AGU Journal Highlights -- July 12, 2007

In the past few years, two very unusual tropical cyclones developed over the Atlantic Ocean. The first was 2004 Hurricane Catarina, which made landfall over the southern coast of Brazil. The second was 2005 Hurricane Vince, which formed next to the Madeira Islands in the Atlantic Ocean as the first detected hurricane to develop over this area and the first known tropical cyclone to make landfall in Spain. Noting that anthropogenic climate change might be responsible for altering the geographical areas where tropical cyclones develop, Gaertner et al. use an ensemble of regional climate models to assess new locations of tropical cyclone occurrence. They find an increase in extremes of cyclone intensity over the Mediterranean Sea in climate change scenario simulations. This increase, at least for the most sensitive model, is clearly related to tropical cyclone formation, revealing for the first time a risk of tropical cyclone development over the Mediterranean Sea under future climate change conditions. Though the uncertainties are large, further application of the method used in the study could yield more specific assessments of this risk.

Title: Tropical cyclones over the Mediterranean Sea in climate change simulations

Authors:
M. A. Gaertner, E. Sánchez and M. Castro: Environmental Sciences Faculty, University of Castilla-La Mancha, Toledo, Spain;
D. Jacob: Max Planck Institute for Meteorology, Hamburg, Germany;
V. Gil, M. Domínguez and E. Padorno: Environmental Sciences Institute, University of Castilla-La Mancha, Toledo, Spain.

Source:
Geophysical Research Letters (GRL) paper 10.1029/2007GL029977, 2007 (in press as of 12 July 2007)

To monitor how climate change will affect the ocean, data bases spanning long time records over wide geographic areas are of critical importance. In 2004, temperature, pressure, and salinity data were taken at various depths from Africa to the Bahamas, representing the fifth such line of data collected from that specific section of the Atlantic Ocean—the other transatlantic hydrographic sections were taken in 1957, 1981, 1992 and 1998. Cunningham and Alderson analyze these five sets of data to assess decadal temperature and salinity changes over the last 50 years along this transatlantic line. They find that waters shallower than about 1780 meters (5840 feet) have been warming and salinizing at least since 1981, and in 2004 were significantly warmer and saltier than at any time since 1957. At depths 3060 meters (10040 feet) below the sea surface, water has been continuously cooling and freshening since 1957. The authors argue that these shallow and deep changes are consistent with the expected reduced southward flux of deep water and with other observed fluctuation trends of temperature with depth.

Title: Transatlantic temperature and salinity changes at 24.5ºN from 1957 to 2004

Authors:
Stuart A. Cunningham and Steve Alderson: National Oceanography Centre, Southampton, U.K.

Source:
Geophysical Research Letters (GRL) paper 10.1029/2007GL029821, 2007 (in press as of 12 July 2007)

Great earthquakes, earthquakes which rupture slowly, or those with large fault areas can pose serious tsunami hazards that can be difficult to immediately deduce from real-time analyses of seismic networks. However, networks of tide gauges and deep-ocean pressure sensors provide important information for tsunami detection. This data can be used to reconstruct seismic events. Sánchez and Cheung perform a hindcast analysis of the 1995 Antofagasta-Chile tsunami with this inverse method. They use a model to retrace the earthquake slip distribution and timing from data recorded by tide gauges close to the rupture. These parameters are then used to estimate possible tsunami hazards across the Pacific Ocean. The authors find that their algorithms produce good estimates of tsunami waveforms at Honolulu based on the tide gauge data along the South American coast, reassuring the effectiveness of strategically positioned tide gauges in providing reliable tsunami forecasts through such an inverse method.

Title: Tsunami forecast using an adaptive inverse algorithm for the Peru-Chile source region

Authors:
Alejandro Sánchez: Coastal and Hydraulics Laboratory, Engineer Research and Development Center, U.S. Army Corps of Engineers Vicksburg, Mississippi, U.S.A.;
Kwok Fai Cheung: Department of Ocean and Resources Engineering, University of Hawaii at Manoa, Honolulu, Hawaii, U.S.A.

Source:
Geophysical Research Letters (GRL) paper 10.1029/2007GL030158, 2007

Samples of lunar rocks returned by Apollo astronauts show large variations in titanium oxide abundance, indicating complex compositional zonation within the lunar mantle. This titanium oxide is likely derived from the mineral ilminite (FeTiO₂), and accurately determining ilminite abundances for the entire lunar surface through remote sensing methods is a long-standing goal of the lunar science community. Noting that ilminite has very low reflective properties, Robinson et al. use images of the Moon's surface taken by the Hubble Space Telescope and determine where ilminite is present by comparing variations in the reflectance of ultraviolet and visible light. They find that areas of high and low ilminite abundance match well with expected values, based on rocks collected by astronauts of the Apollo missions, but the ilminite abundances do not give insight into the ages of lunar soils. The authors expect that their method of remotely mapping the titanium oxide on the lunar surface will enable more refined studies of lunar crustal composition and can guide future human exploration of the Moon.

Title: High resolution mapping of TiO₂ abundances on the moon using the Hubble Space Telescope

Authors:
M. S. Robinson: School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, U.S.A.;
B. W. Hapke: University of Pittsburgh, Pittsburgh, Pennsylvania, U.S.A.;
J. B. Garvin and D. Skillman: NASA Goddard Space Flight Center, Greenbelt, Maryland, U.S.A.;
J. F. Bell III: Cornell University, Ithaca, New York, U.S.A.;
M. P. Ulmer: Northwestern University, Evanston, Illinois, U.S.A.;
C. M. Peters: Brown University, Providence, Rhode Island, U.S.A.

Source:
Geophysical Research Letters (GRL) paper 10.1029/2007GL029754, 2007

In 1997, basalts within 130 million-year-old oceanic crust were sampled on the seaward slope of the Japan Trench. These basalts were found to be unexpectedly young—only about 6 million years old. Noting that there are no known hotspots in the vicinity, Fujwara et al. seek to understand more about the unknown intra-plate volcanics, dubbed 'petit-spot' volcanism, suggested by the discovery of these young basalts in cool, thick oceanic lithosphere. In 2005, they conducted a seismic reflection survey of this region and found that this young basalt pooled between sedimentary layers and oozed to the surface through cracks and vents. The authors anticipate that these results and surveys of other areas of petit-spot volcanism will help scientists better understand the evolution and modification of old oceanic crust.

Title: Subsurface structure of the "petit-spot" volcanoes on the northwestern Pacific Plate

Authors:
Toshiya Fujiwara, Natsue Abe, and Kaoru Takizawa: Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan;
Naoto Hirano: Laboratory for Earthquake Chemistry, University of Tokyo, Tokyo Japan.

Source:
Geophysical Research Letters (GRL) paper 10.1029/2007GL030439, 2007

Italy is the seventh largest European producer of natural gas, with reservoir volumes approaching 2200 billion cubic meters (2877 billion cubic yards). Of this, 74 percent formed through microbial decay of organic matter (biogenic gas), 14 percent formed by thermal breakdown of organic material at greater depth (thermogenic), and 12 percent is mixed. Because most gas fields occur in areas influenced by tectonics, gas migration to the surface is widespread, leading to over a thousand seeps, including mud volcanoes and dry seeps. Etiope et al. assess the gas origin from all main seeps still active today. Noting that methane is a potent greenhouse gas, they seek to quantify its flux to the atmosphere, including contributions from diffuse soil degassing. They find that 80 percent of the seeps release thermogenic gas, and that mud volcano gas is generally lighter (more methane, less ethane and propane) than its original reservoir gas. Dry seeps, instead, maintain the same alkane composition as their reservoirs. The authors estimate that methane emission may reach levels of hundreds of thousands tons per year, comparable to national emissions from the fossil fuel industry.

Title: Methane seeps and mud volcanoes in Italy: Gas origin, fractionation, and emission to the atmosphere

Authors:
Giuseppe Etiope: Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy;
Giovanni Martinelli: ARPA Environmental Protection Agency of the Emilia Romagna Region, Bologna, Italy;
Antonio Caracausi and Francesco Italiano: Istituto Nazionale di Geofisica e Vulcanologia, Palermo, Italy.

Source:
Geophysical Research Letters (GRL) paper 10.1029/2007GL030341, 2007 (in press as of 12 July 2007)

You may read the scientific abstract for any already-published paper by going to http://www.agu.org/pubs/search_options.shtml and inserting into the search engine the portion of the doi (digital object identifier) following 10.1029/ (e.g., 2007GL030158). The doi is found at the end of each Highlight above. To obtain the full text of the research paper, see below.

Ordering information for science writers and general public:

Journalists and public information officers of educational and scientific institutions (only) may receive one or more of the papers cited in the Highlights (including pre-publication copies of articles listed as “in press”) by sending a message to Jonathan Lifland [jlifland@agu.org], indicating which one(s). Include your name, the name of your publication, and your phone number. The papers will be e-mailed as pdf attachments.

Others may purchase a copy of any published paper online for nine dollars:

1. Copy the portion of the digital object identifier (doi) of the paper following "10.1029/" (found under "Source" at the end of each Highlight).

2. Paste it into the second-from-left search box at http://www.agu.org/pubs/search_options.shtml and click "Go."

3. This will take you to the citation for the article, with a link marked "Abstract + Article."

4. Clicking on that link will take you to the paper's abstract, with a link to purchase the full text: "Print Version (Nonsubscribers may purchase for $9.00)."

The Highlights and the papers to which they refer are not under AGU embargo.