and result in isotopically heavy particulate Cu. Incorporating this new data into an isotopic mass balance for Cu in the surface ocean, we estimate an atmospheric flux of 1.2 x 108 mol Cu yr-1 to the surface ocean and a particle export flux from the base of the mixed layer of 2.6 x 109 mol Cu yr-1.
- Oceanography