Letters in 2014

How the atmosphere, hydrosphere and surface materials interacted on early Mars is poorly understood. Oxygen isotopic composition of zircon grains in a martian meteorite reveals a prolonged history of exchange between martian regolith and atmosphere.

Plants may enhance sedimentation and help deltas to keep up with rising sea levels. Numerical simulations show that intermediate vegetation height and density are optimal, whereas too much vegetation inhibits sediment deposition in deltaic marshes.

Global mean surface warming has been slow over the past 15 years. An analysis of climate simulations suggests that the low warming rate can be explained by an unusual phase of El Niño/Southern Oscillation and solar and aerosol variability.

Variations in solar activity have been linked to centennial to decadal-scale interglacial climate fluctuations. A ¹⁰Be-based reconstruction of solar activity from the Last Glacial Maximum indicates a similar Sun–climate link operated during glacial conditions.

Large earthquakes can trigger seismicity in remote regions. Analysis of seismic data from Antarctica reveals ice quakes coincident with passing seismic waves from the 2010 Chile earthquake, suggesting that the ice sheet is sensitive to such triggers.

The levels of aerosols in the atmosphere affect cloud reflectivity and the Earth’s radiative balance. A comprehensive analysis of satellite observations shows that thermodynamics and precipitation govern cloud responses to aerosols.

Atmospheric aerosols can exert an important influence on Earth’s climate. Combustion chamber experiments reveal that the absorption properties of brown carbon aerosols from biomass burning are linked to their black carbon content.

Increased oxygen availability in the Cambrian oceans supported the evolution of animals that mixed the seafloor sediments. Numerical modelling suggests the development of a feedback loop between bioturbation, phosphorus burial and oxygen levels.

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 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.

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.

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.

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.

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.

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.

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.

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.

The factors that control the submarine melt rate at Greenland’s glaciers are uncertain and largely inferred from brief summer surveys in the fjords where glaciers terminate. Continuous records of water properties and velocity for the months September to May from two large Greenland fjords reveal strong variability on 3- to 10-day timescales as a result of pulses of water that are propagated from the shelf ocean.

As northern summer solstice nears on Saturn’s moon Titan, dynamic processes on its surface are expected. Recent observations by the Cassini spacecraft reveal transient bright features in or on a Titan sea that are consistent with an ephemeral phenomenon such as waves.

When basal meltwater refreezes, the resulting warm ice can influence the flow dynamics of the ice sheet above. An analysis of airborne gravity and radar data identifies extensive basal-ice units across the northern Greenland ice sheet that coincide with areas of deformed ice and fast ice flow.