Letters in 2010

Little is known about the source and residence time of sand in the Earth’s largest deserts. Burial ages obtained from cosmogenic nuclides in association with provenance data from geochronology indicate that the sand in the Namib Sand Sea has remained there for at least one million years.

The sulphur cycle plays fundamental roles in the chemistry and climate of Venus. Photochemical modelling suggests that the photolysis of sulphuric acid is a source of observed sulphur oxides in the Venusian mesosphere.

The Enriquillo–Plantain Garden strike-slip fault accommodates the relative motion between the North American and Caribbean plates and was thought to have ruptured during the 2010 Haiti earthquake. Satellite data instead indicate that a blind thrust fault, possibly related to the Haitian fold–thrust belt, was responsible and caused some contractional deformation.

Radiocarbon-depleted carbon dioxide was released to the atmosphere at the end of the last glacial period, but its source remains controversial. Neodymium isotope records of deglacial intermediate water circulation in the eastern North Pacific Ocean from fish teeth support a Southern Ocean source.

The Enriquillo–Plantain Garden fault zone is the primary plate-bounding fault system in Haiti and was initially thought to be responsible for the 2010 earthquake. Palaeoseismic analyses of the fault system indicate that it ruptured during a large earthquake in either 1750 or 1770, but did not rupture during the 2010 earthquake.

Ocean islands formed over hotspots can uplift and subside as the hotspots evolve. The history of the Cape Verde islands reveals large-scale uplift owing to growth of the hotspot swell, but also variable uplift of individual islands resulting from the local intrusion of magma.

Microzonation maps use local geological conditions to characterize seismic hazard, but do not generally consider topography. Ground motions during the Haiti earthquake are found to have been significantly amplified along a high topographic ridge, which caused substantial structural damage, indicating that topography can play an important role in seismic hazard.

Surface winds have declined in China, the Netherlands, the Czech Republic, the United States and Australia over the past few decades. Mesoscale model simulations suggest that an increase in surface roughness is contributing to the stilling trend in the mid-latitude Northern Hemisphere.

Methane concentrations above tropical forests in the neotropics are high, according to space-borne observations. Flux measurements in the field suggest that tank bromeliads, herbaceous plants common throughout tropical forests, emit methane and may contribute to the tropical source.

Decadal fluctuations in the North Pacific Ocean and overlying atmosphere significantly affect the weather and climate of North America and Eurasia. An ensemble of simulations with a coupled ocean–atmosphere model reveals a link between these decadal oscillations and central Pacific El Niño events.

Mars may have once had a CO₂-rich atmosphere, but carbonate rocks that could provide evidence for such conditions are sparse. Spectral analyses of rocks exposed from deep within an impact crater reveal that carbonate deposits may be extensive on Mars, but are buried under layers of younger volcanic rocks.

The 12 January 2010 M_w 7.0 Haiti earthquake exhibited primarily strike-slip motion but unusually generated a tsunami. An extensive field survey reveals that coastal strike-slip fault systems produce relief conducive to rapid sedimentation, erosion and slope failure, so that even modest predominantly strike-slip earthquakes can cause potentially catastrophic slide-generated tsunamis.

Shifts in the position and intensity of the southern westerly winds recorded at single sites have been suggested to reflect uniform variation throughout the wind belt. Sedimentological analyses from the Andes suggest that changes in the intensity of the winds in the core and northern margin of the westerlies were antiphased during the Holocene epoch.

Large earthquakes are known to trigger subsequent earthquakes in nearby regions, but similar triggering has not been confirmed for volcanic hazards. Analysis of the progressive deformation associated with 13 volcanic dykes intruded in Ethiopia between 2005 and 2009 indicates that magmatic intrusions can help to trigger subsequent intrusions.

Above the 410-km discontinuity in the upper mantle, an intermittent layer characterized by low seismic-wave velocities is thought to represent partial melting in areas of subduction or mantle-plume activity. Seismic data now show that the low-velocity layer extends globally with no affinity to a particular tectonic environment.

The geographic extent of cooling associated with the Antarctic Cold Reversal is unclear. Dating of glacial moraines in New Zealand suggests that the cooling extended into the southern mid-latitudes, possibly as a result of the northward migration of the southern subtropical front.

Instrumental records, proxy data and climate modelling show that multidecadal variability is a dominant feature of North Atlantic sea-surface temperature variations. Simulations with a coupled climate model suggest that the timing of this variability is determined mainly by external forcing, for example from volcanic eruption or solar forcing.

Sea-level fluctuations can have a profound impact on coastal groundwater circulation. The geochemistry of groundwater in the Floridan aquifer system suggests that the fresh water in the upper aquifer was emplaced primarily during the last glacial period, when sea level was more than 100 m lower than at present.

In the American west, operational forecasts for spring–summer streamflow rely heavily on snow-water storage. Simulations with a suite of land-modelling systems suggest that snow-water storage generally contributes most to forecasting skill, but that the contribution of soil moisture is often significant, too.

The age of the Solar System is defined by the formation of the first solid grains in the solar nebula. Pb–Pb age dating of these solids, which were later trapped in a meteorite, indicates that the Solar System is 0.34–1.91 million years older than previously thought.