Volume 7 Issue 8, August 2014

The successful launch of a carbon-observing satellite could make a start on tracking emissions shifts around the globe.

Southwest Australia has become increasingly dry over the past century. Simulations with a high-resolution global climate model show that this trend is linked to greenhouse gas emissions and ozone depletion — and that it is likely to continue.

Sandstone arches and other striking landforms are the showpieces of national parks around the globe. Experiments and numerical analyses show that they result from a self-organization process that involves vertical load, wind erosion and grain locking.

The global ocean overturning circulation relies on dense deep waters being mixed back up to the surface. An observational analysis shows that turbulent mixing in the abyss around Antarctica varies with the strength of surface eddies and thus probably also wind speeds.

During the early Pliocene epoch, tropical sea surface temperatures were thought to be similar to those of today, even though global mean temperatures were several degrees warmer. Temperature reconstructions now suggest that the Pliocene tropical warm pools were about two degrees warmer than those at present.

Rapid plate motions at fast-spreading ocean ridges mix the mantle, yet homogeneous lavas erupted at slow-spreading ocean ridges imply a well-mixed mantle there, too. Numerical modelling suggests that small-scale convection efficiently stirs the mantle beneath slow-moving plates.

The removal of trace gases from the troposphere is, in most cases, initialized by reactions with hydroxyl radicals. An evaluation of this process (sometimes termed self-cleansing) using existing observations from environments with different atmospheric compositions suggests that it runs at maximum efficiency.

Unlike the other terrestrial planets, Mercury has a relatively thin silicate mantle. Numerical and statistical models suggest that Mercury and other metallic planetary bodies could be survivors of accretion that had their mantles stripped in collisions with larger impactors.

Tidal dissipation in the Moon depends on the lunar tidal period. Numerical modelling of the Moon’s response to tidal forces suggests that tidal dissipation is localized in an ultralow-viscosity zone at the core–mantle boundary.

The ratio of the refractory lithophile elements niobium and tantalum in the silicate Earth is anomalously low. Partitioning experiments suggest that the ratio of these elements is controlled by oxygen fugacity, and thus can be used to constrain the redox conditions of planetary accretion and core formation.

In the Southern Ocean, deep-water masses of the world ocean upwell to the surface and subsequently sink to intermediate and abyssal depths in two overturning cells. Observational evidence relates changes in abyssal mixing—a key influence on the lower cell—to oceanic eddy variability.

Precipitation in austral autumn and winter has declined over parts of southern and southwestern Australia. Simulations with a high-resolution climate model reproduce many aspects of the observed rainfall decline as a response to anthropogenic changes in atmospheric levels of greenhouse gases and ozone, and project significant further drying for southwest Australia over the twenty-first century.

Whether a precipitation event leads to flooding depends on the watershed’s wetness. A case study of the 2011 Missouri River floods demonstrates that the predisposition of a river basin to flooding can be inferred from satellite-based gravity data months in advance.

Despite the role that calving plays in Greenland mass loss, the mechanisms of calving are poorly constrained. Observations of Greenland’s Helheim Glacier suggest that buoyant flexure at the glacier terminus leads to the propagation of basal crevasses and iceberg calving.

The formation and preservation of sandstone landforms such as pillars and arches is enigmatic. Experiments and numerical modelling show that load-bearing material weathers more slowly, and thus the internal stress field can shape and stabilize sandstone landforms.

The geochemical variability of lavas erupted at mid-ocean ridges is lowest where plate spreading rates are high, implying that large-scale plate motions mix the mantle—yet lavas erupted at slow-spreading ridges are also quite homogeneous. Numerical simulations suggest that small-scale convection in the mantle mixes and homogenizes the lavas erupted at slow-spreading ridges.

Sea surface temperatures in the tropical oceans were thought to have remained stable during a period of warmth about five million years ago. Reconstructions of the sea surface temperature from the Caribbean and Pacific suggest that tropical temperatures have in fact changed in concert with global mean temperatures over the past five million years.