Volume 10 Issue 3, March 2017

Mining the deep seabed is fraught with challenges. Untapped mineral potential under the shallow, more accessible continental shelf could add a new dimension to offshore mining and help meet future mineral demand.

Hints from seismic tomography and geochemistry indicate that Earth's mantle is heterogeneous at large scale. Numerical simulations of mantle convection show that, if it started enriched in silicates, the lower mantle may remain unmixed today.

Dissolved iron is mysteriously pervasive in deep ocean hydrothermal plumes. An analysis of gas, metals and particles from a 4,000 km plume transect suggests that dissolved iron is maintained by rapid and reversible exchanges with sinking particles.

A global cooling trend culminated in the glaciation of Antarctica during the Eocene–Oligocene transition. Simulations suggest that ocean circulation changes and enhanced drawdown of atmospheric carbon dioxide can explain this climate shift.

External metal inputs to oceans affect ocean productivity and metal cycling. A synthesis of researchreveals that internal processes such as metal retention, recycling and remineralizationare also important.

Most of Mars’s initial water has been lost through atmospheric escape, but seasonal imbalances of measured hydrogen loss compared to oxygen are enigmatic. Photochemical models suggest that seasonal water vapour at high altitudes enhances hydrogen loss rates.

Atmospheric rivers have been associated with extreme rainfall events. A global detection algorithm, applied to reanalysis data, suggests that they contribute substantially to extremes in wind as well as precipitation along coasts globally.

Mixing with non-black carbon can enhance the radiative effect of black-carbon aerosols. Lab and field measurements of aerosol properties reveal that the mass ratio of black to non-black carbon determines the amount of enhancement.

Dust-borne nutrients can enhance productivity in the surface ocean. Two years of sediment trap data reveal that dust enhances carbon export to depth by increasing surface nitrogen fixation, productivity and carbon sinking rates in the North Atlantic.

The largest known hydrothermal plume moves dissolved iron halfway across the Pacific. In situ measurements show that dissolved and particulate iron transport is facilitated by reversible exchange of dissolved iron onto organic compounds.

Zinc and silicon distributions co-vary in much of the global oceans. Observations and numerical modelling suggest that this co-variation can arise in the absence of mechanistic links between the uptake of zinc and silicate.

Reconstructions of Holocene summer temperatures differ between models and vegetation-based proxies. A quantitative reconstruction for the Mediterranean region based on fossil midge assemblages suggests warm summers, in line with climate models.

During the latest Eocene, declining atmospheric CO₂ levels led to the inception of the Antarctic ice sheet. Simulations suggest that the deepening of the Drake Passage caused climate changes that enhanced continental weathering and CO₂ drawdown.

Fixed nitrogen is lost from oxygen minimum zones. Experimental data from an anoxic lake show that the presence of Fe(II) limits this loss, suggesting that ancient anoxic and iron-rich oceans may not have been nitrogen limited.

The dominant source for water in Earth’s mantle is unclear. Geochemical analyses of rock samples from mid-ocean ridges and ocean islands globally suggest the water is largely derived from seawater-altered crust introduced during subduction.

Carbonated silicate melts are expected to exist in the mantle, but have been elusive in nature. Geochemical analyses of rocks from the South China Sea identify such melts formed in the mantle and erupted at the surface through thin lithosphere.

Seismic data are inconsistent with a compositionally homogenous lower mantle. Simulations show that viscosity variation with depth in Earth’s early mantle may have prevented efficient mixing and allowed ancient mantle domains to persist.