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Elevated turbulent and double-diffusive nutrient flux in the Kuroshio over the Izu Ridge and in the Kuroshio Extension

Elevated turbulent and double-diffusive nutrient flux in the Kuroshio over the Izu Ridge and in the Kuroshio Extension
Elevated turbulent and double-diffusive nutrient flux in the Kuroshio over the Izu Ridge and in the Kuroshio Extension
While the Kuroshio is known to be a nutrient stream, as these nutrients are in dark subsurface layers, they are not immediately available for photosynthesis unless they are supplied to the sunlit surface layers. Recent microstructure observations have revealed that strong diapycnal mixing caused by the Kuroshio flowing over topographic features and double diffusion in the subsurface layers of the Kuroshio. However, it is still unclear how much nutrient flux can be provided by these microscale mixing processes. In this study, using an autonomous microstructure float and nutrient samplings, nutrient flux caused by the Kuroshio over the Izu Ridge, and that caused by double diffusion in the Kuroshio Extension are quantified. The nitrate diffusive flux is estimated to be >1mmolNm−2day−1 over a distance, 20–30 km near the Izu Ridge and >0.1mmolNm−2day−1, which persists further downstream direction over 100 km along the Kuroshio, increasing the subsurface chlorophyll-a concentration in the region 200 km downstream. The double-diffusion-induced nitrate flux is estimated to be 1-10mmolNm−2day−1 in the pycnostad 26–26.5kgm−3 of the Kuroshio Extension, suggesting that whether this double-diffusion-induced nutrient flux in the subsurface layers can ultimately contribute to surface primary production depends on additional eddy up- and northward fluxes.
Double-Diffusion, Izu-Ridge, The Kuroshio, The Kuroshio Extension, Turbulence
55-74
Nagai, Takeyoshi
071f8aa1-52be-4ce2-aaa5-33d6bd8693c4
Rosales Quintana, Gandy Maria
59a8d15e-c9df-4a5c-85d5-88dd8e15b755
Durán Gómez, Gloria Silvana
e4f9e3b2-7d45-4de8-88b5-f24519e46a8f
Hashihama, Fuminori
68c4f746-022a-44a5-9e7d-52f5bd90e1c7
Komatsu, Kosei
1e91bc28-fee4-4a55-b866-61de4df3abeb
Nagai, Takeyoshi
071f8aa1-52be-4ce2-aaa5-33d6bd8693c4
Rosales Quintana, Gandy Maria
59a8d15e-c9df-4a5c-85d5-88dd8e15b755
Durán Gómez, Gloria Silvana
e4f9e3b2-7d45-4de8-88b5-f24519e46a8f
Hashihama, Fuminori
68c4f746-022a-44a5-9e7d-52f5bd90e1c7
Komatsu, Kosei
1e91bc28-fee4-4a55-b866-61de4df3abeb

Nagai, Takeyoshi, Rosales Quintana, Gandy Maria, Durán Gómez, Gloria Silvana, Hashihama, Fuminori and Komatsu, Kosei (2021) Elevated turbulent and double-diffusive nutrient flux in the Kuroshio over the Izu Ridge and in the Kuroshio Extension. Journal of Oceanography, 77 (1), 55-74. (doi:10.1007/s10872-020-00582-2).

Record type: Article

Abstract

While the Kuroshio is known to be a nutrient stream, as these nutrients are in dark subsurface layers, they are not immediately available for photosynthesis unless they are supplied to the sunlit surface layers. Recent microstructure observations have revealed that strong diapycnal mixing caused by the Kuroshio flowing over topographic features and double diffusion in the subsurface layers of the Kuroshio. However, it is still unclear how much nutrient flux can be provided by these microscale mixing processes. In this study, using an autonomous microstructure float and nutrient samplings, nutrient flux caused by the Kuroshio over the Izu Ridge, and that caused by double diffusion in the Kuroshio Extension are quantified. The nitrate diffusive flux is estimated to be >1mmolNm−2day−1 over a distance, 20–30 km near the Izu Ridge and >0.1mmolNm−2day−1, which persists further downstream direction over 100 km along the Kuroshio, increasing the subsurface chlorophyll-a concentration in the region 200 km downstream. The double-diffusion-induced nitrate flux is estimated to be 1-10mmolNm−2day−1 in the pycnostad 26–26.5kgm−3 of the Kuroshio Extension, suggesting that whether this double-diffusion-induced nutrient flux in the subsurface layers can ultimately contribute to surface primary production depends on additional eddy up- and northward fluxes.

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Accepted/In Press date: 26 November 2020
e-pub ahead of print date: 11 January 2021
Published date: 1 February 2021
Additional Information: Funding Information: Nagai thanks Peter Stern, Dr. Fabian Wolk, Dr. Rolf Lueck at Rockland Scientific for supporting MicroRider observations on the float, SBE for operating the float, OMIX (KAKENHI16H01590 and 18H04914) and KAKENHI (19H01965), SKED (JPMXD0511102330). Rosales Quintana and Dur?n G?mez thank JASSO and MEXT.?All the data that support the findings are available at?(https://ocg.aori.u-tokyo.ac.jp/nextcloud/index.php/s/AK2xeecmKWHRbyZ ). Please contact the corresponding author to use these data. Publisher Copyright: © 2021, The Author(s). Copyright: Copyright 2021 Elsevier B.V., All rights reserved.
Keywords: Double-Diffusion, Izu-Ridge, The Kuroshio, The Kuroshio Extension, Turbulence

Identifiers

Local EPrints ID: 446676
URI: http://eprints.soton.ac.uk/id/eprint/446676
PURE UUID: 249a545c-0493-46df-922c-ebfbef8e79eb

Catalogue record

Date deposited: 17 Feb 2021 17:34
Last modified: 25 Nov 2021 17:46

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Contributors

Author: Takeyoshi Nagai
Author: Gandy Maria Rosales Quintana
Author: Gloria Silvana Durán Gómez
Author: Fuminori Hashihama
Author: Kosei Komatsu

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