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Mino, Y., Sukigara, C., Honda, M. C., Kawakami, H., Wakita, M., Sasaoka, K., Yoshikawa, C., Abe, O., Kaiser, J. 
ORCID: https://orcid.org/0000-0002-1553-4043, Kimoto, K., Kitamura, M., Fujiki, T., Matsumoto, K. and Saino, T.
(2020)
Seasonal and interannual variations in nitrogen availability and particle export in the northwestern North Pacific subtropical gyre.
Journal of Geophysical Research: Oceans, 125 (5).
ISSN 2169-9275
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Abstract
Time series of particulate nitrogen isotope delta (PN-δ 15N) and flux of trapped particles at 200 m were determined in the northwestern North Pacific subtropical gyre between 2010 and 2014 in order to examine temporal variations in mixed layer nitrate availability and downward particle export. Lower PN-δ 15N (<4‰) seen every winter corresponded to convective nitrate supply triggering phytoplankton blooms. Greater particle fluxes were associated with higher CaCO 3 concentrations (mass fraction >50%), implying that new nitrogen supply stimulated predominantly coccolithophore growth and downward transport of coccoliths. Even in the stratified summer of 2011, a δ 15N drop associated with a spike in particulate flux was found and was attributed to the uplift of nitrate-rich deep waters due to a mesoscale cyclonic eddy passing the mooring station. Total nitrate input sustains 86–93% of annual new production in this region while nitrogen fixation accounts for the rest. Trapped particles also showed that the winter δ 15N decrease appeared earlier in the 2011–2012 blooms than those in 2013–2014, coinciding with 8% higher CaCO 3 concentrations and a 40% lower particulate organic carbon to inorganic carbon export ratio, R(POC:PIC). This reflected stronger convective mixing and hence larger nutrient supply in 2011–2012, caused by larger ocean heat loss related to winter monsoon intensity. Such interannual change of winter R(POC:PIC) can affect CO 2 uptake rate in the northwestern North Pacific subtropical gyre where anthropogenic CO 2 accumulates in subtropical mode waters.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | poc:pic export ratio,coccolithophore,delta n-15 of particles,nitrate supply,the western north pacific subtropical gyre,time-series sediment trap,geophysics,forestry,oceanography,aquatic science,ecology,water science and technology,soil science,geochemistry and petrology,earth-surface processes,atmospheric science,earth and planetary sciences (miscellaneous),space and planetary science,palaeontology ,/dk/atira/pure/subjectarea/asjc/1900/1908 |
| Faculty \ School: | Faculty of Science > School of Environmental Sciences University of East Anglia Research Groups/Centres > Theme - ClimateUEA |
| UEA Research Groups: | Faculty of Science > Research Groups > Centre for Ocean and Atmospheric Sciences |
| Related URLs: | |
| Depositing User: | LivePure Connector |
| Date Deposited: | 22 Apr 2020 08:48 |
| Last Modified: | 20 Mar 2023 10:48 |
| URI: | https://ueaeprints.uea.ac.uk/id/eprint/74811 |
| DOI: | 10.1029/2019JC015600 |
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