Concentration and Viability of Airborne Bacteria Over the Kuroshio Extension Region in the Northwestern Pacific Ocean: Data From Three Cruises

Abstract

AbstractAirborne bacteria have been shown to act as condensation and ice nuclei in mixed‐phase clouds and are consequently hypothesized to have significant effects on atmospheric processes and even the global climate. However, few data are available regarding their concentration and variation in the air over the open ocean. Aerosol samples were collected during three cruises in the early summers of 2013, 2014, and 2016 over the Kuroshio Extension region of the northwest Pacific Ocean. The concentrations of viable and nonviable bacterial cells in the marine surface air were quantified using epifluorescence enumeration with the LIVE/DEAD BacLight stain. The concentrations of total bacteria varied between 1.0 × 104 and 2.5 × 105 cells m−3 and averaged 5.2 × 104, 1.0 × 105, and 7.5 × 104 cells m−3 in the three respective cruises. The viabilities, i.e., the ratios of the concentration of viable bacterial cells to that of total bacterial cells, ranged from 80% to 100% (average 93%), and the respective means were 93%, 89%, and 96% in the cruises. The total bacterial concentration had a close correlation with the wind speed near the sea surface, and the bacterial viability correlated negatively with the air temperature, sea surface temperature, and concentration of coarse particles (size > 1 μm). The deposition and sea spray fluxes of bacteria were roughly estimated as hundreds of cells m−2 s−1 on average. The limited data on bacterial concentration and viability from the three cruises indicate the rapid air‐sea exchange of bacteria over the Kuroshio Extension region of the northwest Pacific Ocean.