The ocean’s primary productivity from phytoplankton has been decreasing due to climate change, but new research funded by CPO’s Climate Observations and Monitoring (COM) Program shows how climate change-induced increases in tropical cyclone activity leads to more phytoplankton blooms.
Led by NOAA’s Atlantic Oceanographic and Meteorological Laboratory (AOML) and the Cooperative Institute for Marine and Atmospheric Studies (CIMAS), the research finds that cooling ocean surface temperatures and increasing chlorophyll concentrations associated with tropical cyclone activity have been steadily increasing over the past three decades. The authors theorize that the increase in phytoplankton blooms due to tropical cyclones is partially mitigating the overall decline in primary production by phytoplankton under global warming. The study will be published in an upcoming issue of Geophysical Research Letters.
Researchers Nguyen Dac Da (AOML/CIMAS), Gregory Foltz (AOML), and Karthik Balaguru (Pacific Northwest National Laboratory) analyzed multi-decadal trends from satellite observations, showing for the first time the response of the global upper ocean primary productivity to tropical cyclones in the context of changing cyclone activity and ocean stratification. Warmer ocean surface temperature encourages stronger ocean stratification, which limits the supply of nutrients between layers. As a result, global ocean primary productivity—the process of fixing carbon and other inorganic matter into organic matter, usually through photosynthesis—is declining. At the same time, these warmer temperatures have produced an increase in the frequency and intensity of tropical cyclones. Cyclones are a significant source of mixing for the upper ocean, bringing cool subsurface water to the surface. This cold water is richer in nutrients, which can trigger phytoplankton blooms. The resulting cold water and chlorophyll concentrations can be seen trailing tropical cyclone activity via satellite images.