Date:8/6/2009

o earthquakes. Previous studies had found that this hum is excited by infragravity waves, a type of ocean wave that originates in shallow water along coasts, but it was uncertain whether hum is generated primarily by infragravity waves in the deep ocean or along coastlines. To pinpoint the sources of Earth's hum, Bromirski and Gerstoft correlate hum intensity data from the EarthScope USArray transportable array with ocean wave height measurements and model simulations. Their results show that the hum is generated primarily along coasts, with no significant hum generation in the deep ocean. In particular, they find that the Pacific coasts of North America and Central America are important sources of the hum, and the west coast of Europe is a strong secondary source region, while no significant hum was detected from the Southern Hemisphere during the study period (November 2006 to June 2007). The study is the first to identify these specific source regions for Earth's hum.

Title: Dominant source regions of the Earth's "hum" are coastal

Authors: Peter D. Bromirski and Peter Gerstoft: Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, USA.

Source: Geophysical Research Letters (GRL) paper 10.1029/2009GL038903, 2009 http://dx.doi.org/10.1029/2009GL038903

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3. IPCC models might overestimate methane and nitrous oxide emissions from the ocean

With a global warming potential about 20 times as large as carbon dioxide, methane is a strong greenhouse gas, as is nitrous oxide, which has about 300 times carbon dioxide's warming potential. Both are produced in the ocean by microbial activity. Although more than 30 years old, assessments of the rate of methane emitted by the ocean are included in the Intergovernmental Panel on Climate Change's (IPCC) recent reports and are used as inputs into climate forecasts. Ho
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Contact: Maria-Jose Vinas mjvinas@agu.org 202-777-7530 American Geophysical Union Source:Eurekalert

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