Enhanced vertical turbulent nitrate flux in the Kuroshio across the Izu Ridge
- 111 Downloads
The first direct measurements of vertical turbulent nitrate flux, FluxNO3, were conducted in the Kuroshio across the Izu Ridge and revealed large FluxNO3 near the sill crest at the 1% light depth. This large FluxNO3 possibly enhances downstream phytoplankton growth. Extremely large FluxNO3 was also observed at 26.0–26.6 σθ between the core of the Kuroshio nutrient stream and the North Pacific Intermediate Water. We hypothesize that strong vertical mixing in the Izu Ridge draws sufficient nitrate upward from the North Pacific Intermediate Water to the nutrient stream, which eventually impacts the downstream biogeochemistry in the western North Pacific.
KeywordsVertical turbulent nitrate flux Vertical mixing Izu Ridge Kuroshio Nutrient stream Simultaneous turbulence and nitrate measurement
We thank the officers, crews, onboard scientists, technical staffs, and graduate students of the R/V Shinsei-maru KS-16-10 cruise. We also thank A. Murayama for her support in the nutrient analysis. Finally, we thank two anonymous reviewers for their valuable comments on the manuscript. This study was supported by Grants-in-Aid for Scientific Research on Innovative Areas (MEXT KAKENHI JP15H05818 and JP15H05820).
- Conkright WE, Levitus S, Boyer T (1994) World Ocean Atlas 1994, vol. 1: nutrients. NOAA Atlas NESDIS 1. US Gov. Printing Office, Washington, p 150Google Scholar
- Gill AE (1982) Atmosphere–ocean dynamics. Academic, San Diego, p 662Google Scholar
- Nagai T, Hasegawa D, Tanaka T, Nakamura H, Tsutsumi E, Inoue R, Yamashiro T (2017) First evidence of coherent bands of strong turbulent layers associated with high-wavenumber internal-wave shear in the upstream Kuroshio. Sci Rep. 7:14555. https://doi.org/10.1038/s41598-017-15167-1 CrossRefGoogle Scholar
- Nishikawa H, Yasuda I, Komatsu K, Sasaki H, Sasai Y, Setou T, Shimizu M (2013) Winter mixed layer depth and spring bloom along the Kuroshio front: implications for feeding environment and recruitment of Japanese sardine. Mar Ecol Prog Ser 487:217–229. https://doi.org/10.3354/meps10201 CrossRefGoogle Scholar
- Nishikawa H, Usui N, Kamachi M, Tanaka Y, Ishikawa Y (2016) Link between the interannual variability in the Kuroshio-Oyashio layered structure and the chlorophyll-a concentrations in the Kuroshio Extension during spring. Oceanogr Japan 25(5):133–144 (in Japanese with English abstract and figure captions)CrossRefGoogle Scholar
- Redfield AC, Ketchum BH, Richards FA (1963) The influence of organisms on the composition of sea-water. In: Hill MN (ed) The sea, vol 2. The composition of sea-water: comparative and descriptive oceanography. Wiley, New York, pp 26–77Google Scholar
- Reid JL (1965) Intermediate waters of the pacific ocean. The Johns Hopkins Oceanographic Studies Series, no. 2. The Johns Hopkins Press, Baltimore, p 85Google Scholar
- Talley LD, Pickard GL, Emery WJ, Swift JH (2011) Descriptive physical oceanography: an introduction, 6th edn. Elsevier, Boston, p 560Google Scholar
- Tsuchiya M (1968) Upper waters of the intertropical Pacific Ocean. The Johns Hopkins Oceanographic Studies, no. 4. The Johns Hopkins University Press, Baltimore, p 50Google Scholar
- UNESCO (1981) The practical salinity scale 1978 and the International Equation of State of Seawater 1980. UNESCO Tech Papers Mar Sci 36:25Google Scholar
- Yokouchi K, Tsuda A, Kuwata A, Kasai H, Ichikawa T, Hirota Y, Adachi K, Asanuma I, Ishida H (2006) Simulated in situ measurements of primary production in Japanese waters. In: Kawahata H, Awaya YA (eds) Global climate change and response of carbon cycle in the equatorial Pacific and Indian oceans and adjacent landmasses. Elsevier Sci, Amsterdam, pp 65–88Google Scholar