Volume 3 Issue 3, March 2010

Greenland is losing ice through glaciers that flow into deep fjords. New observations highlight the important fjord processes that supply warm ocean waters to the melting glaciers, and thereby affect Greenland's contribution to sea-level rise.

The earliest evolution of our planet is difficult to reconstruct. Ancient rocks in Western Australia show an isotopic signature that links their formation with 4.3-billion-year-old crust.

About 94.5 million years ago, oxygen levels in the deep ocean dropped while carbon burial rapidly increased. Geochemical analyses suggest that the release of sulphate from extensive volcanism set off a sequence of biogeochemical reactions that led to ocean anoxia.

Predicting an El Niño or La Niña event before the preceding spring has proved to be difficult. Taking into account coupled ocean–atmosphere modes in the Indian Ocean region that have a two-year periodicity may provide the basis for longer forecasting lead times.

The rise in atmospheric carbon dioxide levels at the end of the last glacial period has been attributed to a release of carbon from the abyssal ocean. Radiocarbon analyses from the Chilean margin have failed to find evidence that supports this hypothesis.

At the end of the twentieth century, tropical deforestation was associated with the growth of rural populations. An assessment of the factors involved in forest loss suggests that today's trees are more likely to be affected by economic pressures from farther afield.

Whether the characteristics of tropical cyclones have altered, or will alter, in a changing climate has been subject of considerable debate. An overview of recent research indicates that greenhouse warming will cause stronger storms, on average, but a decrease in the frequency of tropical cyclones.

Jupiter’s large moons Ganymede and Callisto are similar in size and composition, but different in surface and interior characteristics. Simulations with geophysical models of core formation indicate that the difference in impact energy received by the two satellites during the period of late heavy bombardment can explain the dichotomy.

Anomalies of the El Niño/Southern Oscillation in the Pacific Ocean and the Indian Ocean Dipole often occur simultaneously. An analysis of observations and models suggests that, in addition, the negative phase of the Indian Ocean Dipole tends to occur 14 months before an El Niño event, with implications for El Niño predictability.

In the Arctic spring, sunlight-induced reactions convert gaseous elemental mercury into compounds that are rapidly deposited on the snowpack. Analysis of the isotopic composition of mercury in snow samples collected during an atmospheric mercury depletion event suggests that sunlight triggers the re-emission of mercury from the snowpack.

Reducing tropical deforestation is at present considered a cost-effective option for mitigating climate change. Satellite-based estimates of forest loss suggest that urban population growth and urban and international demand for agricultural products are key drivers of deforestation in the tropics.

The recent rapid increase in mass loss from the Greenland ice sheet is primarily attributed to an acceleration of outlet glaciers. Oceanographic data obtained in summer 2008 show that subtropical waters that reside year-round in the shelf ocean off Greenland continuously enter a large glacial fjord in East Greenland and contribute to melting at the glacier terminus.

Widespread glacier acceleration has been observed in Greenland in the past few years. Oceanographic observations taken in summer 2008 show that ocean waters melted a substantial fraction of ice along the calving fronts of three West Greenland glaciers, indicating that submarine melting has a profound influence on grounding-line stability.

The rise in atmospheric carbon dioxide at the end of the Last Glacial Maximum has been attributed to the release of carbon dioxide from the deep Southern Ocean. However, reconstructions of the radiocarbon signature of Chilean margin intermediate waters during the glacial termination do not reflect the influence of such a release.

Increasing concentrations of carbon dioxide in sea water are driving a progressive acidification of the ocean, with as yet unclear impacts on marine calcifying organisms. Simulations with an Earth system model suggest that future changes in the marine environment could be more severe than those experienced during the Palaeocene–Eocene thermal maximum, both in the deep ocean and near the surface.

Several periods of global ocean anoxia punctuated the Cretaceous period. Marine-sediment chemistry indicates that extensive volcanism at the beginning of Oceanic Anoxic Event 2 released sulphur to the oceans, triggering a biogeochemical cascade that led to enhanced surface productivity and depletion of oxygen in the underlying waters.

Ninety-four million years ago, during Ocean Anoxic Event 2, there was a marked increase in the burial of organic carbon in marine sediments. Measurements of stomata in fossil leaves show that the two main pulses of carbon burial were associated with a decline in atmospheric CO₂ levels of up to 26%.

The onset of fluvial erosion in an area of tectonic uplift is thought to reflect the timing of the uplift. Geomorphological data from the Yellow River in Tibet, indicate that the rapid incision of this river channel occurred as a result of climate change, at least six million years after the onset of plateau uplift.

There is evidence for the existence of differentiated crust early in Earth’s history, but little is known about the timing and nature of the crust and its formation. New samarium–neodymium data from the Dresser Formation in Western Australia point to differentiation of the early crust from the mantle more than 4.3 billion years ago.

Fiamma Straneo and colleagues travelled to the heart of a glacial fjord in East Greenland to determine the causes of glacial retreat.