Research articles

Mid-ocean ridges are composed of segmented faults and magma reservoirs. Seismic images from the East Pacific Rise show that the magma reservoirs are segmented on the same fine scale as the surface faults, and that distinct lava eruptions are sourced from largely isolated magma lenses.

Volcanic eruptions can be cyclical, alternating between intense activity and repose over periods of hours to days. Numerical simulations of a viscous, gas-rich magma show that ascent through the volcanic conduit naturally induces a periodic pulse of pressurized gas to travel through the magma, which, on reaching the surface, can trigger the cyclical eruptions.

The structure of oceanic plateaux is unclear, as they are remote and submerged beneath the seas. Seismic images of the Tamu Massif, part of the Shatsky Rise oceanic plateau in the northwestern Pacific Ocean, show that it is a single immense volcano, potentially the largest on Earth.

Palaeoclimate records indicate lower El Niño/Southern Oscillation (ENSO) variance during the middle Holocene compared with today, but the mechanisms leading to this muted variability are not clear. A 175-year oxygen isotope record from a Porites coral microatoll in the NINO3.4 region records persistently reduced ENSO variance about 4,300 years ago, and season-specific analyses of the record suggest that insolation played an important role in this change.

The buoyancy of magma should cause it to rise into the crust, preventing it from ponding in the uppermost mantle. Magnetotelluric data from the Dabbahu rift segment, Ethiopia, identify a magma reservoir that extends well into the mantle beneath the rift, and is so large that it should persist for thousands of years.

Between 80,000 and 70,000 years ago, climate cooled and ice sheets in the high northern latitudes expanded. Pollen and microfossil data from marine sediments indicate that an increasing thermal gradient between cold air and warmer oceans could have supported continental ice growth.

Phosphate is thought to be a chemical nutrient essential for life, but the low solubility of phosphate minerals means that abiogenesis on Earth had to overcome the hurdle of phosphate-limited environments. Dissolution experiments of phosphate minerals commonly found on Mars suggest that phosphate may have been more readily available in early martian environments.

The subduction zone beneath Costa Rica experiences infrequent large earthquakes in its northwestern part, whereas slow slip dominates in the southeast. Seismic data reveal a disparity in fluid accumulation in the overriding continental crust that correlates with this change in seismic behaviour, implying that spatial gradients in fluid content may control subduction-zone seismicity.

Anthropogenic aerosols are highly spatially variable, whereas greenhouse gases are largely well-mixed at the global scale, but both affect climate. Nevertheless, climate simulations suggest that regional changes in sea surface temperature and precipitation to changes in greenhouse gas and aerosol forcings are similar.

Mercury enters marine food webs in the form of microbially generated monomethylmercury. An analysis of the mercury isotopic composition of nine species of North Pacific fish suggests that microbial production of monomethylmercury below the surface mixed layer contributes significantly to the mercury contamination of marine food webs.

Atmospheric methane concentrations varied substantially over the last glacial cycle. An analysis of the δ¹³C of the methane suggests that the relative strength of various methane sources and sinks varied independently of overall changes in methane concentrations.

The remote detection of surface water indigenous to the Moon has proved difficult because of alternative sources, such as the solar wind. Spectroscopic observations of hydroxyl-bearing materials in Bullialdus Crater by the Chandrayaan-1 spacecraft are consistent with indigenous magmatic water that was excavated by impact from the lunar interior.

The influence of inherited tectonic-plate strength on the structure of mountain belts is debated. Analysis of geological data collected from mountain belts worldwide shows that the style and amount of deformation in a mountain range are strongly influenced by the age and strength of the colliding plates.

Mantle minerals in faults above a subducting slab can become aligned. Laboratory analyses show that this mineral alignment can also generate direction-dependent friction that can cause faults to slip both seismically and aseismically, depending on the direction of movement.

Earth’s crust formed from melted mantle, yet the earliest record of this process is recorded only in crustal rocks. Isotopic dating of mantle rocks in the Ujaragssuit Nunât intrusion, southwest Greenland, identify melting events that occurred up to 4.36 Gyr ago, providing a mantle record of ancient melting to complement the crustal record.

Low levels of the micronutrient iron limit primary production and nitrogen fixation in large areas of the global ocean. Measurements in the South Atlantic suggest that slow-spreading submarine ridges serve as a significant oceanic iron source in these waters.

During glacial periods, ice sheets covered continental margins through much of Arctic North America, Greenland and western Eurasia. Marine structures suggest that an ice sheet up to a kilometre in depth periodically covered the East Siberian continental shelf as well.

The thermal state of the Earth’s surface is usually influenced more by climate than by heating from the Earth’s interior. Numerical models show that in the oldest and thickest part of the Greenland Ice Sheet, geothermal heat flux through an anomalously thin lithosphere leads to strong regional variations in basal melting.

The magnitude and rate of seismicity differ between subduction zones. Calculations of background seismicity rates, based on a global model of subduction zone seismicity, reveal a positive correlation between relative plate velocity and background seismicity, yet only the seismically quieter zones seem capable of generating magnitude 9 earthquakes.

Between about 50 and 10 thousand years ago, almost 100 genera of large animals went extinct. Mathematical analyses suggest that the extinctions in Amazonia have led to a reduction in the lateral flux of the limiting nutrient phosphorus—by transport of dung and bodies—by 98%.