Volume 4 Issue 10, October 2011

Naturally produced hydrocarbons such as isoprene influence air quality and climate. Accounting for circadian control of isoprene emissions helps to bring model simulations of ground-level ozone into closer agreement with observations.

The growth of East Africa's high topography during the past 30 million years cannot be explained by typical mountain-building processes. Numerical modelling shows that much of this topography formed in response to upwelling in the underlying mantle.

During the last interglacial period, summer temperatures were warmer and the Greenland ice sheet smaller than today. Modelling suggests that the low ice-sheet volume was not simply a consequence of high ambient temperatures.

Proof that purported fossils of early life are truly old and biological is often controversial. Detailed analyses confirm the early evolution of microbial sulphur cycling and reveal microfossils in 3.4-billion-year-old beach sandstones.

Atmospheric aerosols strongly influence Earth's climate, but how they form has remained a mystery. According to cloud chamber experiments, a mixture of vapours, as well as ions formed by galactic cosmic rays, contribute to the particle formation recipe.

Phyllosilicate minerals are rare in the Noachian-aged crust of the northern lowlands of Mars, compared with the tropical highlands. Geochemical and climate modelling suggest that this dichotomy is consistent with the presence of a cold ocean fringed by cold-based glaciers.

The volatile organic compound isoprene — a precursor to the air pollutant ozone — is produced by many plant species. Canopy-scale measurements in Malaysia, combined with model simulations, suggest that isoprene emissions are under circadian control.

Riverbed cutoffs affect the river-channel geometry and flood-plain morphology. Field studies following two cutoff events in the Wabash River, USA, show that these events also trigger the release of large volumes of sediment, much of which is deposited immediately downstream.

During the last interglacial period, the volume of the Greenland ice sheet was up to 60% smaller than today. Climate and ice-sheet modelling suggests that about 55% of this change was caused by higher ambient temperatures and the remaining 45% was a result of higher insolation and the associated climate feedbacks.

Whether sea level was stable during the last interglacial remains a subject of debate. An analysis of the U–Th ages of coral reefs in the Bahamas, corrected for open-system behaviour, confirms the presence of at least one oscillation within the sea-level highstand.

The effect of expanded glaciation on the relief of mountain ranges is debated. Chronometric and model data from the European Alps suggest that relief in the Rhône Valley was enhanced as a result of the increased incision of the valley following the mid-Pleistocene climate transition.

Microbes were thought to be the dominant reef constructors following the end-Permian mass extinction. Sponge–microbe reef deposits formed in the Early Triassic from the western United States suggest that instead, metazoan-reef building continued immediately following the extinction wherever marine conditions allowed.

Geochemical evidence suggests that sulphur-metabolizing bacteria were present at least 3.5 billion years ago. Geochemical and petrological analyses of microstructures from 3.4-billion-year-old rocks in Western Australia suggest they are the remains of early sulphur-reducing and sulphur-disproportionating bacteria.

The mechanisms by which carbon is transported from subducted oceanic crust into the overlying mantle wedge are poorly understood. Geochemical analyses of diamond-bearing fluid inclusions found in the western Alps indicate that carbon dissolution, driven by fluids released from the subducting plate, provides an efficient mechanism to transport carbon into the mantle.

Africa’s topography is characterized by large-scale uplifted domes and subsided basins. Numerical simulations of mantle flow suggest that high topography along Africa’s eastern margin formed as a result of the northward migration of the tectonic plate over the African superplume during the past 30 million years.

The mantle transition zone beneath China is anomalously hydrated. Geochemical analyses of basalts erupted above the mantle transition zone in northeast China indicate that water may have been added to this zone during the dehydration of subducted slabs, on two separate occasions over the past one billion years.

Low levels of biologically available forms of nitrogen can limit phytoplankton growth. Isotopic analyses of seawater samples collected from the Sargasso Sea in the summer suggest that small phytoplankton obtain half of their nitrogen from upwelled nitrate.

The largest dense-water plume feeding the lower limb of the Atlantic meridional overturning circulation from the Nordic seas comes from Denmark Strait overflow water. Measurements of hydrography and water velocity north of Iceland and ocean model simulations indicate that a significant part of this water is supplied by the North Icelandic Jet.