Reviews & Analysis

The formation and flow of deep water around Antarctica contributes to the global ocean circulation. New measurements report the strongest flow speeds recorded so far in a current below 3,000 m depth, and help to document a pathway for Antarctic Bottom Water.

The use of fossil fuels and fertilizers has increased the amount of biologically reactive nitrogen in the atmosphere over the past century. A meta-analysis suggests that nitrogen deposition typically impedes the decomposition of carbon in forest soils, significantly reducing carbon dioxide emissions to the atmosphere.

Soils are the main terrestrial reservoir of nutrients such as nitrogen and phosphorus, and of organic carbon. Data synthesis reveals that soil erosion can result in lateral fluxes of these nutrients at comparable magnitudes to those induced by fertilizer application and crop removal.

Many species of nannoplankton with carbonate shells vanished during the mass extinction 65 million years ago. An analysis of extinction rates from the world's oceans reveals a geographic bias in the demise and recovery of nannoplankton species.

The fragmentation of continents at convergent plate boundaries is thought to be influenced by the subducting lithosphere. Numerical modelling suggests that instead, the forces exerted by the underlying mantle can drive the formation of continental microplates.

Oceanic crust forms through the addition of volcanic rock to mid-ocean ridges. Widely dispersed, young lavas observed at an ultraslow-spreading ridge provide impetus for the redevelopment of models of oceanic magmatism.

Decision makers are in need of decadal climate forecasts, for example, to help plan infrastructure investments. When — or whether — climate modellers will be able to deliver is not yet clear.

The surface layer of the Southern Ocean connects the atmosphere with the deep subtropical ocean. Ocean observations reveal that the thickness of this layer — important for biological productivity — is controlled by the strength and position of the southern circumpolar winds.

At the end of the twentieth century, tropical deforestation was associated with the growth of rural populations. An assessment of the factors involved in forest loss suggests that today's trees are more likely to be affected by economic pressures from farther afield.

About 94.5 million years ago, oxygen levels in the deep ocean dropped while carbon burial rapidly increased. Geochemical analyses suggest that the release of sulphate from extensive volcanism set off a sequence of biogeochemical reactions that led to ocean anoxia.

The earliest evolution of our planet is difficult to reconstruct. Ancient rocks in Western Australia show an isotopic signature that links their formation with 4.3-billion-year-old crust.

The rise in atmospheric carbon dioxide levels at the end of the last glacial period has been attributed to a release of carbon from the abyssal ocean. Radiocarbon analyses from the Chilean margin have failed to find evidence that supports this hypothesis.

Predicting an El Niño or La Niña event before the preceding spring has proved to be difficult. Taking into account coupled ocean–atmosphere modes in the Indian Ocean region that have a two-year periodicity may provide the basis for longer forecasting lead times.

Whether the characteristics of tropical cyclones have altered, or will alter, in a changing climate has been subject of considerable debate. An overview of recent research indicates that greenhouse warming will cause stronger storms, on average, but a decrease in the frequency of tropical cyclones.

Greenland is losing ice through glaciers that flow into deep fjords. New observations highlight the important fjord processes that supply warm ocean waters to the melting glaciers, and thereby affect Greenland's contribution to sea-level rise.

In the North Atlantic region, six massive iceberg discharge events marked the last glacial period. A numerical model now links these events to ocean temperatures and ice-shelf conditions.