Articles

Precambrian banded iron formations contain thin alternating layers of iron- and silica-rich minerals. Microbial culture experiments show that these alternations could be caused by changes in the relative dominance of microbial iron oxidation and abiotic silica precipitation driven by fluctuating ocean temperature.

The demise of the Laurentide ice sheet during the early Holocene epoch allows rates of ice sheet decay under natural conditions to be assessed. Analysis of terrestrial and marine records of the deglaciation along with a climate model reveal two periods of rapid melting during the final retreat of this ice sheet, with rates of sea level rise of up to 1.3 cm per year.

Thick alluvial fan sediments from the core of the Emeishan Large Igneous Province have been considered as critical field evidence in support of plume-induced pre-volcanic doming and uplift. These sediments are now reinterpreted as mafic hydromagmatic deposits emplaced at sea level, precluding dynamic pre-volcanic uplift as predicted by mantle plume models.

The Arctic soil organic-carbon pool is poorly constrained. Measurements of soil organic carbon in the North American Arctic reveal that the carbon store in this region is larger than previous estimates suggest, and highly dependent on landscape type.

Atmospheric oxygen levels on Earth rose in at least six distinct steps and an examination of the timing of the steps suggests that they coincided with the formation of supercontinents and supermountains. This leads to the hypothesis that increased erosion of these supermountains released large amounts of nutrients to the oceans, stimulating productivity and the release of oxygen to the atmosphere. The subsequent burial of organic carbon along with the mountain sediments would have sustained the increased oxygen levels.

Pristine temperate rainforests are known to produce large amounts of bioavailable nitrogen, with only minimal loss. Tracing ¹⁵N in volcanic soils of a temperate evergreen rainforest in southern Chile helps to further unravel the retention mechanisms for bioavailable nitrogen in these ecosystems.

Arsenic contamination of groundwater resources threatens the health of millions of people worldwide, particularly in the densely populated river deltas of Southeast Asia. Maps of areas at risk of groundwater arsenic concentrations have been produced by combining geological and surface-soil parameters in a logistic regression model. They show that Holocene deltaic and organic-rich surface sediments are key indicators for arsenic risk areas and indicate elevated risks in Sumatra and Myanmar where no groundwater studies exist.

The Earth’s continents amalgamated into the supercontinent Pangaea 320 million years ago. After the supercontinent formed, structural deformation continued, which eventually resulted in the subduction of the ocean margin of Pangaea beneath the continental edge at the other end of the same plate.

Surface waters of most of the world’s oceans are supersaturated with respect to atmospheric methane. Measurements in seawater samples suggest that an aerobic methane production pathway, which involves the decomposition of phosphorus-containing organic compounds, may be responsible.

There has been a strong disagreement between model predictions of troposphere warming and observations of temperature trends from radiosondes and satellites. However, when tropospheric temperature reconstructions are generated from thermal-wind measurements and the thermal-wind equation for 1970–2005, the results show a strong tropospheric warming trend, in agreement with model predictions.

The Eocene–Oligocene transition is the largest global cooling in the Cenozoic period. A comparison of three independent proxies from the continental shelf and deep ocean reveals a three-step transition to cold glacial conditions, with ice sheets 25% larger than their present size.

Nitryl chloride, an active halogen, can be produced through the night-time reaction of dinitrogen pentoxide with chloride-containing aerosol in the polluted marine boundary, and has been measured at levels that are sufficient to affect the photochemistry of oxidants off the southwestern US coast and near Houston, Texas.

Attaching a ‘floating’ tree-ring chronology to ice core records that cover the abrupt Younger Dryas cold interval during the last glacial termination provides a better estimate of the onset and duration of the radiocarbon anomaly. The chronology suggests that marine records may be biased by changes in the concentration of radiocarbon in the ocean, which may affect the accuracy of a popular radiocarbon calibration program during this interval.

In the year AD 365, an earthquake and tsunami destroyed much of the eastern Mediterranean coastal regions. The distribution of uplift at the time suggests that the earthquake occurred on a fault within the overriding plate at the subduction zone beneath Crete, and not on the subduction interface itself.

A large lens-shaped feature bounded by shear zones characterizes the remnant slab beneath the Hindu Kush region. Rather than dripping by viscous flow, the slab is actively stretching and might eventually break off before descending further into the underlying mantle.

Dust input to alpine lakes in the western United States has risen dramatically following westward expansion of human settlements and increased livestock grazing over the past two centuries. The increased dust flux deposits additional nutrients and minerals to the lakes, with important implications for water chemistry, productivity and nutrient cycling.

Over the past 15 million years, Arctic Ocean circulation has exhibited two distinct modes: during the interglacial periods of the past two million years, including the present, Arctic intermediate water was mainly derived from North Atlantic inflow. By contrast, between 15 and 2 million years ago, and during glacial periods thereafter, brine formation on the Eurasian shelves contributed substantially to Arctic intermediate water.