Review Articles

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.

A substantial amount of atmospheric carbon taken up on land is transported laterally from upland terrestrial ecosystems to the ocean. A synthesis of the available literature suggests that human activities have significantly increased soil carbon inputs to inland waters, but have only slightly affected carbon delivery to the open ocean.

Photosynthetic microbes, collectively termed phytoplankton, are responsible for the vast majority of primary production in marine waters. A synthesis of the latest research suggests that two broad nutrient limitation regimes — characterized by nitrogen and iron limitation, respectively — dictate phytoplankton abundance and activity in the global ocean.

Tropical climate and the composition of the global upper atmosphere are affected by the tropical tropopause layer. A synthesis report concludes that transport and mixing in the tropopause region are closely linked with the Asian monsoon and other tropical circulation systems, with possible implications for the impacts of climate change on this important layer.

The world's largest freshwater resource is groundwater. A review of our understanding of groundwater depletion suggests that although the problem is global, solutions must be adapted to specific regional requirements at the aquifer scale.

Magma erupted at subduction-zone volcanoes contains mantle rocks and a mixture of fluids and sediments derived from the subducted slab. A synthesis of work over past years provides an integrated physico-chemical framework for subduction zones with mixing at the slab–mantle interface and transport towards the surface volcanoes by buoyant diapirs.

During periods of glaciation, the Northern Hemisphere was swathed by large ice sheets. A review of ice-sheet retreat during the last two deglaciations shows that land-based ice sheets responded rapidly to rising summer insolation, whereas marine-based ice sheets underwent a delayed, but more abrupt, response.

The geomagnetic field varies on a wide range of timescales. A review of emerging research suggests that field variations on the order of tens of millions of years may be linked to changes in heat flow across the core–mantle boundary.

Over 90% of species were lost during the end-Permian mass extinction. A review of the fossil record shows that the rate of recovery was highly variable between different groups of organisms as a result of complex biotic interactions and repeated environmental perturbations.

Most of Earth's crust is created at mid-ocean ridges that are submerged deep beneath the oceans. Analyses of geodetic and seismic data from rare sections of ridges that are exposed on land in Iceland and the Afar region in east Africa demonstrate that rifting episodes at these sites operate with remarkably similar mechanisms.

The meridional overturning circulation of the ocean plays a central role in the climate and its variability. This Review of recent studies emphasizes the importance of wind-driven upwelling in the Southern Ocean for global ocean circulation.

Throughout the Palaeozoic era, about 540 to 250 million years ago, plants colonized land and rapidly diversified. An analysis of the palaeontologic record shows that this diversification irrevocably altered the shape and form of fluvial systems.

Mixed-phase clouds, comprising both ice and supercooled liquid water, have a large impact on radiative fluxes in the Arctic. Interactions between numerous local feedbacks sustain these complex cloud systems, leading to the development of a resilient mixed-phase cloud system.

Volcanoes formed above the Hawaiian mantle plume exhibit a striking contrast in the geochemical characteristics of the lavas erupted at the northern Kea compared with the southern Loa volcanoes. Isotopic data show that these trends have persisted for more than 5 million years and may mirror compositional heterogeneities in the deep mantle.

Anthropogenic emissions of ozone-depleting gases cause marked changes in surface climate, in addition to rising levels of anthropogenic greenhouse gases. A Review of the influence of the Antarctic ozone hole on Southern Hemisphere surface climate finds that its signature closely resembles the negative phase of the southern annular mode.

Ice sheets, and in particular the West Antarctic ice sheet, are expected to shrink in size as the world warms, which in turn will raise sea level. A Review of the literature suggests that much of this ice sheet will survive beyond this century, but confident estimates of the likelihood of future collapse require further work.

Carbonate rocks of Middle Ediacaran age record the largest excursion in carbon isotopic compositions in Earth history. A review of the data offers two intriguing explanations: an extraordinary perturbation of the carbon cycle, or post-depositional alteration that is global, rather than local.

Earth's topography is attributed to the interactions of the tectonic plates, but flow within the mantle also contributes to surface uplift and subsidence. An overview of recent research indicates that mantle-induced dynamic topography can be reconstructed by integrating the geological record with models of mantle flow.