Hot, nutrient-rich water seeping from a network of deep-sea volcanoes provides a consistent source of iron for the phytoplankton that soaks up carbon dioxide, playing a key role in limiting climate change, according to a new study by French and Australian scientists.
The world’s oceans capture about 25 percent of the carbon dioxide emitted by human activities, including the burning of fossil fuels, scientists say. Among the largest “carbon sinks” is the Southern Ocean between Antarctica and Australia.
Underpinning that cycle is the microscopic plant phytoplankton, which absorbs the carbon dioxide at the ocean surface and then eventually carries it to the ocean floor.
While it is well known that iron carried in dust or in coastal sediments can trigger phytoplankton blooms, the extent and consistency of deep-sea vents as a source of nutrients was not as well understood, according to the study published in the journal Nature Geoscience.
That source, researchers say, produces between 5 and 15 percent of the total carbon storage in the entire Southern Ocean, and as much as 30 percent in some parts.
Article appearing courtesy Yale Environment 360.
photo: Astacus
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I was recently surprised to discover how little of the dead sinking solid organic matter from the upper ocean layer where photosynthesis is possible reaches the deep ocean for long term retention. The following is an extract from my website.
“Myles Allen pointed me to a paper
http://iopscience.iop.org/1748-9326/4/1/014012/pdf/erl9_1_014012.pdf?ejredirect=migration
which shows how very slowly atmospheric carbon dioxide concentration would decline even if emissions stopped. The ocean currently absorbs 2.2 billion tonnes/year of carbon (as noted in my November blog) but as described in the paper, uptake would fall to about a quarter of that value (ie only 6% of current emissions) if atmospheric carbon dioxide concentration stopped rising today.
The arctic ocean downwelling flow corresponding to the ongoing carbon uptake of 0.54 billion tonnes/year predicted in the paper gives an ocean turnover time of 2500 years. The 0.54 billion tonnes/year also implies that only about 1.4 billion tonnes/year of carbon in dead organisms sinks far enough to contribute to the measured increase in dissolved inorganic carbon in the cold downwelled polar water that fills the ocean below about 500 metres depth. Most of the often quoted 10 billion tonnes/year of sinking solid organic matter must decompose in the shallower water and leave the dissolved carbon there.
The observed 2 ppm per year increase in atmospheric carbon dioxide concentration would explain the other three quarters of the current 2.2 billion tonnes/ year of oceanic carbon uptake if the top 350 metres of the ocean were well mixed.
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