Abstract
Mesoscale eddies can have a strong impact on regional biogeochemistry and primary productivity. To investigate the effect of the upwelling of seawater by western Pacific eddies on the composition of the active planktonic marine archaeal community composition of the deep chlorophyll maximum (DCM) layer, mesoscale cold-core eddies were simulated in situ by mixing western Pacific DCM layer water with mesopelagic layer (400 m) water. Illumina sequencing of the 16S rRNA gene and 16S rRNA transcripts indicated that the specific heterotrophic Marine Group IIb (MGIIb) taxonomic group of the DCM layer was rapidly stimulated after receiving fresh substrate from 400 m water, which was dominated by uncultured autotrophic Marine Group I (MGI) archaea. Furthermore, niche differentiation of autotrophic ammonia-oxidizing archaea (MGI) was demonstrated by deep sequencing of 16S rRNA, amoA, and accA genes, respectively. Similar distribution patterns of active Marine Group III (MGIII) were observed in the DCM layer with or without vertical mixing, indicating that they are inclined to utilize the substrates already present in the DCM layer. These findings underscore the importance of mesoscale cyclonic eddies in stimulating microbial processes involved in the regional carbon cycle.
Highlights
Mesoscale eddies are considered oceanic hotspots of prokaryotic activity
Our findings revealed that active Marine Group IIb (MGIIb) members were predominant in the deep chlorophyll maximum (DCM) in early November after additional substrates had been brought from 400 m waters
We demonstrated the distinct niches occupied by autotrophic Marine Group I (MGI) Thaumarchaeota between the DCM layer and mesopelagic water
Summary
Mesoscale eddies are considered oceanic hotspots of prokaryotic activity. Microbial community structure varies greatly from surface waters (i.e., epipelagic zone) to deeper regions (e.g., mesopelagic zone) where different microbial community structures are found (Baltar et al, 2010). The DCM is located close to the bottom of the photic zone connecting to nutrient-rich deep waters (Martin-Cuadrado et al, 2015). The distribution of Marine Group I (MGI) Thaumarchaeota (Fuhrman et al, 1992), Marine Group II (MGII) Euryarchaeota (DeLong, 2006; Ghai et al, 2010; Martin-Cuadrado et al, 2015), and Marine Group III (MGIII) Euryarchaeota (Galand et al, 2010; Haro-Moreno et al, 2017; Parada and Fuhrman, 2017) in the DCM zones have been characterized from different oceanic regions, interaction between these archaea group in the DCM and deeper waters is not well-studied
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