Letters

The mode of carbon storage in Earth’s mantle is unclear. High-pressure laboratory experiments on mantle analogue materials reveal that significant quantities of carbon can be stored in tiny defects within the minerals, providing an efficient mechanism for carbon storage in the mantle.

Sediment grains in rivers are often bound together and stabilized by bacterial films. Experiments and mathematical models show that sediments bound by biofilms behave like a single elastic membrane that can rip catastrophically if the river flows fast enough.

Methane is abundant in marine sediments. Analysis of sediment cores and seismic images of marine sediments obtained off the coast of Pakistan show fracturing of gas hydrates and an increase in upward methane flux in the decades following a large earthquake in the Arabian Sea in 1945, suggesting that quakes can trigger hydrocarbon seepage.

Submarine seeps release substantial amounts of methane into the overlying water column at continental margins, leading to the formation of calcium carbonate deposits. Analyses of methane-derived carbonate build-ups on the Nile Delta suggest that their formation coincided with the development of deep-water anoxic or suboxic conditions.

The precise location of the mantle plume upwelling beneath Hawaii is debated. Seismic data reveal a thick layer of melt in the mantle beneath western Hawaii, implying that the upwelling plume may be deflected around an ancient, resistive root beneath the island.

The Lusi mud eruption in Indonesia has been ongoing since 2006. Numerical simulations show that a parabolic-shaped layer in the rock surrounding the site of the Lusi eruption could have amplified and focussed incoming seismic energy from an earthquake, which then triggered the mud eruption.

Iceberg calving—implicated in the retreat of ice shelves—is a complex process constrained by few observations. Numerical simulations suggest that the pattern of iceberg calving is controlled by the geometry of the glacier, and that regions of Greenland and Antarctica may be particularly vulnerable to catastrophic calving-driven retreat.

The East Antarctic ice sheet is considered to be largely insensitive to temperature changes in the Southern Ocean. Marine sediment records indicate the East Antarctic ice sheet repeatedly retreated by several hundred kilometres during intervals of Pliocene warmth.

The Greenland and Antarctic ice sheets have been reported to be losing mass at accelerating rates. Comparison of mass loss trends over the past decade with reconstructions of past mass loss indicates that the existing satellite record is too short to separate long-term mass loss trends from natural variability.

During the last deglaciation, the North Pacific Ocean was characterized by a spike in primary productivity, which has been attributed to iron input. Marine sediment analyses suggest that, instead, the productivity may have been fuelled by deep convection and subsequent stratification.

Volcanic tremor can be caused by small earthquakes occurring within the volcano. Mechanical modelling of volcanic tremor generated at Redoubt Volcano, Alaska, suggests that high-frequency tremor is the result of stick–slip motion in faults within the volcano conduit.

Owing to the turbulent nature of the ocean, mesoscale eddies are omnipresent. An analysis of atmospheric conditions associated with several hundred thousand eddies in the Southern Ocean suggests that the transitory sea surface temperature fronts associated with these eddies alter near-surface winds, clouds and rainfall.

Over the twentieth century, droughts in southwestern North America have been linked to sea surface temperature variability in the North Pacific Ocean. Speleothem data from southern California suggest that links between the North Pacific and drought were less pronounced during the past millennium.

Large earthquakes in subduction zones can affect nearby volcanoes. Analysis of ground deformation following the 2010 earthquake in Maule, Chile, shows that some volcanoes subsided by up to 15 cm, probably because of quake-triggered release of hydrothermal fluids.

The 2011 Tohoku earthquake caused high levels of crustal deformation in Japan. Analysis of satellite radar and GPS data show that the earthquake caused nearby volcanic regions to subside instantaneously, creating elliptical depressions that are parallel to the direction of quake-induced crustal extension.

The extinction of megafauna in Australia about 43,000 years ago has been linked to both human arrival and vegetation change. Marine sediment analyses from the east coast of Australia suggest that vegetation change was a result, rather than cause, of the extinction.

Coral records from the Barbados have been used to infer that, due to ice expansion, sea level was 120 m lower than today during the Last Glacial Maximum. A 3D simulation of the mantle in this region suggests these estimates were biased by the presence of a subducted slab, and indicates the sea-level difference was closer to 130 m.

The frequency of North Atlantic tropical storms varies markedly on decadal timescales. An analysis of climate model simulations suggests that anthropogenic aerosols lowered the frequency of tropical storms in the North Atlantic over the twentieth century.

Great White Spot—a rare planet-encircling storm—raged on Saturn in 2010–2011. Analyses of high-resolution spacecraft imagery and numerical modelling reveal a dynamic storm head powered by sustained convection in the zonal flow of Saturn’s atmosphere.

How noble gases are recycled from the atmosphere back into the mantle has been unclear. High-pressure experiments demonstrate that noble gases are highly soluble in an important hydrous mineral in altered oceanic crust, suggesting that subduction of this type of crust may be a significant pathway for noble gas flux back into the mantle.