An unprecedented rise in tiny phytoplankton could threaten the spread of larger phytoplankton species, vital for curbing global warming.
Shown to thrive as CO2 levels rise, pico- and nanoplankton — the sea’s smallest plankton — could upset the marine food web and affect key processes involved in counteracting global warming. This is the upshot of a recent publication1 based on research carried out in May 2010 in the Arctic as part of the European Project on Ocean Acidification (EPOCA, 2008–2012), which rallied more than 160 scientists from 32 European institutions.
Since the start of the Industrial Revolution, around 1880, oceans have absorbed approximately one third of man-made CO2 emissions, resulting in a 26% rise in their acidity levels. As CO2 is more soluble at low temperatures, the Arctic Ocean is especially prone to this ongoing trend. To investigate how acidification affects marine ecosystems in situ, an EPOCA team travelled to Kings Bay (west of Norway), to set up nine mesocosms, or giant floating plastic bags holding a range of plankton species in seawater. In seven of the 50 m3 bags, CO2 concentration was increased to reach that expected 20, 40, 60, 80, and 100 years from now, while two controls were maintained in natural conditions.
The five-week study notably showed that at high CO2 levels, pico- and nanoplankton at the base of the marine food chain grow faster and absorb nutrients usually left for larger phytoplankton. Yet, the latter are crucial to sustain two vital climate regulation processes. First, large phytoplankton carry carbon from surface waters to the depths for storage, so their decline would cut the ocean’s carbon uptake capacity. Second, they release dimethyl sulfide (DMS) gas, known to favor the formation of clouds that block out solar radiation and reduce the greenhouse effect.
“Acidification is the root cause of the changes observed in the Arctic, and could hinder resistance to climate change,” explains EPOCA coordinator Jean-Pierre Gattuso of the LOV.2 “The best strategy is to limit CO2 emissions, but current trends are not promising.” In the meantime, the impact of acidification could be partially offset by “locally eliminating stress factors such as pollution to boost sea organisms’ resistance to higher acidity,” he concludes.
01. U. Riebesell et al., “Arctic ocean acidification: pelagic ecosystem and biogeochemical responses during a mesocosm study,” Biogeosciences, 2013. 10: 5619-26.
02. Laboratoire d’océanographie de Villefranche (CNRS/ UPMC).
Fui Lee Luk, CNRS international magazine No.32, January 2014, p. 14. Article.