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Old 04-01-2009, 01:26 PM
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Fertilizing plankton for carbon sequestration

The first time I read about this type of experiment was back in the 1980's IIRC. I think it was a Scripps experiment in the mid-latitude, central Pacific. I don't recall that experiment having the result described below.

Bot

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From: New Scientist published March 27, 2009, authored by Catherine Brahic

“Hungry shrimp eat climate change experiment”

“Earlier this month, the controversial Indian-German Lohafex expedition
fertilised 300 square kilometres of the Southern Atlantic with six tonnes
of dissolved iron. The iron triggered a bloom of phytoplankton, which
doubled their biomass within two weeks by taking in carbon dioxide from
the seawater. Dead bloom particles were then expected to sink to the ocean
bed, dragging carbon along with them. Instead, the bloom attracted a swarm
of hungry copepods. The tiny crustaceans graze on phytoplankton, which
keeps the carbon in the food chain and prevents it from being stored in
the ocean sink. Researchers from the Alfred Wegener Institute for Polar
and Marine Research reported that the copepods were in turn eaten by
larger crustaceans called amphipods, which serve as food for squid and fin
whales.”

“The grazing effect had not been seen in previous fertilisation
experiments. These had caused blooms of diatoms, a type of phytoplankton
that is protected against grazers by a hard shell of silica. But the
Lohafex experiment did not trigger a diatom bloom because there was little
silicic acid available in the water for diatoms to build their shells
from. Lohafex researchers say the results suggest that using iron
fertilisation to increase the ocean carbon sink would rely on a complex
chain of events, making it difficult to control. The Southern Ocean is
thought to be the planet's largest ocean carbon sink. But most of the
northern half of the region is low on silicic acid, ruling it out as an
option for carbon fertilisation. The researchers tried to provoke a second
bloom by fertilising the same patch of ocean three weeks later, with no
success — most probably because the water was already saturated in
iron. ‘It seems that if it is possible to fertilise enough ocean to make a
difference to climate, we would need to turn vast ocean ecosystems into
giant plankton farms,’ says Caldeira.”
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