Understanding the Ocean's Carbon Cycle.

• Position: BACTERIOPLANKTON

The oceans are great at absorbing carbon dioxide from the air but, when their deep waters are brought to the surface, the oceans themselves can be a source of this prevalent greenhouse gas.

Wind patterns together with the Earth's rotation drive deep ocean water--and the C[O.sub.2] it sequesters--upward, replacing surface water moving offshore. A process known as upwelling, it occurs on the west coasts of continents--and it is part of a never-ending loop in which C[O.sub.2] levels in the surface ocean rise and fall in a natural rhythm.

However, when C[O.sub.2] levels rise, ocean pH falls, causing ocean acidification. Seeking to explore how short-term periods of elevated C[O.sub.2] from upwelling impact the bacteria in the water, researchers at the University of California, Santa Barbara, found that the additional C[O.sub.2]--and corresponding drop in pH--increases the respiration of these organisms. This means more resources are recycled rather than retained in the food web.

"Despite their microscopic size, these bacteria drive the major cycling of carbon in the ocean's surface," says Anna K. James, a student in the Interdepartmental Graduate Program in Marine Science. "I wanted to see how much dissolved organic carbon the bacteria were eating and what proportion they dedicated to biomass."

In addition to measuring the organisms' biomass, James calculated bacterial...