B12—an essential vitamin for land-dwelling animals, including humans—also turns out to be an essential ingredient for growing marine plants that are critical to the ocean food web and Earth’s climate, scientists have found.
he presence or absence of B12 in the ocean plays a vital and previously overlooked role in determining where, how much, and what kinds of microscopic algae (called phytoplankton) will bloom in the sea, according to a study published in the May issue of the journal Limnology and Oceanography.
These photosynthesizing plants, in turn, have a critical impact on Earth’s climate: They draw huge amounts of carbon dioxide, a greenhouse gas, from the air, incorporating carbon into their bodies. When they die or are eaten, carbon is transferred to the ocean depths, where it cannot re-enter the atmosphere.
B12 contains the metal cobalt and can be synthesized only by certain singled-celled bacteria and archaea. Humans, animals, and many algae require B12 to manufacture essential proteins, but they cannot make it and must either acquire it from the environment or eat food that contains B12, said the study’s lead authors, Erin Bertrand and Mak Saito. The two biogeochemists at the Woods Hole Oceanographic Institution wondered whether the vitamin was also important in the ocean, where B12 and cobalt are both found in exceedingly low concentrations.
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In a symbiotic relationship, the algae get their required vitamin and the bacteria get a steady supply of carbon made by the plants. When Phaeocystis dies off and the bacteria are eaten or decomposed, B12 is released once again to the ocean and is available to be used by diatoms.
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Any disruption in the timing or abundances of these microbial populations has ramifications on the ecosystem and the climate, the scientists said.
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Any disruption in the timing or abundances of these microbial populations has ramifications on the ecosystem and the climate, the scientists said. For example, Phaeocystis antarctica in the Ross Sea takes up more carbon dioxide than diatoms, so if the marine community shifts to diatoms, the Ross Sea would likely remove less carbon dioxide from the atmosphere. Unlike diatoms, Phaeocystis also produce a compound called dimethylsulfioniopriopionate, or DMSP, which is released into the air and helps produce clouds that block solar radiation.
Polar oceans do not have large bacterial populations to produce B12, making the vitamin a critical factor influencing the food web, the cycling of carbon in the ocean, and the climate, Bertrand and Saito said. At the same time, climate changes could affect the availability of B12 by causing changes in ocean temperatures, bacterial populations, and other factors. The ozone hole produced in the austral spring above Antarctica could also induce a cascade of effects by allowing more penetration of ultraviolet radiation that is known to degrade B12, they said.
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