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Plankton, El Niño, and Sinking Carbon

phytoplanktonnasa.jpgIt's hard to overestimate the importance of phytoplankton to the planet's global ecosystem. Plankton are pretty much the bottom of the food chain, and as their numbers rise and fall, so too do the fortunes of nearly every other creature of the sea. But it turns out that the oceans aren't the only part of the Earth with a fate dependent upon plankton -- they affect the atmosphere, too.

Dr. Wendy Wang and her colleagues at the University of Maryland, working with data from NASA's EOS global monitor satellite, have determined that phytoplankton account for about half of the carbon dioxide absorbed annually by plants. Moreover, the cycle of El Niño/La Niña weather phenomena strongly correlates with the decline and growth of phytoplankton.

During an El Niño year, warm waters from the Western Pacific Ocean spread out over much of the basin as upwelling subsides in the Eastern Pacific Ocean. Upwelling brings cool, nutrient-rich water from the deep ocean up to the surface. So, when upwelling weakens, phytoplankton do not get enough nutrients to maintain their growth. As a result, surface waters turn into "marine deserts" with unusually low populations of phytoplankton and other tiny organisms. With less food, fish cannot survive in the surface water, which then also deprives seabirds of food.

During La Niña conditions, the opposite effect occurs as the easterly trade winds pick up and upwelling intensifies, bringing nutrients to the surface waters, which fuels phytoplankton growth. Sometimes, the growth can take place quickly, developing into what scientists call phytoplankton "blooms." [...]

As phytoplankton flourish, a large amount of carbon is used to build cells during photosynthesis. The plants get carbon from carbon dioxide in surface waters. In the atmosphere, carbon dioxide is an important greenhouse gas. When marine organisms die, they carry carbon in their cells to the deep ocean. Surprisingly, this study found that this "export of carbon increased by a factor of eight due to the large phytoplankton blooms," said Wang. This process, called the oceanic "biological pump." is an important mechanism that enables more carbon dioxide to be transferred from the atmosphere, to be stored in the ocean floor.

Wang & co. measured phytoplankton numbers by watching for surface chlorophyll; as we noted in March, there's a direct correlation between the growth of surface phytoplankton and the "greenness" of measured chlorophyll.

This has a number of implications for climate disruption. Firstly, we'll need to pay close attention to the interaction between a warmed atmosphere and the strength of El Niño and La Niña phenomena. If global warming results in stronger La Niñas and weaker El Niños, the ability of phytoplankton to pull CO2 out of the atmosphere will be strengthened, slowing the rate at which the greenhouse gas concentration grows; if global warming has the opposite result, it would accelerate the growth of atmospheric CO2 as the plankton would have less ability to remove it.

Moreover, it confirms a possible emergency method of carbon dioxide remediation. If phytoplankton growth can be artificially encouraged -- particularly during El Niño years -- the resulting "blooms" will absorb higher levels of atmospheric CO2 than would otherwise have occurred. A 2002 study established that "fertilizing" the ocean with iron sulphate (a mineral found in the soil blown into the ocean from land, and critical to plankton growth) could cause plankton blooms capable of measurably reducing CO2, possibly up to 15% of the above-normal buildup. Questions remain about the long-term marine ecosystem effects of artificially-encouraged blooms, however, and researchers agree that this technique should not be considered a fundamental tool for avoiding extreme climate disruption. However, it's good to know that emergency measures are possible, if the only other alternative is planet-wide disaster.

Comments (2)

This is fascinating stuff and should not be ruled out too hastily. 2/3rd's of the planets surface is water and if its inhabitants can possibly be utilized to help counter the effects of CO2 production without ill effects we would be foolish to dismiss it over fears about 'human interference'. We've already unwittingly breached that concern! Imagine a world where plankton captures CO2 - is turned into biofuel - and then returned into the atmosphere as CO2 again. Doesn't that sound like the kind of closed loop cycle that makes sense?

Talking about the closed loop, are we, as human, accelarating in utilizing biofuel today? Who are our helpers on the Earth to maintain the balance or close the loop by returning CO2 gas into biomass? What will happen if these two processes are out of phase or if the human activities exceed biota activities?


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