Radium-228-derived ocean mixing and trace element inputs in the South Atlantic

Hsieh, YT; Geibert, W; Woodward, EMS; Wyatt, NJ; Lohan, MC; Achterberg, EP; Henderson, GM. 2021 Radium-228-derived ocean mixing and trace element inputs in the South Atlantic. Biogeosciences, 18 (5). 1645-1671. https://doi.org/10.5194/bg-18-1645-2021

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Official URL: http://dx.doi.org/10.5194/bg-18-1645-2021

Abstract/Summary

Trace elements (TEs) play important roles as micronutrients in modulating marine productivity in the global ocean. The South Atlantic around 40◦S is a prominent region of high productivity and a transition zone between the nitrate-depleted subtropical gyre and the iron-limited Southern Ocean. However, the sources and fluxes of trace elements to this region remain unclear. In this study, the distribution of the naturally occurring radioisotope 228Ra in the water column of the South Atlantic (Cape Basin and Argentine Basin) has been investigated along a 40◦S zonal transect to estimate ocean mixing and trace element supply to the surface ocean. Ra-228 profiles have been used to determine the horizontal and vertical mixing rates in the near-surface open ocean. In the Argentine Basin, horizontal mixingfromthecontinentalshelftotheopenoceanshowsan eddy diffusion of Kx =1.8±1.4 (106 cm2 s−1) and an integrated advection velocity w=0.6±0.3cms−1. In the Cape Basin, horizontal mixing is Kx =2.7±0.8 (107 cm2 s−1) andverticalmixing Kz=1.0–1.7cm2 s−1 intheupper600m layer. Three different approaches (228Ra diffusion, 228Ra advection, and 228Ra/TE ratio) have been applied to estimate the dissolved trace element fluxes from the shelf to the open ocean. These approaches bracket the possible range of off-shelf fluxes from the Argentine Basin margin to be 4–21 (×103)nmolCom−2 d−1, 8–19 (×104)nmolFem−2 d−1 and 2.7–6.3 (×104)nmolZnm−2 d−1. Off-shelf fluxes from the Cape Basin margin are 4.3–6.2 (×103)nmolCom−2 d−1, 1.2–3.1 (×104)nmolFem−2 d−1, and 0.9–1.2 (×104)nmolZnm−2 d−1. On average, at 40◦S in the Atlantic, vertical mixing supplies 0.1– 1.2nmolCom−2 d−1, 6–9nmolFem−2 d−1, and 5– 7nmolZnm−2 d−1 to the euphotic zone. Compared with atmospheric dust and continental shelf inputs, vertical mixing is a more important source for supplying dissolved trace elements to the surface 40◦S Atlantic transect. It is insufficient, however, to provide the trace elements removed by biological uptake, particularly for Fe. Other inputs (e.g. particulate or from winter deep mixing) are required to balance the trace element budgets in this region.

Item Type: Publication - Article
Additional Information. Not used in RCUK Gateway to Research.: Correspondence:Yu-Te Hsieh (yu-te.hsieh@earth.ox.ac.uk)
Divisions: Plymouth Marine Laboratory > National Capability categories > Single Centre NC - CLASS
Plymouth Marine Laboratory > Science Areas > Marine Biochemistry and Observations
Depositing User: S Hawkins
Date made live: 26 Mar 2021 10:21
Last Modified: 26 Mar 2021 10:21
URI: http://plymsea.ac.uk/id/eprint/9161

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