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Time-series analysis of ocean biogeochemical and ecological data
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Long-term variation of subsurface oxygen and nutrient in North Pacific: Do they reflect each other? (Invited)
Tuesday 8th @ 1515-1540, Conference Room 5
Tsuneo Ono* , National Research Institute for Far Seas Fisheries, Japan Fisheries Research and Education Agency
Presenter Email: onotsu@biglobe.jp |
| It is well known that the oxygen content of subsurface waters has been decreased in the wide area of North Pacific, but its mechanism is not completely resolved. Nutrients are useful side variable to investigate this mechanism, as oxygen and nutrients are connected by Redfield relationship through the most of biogeochemical processes in subsurface waters. We have examined 20-years concentration change of oxygen and nutrients (phosphate, nitrate and silicate) in 100m-1000m depth range of entire North Pacific, and confirmed that increasing rate of both phosphate and nitrate in this depth range were consistent with decreasing rate of oxygen with normal Redfield stoichiometry. Estimated increase of nitrate inventory in 100m-1000m of North pacific was 200 Gmol/y, whereas no decrease of nitrate inventory in top 100m of North Pacific was observed [Yasunaka et al., 2016]. This discrepancy indicates that either southward transport of subsurface nitrate or decrease of nitrate in the waters below 1000m must be required, if we assume constant nitrate inventory in the whole north Pacific. This conclusion further indicates that either southward transport of low-oxygen signal or oxygen increase in the waters below 1000m must have been occurred in the recent North Pacific, both of which are not predicted from the present studies based only on the oxygen data.
We also found that ilicate concentration in subsurface waters of western subarctic North Pacific had increased at 6~10 times higher rate than that expected from oxygen decrease with normal Redfield stoichiometry. In this presentation, I would like to discuss about these findings and cause of non-Redfield behavior among oxygen and nutrients.
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