[A-OS12] Physical, biogeochemical, and ecological processes and variability in the Indian Ocean

[AOS12-01] Microbial signature of marine aerosols over the Indian Ocean during the KH18-6 cruise of R/V Hakuho Maru

*Koji Hamasaki¹, Poonam Bikkina¹, Md Mehedi Iqbal¹, Yoko Makabe-Kobayashi¹, Yoko Iwamoto² (1.Atmosphere and Ocean Research Institute, The University of Tokyo, 2.Graduate School of Integrated Science for Life, Hiroshima University)

Keywords:Indian Ocean, aerosol, microbe

Microbial aerosols can be generated as sea spray aerosols in marine and ambient environments or can be brought by long-range transport from terrestrial sources. Although microbial community comprises a major part of bioaerosols, the type, amount, and efficiency of microbial particle emissions from the ocean or its atmospheric deposition are still mostly underexplored. Hence, the study of microbial diversity and composition over marine regions can provide valuable insights into the role of marine microbes as a key element of controlling the fate marine organic aerosols. To date, investigations on the microbes in marine aerosols generated from the surface ocean are rather sparse, as is the case for the Indian Ocean. The specific aims of this study are (1) to compare the diversity and community structure of microbes in marine aerosols of the Bay of Bengal (BoB) and the southern Indian Ocean (SIO), and (2) to reveal possible links between the microbial signature of marine aerosols and environmental factors. Here, we performed microbial (bacteria and archaea) profiling in coarse (>2.5 µm) and fine (<2.5 µm) mode aerosol samples collected from the BoB and the SIO during the KH18-6 cruise of R/V Hakuho Maru in late autumn (6-29 November 2018; 16.5 °N-14.3 °S). Filter samples were collected on upper deck with the use of high-volume air sampler equipped with a virtual impactor. Microbial DNA was extracted from the filter and subjected to 16S rRNA gene amplicon sequencing for taxonomic profiling of the microbial community. Firmicutes, especially Bacilli known as dust associated bacteria dominated the abundance in coarse particles over the BoB, which were influenced by the terrestrial inputs, as was evident from backward air mass trajectories. Furthermore, microbial communities and dominant taxa over the SIO were totally different from those over the BoB and found to be of marine origin. Also, the diversity of microbial communities in the coarse particles were higher than those in the fine mode. Notably, the beta diversity of microbial communities in the coarse and fine particles varied with the latitude. Our study highlights the dominance of land derived bacteria caused by prevailing surface winds, which lead to the regional differences in long-range microbial exchange, especially in coarse particles over distant oceanic atmosphere. Implications are the importance of particle association and constant mixing of aerosols in understanding aerial transport of microorganisms and their impact on marine ecosystems as well as cloud formation processes.