Articles

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.

Seismic anisotropy in Earth’s oceanic lithosphere and in the mantle wedge above subduction zones is associated with crystallographic preferred orientations of olivine. Experiments at high pressure and temperature suggest that a pressure of ∼3 GPa can induce the same changes in the crystal structure of olivine as high water activity at lower pressures.

Deep convection in the subpolar North Atlantic, an important component of the global ocean circulation, has been absent in recent years. Profiling float data from the Argo programme document the return of deep mixing to the subpolar gyre in both the Labrador and Irminger seas in the winter of 2007–2008.

The formation and circulation of Antarctic Intermediate Water has varied over glacial–interglacial timescales. A neodymium record from the Atlantic Ocean basin suggests that changes in circulation may have been driven by changes both in Antarctic Intermediate Water formation in the Southern Ocean and in the strength of North Atlantic meridional overturning.

The response of ocean circulation in the Southern Ocean to changes in wind stress and surface buoyancy fluxes is under debate. An analysis of Argo data and historical measurements suggests that transport in the Antarctic Circumpolar Current and the meridional overturning circulation in the Southern Ocean are insensitive to decadal changes in wind stress.

Although the India–Eurasia collision initiated ∼50 Myr ago, major deformation and exhumation of the Himalaya did not begin until the early Neogene (∼23 Myr ago). This coincides with the increased intensity of the Asian monsoons, as indicated by weathering records from the South China Sea, Bay of Bengal and Arabian Sea, and hints at a dynamic coupling between climate and both erosion and deformation in the Himalaya.

Intense glaciation during the middle Pleistocene epoch led to focused denudation and mass redistribution within the St Elias orogen in southern Alaska, and resulted in structural reorganization of the orogen. The tectonic response of this orogen to climate change is consistent with predictions of numerical models.

On orbital timescales, Antarctic climate varies in phase with Northern Hemisphere insolation, but no physical mechanism for such a link is known. A new analysis suggests that at obliquity and precession timescales Antarctic climate may instead be responding to the duration of the local summer, which covaries with Northern insolation.