AGU journal highlights -- Aug. 1, 2007

Title: Observational evidence for a Southern Hemisphere oceanic 'supergyre'

Authors: K. R. Ridgway and J. R. Dunn: Marine & Atmospheric Research and Wealth from Oceans Flagship, Commonwealth Scientific and Industrial Research Organisation (CSIRO), Hobart, Tasmania, Australia.

Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL030392, 2007

7. Synchronized chaos: Mechanisms for major climate shifts

In the mid-1970s, a climate shift cooled sea surface temperatures in the central Pacific Ocean and warmed the coast of western North America, bringing long-range changes to the northern hemisphere. After this climate shift waned, an era of frequent El Ninos and rising global temperatures began. Understanding the mechanisms driving such climate variability is difficult because unraveling causal connections that lead to chaotic climate behavior is complicated. To simplify this, Tsonis et al. investigate the collective behavior of known climate cycles such as the Pacific Decadal Oscillation, the North Atlantic Oscillation, the El Nino/Southern Oscillation, and the North Pacific Oscillation. By studying the last 100 years of these cycles' patterns, they find that the systems synchronized several times. Further, in cases where the synchronous state was followed by an increase in the coupling strength among the cycles, the synchronous state was destroyed. Then. a new climate state emerged, associated with global temperature changes and El Nino/Southern Oscillation variability. The authors show that this mechanism explains all global temperature tendency changes and El Nino variability in the 20th century.

Title: A new dynamical mechanism for major climate shifts

Authors: Anastasios A. Tsonis, Kyle Swanson, and Sergey Kravtsov: Atmospheric Sciences Group, Department of Mathematical Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, U.S.A.

Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL030288, 2007

8. A 30,000-year record of sea surface temperatures off South Australia

Continental glaciers originating at both poles reached their farthest extent about 20,000 years ago, marking a time known as the Last Glacial Maximum. Comparisons of ice cores from Greenland and Antarctica show that as these glaciers melted, warming occurred in asynchronous stages at the poles. While many northern hemisphere climate records match ice core records from Greenland, few southern hemisphere records exist to compare with ice core data from Antarctica. Calvo et al. analyze a marine core collected off South Australia and find that it contains detailed signatures of surface temperatures of waters that washed over it since the glacial maximum. Data from this core match well with Antarctic ice cores and paleoclimate records from the Australian continent, showing no signature of the Younger Dryas, a cooling event known to have occurred in the Northern Hemisphere about 13,000 years ago. The new core data also reveal a progressive drop in sea surface temperatures over the last 6,500 years, an observation not seen before for the Australian region.