Research articles

The Neoproterozoic Snowball Earth glaciations were separated by tens of millions of years, although models suggest glacial inception should occur within millions. Numerical modelling suggests that the delay could be explained by inherent limits on silicate weathering rates controlled by the availability of fresh rock.

The origin of the Bushveld Complex, South Africa, is elusive. Identification and dating of a radial swarm of volcanic dykes suggests that a mantle plume affected the region, but was active 600 million years before the Bushveld Complex formed, implying that the Bushveld magmas could be an indirect consequence of the plume.

At the southern boundary between India and Tibet, the Indian tectonic plate subducts northwards beneath the Tibetan Plateau. Seismic imaging shows that at the northern boundary of Tibet, the Asian plate is also subducting southwards beneath the plateau, and the Tibetan lithosphere is separate.

Two competing models have been suggested to explain the recovery of ecosystems from mass extinctions. An analysis of the recovery of marine pelagic communities from the Cretaceous–Palaeogene mass extinction supports a model of contingent recovery, rather than one based on trophic structure.

Seismic data have identified large-scale compositional heterogeneities in Earth’s deep mantle, but their origin is debated. Numerical modelling demonstrates that seismological and geochemical constraints on the character of these heterogeneities can be satisfied if they are composed of primitive material formed early in Earth’s history.

Eutrophication increases the acidity of coastal waters. Model simulations suggest that the drop in pH in coastal waters of the northern Gulf of Mexico since pre-industrial times is greater than that expected from eutrophication and ocean acidification alone.

Current estimates of carbon dioxide evasion from inland waters are based on incomplete spatial coverage. Streams and rivers in the United States release 97 Tg of carbon to the atmosphere each year, according to an analysis of chemical and morphological data.

Pronounced warming in the Arctic region is an important feature of observed and modelled climate change. Simulations with a coupled climate model show that the thermal inversion at the surface that predominates in Arctic winter amplifies Arctic warming by lowering the ability of the warming surface layer to radiate to space.

The Ganges–Brahmaputra drainage basin represents one of the largest sources of terrestrial biospheric carbon to the ocean. Radiocarbon analyses suggest that 20% of the carbon exported from this system has an average age of more than 15,000 years.

The stability over time of the zonal jets on the giant planets has been debated. An analysis of observations from the Cassini spacecraft reveals an acceleration of wind velocities in Saturn’s high-altitude equatorial jet between 2004 and 2009, by 20 m s⁻¹ at tropopause level and by 60 m s⁻¹ in the stratosphere.

Elevated concentrations of arsenic are common in shallow groundwater in many parts of South and Southeast Asia. Field experiments and model simulations suggest that adsorption of arsenic to sediments could help to limit contamination of deep groundwater.

An influence of solar irradiance variations on Earth’s surface climate has been repeatedly suggested. Simulations with a climate model driven by satellite measurements of solar ultraviolet irradiance show an atmospheric response to the solar minimum that resembles the negative phase of the North Atlantic Oscillation.

Ocean circulation patterns during the Late Cretaceous greenhouse interval remain disputed. Marine sediment geochemistry suggests that the end of the greenhouse interval coincided with the onset or intensification of deep-water formation in the North Atlantic Ocean.

Boninite lavas are erupted during the early stages of subduction, however they have previously been found only in the ancient geological record. Discovery of an active boninite eruption shows that abundant volatile gases derived from the subducting slab drive this violent eruptive activity, even in the deep sea.

Eddies and other mesoscale processes are thought to enhance biological production in the ocean, particularly in nutrient-limited regions. Satellite data and model simulations suggest that eddies suppress production in eastern boundary upwelling systems.

The early Eocene was marked by a series of abrupt warming events. Numerical modelling suggests that the events were the result of nonlinear interactions between orbital forcing, ocean circulation and the carbon cycle.

The amount of radiocarbon-depleted carbon dioxide in the atmosphere rose dramatically during the last deglaciation. Estimates of the radiocarbon content of water at 2.7 km depth in the northeast Pacific Ocean over the past 24,000 years suggest that this water mass was not a significant source of this carbon.

Tropical Atlantic sea surface temperatures and surface winds vary together in a pattern termed the Atlantic Meridional Mode. Simulations with an ocean general circulation model that is driven by a record of dust radiative forcing suggest that dust emissions over West Africa substantially influence the state of the tropical Atlantic Ocean on interannual to decadal scales.

The volatile organic compound isoprene — a precursor to the air pollutant ozone — is produced by many plant species. Canopy-scale measurements in Malaysia, combined with model simulations, suggest that isoprene emissions are under circadian control.

Retreating ice caps overlying volcanoes are thought to relieve surface pressure, causing enhanced magma generation and volcanic activity. Analysis of crustal stress during a dyke intrusion event associated with retreat of Iceland’s largest ice cap indicates that ice retreat could instead promote storage of magma in the crust, rather than eruption at the surface.