Biogeochemical evidence of large diapycnal diffusivity associated with the subtropical mode water of the North Pacific

Sukigara, Chiho; Suga, Toshio; Saino, Toshiro; Toyama, Kenzo; Yanagimoto, Daigo; Hanawa, Kimio; Shikama, Naoki

doi:10.1007/s10872-011-0008-5

Cited by 43 publications

(36 citation statements)

References 28 publications

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“…While the values are only marginally significant during winter, the analysis suggests the presence of enhanced mixing, with diffusivity roughly 3 Â 10 À 4 m 2 /s during the warm season and more than two orders of magnitude larger during winter. Our warm season values are quite similar to those found at the base of the seasonal thermocline by and Sukigara et al (2011). The latter diffusivity estimate was based upon a dissolved oxygen budget analysis; the estimate was based upon the potential vorticity budget of the North Pacific Subtropical Mode Water (STMW).…”

Section: Discussionsupporting

confidence: 79%

“…The latter diffusivity estimate was based upon a dissolved oxygen budget analysis; the estimate was based upon the potential vorticity budget of the North Pacific Subtropical Mode Water (STMW). Using microstructure measurements, Mori et al (2008) found that within and above the core of the STMW, the microstructure diffusivity values were $ 10 À 5 m 2 /s, over an order of magnitude smaller than found in our study and the budget analyses of and Sukigara et al (2011). It may be that the STMW acts as a barrier to internal wave energy and turbulent mixing, and that this trapping enhances the local dissipation in the seasonal thermocline as proposed by .…”

Section: Discussioncontrasting

confidence: 39%

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Formation and erosion of the seasonal thermocline in the Kuroshio Extension Recirculation Gyre

Cronin

Bond

Farrar

et al. 2013

Deep Sea Research Part II: Topical Studies in Oceanography

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a b s t r a c tData from the Kuroshio Extension Observatory (KEO) surface mooring are used to analyze the balance of processes affecting the upper ocean heat content and surface mixed layer temperature variations in the Recirculation Gyre (RG) south of the Kuroshio Extension (KE). Cold and dry air blowing across the KE and its warm RG during winter cause very large heat fluxes out of the ocean that result in the erosion of the seasonal thermocline in the RG. Some of this heat is replenished through horizontal heat advection, which may enable the seasonal thermocline to begin restratifying while the net surface heat flux is still acting to cool the upper ocean. Once the surface heat flux begins warming the ocean, restratification occurs rapidly due to the low thermal inertia of the shallow mixed layer depth. Enhanced diffusive mixing below the mixed layer tends to transfer some of the mixed layer heat downward, eroding and potentially modifying sequestered subtropical mode water and even the deeper waters of the main thermocline during winter. Diffusivity at the base of the mixed layer, estimated from the residual of the mixed layer temperature balance, is roughly 3 Â 10 À 4 m 2 /s during the summer and up to two orders of magnitude larger during winter. The enhanced diffusivities appear to be due to large inertial shear generated by wind events associated with winter storms and summer tropical cyclones. The diffusivity's seasonality is likely due to seasonal variations in stratification just below the mixed layer depth, which is large during the summer when the seasonal thermocline is fully developed and low during the winter when the mixed layer extends to the top of the thermocline.Published by Elsevier Ltd.

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Section: Discussionsupporting

confidence: 79%

Section: Discussioncontrasting

confidence: 39%

Formation and erosion of the seasonal thermocline in the Kuroshio Extension Recirculation Gyre

Cronin

Bond

Farrar

et al. 2013

Deep Sea Research Part II: Topical Studies in Oceanography

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“…4b), at most of the CTDO 2 stations south of the KE jet (the sharp SSH gradient), AOU lower than 30 µmol kg −1 was recorded on the isopycnal of 25.3σ θ deeper than the primary DO maxima, or the shallow maximal oxygen layer, near the sea surface (Reid 1962;Sukigara et al 2011Sukigara et al , 2014; these profiles are shown by black lines in Fig. 5a.…”

Section: Oxygen Consumption and Recovery To Near Saturationmentioning

confidence: 89%

“…Using an Argo float deployed to the south of the KE, Sukigara et al (2011) obtained a DO time series down to a depth of 1000 m at 5-day intervals from March to July 2006. Using quasi-Lagrangian observations, they illustrated the variability of DO in the ventilated water mass trapped within an anticyclonic mesoscale eddy.…”

Section: Introductionmentioning

confidence: 99%

Ventilation revealed by the observation of dissolved oxygen concentration south of the Kuroshio Extension during 2012–2013

et al. 2016

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“…Nutrient, phytoplankton and zooplankton distributions and hydrography are considerably different north and south of the Kuroshio axis (Kawai 1972, Nakata et al 1995, Sukigara et al 2011. For example, satellite data show a high density of chlorophyll a (chl a) along the northern side of the Kuroshio axis (Fig.…”

Section: Introductionmentioning

confidence: 99%

Winter mixed layer depth and spring bloom along the Kuroshio front: implications for the Japanese sardine stock

Nishikawa

Yasuda²,

Komatsu³

et al. 2013

Mar. Ecol. Prog. Ser.

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Recruitment of Japanese sardine Sardinops melanostictus is related to interannual variability in the winter mixed layer depth (MLD) near the Kuroshio axis (line of maximum current), possible because MLD may influence the feeding environment of sardine larvae through phytoplankton productivity. However, a relationship between the winter MLD and phytoplankton productivity has not been shown. Particle release experiments with quasi-observed current fields from ocean reanalysis products and satellite-observed phytoplankton (chlorophyll a) density from 1998 to 2006 showed that deeper waters of the winter mixed layer flowing 0° to 0.5° north of the Kuroshio axis led to a greater bloom in the subsequent spring, although such a relationship was not detected south of the Kuroshio axis. By using the output of a 3-dimensional, high-resolution lower trophic level ecosystem model that reproduced the MLD−phytoplankton relationship, we found that entrainment of deeper nutrient-rich subsurface water leads to abundant nutrients in the early spring and enhances the subsequent spring bloom along the northern side of the Kuroshio axis. On the southern side, where mode water develops in winter, the deeper winter mixed layer does not necessarily contain higher nutrient contents, because nutrient vertical profiles often have inversions. These results support the hypothesis that sardine larvae that are distributed in the deeper winter mixed layer north of the Kuroshio axis (called the Kuroshio frontal zone) encounter a higher phytoplankton density, which yields favorable feeding conditions, resulting in recruitment success.

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Biogeochemical evidence of large diapycnal diffusivity associated with the subtropical mode water of the North Pacific

Cited by 43 publications

References 28 publications

Formation and erosion of the seasonal thermocline in the Kuroshio Extension Recirculation Gyre

Formation and erosion of the seasonal thermocline in the Kuroshio Extension Recirculation Gyre

Ventilation revealed by the observation of dissolved oxygen concentration south of the Kuroshio Extension during 2012–2013

Winter mixed layer depth and spring bloom along the Kuroshio front: implications for the Japanese sardine stock

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