AGU Journal Highlights -- March 19, 2008

Title: Stabilizing climate requires near-zero emissions

Authors: H. Damon Matthews: Department of Geography, Planning and Environment, Concordia University, Montreal, Quebec, Canada;

Ken Caldeira: Department of Global Ecology, Carnegie Institution of Washington, Stanford, California, U.S.A.

Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL032388, 2008; http://dx.doi.org/10.1029/2007GL032388

3. A new method to trace ocean mixing

Before industries phased out chlorofluorocarbon (CFC) production in the 1990s due to its detrimental effect on stratospheric ozone, oceanographers used atmospheric ratios of different CFCs to learn more about ocean circulation rates and pathways. Because air-sea gas exchange processes imprint CFC ratios in the ocean's surface over time, when water mixes it will retain the CFC ratio it had when it was exposed to air at the surface. After CFC production halted, oceanographers began using the steadily increasing atmospheric concentrations of anthropogenic sulfur hexafluoride (SF₆) gas, which is used as an insulator in the electric power industry, to trace ocean circulation in a similar manner. However, SF₆ is also injected into the ocean to study short-term mixing, undermining its utility as an ocean circulation tracer. Searching for a different way to trace short-term mixing, Ho et al. injected trifluoromethyl sulfur pentafluoride (SF₅CF₃) and SF₆ into the waters off southern California's coast in 2005. They find that the tracers' concentrations over about 2 years mirrored each other very closely, indicating that SF₅CF₃ can replace SF₆ in ocean injection experiments and preserving SF₆ as an ocean circulation tracer.

Title: Use of SF₅CF₃ for ocean tracer release experiments

Authors: David T. Ho and William M. Smethie, Jr.: Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York, U.S.A.;

James R. Ledwell: Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, U.S.A.

Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL032799, 2008; http://dx.doi.org/10.1029/2007GL032799

4. Sound reflections reveal ocean temperature profiles

Reflection seismology, using an array of air guns and hydrophones towed from a ship, is commonly used to investigate geologic structures below the ocean floor. Recently, this technique has been applied to investigate oceanographic structures. Noting that layers in the ocean are nearly horizontal, and that sound speed profiles through layered media can be readily determined by reflection seismology inversion techniques, Wood et al. hypothesize that these sound speed profiles can be used to constrain ocean temperature profiles. The authors test their method using modeled seismic data and find good agreement. They then apply their method to actual seismic data acquired in the Norwegian Sea, corroborating the results with direct measurements of ocean temperature. They find that even with a seismic acquisition system not specifically designed or calibrated for seismic oceanography, temperature contrasts within the ocean can be recovered to within 1 degree Celsius. Because this method can be used remotely and rapidly, the authors expect that this new technique may prove useful in constraining models of ocean mixing and global heat transfer.