Press releases
Please quote Nature Geoscience as the source of these items.
December 2007
Fast-rising sea levels
Sea levels rose by between 0.6 and 2.6 metres per century during the last interglacial period 120,000 years ago, suggests a paper published online in Nature Geoscience this week.
These figures are well above the IPCC's estimated rise of 0.18 to 0.58 metres for the coming century and indicate that sea levels can quickly adjust to climatic changes.
Eelco Rohling and colleagues studied changes in the salinity of Red Sea water and reconstructed the sea-level-dependent water exchange between the basin and the open ocean across the straits. Their high-resolution records point to at least one period of rapid sea-level rise during the last interglacial period. At that time, global mean temperatures were about 2 degrees Celsius warmer than today, but with a different regional temperature distribution.
High rates of sea-level rise during the last interglacial period
Eelco Rohling (National Oceanography Centre, Southampton, UK)
Published online: 16 December 2007 | doi 10.1038/ngeo.2007.28
Meteoritic boost to biodiversity?
The breakup of an asteroid and the resultant meteoritic bombardment of Earth probably led to more varied environmental conditions and a marked spurt in the number of new species around 470 million years ago, suggests a study online this week in Nature Geoscience. These results are surprising as meteorite impacts are often more commonly associated with mass extinctions.
Birger Schmitz and colleagues studied rocks of Middle Ordovician age from the Baltic and Scandinavian region as well as from China, and documented the diversity of ancient clam-like organisms and the abundance of material of meteoritic origin. They found that the marked increase in biodiversity - as inferred from the number of fossils of various species – occurred at precisely the same time as an increase in meteoritic bombardment in those regions.
Meteoritic impacts on Earth have often been linked to major extinction events – for example, the end-Cretaceous impact 65 million years ago is implicated in the demise of the dinosaurs. This study suggests, however, that depending on their size, frequency and timing in Earth's evolution, impacts could have also created conditions that were conducive to an increase in the diversity of plant and animal life.
Asteroid breakup linked to the Great Ordovician Biodiversification Event
Birger Schmitz (University of Lund, Sweden)
Published online: 16 December 2007 | doi 10.1038/ngeo.2007.37
Climate policy: Complementing IPCC
Climate services that give policy makers annual assessments of the climatic challenges ahead are needed to complement the Nobel-prize winning Intergovernmental Panel for Climate Change (IPCC), argues a Commentary published online this week in Nature Geoscience.
These climate services should also help with the verification of governments' self-reported carbon sequestration achievements that are part of the current discussions at the UN climate conference in Bali.
Martin Visbeck proposes that the IPCC should take a step back and change its role to include reviewing the work of the climate services as well as the scientific literature, in a decadal rhythm rather than at the current frequency of 5-6 years.
As the reality of human-made climate change has become increasingly certain, the focus of the research community should shift from confirming the problem to tackling solutions, the author argues. This requires near-continuous updates of the likely future climate evolution, at the regional as well as global scale.
From climate assessment to climate services
Martin Visbeck (Leibniz Institute of Marine Sciences, Kiel, Germany)
Published online: 9 December 2007 | doi 10.1038/ngeo.2007.55
Cooling the Cretaceous greenhouse
The Earth may not have been such a hot greenhouse world during the Jurassic and Cretaceous periods, suggests a study published online in Nature Geoscience.
The research reconciles records of ancient climate and atmospheric carbon dioxide levels with our understanding of how the two are linked.
Marine data indicate a series of cold spells during the time of the dinosaurs, but these did not seem to tally with records of high carbon dioxide levels, which would suggest higher temperatures and 'greenhouse' conditions.
David Beerling and colleagues studied the fossilized remains of ancient liverworts and, using the isotopic composition of the fossils, they reconstructed atmospheric CO2 levels for the period between 200 and 60 million years ago. The new records show lower and more variable CO2 concentrations than previous estimates. These results suggest that carbon dioxide was in fact the main driver of long-term climate change during this period, and that the previously unexplained cold periods were tied to natural decreases in atmospheric CO2 concentration.
Atmospheric carbon dioxide linked with Mesozoic and early Cenozoic climate change
David Beerling (University of Sheffield, Sheffield, UK)
Published online: 9 December 2007 | doi 10.1038/ngeo.2007.29
The pulse of the San Andreas
The existing configuration of earthquake-producing segments and quiet gaps of the San Andreas fault is likely to remain stable in the long term for small- to moderate-sized earthquakes, according to a study online this week in Nature Geoscience.
The results suggest that earthquakes of magnitude up to 7 are most likely to occur at places where such earthquakes have occurred before.
Tom Parsons conducted a statistical analysis of all but the largest earthquakes that have occurred along the San Andreas fault – the boundary between the Pacific and North American tectonic plates. He found that earthquakes up to magnitude 7 cluster in space. Numerical modelling revealed that this can be explained by the fact that some sections of the fault surface are under higher levels of stress than others, and that this distribution of stresses remains stable over tens of thousands of years.
These findings suggest that only the largest earthquakes are capable of propagating into regions of the fault that were previously dormant. In addition, it appears that earthquakes are less likely to be generated in these regions.
Global warming: Tropics expand poleward
The tropical belt, defined by its typical rain and wind patterns, has started to expand during the last few decades as a result of climate change, according to a progress article published online this week in Nature Geoscience.
This ongoing expansion, emerging from a number of independent studies, will affect climate worldwide as the dry subtropical zones are pushed polewards and could come to encompass the Mediterranean region, the southwest USA, Mexico, southern Australia, South Africa and parts of South America.
Dian Seidel and colleagues review recent studies on the width of the tropical belt from independent signs such as changes in atmospheric temperatures, winds and ozone observations, which all distinguish the tropical from the subtropical regions. According to their findings, the tropics have expanded by about 2.5 degrees latitude over the past 25 years or so - an expansion that had not been expected to occur before the end of the twenty-first century from climate model projections.
Widening of the tropical belt in a changing climate
Dian Seidel (NOAA Air Resources Laboratory, Silver Spring, MD, USA)
Published online: 2 December 2007 | doi 10.1038/ngeo.2007.38
In search of a plate boundary
Important insights into the structure and evolution of the Owen fracture zone - one of the world's least understood plate boundaries - are presented online this week in Nature Geoscience.
The authors present the first evidence for active strike-slip motion along the fault and find that fairly powerful, but infrequent, earthquakes could occur along the boundary between the Arabian and Indian plates.
Marc Fournier and colleagues mapped the floor of the Arabian Sea and constructed a detailed map of part of the Owen fracture zone. This revealed that the Arabian plate is moving northward relative to the Indian plate along an active fault, which is opening up a sedimentary basin at the southern end of the fault. Their calculations show that the rate of northward motion of the Arabian relative to the Indian plate is 2-4 millimetres per year. The active faulting was initiated around 8 million years ago, probably in response to a regional reorganization of plate velocities and directions.
In situ evidence for dextral active motion at the Arabia–India plate boundary
Marc Fournier (Centre National de la Recherche Scientifique, Paris, France)
Published online: 2 December 2007 | doi 10.1038/ngeo.2007.24
Modern Arctic Ocean circulation exceptional?
During most of the last fifteen million years, circulation in the Arctic Ocean was driven by sea-ice formation rather than the inflow of North Atlantic deep water, according to a new study published online in Nature Geoscience.
The new findings suggest that the modern flow of water and heat into the far-northern reaches of the Atlantic Ocean may be an anomaly rather than the typical oceanographic pattern.
Brian Haley and colleagues used a trace-metal analysis of ancient marine sediments collected in the Arctic Ocean to reconstruct deep and intermediate water circulation. They found that over the last fifteen million years, the seawater above the sediments probably came from a region in the Arctic Ocean rather than from the North Atlantic influx that dominates the site today. It is likely that this Arctic-sourced deep water originated from briny water that was created during sea-ice formation, which then sank. North Atlantic deep water previously formed farther south than it does today and did not penetrate as far into the Arctic.
Press contacts
Ruth Francis, Nature London.
Tel: +44 20 7843 4562; E-mail: r.francis@nature.com
Katherine Anderson, Nature London.
Tel: +44 20 7843 4502; E-mail: k.anderson@nature.com
For media inquiries relating to editorial content/policy for Nature Geoscience please contact the journal directly:
Heike Langenberg, Nature Geoscience London.
Tel: +44 20 7843 4042; E-mail: h.langenberg@nature.com
