Oceans are some of the largest carbon sinks on our planet, due to the “biological carbon pump” represented by microorganism like algae and phytoplankton which absorb carbon dioxide from the atmosphere through photosynthesis. When these organisms sink at the bottom of the ocean, the carbon they contain often remains intact for millennia. A new study led by the Alfred Wegener Institute for Polar and Marine Research (AWI) has found that meltwater from sea ice floes can delay this process by up to four months.
Between 2016 and 2018, the scientists used the ocean observation system FRAM (Frontiers in Arctic Marine Monitoring), to gather data about the coupled physical-biological processes taking place in the Fram strait, located between Greenland and Svalbard.
“For the first time, for two entire years we were able to comprehensively monitor not only the seasonal developments of microalgae and phytoplankton, but also the complete physical, chemical, and biological system in which these developments take place,” said study lead author Dr. Wilken-Jon von Appen, a climate researcher at the AWI.
While in the summer of 2017, a huge amount of ice was transported out of the Arctic through the Fram strait, producing a great deal of low-saline meltwater and a pronounced stratification of the water (“the meltwater regime”), in the summer of 2018 an uncharacteristically low amount of ice went out of the Arctic, producing thus very little meltwater and salinity-based stratification (“the mixed-layer regime”).
The scientists found that during the meltwater regime from 2017, very little carbon made its way to the seafloor, and although the algae and phytoplankton had already bloomed by mid-May, it took another four months for the carbon to reach the seafloor, with the microorganisms being able to fix up to 25 grams of carbon per square meter.
By contrast, during the mixed-layer regime from 2018, only two to three weeks after the algae and phytoplankton had started to bloom, organic carbon reached depths of up to 1,200 meters, and a few more weeks later, it reached the seafloor. Furthermore, the microorganisms were able to fix 50 grams of carbon per square meter, thus twice as much as in the meltwater regime.
“In the future, the mixed-layer regime could spread over larger regions of the Arctic,” Dr. von Appen explained. “The conditions in this regime are similar to those in lower latitudes, and the Arctic Ocean could increasingly behave more like oceans in southern regions.”
The study is published in the journal Nature Communications.