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Please quote Nature Geoscience as the source of these items.

May 2010

Methane from extinct herbivores

The extinction of large plant-eaters such as mammoths and mastodons, which began about 13,000 years ago, led to a dramatic decline in the total amount of methane emitted to the atmosphere annually, suggests a paper online this week in Nature Geoscience. Over 114 species of large-bodied herbivores — megafauna — throughout North and South America vanished during the extinction.

Like modern plant-eaters, such as cattle, the extinct herbivores released methane as part of their digestive process. Felisa Smith and colleagues estimate that these megafauna released about 9.6 teragrams of methane annually — with the range of estimates between 2.3 and 25.5 teragrams — to the atmosphere. Intriguingly, the extinction coincides with a significant drop in atmospheric methane concentrations, as recorded in ice cores. The team suggests that the loss of methane emissions could account for between 12 and 100% of that decline.

Methane emissions from extinct megafauna

Felisa A. Smith, Scott M. Elliott and S. Kathleen Lyons

Published online: 23 May 2010 | doi 10.1038/ngeo877

How will global warming affect El Niño?

Global warming will probably change the balance of the physical processes that determine the strength and frequency of El Niño and La Niña events, reports a review online this week in Nature Geoscience. Because amplifying and dampening effects are both expected to be affected, it is not yet possible to predict the overall evolution of this Pacific climate 'see-saw' in a warming world.

Mat Collins and co-authors reviewed projected changes in the tropical Pacific climate over the next century. They found that the effect of climate warming on individual components of the ocean–atmosphere system, such as the strength of upwelling in the eastern tropical Pacific, and the temperature of the sea surface and its interplay with that of the air is well understood. But not all of the expected changes will affect El Niño characteristics in the same way. The authors conclude that the climate variability associated with El Niño and La Niña events could intensify, weaken or even undergo little change depending on the balance of changes in the underlying processes.

The impact of global warming on the tropical Pacific Ocean and El Niño

Mat Collins, Soon-Il An, Wenju Cai, Alexandre Ganachaud, Eric Guilyardi, Fei-Fei Jin, Markus Jochum, Matthieu Lengaigne, Scott Power, Axel Timmermann, Gabe Vecchi and Andrew Wittenberg

Published online: 23 May 2010 | doi 10.1038/ngeo868

Ancient warming caused increased wildfire risk

Warming climate 200 million years ago caused increased wildfire activity in East Greenland, according to a paper published online this week in Nature Geoscience. This increased fire risk was linked not only to rising temperature, but also to a climate-driven shift to more flammable vegetation in the Jurassic forests.

Claire Belcher and colleagues studied charcoal and the remains of plants preserved in fossil-rich deposits in East Greenland. They found evidence for warming climate at the boundary between the Triassic and Jurassic periods, along with charcoal evidence of increased wildfire activity. They also noticed a change in the vegetation, with broad-leaved plants prevalent in the Triassic and narrow-leaved and needled plants dominating the Jurassic. Laboratory experiments confirmed that the Jurassic-type leaves were more prone to igniting and spreading fire.

The team concludes that, at least in East Greenland, the vegetation shift, along with warm temperatures and more frequent storms, led to increased fire risk early in the Jurassic period.

Increased fire activity at the Triassic/Jurassic boundary in Greenland due to climate-driven floral change

Claire M. Belcher, Luke Mander, Guillermo Rein, Freddy X. Jervis, Matthew Haworth, Stephen P. Hesselbo, Ian J. Glasspool and Jennifer C. McElwain

Published online: 23 May 2010 | doi 10.1038/ngeo871

Patterns in future health impacts from heatwaves

People living in southern European river basins and along the Mediterranean coasts will probably be hit hardest by future European heatwaves, suggests a study published online this week in Nature Geoscience. The frequency of health-endangering heatwaves is projected to increase fastest and strongest in these locations, which include many densely populated urban centres.

Erich Fischer and Christoph Schär analysed a set of regional climate projections for Europe to assess the likely occurrence of heatwaves with a high impact on human health, based on known factors such as heatwave duration, minimum night-time temperatures and humidity. The analysis reveals remarkably consistent geographical patterns of predicted heatwave impacts up to the year 2100, suggesting crucial influence from local topography and proximity to the Mediterranean Sea.

Consistent geographical patterns of changes in high-impact European heatwaves

E. M. Fischer and C. Schär

Published online: 16 May 2010 | doi 10.1038/ngeo866

Recent Lake Tanganyika warming unprecedented since AD 500

Late-twentieth-century warming of the surface of Lake Tanganyika, the largest of the East African rift lakes, is the biggest temperature change in the past 1,500 years, according to a study published online this week in Nature Geoscience. Lake surface warming is linked to declining growth and abundance of the plankton that form the base of the lake's food chain, which could have negative effects on the region's fisheries.

Jessica Tierney and colleagues used lake sediment cores to reconstruct temperatures and primary productivity at the surface of Lake Tanganyika. They report a number of temperature fluctuations during the past 1,500 years, but the highest temperatures in their record occurred during the past few decades. In addition, they show that warmer surface temperatures were consistently associated with lower primary productivity, which they attribute to stratification between the lake's surface and the nutrient-rich waters below.

The team describes the field work that supported these conclusions in an accompanying Backstory.

Late-twentieth-century warming in Lake Tanganyika unprecedented since AD 500

Jessica E. Tierney, Marc T. Mayes, Natacha Meyer, Christopher Johnson, Peter W. Swarzenski, Andrew S. Cohen and James M. Russell

Published online: 16 May 2010 | doi 10.1038/ngeo865

Coring climate change

Andrew Cohen and colleagues

Published online: 16 May 2010 | doi 10.1038/ngeo875

Seasonal changes in glacier movement

Ice velocities in a west Greenland glacier during the summer can exceed its velocity during the winter by 220%, according to a study published online this week in Nature Geoscience. The findings are important for understanding the response of glacier movement to surface melting and to changes in the water drainage system beneath the glacier.

Ian Bartholomew and colleagues used GPS receivers along a 35-km transect into the western margin of the Greenland ice sheet to measure ice velocity throughout summer 2008 and into the subsequent winter season. The scientists found increases in glacier speed that coincided with an uplift of the glacier surface, indicative of the delivery of surface melt water to the glacier bed. Further inland, glaciers sped up later in the year.

The authors conclude that if summer melt seasons become longer and more intense, glacier acceleration events in response to meltwater will reach further inland, thus drawing ice from a larger area of the ice sheet.

Seasonal evolution of subglacial drainage and acceleration in a Greenland outlet glacier

Ian Bartholomew, Peter Nienow, Douglas Mair, Alun Hubbard, Matt A. King and Andrew Sole

Published online: 9 May 2010 | doi 10.1038/ngeo863

Sunken plates cause dents in Earth's shape

Low points in the geoid—the shape the Earth's surface would take if it was entirely covered by motionless water—arise from anomalies in the Earth's mantle where ancient tectonic plates have sunk, concludes a study published online this week in Nature Geoscience. The findings explain the low points in the geoid that are found around the Pacific Ocean, including troughs in the Indian Ocean, the Ross Sea off Antarctica, northeast Pacific and west Atlantic Oceans.

Sonja Spasojevic and colleagues used a model of the dynamics of Earth's mantle to identify anomalies in mantle velocities associated with the geoid low points. They attribute these unusual velocities to the presence of ancient tectonic plates in the deep mantle, where they form 'slab graveyards', and to the effect of their chemical make-up on the overlying mid-to-upper mantle.

Mantle upwellings above slab graveyards linked to the global geoid lows

Sonja Spasojevic, Michael Gurnis and Rupert Sutherland

Published online: 9 May 2010 | doi 10.1038/ngeo855


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