New Findings on Carbon Dioxide Release from World's Oceans
Carbon Dioxide (CO2), a greenhouse gas, is intricately linked to global warming. The largest store of CO2 is the world's oceans. How the oceans sequester or release CO2 to or from the atmosphere is important to understand as mankind alters Earth's climate with the burning of fossil fuels. A new report from researchers at the University of California, Davis offers clues on how that mechanism works by analyzing the shells of plankton fossils.
CO2 from the atmosphere touches the ocean surface is absorbed by the water. Marine phytoplankton consume the CO2 from the surface as they grow. After the plankton dies, it sinks to the bottom of the ocean. Decomposition then transforms the organic compounds of the plankton into dissolved CO2. This cycle, known as the biological pump, is extremely effective at removing CO2 from the atmosphere and depositing it in the deep ocean waters.
As global temperatures rise, one of the first symptoms is the melting of glaciers and sea ice. This frigid water then sinks to the bottom of the ocean, pushing up the carbon-rich waters that have been trapped under the warmer water for so long, like fizzy soda under a bottle cap). Once the older carbon-rich water reaches the surface, the collected greenhouse gas is released back into the atmosphere, accelerating the cycle of temperature rise.
This is what occurred at the end of the last great ice age, about 18,000 years ago. The question is, where and how quickly does the release of CO2 from the oceans occur? Earlier studies suggest that the release took place all over the northern and southern hemisphere and over centuries and millennia. However, Howard Spero, a UC Davis geology professor, and his colleagues disagree.
According to Spero, the CO2 release that preceded the current warm period was akin to a big fizz rather than a slow leak, and took place largely in the Southern Ocean which surrounds Antarctica. This theory was tested by examining the carbon-14 content in the fossil shells of phytoplankton that were alive at the end of the last ice age. These shells were obtained from core samples, which took up ancient sediment from deep in the sea floor.
"We now understand that the Southern Ocean was the fundamental release valve that controlled the flow of carbon dioxide from the ocean to the atmosphere at the end of the last ice age. The resulting atmospheric increase in this greenhouse gas ultimately led to the warm, comfortable climate that human civilization has enjoyed for the past 10,000 years," Spero concluded.
The UC Davis study was published in the recent issue of the journal, Nature. The lead authors are Kathryn Rose, one of Spero's students at UC Davis, and Elisabeth Sikes of Rutgers University.
Link to published article: http://www.nature.com/nature/journal/v466/n7310/abs/nature09288.html