Volume 2 Issue 1, January 2009

The oceans soak up a large fraction of the carbon dioxide we emit into the atmosphere. The long-term strength and efficiency of this carbon sink relies on the transport of surface waters to the deep ocean.

Volcanism in the enormous Tharsis region on Mars migrated from south to north. Numerical modelling suggests that this migration as well as the current location of the region can be explained by net rotation of the lithosphere relative to the mantle.

Meteorites frequently bombarded the surface of the early Earth. Could these impacts have provided the energy and materials to form the basic building blocks of life?

Measurements of directional travel speed of seismic waves constrain flow in the upper mantle. Laboratory experiments suggest that high pressure can change the mantle's mineral alignment, leading to a 90° offset in the direction of the fastest seismic waves.

The lack of deep mixing in the subpolar North Atlantic Ocean for over a decade has raised concerns that climate warming may already be affecting the ocean circulation. A vigorous convection event last winter shows that the system holds some surprises yet.

Sub-surface oceans probably exist on several large satellites of Jupiter and Saturn. An analysis of Europa's tides suggests that some of the Rossby waves are resonantly enhanced by the obliquity, producing sufficient heat and flow to keep the ocean liquid.

Climate models predict that increasing greenhouse gas levels will invigorate the circulation in the upper atmosphere. But a close look at observations of the age of stratospheric air over 30 years reveals no acceleration in the circulation.

As a single-plate planet, Mars cannot support large-scale motion of the lithosphere, according to the standard theory of stagnant-lid convection, but such motion is required to explain the position of the Tharsis Rise. Modelling work suggests that differential rotation of the lithosphere can resolve this problem.

The Earth constantly loses matter, mostly in the form of H⁺ and O⁺ ions. Analysis of measurements from the Cluster spacecraft reveals that the total loss of cold ions, below 1 eV in thermal energy, is larger than the previously observed, more energetic, outflow.

The rising abundance of greenhouse gases in the atmosphere has been associated with a change in the stratospheric circulation and a decrease in the mean age of stratospheric air. Balloon-borne measurements of trace gases over 30 years suggest that, in contrast to model predictions, there have been no significant trends (at a 90% confidence limit) in the age of stratospheric air.

Observational studies show a clear response in European climate to El Niño/Southern Oscillation in late winter. Simulations with an atmospheric general circulation model identify a long-distance pathway connecting climate variability in the Pacific region and Europe via the stratosphere, the upper layer of the atmosphere.

Nearly 40% of the Earth’s ice-free surface area is cropland or pasture. Measurements of dissolved organic matter along a gradient of agricultural land use suggest that agricultural watersheds contain less complex, more microbially derived dissolved organic matter than natural wetlands.

Biological nitrogen fixation limits plant growth and carbon exchange at local to global scales. Long-term nutrient manipulation experiments in forests and short-term manipulation experiments in microcosms suggest that the micronutrient molybdenum, a component of the nitrogen-fixing enzyme nitrogenase, limits nitrogen fixation by asymbiotic bacteria in tropical soils in Panama.

Climate variability in the tropical Pacific Ocean influences climate across much of the planet. A diatom-based record of sea surface temperatures from El Junco lake, Galapagos, reveals that the most recent half-century is the warmest 50-year period in the past 1,200 years.

The effect of volcanism on low-latitude climate has been difficult to quantify. A compilation of tropical and subtropical annually resolved climate reconstructions shows a correlation between low sea surface temperatures and low-latitude volcanic activity over the past four centuries.

The break-up of an asteroid led to the rapid delivery of meteorites to Earth around 470 million years ago. The widespread occurrence of sedimentary megabreccias deposited at the same time suggests this high influx of meteorites could have triggered mass wasting — downslope movement of rock and sediment — at continental margins, by inducing the destabilization of sedimentary slopes.

Impacts of extraterrestrial objects were frequent on the early Earth. Shock experiments suggest that the impact of the most common type of meteorites into sea water could have synthesized the organic molecules that served as the building blocks of life.

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.

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.

Jessica Conroy and colleagues braved mud and rain and got nipped by sea lions in an attempt to unravel the record of tropical Pacific climate change.

Yoshihiro Furukawa and colleagues stuck to their guns in an attempt to recreate life on the early Earth.