Letters in 2012

Zinc is a marine nutrient that may have been limited in the early oceans. Estimates of marine zinc availability through time suggest that values were instead near-modern during the Proterozoic eon.

Wind power inputs at the surface ocean are dissipated through smaller-scale processes in the ocean interior and turbulent boundary layer. Simulations suggest that seafloor topography enhances turbulent mixing and energy dissipation in the ocean interior.

The recovery from the end-Permian mass extinction was slow and prolonged. A temperature reconstruction shows that further biotic crises during the recovery were associated with extreme warmth.

The tropical Atlantic Ocean shows sea surface temperature variability on interannual timescales. Observational and model data suggest that some of this variability can be attributed to the advection of anomalously warm northern subtropical waters toward the Equator.

Tropospheric thunderstorms have been reported to disturb the lower ionosphere, at altitudes of 65–90 km. The use of lightning signals from a distant mesoscale storm to probe the lower ionosphere above a small tropospheric thunderstorm reveals a reduction in ionospheric electron density in response to lightning discharges in the small storm.

Every year, thousands of mesoscale storms (termed polar lows) cross the climatically sensitive subpolar North Atlantic Ocean. High-resolution numerical simulations of the ocean circulation, taking into account the effect of these storms on deep-water formation, suggest that polar lows significantly affect the global ocean circulation.

Changes in continental water storage have been difficult to constrain from space-borne gravity data in regions experiencing both ice melting and glacial isostatic adjustment. Separation of the hydrologic and isostatic signals reveals increases in water storage in both North America and Scandinavia over the past decade.

Sulphate concentrations in the ocean prior to 2.4 Gyr ago were lower than today. The sulphur isotope systematics of 2.7-Gyr-old sulphide deposits suggests that these low concentrations were maintained by a balance between hydrothermal sources and microbial sulphate reduction.

Over 90% of marine species were lost during the end-Permian extinction. Fossil data show that the crisis in China was marked by two distinct phases of marine extinction separated by a 180,000-year recovery period.

A pulse of sulphur dioxide in Venus’s upper atmosphere was observed by the Pioneer Venus spacecraft in the 1970s and 1980s and attributed to volcanism. Recent sulphur dioxide measurements from Venus Express indicate decadal-scale fluctuations in sulphur dioxide above Venus’s cloud tops in an atmosphere that is more dynamic than expected.

As a result of ocean acidification, aragonite may become undersaturated by 2050 in the upper layers of the Southern Ocean. Analyses of sea snail specimens, extracted live from the Southern Ocean in January and February 2008, show that the shells of these organisms are already dissolving.

The West Antarctic Ice Sheet is sensitive to ocean warming and contains enough ice to significantly raise sea level. Direct oceanographic measurements in the Amundsen Sea during 2010 show continuous inflow of warm water towards the thinning ice shelves in West Antarctica.

Diatoms—unicellular algae that form substantial blooms in cold, nutrient-rich waters—are thought to be responsible for the export of marine silica to depth. An analysis of the elemental composition of marine cyanobacteria suggests that picocyanobacteria also accumulate significant quantities of silicon.

Considerable climatic variability on decadal to millennial timescales has been documented for the Holocene epoch. A reappraisal of estuarine and coastal sediment records reveals five periods of enhanced storminess during the past 6,500 years, at a frequency of approximately every 1,500 years and unrelated to solar irradiance variations.

In contrast to the dramatic decline of Arctic sea ice, Antarctic sea ice has increased over recent decades. A 19-year satellite record of sea-ice motion shows that winds are driving decadal trends in Antarctic ice concentrations.

Decadal- to centennial-scale variability has been identified in the Arctic Oscillation, but less is known about variations on the millennial scale. A record of sea-ice drift from off the Alaskan coast shows a 1,500-year cycle in the phase of the Arctic Oscillation.

Episodes of ice sheet disintegration and meltwater release over glacial–interglacial cycles are recorded in the sediments of the Labrador Sea. Analyses of sediment cores along the Labrador and Greenland margins reveal a layer of red material that was probably carried to the Labrador Sea during a glacial outburst flood through the Hudson Strait, early in the last interglacial period.

Above an altitude of about 50 km, carbon dioxide is the primary radiative cooling agent. Carbon dioxide and carbon monoxide mixing ratios derived from satellite-based solar occultation spectra document an estimated increase in global CO_x concentrations of about 23.5 ppm per decade at an altitude of 101 km.

The nearside and farside of the Moon are compositionally distinct. The detection of low-calcium pyroxene around large impact basins suggests that the huge Procellarum basin on the nearside may be an ancient impact structure and a relic scar of the violent collision that produced the lunar dichotomy.

Recent changes in the Southern Annular Mode are associated with warmer, drier conditions in the Southern Hemisphere. An analysis of tree-ring records there suggests that these changes have significantly altered tree growth.