TY - JOUR
T1 - Apparent oxygen utilization rates based on tritium-helium dating in the South China Sea
T2 - Implications for export production
AU - Xie, Tengxiang
AU - Newton, Robert
AU - Schlosser, Peter
AU - Guo, Liguo
AU - Wang, Lifang
AU - Huang, Tao
AU - Li, Yan
AU - Wang, Zhe
AU - Dai, Minhan
N1 - Funding Information:
We thank the Captain and Crew of the R/V Dongfanghong II for their assistance in sample collection during the cruise. This study was partially supported by National Key Scientific Research Project sponsored by the Ministry of Science and Technology through grants 2015CB954000 and National Natural Science Foundation of China through grant # 41890800 . We thank Tobias Koffman for assistance with analysis of Tritium and Helium isotopes samples and Qing Li for shipping samples.
Publisher Copyright:
© 2021 The Authors
PY - 2021/11
Y1 - 2021/11
N2 - We present tritium (3H) and helium isotope (δ3He) data from the South China Sea (SCS), to estimate apparent oxygen utilization rates (AOURs). The observed δ3He values are close to the theoretical solubility equilibrium value of -1.7% in the upper mixed layer, followed by an increase with depth down to ~1500 m. Below 1500 m depth, δ3He is homogenously distributed with a value of 20.9% ± 1.0%. The distribution of δ3He reveals that a significant fraction of 3He throughout the water column over the entire SCS basin is allochthonous, derived from mantle sources originated from the Pacific Ocean. By using the salinity-normalized “potential” alkalinity (NPA) as a conservative mixing tracer, 3He produced by tritium decay (tritiogenic) was separated from mantle 3He, and the apparent 3H–3He ages of the SCS water masses were subsequently calculated to be 11 ± 5 years at 100 m depth and 50 ± 4 years at 1000 m. Together with the observed dissolved oxygen concentrations, we estimated the mean AOURs and obtained values of 4.15 ± 0.27 μmol kg−1·yr−1 for the depth range of 100–500 m, and 0.81 ± 0.23 μmol kg−1·yr−1 for that between 800 and 1000 m depth. The depth-integrated AOURs between 100 and 1000 m depth, yield a spatially and temporally averaged export flux of organic carbon of 1.96 ± 0.16 mol-C·m−2·yr−1, comparable with previous estimates based on either 238U/234Th disequilibrium or nutrient and oxygen mass balance calculations in the SCS.
AB - We present tritium (3H) and helium isotope (δ3He) data from the South China Sea (SCS), to estimate apparent oxygen utilization rates (AOURs). The observed δ3He values are close to the theoretical solubility equilibrium value of -1.7% in the upper mixed layer, followed by an increase with depth down to ~1500 m. Below 1500 m depth, δ3He is homogenously distributed with a value of 20.9% ± 1.0%. The distribution of δ3He reveals that a significant fraction of 3He throughout the water column over the entire SCS basin is allochthonous, derived from mantle sources originated from the Pacific Ocean. By using the salinity-normalized “potential” alkalinity (NPA) as a conservative mixing tracer, 3He produced by tritium decay (tritiogenic) was separated from mantle 3He, and the apparent 3H–3He ages of the SCS water masses were subsequently calculated to be 11 ± 5 years at 100 m depth and 50 ± 4 years at 1000 m. Together with the observed dissolved oxygen concentrations, we estimated the mean AOURs and obtained values of 4.15 ± 0.27 μmol kg−1·yr−1 for the depth range of 100–500 m, and 0.81 ± 0.23 μmol kg−1·yr−1 for that between 800 and 1000 m depth. The depth-integrated AOURs between 100 and 1000 m depth, yield a spatially and temporally averaged export flux of organic carbon of 1.96 ± 0.16 mol-C·m−2·yr−1, comparable with previous estimates based on either 238U/234Th disequilibrium or nutrient and oxygen mass balance calculations in the SCS.
KW - AOUR
KW - Export production
KW - Mantle He
KW - South China Sea
KW - “Tritiogenic” He
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U2 - 10.1016/j.dsr.2021.103620
DO - 10.1016/j.dsr.2021.103620
M3 - Article
AN - SCOPUS:85114167550
VL - 177
JO - Deep-Sea Research Part I: Oceanographic Research Papers
JF - Deep-Sea Research Part I: Oceanographic Research Papers
SN - 0967-0637
M1 - 103620
ER -