May 2007, Vol. 19, No.5

Waterline

Sneak Preview of Warmer Future

A 1-month delay in the annual spring “upwelling” of the California current in 2005 provided scientists with a sneak preview of what conditions may be like if global climate change models prove accurate, according to an Oregon State University (OSU; Corvallis) news release. Upwelling is when water from the ocean’s depths rises to the ocean’s surface because of wind patterns, bringing nutrients to the ocean’s top.
Research results published online in March in the Proceedings of the National Academy include numerous anomalies affecting West Coast marine ecosystems. “Delays in the onset of upwelling and strong late-season upwelling are consistent with regional climate change models, and that’s exactly what we saw in 2005 off the West Coast of the United States,” said Jack Barth, a professor in the College of Oceanic and Atmospheric Sciences at OSU and lead author on the study. “The winds were late in arriving by one month, resulting in the lowest upwelling-favorable ‘wind stress’ in the region during the past 20 years.”

Barth said the winds “eventually picked up and triggered strong upwelling late in the season, but for some species that depend on those nutrients being there, it was too late. The juvenile recruits for both barnacles and mussels, for example, were down considerably.”

Mussel recruits were down 83%, while barnacle recruits were only 66% of normal, the study found.

During the spring of 2005, upwelling didn’t begin until June — 1 month later than usual. During that time, nearshore waters were 2°C warmer than usual, while chlorophyll levels in the surf zone were only 50% of normal levels, and nutrient levels were about 30% lower.

Barth said the 1-month delay was associated with 20- to 40-day wind oscillations that accompanied a southward shift of the jet stream in 2005. In recent years, the jet stream has experienced “wobbles” that can warm the waters of the Pacific Ocean off the U.S. northwest coast and hamper upwelling when the shift is to the south, or it can accelerate upwelling when it shifts northward.

OSU’s Jane Lubchenco, who organized a symposium on West Coast variability for the American Association for the Advancement of Science (Washington, D.C.) annual meeting, said the bottom line is that the dramatic events of the past few years have shown how vulnerable oceans are to changes in overall climate — and how quickly ecosystems respond.

“Improved monitoring and understand[ing] of the connection between temperatures, winds, upwelling, and ecosystem responses will greatly facilitate capacity to manage those parts of the system we can control,” Lubchenco said.

Contact Barth at barth@coas.oregonstate.edu.

Scientist Links Climate Change, Waterborne Disease

Speaking in a symposium titled “New Vistas in the Mathematics of Ecology and Evolution” at the annual meeting of the American Association for the Advancement of Science (Washington, D.C.) in San Francisco in February, theoretical ecologist Mercedes Pascual discussed how models that she and co-workers have developed can aid short-term forecasting of infectious, waterborne diseases, such as cholera, and inform decisions about vaccination and other disease-prevention strategies.

According to a University of Michigan (Dearborn) press release, Pascual and colleagues have found evidence that a phenomenon known as the El Niño–Southern Oscillation (ENSO), a major source of climate variability from year to year, influences cycles of cholera in Bangladesh. They also showed that the coupling between climate variability and cholera cycles has become stronger in recent decades.
Now, Pascual is examining the feasibility of using a model developed during that work as an early warning system.

“The question we asked was whether, using data from 1966 to 2000, we could have predicted cholera outbreaks over the past 5 years,” said Pascual, an associate professor of ecology and evolutionary biology at the University of Michigan. “We also wanted to know whether incorporating ENSO into the model would improve the accuracy of our predictions.”

The challenge for the model was particularly interesting because the past 5 years were atypical, according to the press release, with fewer cholera cases than usual and no strong climate anomalies. However, the model performed well, Pascual said.

“Our results showed that for the past 5 years, we would have done fairly well predicting cholera cases one year ahead, and that the model that uses ENSO makes prediction even more accurate,” she said.

Contact Pascual at pascual@umich.edu.