Impacts of Aerosol Depositions from Ship Emissions on Marine Primary Productivity, Biological Community Composition and Biogeochemical Cycling

The combustion of diesel and low-grade fuels in the engines of oceangoing vessels releases aerosols that are rich in inorganic components and metals. These aerosols contain some components that are known to promote phytoplankton growth (e.g. N, S, Fe), and others that can be toxic and decrease marine productivity (e.g. Cu). The deposition of such aerosols to the sea surface, therefore, has the potential to change both primary production rates and the structure of phytoplankton populations, which can alter the efficiency of the biological pump, carbon sequestration rates and climate. Here, we investigate the fertilization effects of ship emissions in oligotrophic ocean gyres, as well as in high-nutrient low-chlorophyll regions, and in selected coastal regions. A suite of remote sensing products (MERRA-2, OMI, and various data sets from MODIS) was used to conduct grid-based correlation analyses that explore the relationship between ship emissions and marine primary productivity for each of these case studies in different seasons. The results from the correlation analyses were then combined with in situ observations of phytoplankton populations and with new experimental data from mesocosm incubations that tested the direct effects of aerosol samples from ship emissions on chlorophyll concentration and on phytoplankton composition. Seasonal and regional maps were generated, identifying the conditions for which ship emissions have strong impacts on ocean biogeochemistry, phytoplankton biogeography and marine primary production.