Dimethyl sulfide (DMS) is a climatically active gas released into the atmosphere from oceans. It is produced mainly by bacterial enzymatic cleavage of dimethylsulfoniopropionate (DMSP), and six DMSP lyases have been identified to date. To determine the biogeographical distribution of bacteria relevant to DMS production, we investigated the diversity of dddP—the most abundant DMS-producing gene—in the northwestern Pacific Ocean using newly developed primers and the pyrosequencing method. Consistent with previous studies, the major dddP-containing bacteria in coastal areas were those belonging to the Roseobacter clade. However, genotypes closely related to the SAR116 group were found to represent a large portion of dddP-containing bacteria in the surface waters of the oligotrophic ocean. The addition of DMSP to a culture of the SAR116 strain Candidatus Puniceispirillum marinum IMCC1322 resulted in the production of DMS and upregulated expression of the dddP gene. Considering the large area of oligotrophic water and the wide distribution of the SAR116 group in oceans worldwide, we propose that these bacteria may play an important role in oceanic DMS production and biogeochemical sulfur cycles, especially via bacteria-mediated DMSP degradation.

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The Pacific western boundary currents (WBC) are of great scientific interest due to their key role in the global water mass transport and the heat budget of the western Pacific warm pool, which is essential to the evolution of the El Niño-Southern Oscillation (ENSO) and the anomalous climate events (e.g., Fine et al., 1994;Hu et al., 2015;Jin, 1997). The North Pacific WBC includes the Kuroshio Current (KC) and Mindanao Current (MC) at the upper layer, and the Luzon Undercurrent and Mindanao Undercurrent (MUC) below the thermocline. Upon approaching the western boundary, the broad westward-flowing North Equatorial Current bifurcates into poleward KC and equatorward MC (e.g., Ando et al., 2021;Qu & Lukas, 2003). Along the Philippine coast, the MC flows southward steadily with a maximum speed exceeding 100 cm s −1 near the surface (e.g., Lukas et al., 1991;Ren et al., 2018). At the southern tip of Mindanao Island, part of the MC turns westward entering the Sulawesi Sea to feed the Indonesian Throughflow, while the remainder flows southward and then turns

Wind-induced near-inertial oscillations (NIOs) have been known to propagate their energy downward and equatorward, yet few observations have confirmed this in tropical regions. Using measurements from a moored ADCP in the tropical northwestern Pacific, we report an energetic NIO event associated with Typhoon Rammasun in May 2008, when an anti-cyclonic warm eddy existed around the mooring site. Our analyses reveal that the anti-cyclonic eddy traps the NIO energy at two layers around 120 and 210 m where the buoyancy frequency show high values. The NIO energy continuously decays at layers below its maximum at 210 m, and disappears at depths below the thermocline. During their propagation from 137 to 649 stretchedmeter depths (equivalent to 100 -430 m), NIOs shift their frequencies from 0.92f to 1.05f probably due to the effective f, which changes its magnitude from smaller to larger than local inertial frequency f in the anti-cyclonic eddy. In addition, their vertical energy propagation becomes faster from 0.17 to 0.64 mm s -1 . Decomposition of downward and upward NIO energy propagation shows that the typhoon-induced NIOs remain 29% of their energy in the upper layer, and transfer 71% to the subsurface layers. Our results suggest that typhoon-induced NIOs interacting with meso-scale eddies can play an important role in providing the energy source available for ocean mixing in the tropical regions.