How a Small Reef in the Kuroshio Cultivates the Ocean

Hasegawa, Daisuke; Matsuno, Takeshi; Tsutsumi, Eisuke; Senjyu, Tomoharu; Endoh, Tatsuo; Tanaka, Takahiro; Yoshie, Naoki; Nakamura, Hirohiko; Nishina, Ayako; Kobari, Toru; Nagai, Takeyoshi; Guo, Xinyu

doi:10.1029/2020gl092063

Cited by 20 publications

(14 citation statements)

References 21 publications

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“…This was because when cyclonic and anticyclonic eddies encounter the Kuroshio, they reduce and enhance poleward transport which characterized the SBC and LBC in this study, respectively (Jan et al, 2015;Tsai et al, 2015;Chang et al, 2018). On the other hand, the presence of the KH billows have been demonstrated to be an S-shaped echo band, similar to this study (Geyer et al, 2010;Chang et al, 2016;Hasegawa et al, 2021). In describing the KH billows, their transitory nature was observed during the time-series surveys.…”

Section: Hydrographic Conditions and Response To Variable Kelvin-helm...supporting

confidence: 78%

Vertical Nitrate Flux Induced by Kelvin–Helmholtz Billows Over a Seamount in the Kuroshio

et al. 2021

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Kelvin–Helmholtz (KH) billows can facilitate microscale turbulent mixing around seamounts in the Kuroshio. This study sought to describe the influence of billow intensity (i.e., “intermittent and small” and “steady and large” billows) on vertical nitrate fluxes. KH billows led to turbulent kinetic energy dissipation rates [ε = O (10–7 to 10–6) W kg–1] and eddy diffusivities [Kρ = O (10–4 to 10–3) m2 s–1] that were significantly stronger than those outside the billow depths. The mean nitrate flux estimated using Kρ in the billow depths had a maximal value of 10.0 mmol m–2 day–1, which was much higher than estimates for the open ocean. The nitrate flux associated with the shallow KH billows at two vertical levels contributed to enrich the subsurface phytoplankton maximum, while the deeper billows closer to the summit were found to induce a large amount of nitrate flux from the deeper to the subsurface water. This study showed that KH billows make important contributions to seamount ecosystems, particularly in the cycling and vertical mixing of nutrients to make them available for potential downstream transport.

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Section: Hydrographic Conditions and Response To Variable Kelvin-helm...supporting

confidence: 78%

Vertical Nitrate Flux Induced by Kelvin–Helmholtz Billows Over a Seamount in the Kuroshio

et al. 2021

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“…However, it has still been elusive on how much nutrients can be supplied by the turbulent vertical mixing in the geostrophic currents flowing over the topographic features, including the Kuroshio 43 . This is because the simultaneous measurements of turbulence and nutrient concentrations are still very limited 44 , calling for more observational and modeling studies in the near future. These submesoscale processes and concomitant mixing are currently missing in the climate models and need to be resolved or well parameterized for better understanding and prediction of the ocean's response to climate variability.…”

Section: Discussionmentioning

confidence: 99%

The Kuroshio flowing over seamounts and associated submesoscale flows drive 100-km-wide 100-1000-fold enhancement of turbulence

Nagai

Hasegawa

Tsutsumi

et al. 2021

Commun Earth Environ

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Although previous studies reported that currents over topographic features, such as seamounts and ridges, cause strong turbulence in close proximity, it has been elusive how far intense turbulence spreads toward the downstream. Here, we conducted a series of intensive in-situ turbulence observations using a state-of-the-art tow-yo microstructure profiler in the Kuroshio flowing over the seamounts of the Tokara Strait, south of Kyusyu Japan, in November 2017, June 2018, and November 2019, and employed a high-resolution numerical model to elucidate the turbulence generation mechanisms. We find that the Kuroshio flowing over seamounts generates streaks of negative potential vorticity and near-inertial waves. With these long-persisting mechanisms in addition to other near-field mixing processes, intense mixing hotspots are formed over a 100-km scale with the elevated energy dissipation by 100- to 1000-fold. The observed turbulence could supply nutrients to sunlit layers, promoting phytoplankton primary production and CO2 uptake.

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“…Nevertheless, dinoflagellates were frequently ingested as prey by most omnivorous mesozooplankton groups and species. Although phytoplankton standing stocks and productivity in the Kuroshio are stimulated by a supply of nutrients 16,46,47 and intermittently increase through advection from coastal communities 19 , mesozooplankton feeding experiments show no significant ingestion of autotrophic dinoflagellates 15 . Estimates of the carbon budget have demonstrated that heterotrophic nanoflagellates contributed to mesozooplankton food requirements 19 .…”

Section: Discussionmentioning

confidence: 99%

Metabarcoding analysis of trophic sources and linkages in the plankton community of the Kuroshio and neighboring waters

Kobari

Tokumo

Sato

et al. 2021

Sci Rep

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Trophic sources and pathways supporting early life stages are crucial for survival of forage fishes recruiting around the oligotrophic and unproductive Kuroshio. However, information is limited for the Kuroshio planktonic food web and its trophodynamics because of its high biodiversity. Here, we explore trophic sources and linkages in the Kuroshio plankton community using metabarcoding analysis of gut-content DNA for 22 mesozooplankton groups. The major prey was dinoflagellates and calanoids for omnivorous groups, and calanoids and gelatinous organisms for carnivorous groups. Larvaceans and hydrozoans were the most frequently appeared prey for both omnivores and carnivores, whereas they were minor constituents of the available prey in water samples. Although calanoids overlapped as major prey items for both omnivores and carnivores because they were the most available, contributions from phytoplankton and gelatinous prey differed among taxonomic groups. Further analysis of the metabarcoding data showed that in addition to omnivorous copepods like calanoids, gelatinous groups like larvaceans and hydrozoans were important hubs in the planktonic food web with their multiple trophic linkages to many components. These findings suggest that gelatinous organisms are important as supplementary prey and provide evidence of niche segregation on trophic sources among mesozooplankton groups in the Kuroshio.

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How a Small Reef in the Kuroshio Cultivates the Ocean

Cited by 20 publications

References 21 publications

Vertical Nitrate Flux Induced by Kelvin–Helmholtz Billows Over a Seamount in the Kuroshio

Vertical Nitrate Flux Induced by Kelvin–Helmholtz Billows Over a Seamount in the Kuroshio

The Kuroshio flowing over seamounts and associated submesoscale flows drive 100-km-wide 100-1000-fold enhancement of turbulence

Metabarcoding analysis of trophic sources and linkages in the plankton community of the Kuroshio and neighboring waters

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