Enhanced vertical turbulent nitrate flux in the intermediate layer of the Kuroshio in the Tokara Strait

Abstract A linear stability analysis was conducted for a three-layer primitive equation model including viscosity with a basic state, which modeled the stratification and velocity fields with the vertical and horizontal variations across the Kuroshio Extension. An unstable wave with a wavelength of 220 km and a phase speed of 0.24 m s−1 propagating in the downstream direction was found to grow the fastest. Characteristics of this unstable baroclinic wave were similar to those of waves observed along the Kuroshio Extension. The growth rate of the fastest-growing waves became greater with an increase of the cross-stream difference of the potential vorticity (PV) in the intermediate layer. For a cross-frontal stratification structure without the PV gradient in the intermediate layer, which is similar to that in the Gulf Stream, the wavelength of the fastest-growing unstable wave changed to 390 km and the unstable wave had a much different structure. Thus, the unstable frontal waves observed along the Kuroshio Extension occur only for the cases when low-PV Oyashio water exists on the northern side of the main stream in the intermediate layer. The unstable frontal waves revealed in the present study greatly contribute to the formation of a clear salinity minimum in the Kuroshio Extension.

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Favorable conditions for cold-water intrusion from the Kuroshio intermediate layer into Osaka Bay

Journal of Oceanography ◽

10.1007/s10872-011-0013-8 ◽

2011 ◽

Vol 67 (2) ◽

pp. 149-158 ◽

Cited By ~ 5

Author(s):

Koichi Sugimatsu ◽

Atsuhiko Isobe

Keyword(s):

Intermediate Layer ◽

Cold Water ◽

Water Intrusion ◽

Osaka Bay ◽

Favorable Conditions ◽

The Kuroshio

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Variation of the sea surface temperature distribution across the Kuroshio in the Tokara Strait

Journal of Engineering Physics and Thermophysics ◽

10.1007/bf02109274 ◽

1985 ◽

Vol 41 (4) ◽

pp. 244-258 ◽

Cited By ~ 18

Author(s):

Yutaka Nagata ◽

Katsuichi Takeshita

Keyword(s):

Temperature Distribution ◽

Surface Temperature ◽

Sea Surface Temperature ◽

Sea Surface ◽

Surface Temperature Distribution ◽

Tokara Strait ◽

The Kuroshio

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Numerical Study of the Kuroshio Current in the Tokara Strait

Proceedings of the International Workshop on Environment and Geoscience ◽

10.5220/0007430903950399 ◽

2018 ◽

Author(s):

Bin Wang ◽

Tianran Liu ◽

Naoki Hirose ◽

...

Keyword(s):

Numerical Study ◽

Kuroshio Current ◽

Tokara Strait ◽

The Kuroshio

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Phytoplankton productivity and rapid trophic transfer to microzooplankton stimulated by turbulent nitrate flux in oligotrophic Kuroshio Current

10.5194/bg-2019-377 ◽

2019 ◽

Author(s):

Toru Kobari ◽

Taiga Honma ◽

Daisuke Hasegawa ◽

Naoki Yoshie ◽

Eisuke Tsutumi ◽

...

Keyword(s):

Turbulent Mixing ◽

Euphotic Zone ◽

Kuroshio Current ◽

Biological Productivity ◽

Phytoplankton Productivity ◽

Kuroshio Front ◽

Dilution Experiments ◽

Nitrate Flux ◽

Enrichment Experiments ◽

The Kuroshio

Abstract. The Kuroshio Current has been thought to be biologically unproductive due to oligotrophic conditions and low plankton standing stocks. Nevertheless, major foraging fishes are known to grow and recruit around the Kuroshio Current. While mixing and advection supplying nutrients to the euphotic zone are happened by eddies and meanders but limited at the Kuroshio front, there is a risk that survival of vulnerable life stages is encountered under the low food availability. Here we report that phytoplankton productivity is stimulated by turbulent nitrate flux amplified with the Kuroshio Current and rapidly transferred to microzooplankton through their grazing. Oceanographic observations demonstrate that the Kuroshio Current topographically enhances significant turbulent mixing and nitrate influx to the euphotic zone. Gradual nutrient enrichment experiments show growth rates of phytoplankton and microzooplankton communities stimulated within a range of the turbulent nitrate flux. Dilution experiments imply a significant microzooplankton grazing on phytoplankton. We propose that these rapid and systematic trophodynamics enhance invisible biological productivity in the Kuroshio.

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Effects of Mesoscale Eddies On Intraseasonal Variability of Intermediate Water East of Taiwan

10.21203/rs.3.rs-1198576/v1 ◽

2022 ◽

Author(s):

Qiang Ren ◽

Fei Yu ◽

Feng Nan ◽

Yuanlong Li ◽

Jianfeng Wang ◽

...

Keyword(s):

Intermediate Layer ◽

Intraseasonal Variability ◽

Correlation Coefficients ◽

Mesoscale Eddies ◽

Vertical Movement ◽

Intermediate Water ◽

Sea Level Anomalies ◽

Anticyclonic Eddies ◽

Counter Current ◽

The Kuroshio

Abstract The variability of intermediate water (IW) east of Taiwan was investigated utilizing 17 months of long-term, continuous and synchronous measurements of temperature, salinity and current from mooring sites deployed at 122ºE/23ºN from January 2016 to May 2017. For the first time, we prove that the intraseasonal variability in the IW within significant periods of ~80 days was caused by mesoscale eddies propagating westward from the Subtropic Counter Current (STCC) area. The correlation coefficients between sea level anomalies (SLAs) and the Kuroshio, and between SLAs and the minimum salinity in the intermediate layer, were 0.63 and 0.52, respectively. The anticyclonic (cyclonic) eddies from the STCC, increased (decreased) the speed of the Kuroshio as well as increase (decrease) the temperature and salinity in the 400–600 m in east of Taiwan. Combines Archiving, Validation and Interpretation of Satellite Oceanographic (AVISO) products data, showed that temperature and salinity increased (decreased) in the intermediate layer due to the downward (upward) vertical movement of the water mass by anticyclonic (cyclonic) eddies. Anticyclonic eddies strengthened the Kuroshio and benefitted SCSIW flowing through the Luzon Strait to enhance salinity, while cyclonic eddies weakened the Kuroshio and favored relatively low-salt NPIW, in the area east of Taiwan.

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