Carbon and nitrogen uptake rates of phytoplankton in the East Sea (Japan Sea) in 2012
HuiTae Joo, Jung-Woo Park, JangHan Lee and Sang Heon Lee
Department of Oceanography, Pusan National University, Geumjeong-gu, Busan, R Korea
E-mail: huitae@pusan.ac.kr
Carbon and nitrogen uptake rates were measured at 10 selected stations in the East Sea using
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C- N dual stable isotope tracer technique during Korea-Russian joint research cruise from
late October to early November, 2012. The mean carbon uptake rate was 18.04 mg C m-2 h-1
(S.D. = ± 1.50 mg C m-2 h-1) and total nitrogen uptake rate was 9.64 mg N m-2 h-1 (S.D. = ±
0.68 mg N m-2 h-1). Based on nitrate and ammonium uptake rates, f-ratio was 0.16 (S.D. = ±
0.15). For regional comparison, the mean carbon uptake rates were 27.26 mg C m -2 h-1 (S.D.
= ± 9.45 mg C m-2 h-1) and 14.09 mg C m-2 h-1 (S.D. = ± 5.56 mg C m-2 h-1) whereas the
mean nitrogen uptake rates were 11.01 mg N m-2 h-1 (S.D. = ± 5.94 mg N m-2 h-1) and 9.06
mg N m-2 h-1 (S.D. = ± 7.31 mg N m-2 h-1) in the south and north regions, respectively.
Generally, carbon and nitrogen uptake rates were higher in the south than the north region.
The contribution of small phytoplankton (<2 μm) was higher in the north (56.95%) than the
south (35.29%) based on different size chlorophyll-a concentrations. In conclusion, the
carbon and nitrogen uptake rates and f-ratio in this study were lower than those reported
previously in the East Sea. Deepened surface mixed later and nitracline probably caused low
nitrate availability to phytoplankton and consequently low rates of carbon and nitrogen
uptake during the study period.