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Researchers from the renowned Massachusetts Institute of Technology (MIT) have identified future changes in phytoplankton community structure that will alter the oceans’ colour. The colour of the ocean surface depends on the presence of phytoplankton in the water, which reflects green light making the water greenish if abundant. That’s why the middle of the ocean looks blue, given the lower concentrations of phytoplankton. Computer models were used to predict phytoplankton growth, using established predictors such as temperature, ocean currents and ocean acidity. Besides predicting changes of phytoplankton in form of Chlorophyll-a, absorption and reflection of light were also analysed using satellite data of remote sensing reflectance. The authors concluded that at current levels of greenhouse gas emissions 63% of the ocean will experience a significant change in colour by 2100. Dr Anna Hickman, co-author from the study, stated “Crudely speaking, where the water is currently quite blue because the phytoplankton have a relatively low biomass, you are going to see the water getting more blue, and where the ocean is relatively more green because the biomass is higher, you are going to see it getting greener.” Phytoplankton play an essential role in aquatic ecosystems, producing half the world’s oxygen and representing the foundation of the marine and freshwater food web. The primary producers are a food source for many marine organisms ranging from microscopic zooplankton to enormous whales. Phytoplankton are also essential in the functioning of the biological carbon pump, a cycle in which oceans take up and store large amounts of carbon dioxide, whereby the phytoplankton take up carbon dioxide and water, turning it into glucose. The study, published in Nature Communications, highlights how climate change will impact phytoplankton growth, leading to less phytoplankton in the open ocean and hence, the trend towards increasingly bluer ocean colour. In contrast, coastal waters are expected to show increasing phytoplankton concentrations, becoming greener. Lead author Dr Dr Stephanie Dutkiewicz concluded "It could be potentially quite serious. Different types of phytoplankton absorb light differently, and if climate change shifts one community of phytoplankton to another, that will also change the types of food webs they can support."

Isabella Engberg | Sat, 16 Mar 2019