Eastern equatorial Pacific Ocean is a remote open ocean with relatively high marine biological activity. Enhanced effect of marine natural processes may reflect to atmospheric composition above the surface ocean. This region is also characterized as a high nutrient low chlorophyll (HNLC) ocean, in which availability of trace metals such as iron may limit marine primary production. Atmospheric deposition of these trace elements to the ocean surface may play an important role in regulating marine primary productivity and defining unique microbial community. Tropical deep convection over this region is expected to bring marine biogenic substances emitted from the surface ocean into stratosphere, efficiently.
In this unique eastern equatorial Pacific Ocean, the EqPOS (Equatorial Pacific Ocean and Stratospheric/Tropospheric Atmospheric Study) research cruise was organized as a part of SOLAS Japan activity to understand biogeochemical ocean-atmosphere interaction and exchange processes between stratosphere and troposphere. Coordinated atmospheric, oceanic, and marine biological observations including sampling/characterization of thin air-sea interfacial layer (sea surface microlayer: SML) and stratospheric air sampling using balloon-borne cryogenic air samplers were carried out on-board R/V Hakuho Maru starting from 29 January for 39 days.
Biogeochemically important trace/long-lived gases such as CO2, dimethyl sulfide (DMS), and some volatile organic carbons (VOCs) both in the atmosphere and seawater were continuously monitored and their air-sea fluxes were observed using gradient and eddy-covariance techniques. Atmospheric gas measurement of CO2, CH4, N2O, SF6, CO, H2, Ar and isotopic composition of the selected gases were further extended to stratospheric air with balloon-born sampling in addition to a vertical profiling of O3, CO2, and H2O with sounding sondes. Physical and chemical properties of marine atmospheric aerosols such as size distribution, total and cloud condensation nuclei concentrations, microscopic morphological observation, bulk and single particle chemical composition were also continuously determined to find out potential link between biogenic VOCs emitted from the ocean and aerosol composition. Biological and biogeochemical characterizations of marine microorganisms, suspended particulate matter, dissolved nutrients in seawater and SML were also conducted.
In the presentation, brief overview of the research activities during the EqPOS cruise and preliminary findings on biogeochemical linkage atmosphere and ocean via atmospheric and oceanic gaseous and particulate matter from ocean surface to stratosphere observed during the cruise would be presented.