Biogeochemical Characteristics of Isoprene and Non-methane Hydrocarbons in the Northwest Pacific Ocean and Their Responses to Atmospheric Aerosol Deposition

In this work, we used field investigations in the Northwest Pacific Ocean and determined the surface seawater distributions of atmospheric non-methane hydrocarbons (NMHCs) and their oceanic sources. We conducted deck incubation experiments to investigate the responses of NMHCs to atmospheric aerosol deposition. The geographical distributions of NMHCs in seawater were related to ocean currents by controlling nutrient levels and phytoplankton biomasses and communities. The high nutrient levels caused by the Oyashio Current promoted the concentration of biogenic isoprene. In addition, the transformation of predominant phytoplankton also affected the isoprene formation. The increasing proportion of diatoms (68%) in the Oyashio Current and Kuroshio Extension contributed significantly to isoprene generation, and isoprene was 3-7 fold higher than that in other areas. Corresponding to seawater, the atmospheric NMHCs apart from isoprene displayed upward trends with increasing latitude. The deck incubation experiments revealed that the dynamic changes in phytoplankton biomass and community incurred by aerosol and acidic aerosol deposition were significantly accelerated isoprene production. However, no obvious responses of the other six NMHCs to atmospheric aerosol deposition were found in the incubation studies. Both ocean current movements and atmospheric deposition jointly influenced the generation and release of isoprene in the Northwest Pacific Ocean.