Volume 5 Issue 3, March 2012

During the middle of the Cretaceous period, the polarity of Earth's magnetic field remained stable. A magnetic survey of oceanic crust formed during that time, however, suggests that the field intensity was surprisingly variable.

The Arctic Ocean has become less saline, perhaps in response to climate change. Satellite and in situ observations reveal changes in the regional wind patterns that have re-routed freshwater and prevented it from leaving the Arctic Ocean in the past decades.

Dune fields often exhibit complex patterns of vegetation and morphology over relatively short distances. An analysis of the White Sands dune field in New Mexico attributes the shift in dune form to the development of an internal boundary layer over the rough dune-field surface.

The configurations of ancient tectonic plates are difficult to reconstruct. Seismic images of deep subducted plates, combined with data from ancient volcanic arcs, help to derive a tectonic map of the Pacific Ocean as it was 200 million years ago.

Glaciers supply downstream ecosystems with reactive dissolved organic carbon during periods of ice and snow melt. An analysis of glacier meltwaters in Alaska shows that anthropogenic aerosols fertilize these waters, raising questions about glacier greening.

Atmospheric measurements reveal unexpectedly high concentrations of hydroxyl radicals over tropical forests. Incorporation of a new mechanism of isoprene oxidation into a chemistry model brings simulations into closer agreement with these observations.

The meridional overturning circulation of the ocean plays a central role in the climate and its variability. This Review of recent studies emphasizes the importance of wind-driven upwelling in the Southern Ocean for global ocean circulation.

On the Moon, extensional tectonic features have only been observed close to the influence of the mare basalt-filled basins and floor-fractured craters. Analysis of Lunar Reconnaissance Orbiter Camera images reveals several potentially very young extensional tectonic features in the farside highlands, implying that extensional stresses may locally exceed compressional ones.

The absence of very deep moonquakes implies that the lower mantle of the Moon is partially molten. An analysis of the density range of lunar melts at high pressures suggests that only titanium-rich melt is neutrally buoyant deep within the Moon.

The hydroxyl radical is a key oxidant in the Earth’s atmosphere. The inclusion in an atmospheric chemistry model of a detailed mechanism of isoprene oxidation, involving the buffering of hydroxyl radical concentrations, improves agreement between model simulations of hydroxyl radical levels and observations.

An increasing amount of freshwater has been stored in the Arctic Ocean over the past few decades. Satellite measurements of sea surface height reveal a spin-up of the Beaufort Gyre in the western Arctic that is associated with changes in the wind field, and is estimated to have led to the additional storage of about 8,000 km³ of freshwater.

Glacier-derived dissolved organic matter represents a quantitatively significant source of ancient, but bioavailable, carbon to downstream ecosystems. Anthropogenic aerosols supply glaciers with aged organic matter, according to an analysis of organic matter from glaciers in Alaska.

A large volcanic eruption in AD 1258–1259 is expected to have caused substantial climate cooling, but evidence for this effect is absent from tree-ring-based temperature reconstructions. Numerical modelling of tree growth shows that the lack of cooling is probably an artefact caused by low sensitivity to cooling in trees growing near the treeline.

Dune fields often show abrupt changes in morphology over short distances, but the mechanism driving the changes has been unclear. Physical modelling and airborne altimetry from White Sands, New Mexico, show that the development of an internal boundary layer is linked to the vegetation and hydrologic patterns observed there.

The depth of the Earth’s soil cover is controlled by the competing processes of soil production and erosion. Estimates of the rates of these processes over rugged topography suggest that soil-production rates will increase over surfaces that are subject to rapid erosion.

The plate tectonic configuration of the Triassic–Jurassic palaeo-Pacific Ocean is unresolved. Analyses of ancient geological rocks that are preserved at the margins of North American and Asian continents, combined with tomographic images of subducted slab remnants, indicate that subduction zones may have once existed in the centre of the palaeo-Pacific Ocean.

During the Cretaceous Normal Superchron 121–83 million years ago, the polarity of the Earth’s geomagnetic field remained stable for an unusually long time. Deep-tow magnetic data suggest that despite the stability of the polarity, the field varied greatly throughout the interval.

Subduction transports water into the mantle, but it is uncertain whether the water is preserved in the slab or is rapidly diffused. Analysis of hydrogen and boron isotopes in volcanic rocks sourced from an ancient subducted slab beneath the southwestern Pacific Ocean provides evidence for the long-term preservation of subducted water in the mantle.