Recent and original results in the Southern Ocean on mercury speciation and cadmium isotopes

AU_cruise_lowFor the first time detailed mercury (Hg) speciation was determined along an Australia-Antarctic section (Cossa, et al., 2011) and cadmium (Cd) isotopes along a South Africa-Antarctic section (Abouchami W., et al., 2011). Both were acquired along two IPY-GEOTRACES sections: SR3 CASO-GEOTRACES (GIPY6) and ZERO&DRAKE (GIPY5) respectively.

Hg species distribution suggests distinct features in the Southern ocean Hg cycle: (i) a net atmospheric Hg deposition on surface water near the ice edge, (ii) Hg enrichment in brines during sea-ice formation and (iii) a methylmercury maximum close to Antarctica, far from anthropogenic Hg emissions (Figure 1).

Cd isotope ratios and concentrations are distributed into two distinct Cd isoscapes, delimiting two biogeochemical provinces the Antarctic Circumpolar Current (ACC) and Weddell Gyre (Figure 2). A doubling of the isotope effect due to biological consumption of Cd is observed during water transport from the Weddell Sea into the ACC. The increase in the magnitude of Cd isotope fractionation, as a result of enhanced phytoplankton biomass and altered species composition in the Southern Ocean, demonstrates that Cd isotopes could potentially serve as a useful measure of biological productivity.

cossa

Figure 1. Methylated mercury species (MeHgT) distribution along the SR3 CASO–GEOTRACES transect in the Southern Ocean. Source: Author’s manuscript, definitive authenticated version published in “Geochimica et Cosmochimica Acta“.

 

Abouchami

Figure 2. (Left) Latitudinal variations in seawater Cd isotope composition, expressed as ε112/ 110Cd (solid symbol) and Cd concentration (open symbol) along Zero Meridian.  (Right) Co-variations between ε112/110Cd and [Cd] (nmol kg−1) in Southern Ocean surface waters. Source: Earth and Planetary Science Letters

 

References:

Abouchami W., Galer S.J.G., de Baar H.J.W., et al. (2011), Modulation of the Southern Ocean cadmium isotope signature by ocean circulation and primary productivity, Earth and Planetary Science Letters, 305(1-2) DOI: 10.1016/j.epsl.2011.02.044

Cossa, D., Heimbürger, L.-E., Lannuzel, D., Rintoul, S.R., Butler, E.C.V., Bowie, A.R., Averty, B., Watson, R.J., Remenyi, T., (2011), Mercury in the Southern Ocean, Geochimica et Cosmochimica Acta, 75(14): 4037-4052 DOI: 10.1016/j.gca.2011.05.001

Latest highlights

Science Highlights

Icebergs as sources of trace metals to the ocean: which impact?

Earth’s Ice Sheets are known to release significant quantities of lithogenic particles into the ocean every year, but how does this material affect trace metal availability in the ocean?

18.10.2021

Science Highlights

Microbial trace metal trafficking on marine particles

This study provides evidence for the processing of nine particulate trace metals in multiple manners by diverse microbial communities.

28.09.2021

Science Highlights

Volcanic emissions in the Southern Ocean: an efficient and unexpected source of iron for this remote area

This study suggests that volcanic emission can represent a significant source of bioavailable Fe to open ocean anaemic ecosystems.

20.09.2021

Science Highlights

Surprisingly heavy silicon isotopes in the surface and deep Arctic Ocean

Brzezinski and his colleagues report on a comprehensive study of the Arctic Ocean silicic acid concentrations and silicon isotopic composition…

14.09.2021

Rechercher