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Article Released Sun-2nd-December-2007 18:46 GMT
Contact: Ruth Institution: Nature Publishing Group
 Global warming: Tropics expand poleward

Summaries of newsworthy papers in Nature Geoscience including: In search of a plate boundary and Modern Arctic Ocean circulation exceptional?

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[1] Global warming: Tropics expand poleward

DOI: 10.1038/ngeo.2007.38

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.

Author contact:
Dian Seidel (NOAA Air Resources Laboratory, Silver Spring, MD, USA)
Tel. +1 301 713 0295 ext. 126; E-mail: dian.seidel@noaa.gov


[2] In search of a plate boundary

DOI: 10.1038/ngeo.2007.24

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.

Author contact:
Marc Fournier (Centre National de la Recherche Scientifique, Paris, France)
Tel: +33 1 44 27 52 68; E-mail: mark.fournier@lgs.jussieu.fr


[3] Modern Arctic Ocean circulation exceptional?

DOI: 10.1038/ngeo.2007.5

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.

Author contact:
Brian Haley (Leibniz Institute for Marine Research, Kiel, Germany)
Tel: +49 431 600 2252; E-mail: bhaley@ifm-geomar.de


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Nature Geoscience

Keywords associated to this article: Global warming, plate boundary, Owen fracture zone, Arctic Ocean circulation
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