Volume 5 Issue 6, June 2012

Greenland's glaciers have lost significant amounts of ice over the past decade. Rediscovered historical images of the ice margin show a record of southeast Greenland's response to the last major warming event in the 1930s.

Of the West Antarctic ice shelves, those in the Amundsen Sea sector have given the most cause for concern. Ocean modelling of the Weddell Sea region, together with a detailed survey of the ice bed morphology, indicates that this region, too, may change soon.

Earthquakes may trigger or retard quakes on nearby faults, but such relationships are difficult to verify. Observations showing that the Landers earthquake in California shut down aftershocks from a preceding event validate such relationships.

Methane emissions from natural gas reservoirs have long been largely overlooked. The discovery of abundant geological gas seeps in areas of cryosphere degradation highlights the relevance of these emissions to the greenhouse gas budget.

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.

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.

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.

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.

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.

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.

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.

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.

Both marine- and land-terminating glaciers in southeast Greenland have experienced dramatic recent retreat. An 80-year record of historical aerial photographs and satellite imagery shows that many land-terminating glaciers in this region retreated more rapidly in the 1930s than today, whereas marine-terminating glaciers have retreated faster in the 2000s.