Increased Carbon Dioxide Levels Lead To Rapid Plankton Growth
Written by Ted Ranosa, Tech Times
Abnormal levels of carbon dioxide in the North Atlantic are being linked to the rapid growth of plankton population in the ocean over the past 45 years, according to a study featured in the journal Science.
A team of marine researchers, led by associate professor Anand Gnanadesikan of Johns Hopkins University, discovered that the population of microscopic marine alga known as Coccolithophores in the North Atlantic experienced a tenfold increase from 1965 to 2010.
This recent finding contradicts earlier assumptions made by scientists that the phytoplankton would find it difficult to produce plates from calcium carbonate as ocean waters become increasingly more acidic.
Sea Ice Declines Boost Arctic Phytoplankton Productivity
Like plants, phytoplankton have chlorophyll to absorb sunlight and use photosynthesis to produce food. In the Arctic Ocean, photosynthesis is frequently limited by the low angle of the winter Sun and short daylight hours, as well as by the blanket of sea ice that melts and refreezes with the changing seasons.
Over the last 30 years, however, the Arctic has warmed, and larger areas of the Arctic Ocean are now free of sea ice in the summer, which means phytoplankton are getting more sunlight. The result is that phytoplankton productivity has increased by about 20 percent based on satellite estimates of the amount of chlorophyll in the water.
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Growth of microscopic phytoplankton in the Southern Ocean could double in size in the next 80 years because of climate change, according to scientists. The microscopic organisms form the basis of the entire food web, feeding everything from small fish and krill to giant whales.
Professor Phillip Boyd from the Institute of Marine and Antarctic Studies (IMAS) in Hobart has been measuring how changes in conditions affect phytoplankton in a lab setting. He has been using sophisticated modelling to predict changes.
He said oceans are warming because of climate change, and are also absorbing more carbon and become more acidic. Also, nutrient levels are rising and there are changes to the amount of light which penetrates the ocean.
“We designed an experiment where we basically threw the kitchen sink at this phytoplankton species in the lab,” he said.
“We changed the acidity of the ocean, the nutrients supplied, the amount of light and the amount of this trace element iron.
“We found that in a future ocean, in the sub-Antarctic waters our lab experiment showed that the growth rate will be about twice as high as it is at present.” He said the change would mean significant knock-on effects higher in the food chain. “For example the species diatoms are important food for krill and for other species,” he said.
“So you would expect then to see higher levels of productivity and therefore a more productive food web in the future for the sub-Antarctic.”
Results may vary between hemispheres
But the increase in productivity is not likely to extend to oceans in the northern hemisphere. “When we talk about climate change and a changing ocean, the stories are normally very doom and gloom,” Professor Boyd said.
“But really it’s going to be a balance, there will be some regions of the ocean particularly at the higher latitudes where we may see more productivity.“The flip side of that is that from other computer modelling simulations, they’re suggesting that the lower latitudes we may see a decrease in productivity.
“So there may be quite a change from region to region in ocean productivity.”
He said people sometimes attempted these experiments changing only one or two of the conditions likely to be affected by climate change. He warned his findings showed that not modelling all of the forecast changes made for extremely varied results.
“You may get a very different picture,” he said. “For example, in a different experiment published as part of this study we see that if we only change four out of the five properties we get a very different result.
“It looks like a very detrimental affect on phytoplankton.” The findings will be published in the journal Nature: Climate Change today