Research articles

The ratio of nitrogen to phosphorus in phytoplankton varies greatly with taxa and growth conditions. An ecosystem model suggests that the relative abundance of fast- and slow-growing phytoplankton controls the amount of new nitrogen added to the ocean.

Climate-change projections suggest that European summer heatwaves will become more frequent and severe during this century. An analysis of a set of high-resolution regional climate simulations reveals consistent geographical patterns in these changes, with the most severe health impacts in southern European river basins and along the Mediterranean coasts.

The global geoid is characterized by a semi-continuous belt of minima that surround the Pacific Ocean. Simulations with mantle flow models suggest that these geoid lows are correlated with high-velocity anomalies near the base of the mantle and low-velocity anomalies in the mid-to-upper mantle.

An acceleration of ice-mass loss has been observed near the margin of the Greenland ice sheet, partly as a result of faster ice motion. Observations by GPS receivers reveal high seasonal variability in ice motion, with summer motion up to 220% higher than winter background levels.

Seismotectonic studies seek to provide ways of assessing the timing, magnitude and spatial extent of future earthquakes. Numerical simulations of seismic and aseismic fault slip in a fully dynamical numerical model open the possibility of predicting a fault system’s seismic rupture patterns from observations of its slip properties.

Nitrous oxide is a potent atmospheric greenhouse gas that is thought to be produced in soils through biological processes. Field measurements reveal nitrous oxide fluxes near Don Juan Pond, Antarctica — of comparable magnitude to those found in tropical soils — which may result from abiotic water–rock reactions.

Deep western boundary currents east of the Antarctic Peninsula and the Kerguelen plateau are important pathways for transporting deep Antarctic water masses to the global ocean. An array of moored current meters, used to quantify the water transport in this system, reveals a flow that is stronger than any measured in a deep western boundary current at similar depths so far.

The loss of carbon dioxide from soils increases initially under climate warming, but tends to decline to control levels within a few years. Simulations of the soil-carbon response to warming with a microbial-enzyme model show that a decline in both microbial biomass and the production of degrading enzymes can explain this attenuation response.

Natural petroleum seepage emits large volumes of oil and methane to the oceans every year, accompanied by the formation of asphalt volcanoes on the sea floor. The discovery of seven asphalt volcanoes off the coast of southern California may help to explain high methane emissions recorded during the late Pleistocene.

Deformation of the Himalaya and Tibet is thought to relate to flow within a weak crustal channel at depth. Magnetotelluric imaging of the Earth’s subsurface reveals a complex pattern of deformation, with two distinct weak crustal channels at 20–40 km depth.

The 100,000-year glacial cycles are generally thought to be driven by the eccentricity of the Earth’s orbit. Statistical analyses of climate variability and orbital forcing over the past five million years indicate that the glacial cycles are the result of an internal climate oscillation phase locked to the 100,000-year eccentricity cycle.

The impact of thawing permafrost on the nitrogen cycle is uncertain. Laboratory experiments using permafrost cores from northeast Greenland reveal that rewetting of thawed permafrost increases nitrous oxide production over 20-fold.

The sedimentary deposits at Meridiani Planum on Mars were formed in acidic surface waters. Geochemical calculations show that the oxidation of dissolved iron and the precipitation of oxidized iron minerals in the surface waters could be sufficient to generate the inferred acidity.

Stratospheric water vapour affects Earth’s radiation budget. A 19-month record of the hydrogen isotopic composition of water in the tropical stratosphere, collected through remote sensing measurements, shows a clear seasonal cycle in the isotopic composition that propagates upwards in this region, and is most likely created in the tropical tropopause layer.

The cause of the Laramide phase of mountain building remains uncertain. Modelling and plate reconstructions show that Laramide events coincide with subduction of the Shatsky oceanic plateau, implicating surface rebound after removal of the subducting plateau in Laramide uplift.

Mid-ocean ridges grow through tectonic and volcanic processes. Uranium-series dating of volcanic rocks at the ultraslow-spreading Southwest Indian Ridge reveals widely dispersed, young, off-axis volcanism that is spatially coincident with fault surfaces. Faults may therefore provide a mechanism for the wide dispersal of magma at ultraslow-spreading ridges.

Ice clouds in the tropical tropopause layer have a key role in dehydrating air that is entering the stratosphere. Cloud-chamber measurements suggest that their high humidity can be explained if heterogeneous ice nucleation on glassy aerosols is a significant nucleation mechanism in this region.

The evolution of Cordilleran-type orogens is controlled by a balance between forces that result in uplift and forces that destabilize the crustal growth. Numerical modelling indicates that the buoyancy of the underlying mantle wedge is an important factor in the collapse and fragmentation of Cordilleran orogens.

Interactions between the atmosphere and ocean are mediated by the mixed layer at the ocean surface. Analyses of ocean temperature and salinity data from Argo floats show that changes in the Southern Annular Mode, including recent and projected trends attributed to human activity, drive variations in mixed-layer depth in the Southern Ocean.

Mineral dust and marine sediment resuspension are generally considered the primary sources of the nutrient iron to the oceans. Numerical model results suggest that iron released by hydrothermal activity is also an important source of dissolved iron, particularly in the Southern Ocean.