5:15 PM - 7:15 PM
[ACG50-P06] Microbial aerosols during a Trichodesmium bloom in the subtropical western North Pacific
Keywords:marine microbes, aerosol, western North Pacific
Aerosols observed over the ocean contain organic matter and microbial particles in addition to sea salt particles, and the cloud properties of aerosols change depending on the ratio of these particles. In addition, both theoretical models and experiments have shown that cloud nucleation activity changes depending on the structure of organic matter, such as the type of functional group and the number of carbon skeletons, so there is strong interest in the extent to which these changes affect actual cloud formation. Changes in the microbial community and decomposition of organic matter in seawater and aerosols should cause changes in the cloud properties of aerosols, but the relationship between marine microbial activity and aerosol composition has not been fully elucidated.
Therefore, in this study, we stayed in the subarctic and subtropical waters of the western North Pacific for about a week each to monitor the prokaryotic community structure of seawater and aerosol samples and to clarify the factors that affect their spatiotemporal variations. In particular, in this presentation, we will report in detail on the significant changes in the prokaryotic community of aerosol samples due to the bloom of the nitrogen-fixing cyanobacterium Trichodesmium that occurred during observations in the subtropical waters.
Sampling was conducted in July 2023 on the research cruise of the R/V Hakuho-Maru (cruise number: KH23-3) at three locations: K2 (N47°E160°) in the subarctic and S1 (N30°E145°) and KEOS (N25°E145°) in the subtropics. A small boat was used to sample the sea surface microlayer (SML) and underwater water (UW) at a point half a mile away from the mother ship three times at K2, five times at S1, and one time at KEOS. The first sampling at S1 observation point was in a Trichodesmium bloom, but the bloom was disappeared after the next sampling conducted two days later. The SML and UW were fractionated and collected by filtering them through filters with two different pore sizes into particle-attached bacteria (>3.0 μm) and free-living bacteria (0.22-3.0 μm). In addition, SML and UW were placed in glass bottles and bubbled on board to obtain aerosols, which were used as sea spray aerosol (SSA) samples. After extracting DNA from these samples, the relative abundance of each taxonomic group was determined by PCR amplification of the 16S rRNA gene, sequencing, and sequence data analysis.
A total of 11,870 sequence variants (ASVs: species indicators) were obtained from the 56 samples. Furthermore, the similarity of the taxonomic group composition between samples was calculated and clustering was performed, which allowed for a broad classification into seven clusters. All of the subarctic samples were classified into one cluster, while the subtropical samples were divided into four major clusters: the SSA cluster, the SML and UW free-living cluster, the SML particle-attached cluster, and the UW particle-attached cluster. However, the SSA and SML particle-attached clusters on the day of the bloom were classified into two separate clusters. Our results indicate that Trichodesmium itself does not transport into aerosols, but that blooms can significantly alter the prokaryotic composition of the SSA by modifying the organic matter and prokaryotic composition of the SML. We also suggest that taxon selection occurs during ocean-to-atmosphere emissions, and that prokaryotic aerosolization patterns differ between subarctic and subtropical regions.
Therefore, in this study, we stayed in the subarctic and subtropical waters of the western North Pacific for about a week each to monitor the prokaryotic community structure of seawater and aerosol samples and to clarify the factors that affect their spatiotemporal variations. In particular, in this presentation, we will report in detail on the significant changes in the prokaryotic community of aerosol samples due to the bloom of the nitrogen-fixing cyanobacterium Trichodesmium that occurred during observations in the subtropical waters.
Sampling was conducted in July 2023 on the research cruise of the R/V Hakuho-Maru (cruise number: KH23-3) at three locations: K2 (N47°E160°) in the subarctic and S1 (N30°E145°) and KEOS (N25°E145°) in the subtropics. A small boat was used to sample the sea surface microlayer (SML) and underwater water (UW) at a point half a mile away from the mother ship three times at K2, five times at S1, and one time at KEOS. The first sampling at S1 observation point was in a Trichodesmium bloom, but the bloom was disappeared after the next sampling conducted two days later. The SML and UW were fractionated and collected by filtering them through filters with two different pore sizes into particle-attached bacteria (>3.0 μm) and free-living bacteria (0.22-3.0 μm). In addition, SML and UW were placed in glass bottles and bubbled on board to obtain aerosols, which were used as sea spray aerosol (SSA) samples. After extracting DNA from these samples, the relative abundance of each taxonomic group was determined by PCR amplification of the 16S rRNA gene, sequencing, and sequence data analysis.
A total of 11,870 sequence variants (ASVs: species indicators) were obtained from the 56 samples. Furthermore, the similarity of the taxonomic group composition between samples was calculated and clustering was performed, which allowed for a broad classification into seven clusters. All of the subarctic samples were classified into one cluster, while the subtropical samples were divided into four major clusters: the SSA cluster, the SML and UW free-living cluster, the SML particle-attached cluster, and the UW particle-attached cluster. However, the SSA and SML particle-attached clusters on the day of the bloom were classified into two separate clusters. Our results indicate that Trichodesmium itself does not transport into aerosols, but that blooms can significantly alter the prokaryotic composition of the SSA by modifying the organic matter and prokaryotic composition of the SML. We also suggest that taxon selection occurs during ocean-to-atmosphere emissions, and that prokaryotic aerosolization patterns differ between subarctic and subtropical regions.