A Journey of Biogeochemistry from the Tropical to the Polar Ocean
Henry Charnock Lecture Southampton, 8 December 2017
Ocean biology is an important, but slow, actor in the climate system. Much emphasis has been put on the removal of CO2 from the atmosphere by the biological pump, but climate change is altering some of the limiting factors of ocean productivity. In the nutrient limited tropical ocean nitrogen fixation is an important factor to overcome nutrient limitation. It can be stimulated by input of iron from dust sources. However, warming of the ocean and expanding low oxygen zones may alter the nutrient balances with consequences or ocean productivity. Iron also plays a role in the Southern Ocean as demonstrated by iron fertilization experiments. An important habitat in the polar ocean is sea ice that is populated by ice algae and provides a food source for krill and other consumers. Progressive loss of summer sea ice, as observed in the Arctic Ocean, has profound impacts on the whole marine ecosystem. The ice dominated production system is progressively replaced by a planktonic system and due to inflow of warmer Atlantic waters the plankton composition changes. This is observed in the Fram Strait and will likely extend further into the Arctic Ocean. Sea ice changes have been observed via satellites over more than three decades, but major processes of ice loss are still not understood and hamper prediction of futures changes. A large international effort (MOSAiC) is now underway to close a gap in the observation of the annual cycle of Arctic sea ice and related processes. The rapid changes in sea ice trigger commercial interest in Arctic resources and science-based advice for sustainable development clearly lags behind. This need to be addressed in international collaboration and advanced observational technologies.