Research articles

The oceans are becoming more acidic as they absorb anthropogenic carbon dioxide—this may limit the ability of marine organisms to secrete carbonate. A sediment-trap study shows that in the Southern Ocean the shell weights of a surface-dwelling single-celled organism with a calcite shell are lower than pre-industrial values, probably as a result of increasing ocean acidity.

Aerosols from biomass burning can alter the radiative energy balance of the Earth by reflecting or absorbing solar radiation. Satellite measurements indicate that the amount of energy absorbed by aerosols at the top of the atmosphere increases with underlying cloud coverage.

Interactions between microbes and minerals are evident in modern global elemental cycles. Relationships between minerals in Cambrian mudstones indicate that such interactions may have released otherwise unavailable, mineral-bound iron and silica into the ancient oceans.

Under drought conditions, biomass burning in Indonesia is a disproportionate contributor to the global carbon dioxide emissions from such events. An analysis of Indonesian records of large fires shows that their occurrence is linked to land use and population dynamics, and that the Indian Ocean climate and El Niño both have an equally important influence.

The timing and mechanisms of the transition from a glacial to an interglacial state are controversial. An analysis of Antarctic ice-core records indicates that glacial terminations may begin as millennial-scale warmings in the southern hemisphere that, unlike previous events, are not reversed by abrupt warming in the northern hemisphere.

The variations of tropical precipitation are antiphased between the hemispheres on orbital timescales. A comparison between a speleothem record of precipitation in northeast Brazil and rainfall reconstructions from the rest of tropical South America shows that a similar antiphasing operated in the same hemisphere during the Holocene.

The Younger Dryas event was a brief return to cold conditions before the onset of interglacial warmth. An analysis of sediment records from Lake Kråkenes in Norway and the Nordic Seas shows that during the late Younger Dryas, Northern Europe underwent rapidly oscillating climate conditions, possibly related to the break-up of Nordic sea-ice.

Nitrous oxide is a potent greenhouse gas whose concentration is increasing in the atmosphere; the highest emissions have been observed from agricultural and tropical soils. Now, measurements in subarctic East European tundra show that bare surfaces on permafrost peatlands, known as peat circles, release large quantities of nitrous oxide.

Although a number of hypotheses have been put forward to explain the sulphate deposits discovered by the Opportunity rover at Meridiani Planum, Mars, the sedimentary layers remain enigmatic. A re-analysis of the chemistry, sedimentology and geology of the deposits suggests they formed through a reworking of the sublimation residue from a large-scale deposit of ice and dust.

Hydrothermal vents release significant quantities of dissolved iron into the oceans. Spectromicroscopic examination of a hydrothermal plume suggests that carbon-rich matrices protect this iron from oxidation and precipitation.

Groundwater seepage is expected to affect channel features, but its role remains controversial. Two linear response relationships that describe channel evolution from groundwater flux are sufficient to characterize seepage-driven channel networks, linking the dynamics of channel growth to channel morphology.

The primitive Moon was covered with a thick layer of melt known as the lunar magma ocean, whose crystallization resulted in the Moon’s surface as it is observed today. Dating of the oldest zircon so far in lunar rocks indicates that much of the magma was probably crystallized within 100 million years of the Moon’s formation.

The conditions leading to rock failure during intermediate-depth earthquakes in subduction zones are not clear, particularly in the absence of free fluid. Field observations and numerical simulations indicate that thermal weakening due to high-temperature shear instabilities may trigger earthquakes under such circumstances.

Continued global warming could persist far into the future, because natural processes require decades to hundreds of thousands of years to remove carbon dioxide produced by fossil-fuel burning from the atmosphere. A 100,000-year simulation indicates that severe ocean oxygen depletion could last for thousands of years.

Photochemical ozone production near the Earth’s surface is considered to be a summertime, urban phenomenon. However, air-quality measurements in the rural Upper Green River Basin, Wyoming, show rapid, diurnal photochemical production of ozone during air temperatures as low as −17 ^∘C.

Stress accumulation between earthquakes results from slip that is insufficient to fully accommodate plate movement. An inverse analysis of GPS data from the Kuril–Japan trench reveals a trench-parallel belt of stress accumulation with six peaks in the depth range of 10–40 km, suggesting potential source regions for future earthquakes.

Surface solar radiation has undergone decadal variations, producing global ‘dimming’ and ‘brightening’ effects, probably owing to changes in aerosol burden and clouds. An analysis of multidecadal data of horizontal visibility shows that the occurrence of fog, mist and haze has declined in Europe over the past 30 years.

The carbon cycle plays a central role in climate change. An analytical framework shows that the influence of atmospheric carbon dioxide concentrations on climate is more sensitive to carbon perturbations now than it has been over much of the preceding 400 million years.

A quantitative reconstruction of the global climate during the last glacial maximum was published in the early 1980s. A synthesis of global sea-surface temperature reconstructions shows global cooling of the tropical oceans and strong longitudinal temperature-gradients.

Methylmercury bioaccumulates in aquatic food chains and can cross the blood–brain barrier, making this organometallic compound a much more worrisome pollutant than inorganic mercury. Experimental evidence now indicates that mercury methylation by the bacterium Geobacter sulfurreducens can be greatly enhanced in the presence of the amino-acid cysteine.