Chasing iron bioavailability in the Southern Ocean: Insights from and iron speciation.

Dissolved iron (dFe) availability limits the uptake of atmospheric CO by the Southern Ocean (SO) biological pump. Hence, any change in bioavailable dFe in this region can directly influence climate. On the basis of Fe uptake experiments with , we show that the range of dFe bioavailability in natural samples is wider (<1 to ~200% compared to free inorganic Fe') than previously thought, with higher bioavailability found near glacial sources.

Chromium Cycling in Redox-Stratified Basins Challenges δCr Paleoredox Proxy Applications.

Chromium stable isotope composition (δCr) is a promising tracer for redox conditions throughout Earth's history; however, the geochemical controls of δCr have not been assessed in modern redox-stratified basins. We present new chromium (Cr) concentration and δCr data in dissolved, sinking particulate, and sediment samples from the redox-stratified Lake Cadagno (Switzerland), a modern Proterozoic ocean analog. These data demonstrate isotope fractionation during incomplete (non-quantitative) reduction and removal of Cr above the chemocline, driving isotopically light Cr accumulation in euxinic deep waters.

Biological Control of Chromium Redox and Stable Isotope Composition in the Surface Ocean.

While chromium stable isotopes (δCr) have received significant attention for their utility as a tracer of oxygen availability in the distant geological past, a mechanistic understanding of modern oceanic controls on Cr and δCr is still lacking. Here we present total dissolved δCr, concentrations of Cr (III) and total dissolved Cr, and net community productivity (NCP) from the North Pacific. Chromium concentrations show surface depletions in waters with elevated NCP, but not in lower productivity waters.

A call for refining the role of humic-like substances in the oceanic iron cycle.

Primary production by phytoplankton represents a major pathway whereby atmospheric CO is sequestered in the ocean, but this requires iron, which is in scarce supply. As over 99% of iron is complexed to organic ligands, which increase iron solubility and microbial availability, understanding the processes governing ligand dynamics is of fundamental importance. Ligands within humic-like substances have long been considered important for iron complexation, but their role has never been explained in an oceanographically consistent manner.

Undocumented water column sink for cadmium in open ocean oxygen-deficient zones.

Cadmium (Cd) is a micronutrient and a tracer of biological productivity and circulation in the ocean. The correlation between dissolved Cd and the major algal nutrients in seawater has led to the use of Cd preserved in microfossils to constrain past ocean nutrient distributions. However, linking Cd to marine biological processes requires constraints on marine sources and sinks of Cd.