Mechanism of Nutrient Supply to Warm-Core Ring off Sanriku, Japan |
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Authors: | Katsuyuki Sasaki Yutaka Hiroe |
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Institution: | (1) National Research Institute of Fisheries Science, Fisheries Research Agency, Fukuura, Kanazawa-ku, Yokohama 236-8648, Japan |
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Abstract: | The mechanism by which nutrient is supplied to a warm-core ring (WCR) was investigated in order to understand the greater
productivity of WCR than that of the Kuroshio, where the WCR originattes. A single WCR was observed in January and May, 1997.
The thermostad (a layer of isothermal and isohaline water) of the WCR had different properties from January to May, the differences:
Δwater temperature: −0.698°C, Δsalinity: −0.048, Δsigma θ: +0.072, Δnitrite+nitrate-N: +1.83 μM, Δphosphate: +0.011 μM and
Δsilicate: +3.2 μM. We examined three possible mechanisms for nutrient supply to WCR in winter, namely: 1) inflow of the Oyashio
surface water into WCR; 2) isopycnal mixing with Oyashio water; 3) entrainment of the water below the WCR into the WCR. The
results were as follows: 1) When the decrease of salinity was due to the inflow of the Oyashio surface water, the increase
of nutrients (nitrite+nitrate-N, phosphate-P and silicate-Si) was estimated to be only 17–27% of the observed increase. 2)
When the decrease of salinity was due to isopycnal mixing, the increase of nutrients was estimated to be 30–42% of the observed
increase. 3) When the decrease of salinity in the WCR in May was due to entrainment of the water below the WCR in winter by
convection, the mixing depth was calculated be 620 m according to the salt budget. The increase of nutrients in this case
was calculated to be 82–95% of the observed increase. The main mechanism of nutrient supply to WCR was concluded to be due
to the entrainment of the water below the WCR by winter mixing.
This revised version was published online in August 2006 with corrections to the Cover Date. |
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Keywords: | Warm-core ring nutrient supply mechanism Oyashio off Sanriku |
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