Despite all these differences between the two regimes, the biological carbon pump wasn’t necessarily more productive in the summer of 2018: “We found that, in the summer of 2017, the majority of the organic carbon didn’t reach the seafloor until after September,” says von Appen. “If you look at the period between early May and late November, the carbon export in the mixed-layer regime was only a third higher than in the meltwater regime.” Rather, the pronounced stratification in 2017 promoted longer-term growth over several months, since carbon and nutrients were trapped in the upper layers. In contrast, the ice-free situation in 2018 produced a brief, intense bloom and rapid export, providing food and carbon for deep-sea ecosystems on the ocean floor. As such, the latter would seem to particularly benefit from the summertime conditions in the mixed-layer regime; in the meltwater regime, the intense stratification blocks nutrient input in the summer and deep water mixing in the winter.
“In the future, the mixed-layer regime could spread over larger regions of the Arctic,” von Appen explains. “The conditions in this regime are similar to those in lower latitudes, and we conclude that the Arctic Ocean could increasingly behave more like oceans in southern regions.”
In the polar regions, making scientific observations and gathering data are particularly challenging: extremely low temperatures, brutal storms and prolonged darkness make it far more difficult to use monitoring technologies. But the Arctic observatory FRAM (FRontiers in Arctic Marine Monitoring) is up to the task: its modular monitoring platforms are equipped with cutting-edge sensors that can be deployed on and below the ice, in the ice-covered water column, and on the ocean floor. In this way, they can make monitoring faster, more economical and more sustainable. “FRAM is a unique marine infrastructure asset used by national and international research projects to better grasp and describe polar ecosystems and their influences on the global climate system,” says Prof Antje Boetius, Director of the AWI. “The worsening climate change is also affecting the Arctic Ocean. Observing these changes in all their facets in order to grasp the causes and effects down to the ocean depths is one of our most important goals.” The FRAM infrastructure is funded by the Helmholtz Association and operated by the AWI.
Melting sea ice: An unsuspected domino effect