Greenhouse Gas CO2 Sidetracked in Oceans

Greenhouse Gas CO2 Sidetracked in Oceans



   
April 2007 -   Climate experts have relied on the oceans to
 absorb enough of the 
greenhouse gas carbon dioxide to slow global warming, but new 
research by an international team of scientists shows that the 
oceans may have little impact on changes in the atmosphere or 
climate. 
The research indicates that instead of sinking, carbon dioxide 
is often consumed by animals and bacteria and recycled in the 
"twilight zone," a dimly lit area 100 to 1,000 meters below 
the surface. 
Because the carbon often never reaches the deep ocean, where 
it can be stored and prevented from re-entering the atmosphere 
as a green-house gas, the oceans may not be able to perform 
the crucial role in greenhouse gas absorption and storage that 
has been assumed. 
The research, funded by the National Science Foundation, is 
the result of two international expeditions to the Pacific 
Ocean, and is reported in the April 27 issue of the journal 
"Science," published by the American Association for the 
Advancement of Science. 
"These results are particularly important to our efforts today 
to improve the predictive capacity of numerical models that 
relate ocean carbon to global climate change on different time 
scales," said Don Rice, director of National Science 
Foundation's chemical oceanography program. 
The study adds a new complication to proposals to mitigate 
climate change by fertilizing the oceans with iron. The iron 
was supposed to promote blooms of photosynthetic marine plants 
and transfer more carbon dioxide from the air to the deep 
ocean. 
"The twilight zone is a critical link between the surface and 
the deep ocean," said Ken Buesseler, a biogeochemist at Woods 
Hole Oceanographic Institution and lead author of the new 
study, which is co-authored by 17 other scientists. 
"We're interested in what happens in the twilight zone, what 
sinks into it and what actually sinks out of it," said 
Buesseler. "Unless the carbon goes all the way down into the 
deep ocean and is stored there, the oceans will have little 
impact on climate change." 
Buesseler was the leader of a project called Vertical 
Transport In the Global Ocean, VERTIGO. 
Scientists deploy a Neutrally Buoyant Sediment Trap in the 
ocean off Hawaii on a VERTIGO research voyage in 2004. 
The researchers found that the twilight zone acts as a "gate" 
that allows more sinking particles through in some regions and 
fewer in others, complicating scientists' ability to predict 
the ocean's role in offsetting the impacts of greenhouse 
gases. 
These sinking particles, often called "marine snow," supply 
food to organisms deeper down, including bacteria that 
decompose the particles. In the process, carbon is converted 
back into dissolved organic and inorganic forms that are 
re-circulated and reused in the twilight zone and that can 
make their way to the surface and back into the atmosphere. 
The problem, say scientists, is that particles sink slowly, 
perhaps 10 to a few hundred meters per day, but they are swept 
sideways by ocean currents traveling many thousands of meters 
per day. To collect sinking particles, oceanographers use 
cones or tubes that hang beneath buoys or float up from sea 
floor. That, Buesseler said, "is like putting out a rain gauge 
in a hurricane." 
Using new technology, the researchers found that only 20 
percent of the total carbon in the ocean surface made it 
through the twilight zone off Hawaii, while 50 percent did in 
the northwest Pacific near Japan. 
The sites off Hawaii and Japan were selected because they had 
been the focus of long-term ocean observations by co-authors 
David Karl of the University of Hawaii and Makio Honda of the 
Japan Agency for Marine-Earth Science and Technology. 
"As we learn more and more about the sea around us, including 
the deep ocean, we gain an appreciation for how important and 
how fragile life in these regions can be," says Karl. 
"By gaining a better understanding of how organic matter and 
energy are processed in the mid-depths of the ocean we can 
better predict how life in the sea may be affected by 
human-imposed climate change including greenhouse gas 
production," he said. 
"The twilight zone may be the largest habitat for life on our 
planet in terms of volume, yet we are just beginning to 
understand who lives there and how they make their living." 
While many studies have investigated the surface of the ocean, 
little research has been conducted on the carbon cycle below. 
The VERTIGO team examined a variety of processes to open a new 
window into the difficult-to-explore twilight zone. They 
successfully used a wide array of new tools, including an 
experimental device that overcame a longstanding problem of 
how to collect marine snow falling into the twilight zone. 
James Bishop of the Lawrence Berkeley National Laboratory and 
University of California, Berkeley was funded by the U.S. 
Department of Energy to deploy new autonomous optical sediment 
traps designed to follow the hourly changes in sedimentation 
as well as ship deployed particle sampling systems to quantify 
the abundance and composition of particles in the twilight 
zone. 
More than 40 biologists, chemists, physical oceanographers, 
and engineers from 14 institutions and seven countries 
participated in the two VERTIGO oceanographic research cruises 
in 2004 and 2005 to investigate how marine plants die and 
sink, or are eaten by animals and converted into sinking fecal 
pellets. 

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