Articles in 2009

Bangladesh relies heavily on groundwater for the irrigation of dry-season rice. Analysis of soil porewater and floodwater in rice paddy fields during the monsoon season in Bangladesh suggests that flooding removes a significant amount of arsenic from the soils.

The equilibrium response of global temperatures to an increase in atmospheric carbon dioxide concentrations is difficult to quantify. Simulations and proxy data of the mid-Pliocene warm climate suggest that the response is 30 to 50% higher than traditionally calculated when slowly adjusting components of the Earth system, such as ice sheets and vegetation, are included in the estimate.

Geochemical analyses and climate modelling suggest that 2.5 billion years ago much of the nitrogen now stored in the solid Earth was in the atmosphere, and that the higher atmospheric nitrogen levels would have increased the efficacy of greenhouse gases, thus warming the Earth.

Microbially mediated oxidation of organic carbon is thought to drive the release of arsenic into groundwater. Hydrological and geochemical analyses suggest that pond water is the source of organic carbon in groundwater in Bangladesh.

The devastating Wenchuan earthquake in 2008 struck along a fault zone that showed low rates of deformation. Analysis of GPS and InSAR data suggests that, as structural barriers failed during a single earthquake, the rupture cascaded across multiple fault segments, which may explain the high magnitude of the event.

The initial production of oxygen in early Earth’s oceans altered the redox chemistry and cycling of nitrogen. A record of nitrogen isotopes from preserved organic matter indicates nitrogen cycling in the presence of free oxygen 2.67 billion years ago, about 200 million years before the first geochemical evidence for atmospheric free oxygen.

Atmospheric concentrations of nitrous oxide, a greenhouse gas, have increased since 1860. A regression model indicates that conversion of 2% of manure nitrogen and 2.5% of fertilizer nitrogen could explain the pattern of increasing nitrous oxide concentrations between 1860 and 2005, including a rise in the rate of increase around 1960.

The formation of dunes is controlled by the direction of the prevailing winds and the characteristics of the sediments. Linear dunes in the Qaidam Basin, China, are shown to form from cohesive sediments, a model that could be applicable to dunes on Titan.

Most discharge from large ice sheets takes place through fast-flowing ice streams. A combination of radar and seismic data reveal megascale glacial lineations at the bed of a West Antarctic ice stream that undergo significant change by erosion and deposition on decadal timescales.

The extinction at the Triassic/Jurassic boundary is one of the five largest in Earth’s history. Microfossil and organic geochemical analyses link the vegetation turnover in Europe to the release of pollutants and toxic compounds from flood basalt volcanism in the central Atlantic Ocean.

Seasonal changes in tropical rainfall patterns are associated with changes in the position of the intertropical convergence zone. Microbiological, molecular and hydrogen isotopic evidence from island lake sediments shows that the Pacific intertropical convergence zone was south of its modern position by as much as 500 km during the Little Ice Age.

The interglacial period that occurred about 400,000 years ago—Marine Isotope Stage 11—was the longest out of the past five glacial cycles. A proxy-based alignment of this interglacial with the Holocene, and a subsequent analysis of carbon isotopic data from marine sediments, indicates that the unusual length may have been driven by strong poleward oceanic heat transport.

Seismic anisotropy data for the Great Basin region of the western United States, coupled with tomographic images, help delineate a northeast-dipping lithospheric drip. Numerical experiments suggest that the drip could have formed owing to gravitational instability triggered by a density increase of about 1% and a temperature increase of about 10%.

Tectonic activity severely restricted the seaway connecting the tropical Pacific and Indian oceans sometime between about 3 and 4 million years ago. Ocean temperature and salinity reconstructions indicate that the Indonesian Gateway reached its present configuration about 2.95 million years ago, leading to the cooling and freshening of subsurface water in the tropical eastern Indian Ocean.

The relative importance of regional and global changes in atmospheric greenhouse gas and aerosol concentrations for regional changes in climate is not well known. A climate model analysis of tropical, mid-latitude and polar regions shows that the extratropics and, in particular, the Arctic region are sensitive to local changes in radiative forcing.

The timing of the origin of photosynthesis remains controversial. The discovery of ancient haematite crystals that formed in a jasper formation in Australia, which was created in a marine setting, suggests that oxygen was being produced, at least locally, by photosynthesis as early as 3.46 billion years ago.

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.

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.

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.