Press releases
The first papers of the June 2008 issue of Nature Geoscience are now available online as advance online publication.
Please quote Nature Geoscience as the source of these items.
May 2008
To set off an earthquake
A large earthquake can trigger distant smaller earthquakes throughout the world, independent of geologic setting, reports a study published online this week in Nature Geoscience. The study suggests that earthquake triggering – caused by deformation of the Earth's crust as a result of the passage of surface seismic waves – is a common and widespread phenomenon.
Tom Parsons and colleagues analysed global and regional earthquake catalogues to identify small earthquakes indicative of triggering. They found that 12 out of 15 large earthquakes that had occurred since 1990 generated surface waves that in turn set off smaller quakes around the world. For example, the December 2004 mega-earthquake at the Sumatra-Andaman islands triggered small earthquakes as far away as Alaska, California and Ecuador.
This study identifies triggered earthquakes around the world that would otherwise have escaped attention. The variety of tectonic settings and triggering waves observed in relation to this phenomenon implies that many different physical mechanisms are involved.
Global ubiquity of dynamic earthquake triggering
Tom Parsons (United States Geological Survey, Menlo Park, CA, USA)
Published online: 25 May 2008 | doi 10.1038/ngeo204
Observed upper atmosphere warming in line with models
Whether the tropical upper atmosphere has been warming, and at what rate, has been a controversial issue over the past decades, given the differences between direct observations and climate model simulations. New observational data published online this week in Nature Geoscience. show a warming rate of about 0.65ºC per decade since 1970, which is broadly in line with model simulations, and therefore increases confidence in the climate models.
Previous studies using satellite and direct temperature measurements of the troposphere – the lowest region of the earth's atmosphere – failed to show the warming trend predicted by climate models; most likely because of biases within the methods. To get around these potential biases, Robert Allen and Steven Sherwood used wind measurements, which are more robust than temperature observations, and a meteorological equation linking winds to temperatures, to derive temperature trends. Their results show a warming maximum in the upper atmosphere over the tropics, as expected from climate models.
In an accompanying News and Views article, Peter Thorne states that the authors 'provide [. . .] long-awaited experimental verification of model predictions.' He suggests that 'this story of tropical tropospheric warming highlights the fact that monitoring climate change requires a fundamentally different observational approach to that used in weather forecasting.'
Warming maximum in the tropical upper troposphere deduced from thermal winds
Robert Allen and Steven Sherwood (Yale University, New Haven, CT, USA)
Published online: 25 May 2008 | doi 10.1038/ngeo208
Accompanying News and Views
The answer is blowing in the wind
Peter Thorne (Hadley Centre for Climate Prediction and Research, Exeter, UK)
Published online: 25 May 2008 | doi 10.1038/ngeo209
Fewer Atlantic hurricanes under global warming
Hurricanes and tropical storms will become rarer under the pronounced global warming expected by the end of the twenty-first century, suggests a regional climate model study of the Atlantic basin published online this week in Nature Geoscience. These findings are at odds with the notion that climate change will drive an increase in tropical storm and hurricane frequency.
Tom Knutson and co-workers use a regional model of the Atlantic Ocean basin that was designed for the simulation of hurricanes and that reproduces the observed increase in hurricane frequency between 1980 and 2006. Using an ensemble of climate model projections for the end of the twenty-first century to drive their model, they simulate a decrease in hurricane frequency but a substantial increase in rainfall associated with hurricanes and tropical storms.
The model supports the hypothesis that the main cause of the recent increase in Atlantic hurricane numbers was the warming of the tropical Atlantic Ocean relative to the other tropical ocean basins, whereas a uniform warming of all tropical ocean basins, as expected from global warming, would not lead to increases in Atlantic hurricane frequency.
Simulated reduction in Atlantic hurricane frequency under twenty-first-century warming conditions
Tom Knutson (National Oceanic & Atmospheric Administration, Princeton, NJ, USA)
Published online: 18 May 2008 | doi 10.1038/ngeo202
Other papers from Nature Geoscience to be published online at the same time and with the same embargo:
Rapidly changing flows in the Earth's core
Nils Olsen (Danish National Space Center/DTU, Copenhagen, Denmark)
Published online: 18 May 2008 | doi 10.1038/ngeo203
Clay minerals in delta deposits and organic preservation potential on Mars
Bethany L. Ehlmann (Brown University, Providence, Rhode Island, USA)
Published online: 18 May 2008 | doi 10.1038/ngeo207
When glaciers cut deep
Scientists have found that preferential ice flow and erosion explain why fjords often extend to depths below sea level, according to research published online in Nature Geoscience this week.
Mark Kessler and colleagues use a two-dimensional numerical model to examine the conditions that lead to the intense glacial erosion that is associated with fjord formation. Starting from a landscape with four shallow valleys, the team found that the ice preferentially flows through the lowest valley. The amount of erosion increases proportionally with increasing ice discharge through each channel, and therefore quickly exaggerates the relief of the landscape. Over a few million years, these small valleys are eroded into the dramatic features we see throughout the Arctic region today, with fjords plunging kilometres below sea level.
In an accompanying News and Views, Johan Kleman says 'The model clearly shows that the glacial system is extremely relief-enhancing and capable of greatly magnifying subtle height differences in the initial relief. This […] has not previously been shown numerically.'
Fjord insertion into continental margins driven by topographic steering of ice
Mark Kessler (University of Colorado, Boulder, CO, USA)
Published online: 11 May 2008 | doi 10.1038/ngeo201
Accompanying News and Views
Geomorphology: Where glaciers cut deep
Johan Kleman (Stockholm University, Sweden)
Published online: 11 May 2008 | doi 10.1038/ngeo210
Other papers from Nature Geoscience to be published online at the same time and with the same embargo:
Geochemical evidence for enhanced fluid flux due to overlapping subducting plates
Hitomi Nakamura (University of Tokyo, Japan)
Published online: 11 May 2008 | doi 10.1038/ngeo200
Earth's early magnetic field
The Earth's magnetic field reversed less frequently on early Earth, reports a paper online this week in Nature Geoscience. The Earth's magnetic field, and the location of the magnetic North Pole, wanders and even reverses over the course of millions of years.
Andrew Biggin and colleagues analysed palaeomagnetic data – records of the magnetic field recorded in minerals from volcanic rocks – for a period from 2.82 to 2.45 billion years ago. They found that, relative to the past 200 million years, reversals were far less common. The team suggests that the geodynamo, which generates the Earth's magnetic field, was far more stable 2 billion years ago. They link this to the small size of the inner core on early Earth, which could have stabilized the field behaviour.
Evidence for a very-long-term trend in geomagnetic secular variation
Andrew Biggin (Universiteit Utrecht, Netherlands)
Published online: 4 May 2008 | doi 10.1038/ngeo181