Massive Southern Ocean phytoplankton bloom fed by iron of possible hydrothermal origin.

Primary production in the Southern Ocean (SO) is limited by iron availability. Hydrothermal vents have been identified as a potentially important source of iron to SO surface waters. Here we identify a recurring phytoplankton bloom in the high-nutrient, low-chlorophyll waters of the Antarctic Circumpolar Current in the Pacific sector of the SO, that we argue is fed by iron of hydrothermal origin.

First Quantification of the Controlling Role of Humic Substances in the Transport of Iron Across the Surface of the Arctic Ocean.

One of the main reasons behind our current lack of understanding of iron cycling in the oceans is our inability to characterize the ligands that control iron solubility, photosensitivity, reactivity, and bioavailability. We currently lack consensus about the nature and origin of these ligands. Here, we present the first field application of a new methodological development that allows the selective quantification of the fraction of Fe complexed to humic substances (HS).

Determination of the contribution of humic substances to iron complexation in seawater by catalytic cathodic stripping voltammetry.

Improving our understanding of iron cycling in ocean waters is one of the most challenging tasks in oceanographic studies and requires new analytical strategies. The low solubility of inorganic iron in oxygen saturated waters is increased by organic complexation with a variety of natural ligands, the nature of which is a topic of debate. Electrochemical methods are important for speciation studies since they allow direct measurement of iron complexes at limits of detection below iron concentrations in ocean waters.

Mercury in the Black Sea: New Insights From Measurements and Numerical Modeling.

Redox conditions and organic matter control marine methylmercury (MeHg) production. The Black Sea is the world's largest and deepest anoxic basin and is thus ideal to study Hg species along the extended redox gradient. Here we present new dissolved Hg and MeHg data from the 2013 GEOTRACES MEDBlack cruise (GN04_leg2) that we integrated into a numerical 1-D model, to track the fate and dynamics of Hg and MeHg.

Return of naturally sourced Pb to Atlantic surface waters.

Anthropogenic emissions completely overwhelmed natural marine lead (Pb) sources during the past century, predominantly due to leaded petrol usage. Here, based on Pb isotope measurements, we reassess the importance of natural and anthropogenic Pb sources to the tropical North Atlantic following the nearly complete global cessation of leaded petrol use. Significant proportions of up to 30-50% of natural Pb, derived from mineral dust, are observed in Atlantic surface waters, reflecting the success of the global effort to reduce anthropogenic Pb emissions.