The concentration, size distribution and dry deposition flux of microbes in atmospheric aerosols over the marginal seas and Northwest Pacific Ocean

The concentration and flux of biological aerosol particles over oceans are important for understanding the ecological implications of airborne microbes in marine ecosystems. Airborne microbes over oceans remain uncharacterized, especially the difference between those over the marginal seas and those over the open oceans. Atmospheric aerosol samples were collected over Qingdao (QD), the Yellow and Bohai Seas (YBS) and the Northwest Pacific Ocean (NWPO) during three cruises in the spring of 2014 and 2016. The total airborne microbes (TAM) in the samples were assessed based on microscope counts. The TAM concentration was (4.07 +/- 1.42) x 105 cells.m- 3 and (2.75 +/- 0.91) x 105 cells.m- 3 over the NWPO in 2014 and 2016, respectively, significantly lower than that over QD ((8.02 +/- 4.04) x 105 cells.m- 3 and (14.04 +/- 23.95) x 105 cells.m- 3 in 2014 and 2016, respectively) due to the continental source of microbes, but the TAM concentration over the NWPO in 2014 was significantly higher than that over the YBS (p < 0.01). The microbe concentration over the NWPO was affected by wind speed and direction, the horizontal offshore distance and the ratio of the distance over the sea to the total transport distance (RS), but the microbe concentration over the YBS was affected by air temperature, NO, NO2, the distance over the sea, the horizontal offshore distance and RS. Compared with those in the marine samples, the TAM in coastal samples was affected by many factors, such as air temperature, relative humidity, atmospheric pressure, PM2.5, PM10, SO2 and O3. A dust event significantly increased the concentration of TAM by a factor of 1.6-49 and changed the size distribution of TAM in the samples. The dry deposition flux of TAM was 8.83 x 107-5.12 x 108 cells.m- 2.d- 1 over the NWPO, close to the flux of 1.20 x 108-2.63 x 108 cells.m- 2.d- 1 over the YBS. Our results suggest that airborne microbes are input to the ocean via atmospheric deposition, which may have important impacts on marine ecosystems.