Research articles

During subduction, the seawater-altered lithosphere becomes dehydrated and expels fluids. Isotopic analysis of an exhumed oceanic slab in the Tianshan Mountain Range shows that although subduction can continue for many millions of years, fluids are expelled in short-lived channels over periods of just a few hundred years.

Seagrass meadows are some of the most productive ecosystems on Earth. An analysis of organic carbon data from just under one thousand seagrass meadows indicates that, globally, these systems could store between 4.2 and 8.4 Pg carbon.

Changes in terrestrial water storage are likely to affect sea level, but comprehensive and reliable data are scarce. Simulations of global terrestrial water stocks and flows, with an integrated model that specifically accounts for human activities, indicate that groundwater depletion and reservoir storage have together led to a sea-level rise of about 0.66 mm yr⁻¹ between 1961 and 2003, about 36% of the observed rise.

In the Arctic, permafrost and glaciers form a ‘cryosphere cap’ that traps methane leaking from hydrocarbon reservoirs, restricting flow to the atmosphere. Aerial surveys and ground-based measurements reveal the release of radiocarbon-depleted methane along boundaries of permafrost thaw and retreating glaciers in Alaska and Greenland.

Human activities, including industry and mining, have increased inorganic mercury deposition in terrestrial and aquatic ecosystems. Model simulations indicate that circumpolar rivers deliver large quantities of mercury to the Arctic Ocean during summer.

The vast majority of Earth’s volcanoes are under water, but little is known of the structure and evolution of submarine volcanoes. A bathymetric survey mapping the Monowai submarine volcano in the Tonga–Kermadec Arc twice within 14 days reveals dramatic changes in bathymetry of up to 71.9 m, associated with volcanic activity.

The bed of the West Antarctic ice sheet is, in places, more than 1.5 km below sea level. Radio-echo sounding data from the Weddell Sea sector of Antarctica reveal a large subglacial basin immediately upstream of the ice sheet’s grounding line, with a steep reverse gradient and a smooth floor.

Changes in solar emissions can be amplified in atmospheric circulation patterns and lead to climate changes. Proxy data from lake sediments and long-term climate models support such a top-down mechanism of Late Holocene cooling induced by a concurrent grand solar minimum.

At subduction zones, slip along the shallowest parts of the plate boundary is generally thought to be aseismic. Observations of very-low-frequency earthquakes occurring at shallow levels on the plate boundary of the Nankai Trough subduction zone imply that slow but seismic slip can occur there, and could potentially generate tsunamigenic earthquakes.

The role of permanent versus transient crustal stress changes in triggering earthquakes is debated. Analysis of the stress imparted by the Joshua Tree and nearby Landers earthquakes in California in 1992 implies that a permanent drop in stress can halt aftershocks, so such static stress changes should be incorporated into seismic-hazard assessments.

The origin of the dichotomy between the lunar nearside and farside is unclear. Analysis of spectral reflectance data from the Kaguya lunar orbiter indicates a systematic difference in the degree of differentiation in the oldest lunar crustal terrains, linking the lunar dichotomy to crystallization of the magma ocean.

The size of the caldera formed when the surface collapses after a large volcanic eruption is thought to reflect the size of the evacuated magma chamber. Numerical modelling shows that magma stored in different parts of the chamber can be mobile or locked, so caldera size may only correspond to the volume of evacuated mobile magma.

Continental breakup and volcanism in Afar, Africa, has been linked to mantle plume activity. Seismic imaging of the mantle beneath Afar, however, identifies an increase in seismic velocities at shallow depths that is consistent with decompression melting and magmatism in the absence of strong plume activity today.

Uncertainty in the future atmospheric burden of methane—a potent greenhouse gas—represents an important challenge to the development of realistic climate projections. Airborne observations of methane suggest that the remote Arctic Ocean could prove to be a potentially important methane source.

Mid-ocean ridge transform faults experience more foreshocks than continental faults, yet the mainshock rarely ruptures the entire fault. Analysis of seismic data from the Gofar transform fault at the East Pacific Rise indicates that the foreshock region has different material properties from the mainshock region, and acts as a barrier to rupture propagation.

The transition between the weak lithosphere of the Tibetan plateau and the surrounding rigid crustal blocks has a key role in the ongoing collision between India and Asia. A reanalysis of existing magnetotelluric data suggests that crustal melt penetrates north from the Tibetan plateau beyond the Kunlun Fault, and weakens the crust beneath the Kunlun Shan.

Carbon capture and geological storage represents a potential means of managing atmospheric carbon dioxide levels. An analysis of a 135,000 palaeorecord shows that pulses of carbon dioxide leakage from a natural reservoir in Utah are associated with episodes of glacial unloading.

The mass balance of Hindu-Kush–Karakoram–Himalaya glaciers has been debated, partly because of a severe lack of observations from the region. An analysis of the regional mass balance of Karakoram glaciers by comparison of digital elevation models from 1999 to 2008 reveals a small glacier mass gain in the area.

Ocean acidification may seriously impair marine calcifying organisms. Emiliania huxleyi, the world’s single most important calcifying organism, may be able to evolve in response to ocean acidification conditions, according to laboratory selection experiments.

The Chilean subduction zone, where the oceanic Nazca plate subducts beneath the continental South American plates, is a very active convergent margin. Wide-angle seismic refraction and reflection data, combined with records of aftershocks following the 2007 Tocopilla earthquake, document an abrupt change in the dip of the subducting plate from less than 10° to about 22°.