Mechanisms of Carbon Flow
Researchers at the University of California, Davis, report new information on the mechanism of carbon flow
from the Earth's oceans at the end of the last ice age, based on chemical analyses of the shells of tiny plankton fossils.
"As we alter Earth's climate by burning oil, gas and coal, we urgently need to understand how the deep ocean sequesters
carbon, and how that carbon can flow between the atmosphere and ocean in Earth's past," said study co-author Howard Spero,
a UC Davis geology professor.
"This study tells us more about the where-and-when mechanics of this cycle, which are still critical questions in climate science."
The new report appears in the August 26, 2010 issue of the journal Nature. Spero's co-author, Elisabeth Sikes of Rutgers University,
presented the findings on August 30, 2010 at the 10th International Conference on Paleoceanography at Scripps Institute
of Oceanography in San Diego.
Marine Phytoplankton and the Biological Pump
Spero said most experts agree on this general scenario: Marine phytoplankton remove carbon dioxide from the ocean surface,
grow, die and sink down into the ocean's interior, where they are broken down into carbon dioxide by the ocean's microbial
community. (This mechanism is so effective at pulling carbon dioxide out of the atmosphere and upper ocean, it's called the "biological pump.")
Warm upper water layers form a cap on the cold, deep waters -- and the carbon dioxide -- somewhat akin to a bottle cap that
holds the fizz in a carbonated drink. Deepwater currents move the dissolved carbon dioxide around the planet. Thousands of
years pass; glaciers grow, then start to melt.
Eventual Carbon Dioxide Release
Eventually, these "old" carbon-rich waters well up to the surface and release their carbon dioxide -- a greenhouse gas that
contributes to climate change -- back into the atmosphere.
Where experts diverge is: Where and how quickly does this release occur at the end of an ice age?
A Slow CO2 Release at Diverse Locations?
Earlier studies suggested that it was spread out over time and place, taking centuries to millennia, and occurring in both the
southern and northern hemispheres.
Spero and his colleagues tested that theory by analyzing the carbon-14 content in the fossil shells of tiny sea animals called
foraminifera that were living at the end of the last ice age, about 18,000 years ago.
Spero is a leader in using foraminifera to reconstruct Earth's paleoclimate. The fossil shells, sifted from ancient sediments
drilled from beneath the ocean, contain records of the physical and chemical conditions that existed when the animals were
alive. Spero previously has used foraminifera to better understand the oceans' acid-base (pH) balance; correlate temperature
shifts in the tropical Pacific Ocean with the birth and death of ice ages; and link the circulation system of the north Atlantic
Ocean to salinity levels in the Caribbean Sea.
A Faster CO2 Release at a Single Location
In the new study, Spero and his colleagues say, the foraminifera carbon-14 data suggest that the carbon-dioxide release that
preceded the current warm period on Earth was more of a big fizz than a slow leak. It lasted about 6,000 years and took place
largely in the icy Southern Ocean (the waters south of 60 degrees south latitude that encircle Antarctica).
This has important implications for understanding where and how carbon dioxide comes out of the ocean -- and, especially critical,
how fast it comes out.
The Southern Ocean as CO2 Release Valve
"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 Author Team
The two lead authors on the paper are Kathryn Rose, who conducted her master's degree research in Spero's UC Davis laboratory
and now is a research associate at the Woods Hole Oceanographic Institute in Woods Hole, Mass.; and Elisabeth Sikes, a Rutgers
University marine scientist. Co-authors are Spero; Tessa Hill, also a UC Davis geology professor; Thomas Guilderson of Lawrence
Livermore National Laboratory; Phil Shane of the University of Auckland, New Zealand; and Rainer Zahn of Autonomous University of Barcelona, Spain.
Support for the Study
The study was funded by the National Science Foundation, Evolving Earth Foundation, Geological Society of America and the U.S.
Department of Energy's Lawrence Livermore National Laboratory.
About UC Davis
For more than 100 years, UC Davis has engaged in teaching, research and public service that matter to California and transform
the world. Located close to the state capital, UC Davis has 32,000 students, an annual research budget that exceeds $600 million,
a comprehensive health system and 13 specialized research centers. The university offers interdisciplinary graduate study and more
than 100 undergraduate majors in four colleges - Agricultural and Environmental Sciences, Biological Sciences, Engineering, and
Letters and Science. It also houses six professional schools - Education, Law, Management, Medicine, Veterinary Medicine and the
Betty Irene Moore School of Nursing.
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| Phytoplankton Bloom in the Southern Ocean Off Antarctica: The bright blue water is alive with billions of microscopic plants, phytoplankton, that grow in the upper few feet of the water column. Their scales are composed of calcium carbonate, a white material that reflects sunlight and when viewed through ocean water produces a bright blue color. When the phytoplankton die they sink to the bottom, contributing their calcium carbonate scales to the bottom sediments. A MODIS image from NASA's Aqua satellite. |
| Phytoplankton near the ocean surface remove carbon dioxide from the water and use it to produce their calcium carbonate scales. When the phytoplankton die they sink to the bottom, adding this "organic carbon" to the sea floor sediment. This movement of carbon dioxide from ocean surface to seafloor is known as the "biological pump". Image by NASA. |
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