Tiny organisms in the ocean called phytoplankton consume CO₂, affecting its air-sea exchange rate and the efficiency with which carbon is sequestered in the deep ocean. The intense vertical mixing induced by some tropical cyclones has been shown to significantly enhance surface chlorophyll a (chl a) concentration, which influences CO₂ uptake through photosynthesis. While individual hurricanes have been shown to induce sea surface chlorophyll blooms along their tracks, some studies suggest that their cumulative impact may not be significant.A team of scientists–including two U.S. Department of Energy scientists at Pacific Northwest National Laboratory–assessed the tropical cyclone-induced chl a enhancement in the subtropical North Atlantic Ocean during 1998-2011. Using an integrated and comprehensive approach that includes quantification of cyclone-induced changes in the mixed layer depth, the team found that tropical cyclones indeed have a substantial impact on integrated chlorophyll. The accumulated cyclone energy explains 22% of the interannual chl a variance during the hurricane season (June–November), after removing the influence of the North Atlantic Oscillation. The variance of chlorophyll concentrations explained by tropical cyclones is thus about 70% of that explained by the NAO, which has well-known impacts in this region. Thus the team found that tropical cyclones contribute significantly to interannual variations of primary productivity in the western subtropical North Atlantic during the hurricane season. Tropical cyclone-induced changes in chl a concentration may also affect the survival rates of fish larvae and their advancement to adulthood.