Sea but no climate buffer?

The "ocean zone" of the ocean inhibits the transport of carbon into the deep sea

Particle "snow" and VERTIGO sampling in the ocean © Woods Hole Oceanographic Institution (WHOI)
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The oceans of the earth could be less effective carbon dioxide storage than previously thought. Scientists now report in Science that a large part of the CO2 does not sink into the deep sea, but in the so-called twilight zone of the sea of ​​bacteria and microorganisms "recycled" and thus quickly fed back into the circulation and the atmosphere.

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So far, the ocean has been considered an effective buffer for the greenhouse gas carbon dioxide. The carbon contained in plankton and other organisms as well as the gas dissolved in the water descend into the deep sea and are stored there and thus removed from the atmosphere and carbon cycle for a long time.

But now a new study has largely refuted this idea. As part of two expeditions in the Pacific region, international research teams used VERTIGO's (Vertical Transport In the Global Ocean) project to study the transport of gases and substances between the various water layers in the ocean. The scientists paid particular attention to the twilight zone, a range between 100 and 1, 000 meters of water depth, in which the light intensity slowly decreases.

Lock between surface and Tieffee

"The twilight zone is a crucial link between the surface and the deep ocean, " explains Ken Buesseler, biogeochemist at the Woods Hole Oceanographic Institution and lead author of the study published by a total of 18 researchers. "We are interested in what happens in the twilight zone, what falls into it and what drops out again. Unless the carbon travels all the way to the deep sea and is stored there, the oceans also have no major impact on the climate. "

The twilight zone acts as a kind of "gateway" to the deep sea. However, as they lower more particles deeper in some regions than in others, this makes it difficult for researchers to predict exactly what role the ocean plays as a buffer for the greenhouse effect. While numerous studies have studied the processes at the ocean surface, little was known about the carbon cycle in the underlying layers.

The VERTIGO team used a variety of new technologies, including special sampling techniques, to capture and quantify marine "snow". Marine snow refers to the sinking organic particles that consist, for example, of dead algae or plankton animals. Bacteria decompose the particles and convert the carbon into chemical forms, which in turn can be taken up by other organisms and thus returned to the circulation and into the atmosphere.

Less than half comes through

The result was surprising: the scientists found that only 20 percent of the ocean's surface carbon reached the deep sea off Hawaii before Hawaii - much less than previously thought. After all, it was slightly more in the northwestern Pacific off Japan. Here, around 50 percent of the particles still reached depths.

"These results are particularly important for our efforts to improve numerical models of the oceanic carbon cycle and climate system, " explains Don Rice, director of the National Science Foundation's marine research program. Thus, the study also sheds new light on the plans, possibly by increasing the iron content of the oceans, to increase algae growth and thus the CO2 uptake of the ocean. For if the algae and the carbon stored in them do not disappear in the deep sea for centuries anyway, as expected, this process would have little to no impact on climate change.

(National Science Foundation, 30.04.2007 - NPO)