Reviews & Analysis

The neurotoxin methylmercury can accumulate in marine food webs, contaminating seafood. An analysis of the isotopic composition of fish in the North Pacific suggests that much of the mercury that enters the marine food web originates from low-oxygen subsurface waters.

During the Last Glacial Maximum, ice sheets in Eurasia terminated at the edge of the Laptev Sea. Seismic data now suggest that a separate ice sheet was repeatedly centred further east, in the East Siberian Sea, during previous glacial periods.

Methane is an important greenhouse gas, responsible for about 20% of the warming induced by long-lived greenhouse gases since pre-industrial times. A compilation of observations and results from chemical transport, ecosystem and climate chemistry models suggests that a rise in wetland and fossil fuel emissions probably accounts for the renewed increase in global methane levels after 2006.

Intrusions of magma into the crust help accommodate the divergence between tectonic plates. A magnetotelluric survey of the crust and mantle beneath Afar, Ethiopia, has identified enough magma to accommodate plate separation there for about 50,000 years.

Phosphorus is an important element for biogeochemical development. According to a set of experiments, martian phosphate minerals dissolve more quickly than terrestrial ones, possibly providing nutrients in aqueous environments for early martian life.

The classical view of fluvial sediment transport considers only physical interactions between the river flow and riverbed particles. Experiments and theory suggest that microbial biofilms reduce sediment mobility by binding many grains together.

The Arctic is warming faster than any other region in the world. The resultant large-scale shift in sea ice cover could increase oceanic emissions of dimethylsulphide, a climate-relevant trace gas generated by ice algae and phytoplankton.

Coastal upwelling regimes associated with eastern boundary currents are the most biologically productive ecosystems in the ocean. A suite of human-induced changes could perturb primary production and nutrient cycling in these highly dynamic systems.

The leakage of cold, methane-rich fluids from subsurface reservoirs to the sea floor sustains some of the richest ecosystems on the sea bed. These cold-seep communities consume around two orders of magnitude more oxygen than the surrounding sea floor as a result of the microbial consumption of seep methane.

The flux of carbon out of the ocean surface is not sufficient to meet the energy demands of microbes in the dark ocean. A review of the literature suggests that non-sinking particles and microbes that convert inorganic carbon into organic matter could help to meet this deep-ocean energy demand.

The end of the Pleistocene epoch saw the extinction of large-bodied herbivores around the world. Numerical modelling suggests that continental-scale effects of this extinction on nutrient transport are ongoing.

Climate change is affecting the cryosphere from above. Geothermal heat flux from below is also contributing to conditions at the base of Greenland's ice sheet, which sits atop a lithosphere of variable thickness.

The Indonesian government ruled that the Lusi mud eruption was triggered by drilling and held an oil company responsible. Instead, a curved rock layer capping the mud reservoir may have amplified passing seismic waves and the trigger may have been natural.

Interactions between the ocean and atmosphere are complex. An analysis of satellite data from the Southern Ocean reveals a tight coupling of ocean and atmosphere on horizontal scales of around 100 km that modifies both near-surface winds and ocean circulation.

The extinction of megafauna in Australia roughly coincided with shifts in vegetation and fire regimes. Sediment geochemistry shows that the vegetation shift followed the extinction, indicating that the loss of browsers promoted fire and altered plant composition.

The East Antarctic ice sheet is believed to be Earth's most stable ice sheet. Changes in geochemical composition of offshore sediments suggest that its margin repeatedly retreated by at least 350–550 kilometres inland between 5.3 and 3.3 million years ago.

Subduction zone earthquakes cause the overriding plate to stretch and subside. Excessive subsidence of volcanoes during the large quakes in Chile in 2010 and Japan in 2011 highlight an unexpected response of volcanic areas to the sudden tectonic pull.

Mantle flow patterns may be reconstructed from mineral orientations. Experiments show that the high-pressure mineral post-perovskite can inherit texture from its lower-pressure counterpart, suggesting new ways of interpreting flow in the deepest mantle.

The daily vertical migration of small marine animals transfers organic carbon from the surface ocean to depth. An assessment of acoustic data reveals that the depth of migration is closely tied to subsurface oxygen levels throughout much of the global ocean.