Abstract
234Th was utilized as a tracer of particulate organic carbon (POC) export in the northwestern South China Sea (SCS) on the basis of the data collected at four stations during a spring cruise. Depth profiles of dissolved and particulate 234Th activities were measured in the upper 60 m, showing a significant deficit relative to 238U over the investigated stations. A stratified structure of 234Th-238U disequilibrium was in general observed in the upper 60 m water column, indicating that the euphotic zone of the northwestern SCS in this reason can be divided into two layers, an upper and lower layer, with different export rates. POC export fluxes were estimated from a one-dimensional steady state model of 234Th fluxes in combination with the measurement of POC/234Th ratios on suspended particles. The POC export in this region ranged from 8.2 to 20.0 mmol/(m2·d), with an average of 16.0 mmol/(m2·d), and was slightly higher than those previously reported in the southern SCS.
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References
Benitez-Nelson C R, Buesseler K O, Glenn C. 2000. Upper ocean carbon export, horizontal transport, and vertical eddy diffusivity in the southwestern Gulf of Maine. Continental Shelf Research, 20: 707–736
Buesseler K O, Bacon M P, Cochran J K, et al. 1992. Carbon and Nitrogen Export During the JGOFS North-Atlantic Bloom Experiment Estimated From Th-234/U-238 Disequilibria. Deep-Sea Research Part A—Oceanographic Research Papers, 39: 1115–1137
Buesseler K O, Benitez-Nelson C R, Moran S B, et al. 2006. An assessment of particulate organic carbon to thorium-234 ratios in the ocean and their impact on the application of Th-234 as a POC flux proxy. Marine Chemistry, 100: 213–233
Buesseler K O, Benitez-Nelson C, Rutgers Van Der Loeff M, et al. 2001. An intercomparison of small- and large-volume techniques for thorium-234 in seawater. Marine Chemistry, 74: 15–28
Buesseler K O, Boyd P W. 2009. Shedding light on processes that control particle export and flux attenuation in the twilight zone of the open ocean. Limnology and Oceanography, 54: 1210–1232
Buesseler K O, Ball L, Andrews J, et al. 1998. Upper ocean export of particulate organic carbon in the Arabian Sea derived from thorium-234. Deep-Sea Research Part II: Topical Studies in Oceanography, 45: 2461–2487
Cai Pinghe, Chen Weifang, Dai Minhan, et al. 2008. A high-resolution study of particle export in the southern South China Sea based on 234Th:238U disequilibrium. Journal of Geophysical Research, 113: C4019
Cai Pinghe, Dai Minhan, Lv Dongwei, et al. 2006. An improvement in the small-volume technique for determining thorium-234 in seawater. Marine Chemistry, 100: 282–288
Cai Pinghe, Huang Yipu, Chen Min, et al. 2002. New production based on 228Ra-derived nutrient budgets and thorium-estimated POC export at the intercalibration station in the South China Sea. Deep-Sea Research Part I: Oceanographic Research Papers, 49: 53–66
Cai Pinghe, Huang Yipu. 2002. New production in the South China Sea—A coupled Ra-228-nitrate approach. Science in China Series D, 45: 103–109
Cai Pinghe, Huang Yipu, Chen Min, et al. 2001. Export of particulate organic carbon estimated from 234Th-238U disequilibria and its temporal variation in the South China Sea. Chinese Science Bulletin, 46: 1722–1726
Charette M A, Moran S B, Pike S M, et al. 2001. Investigating the carbon cycle in the Gulf of Maine using the natural tracer thorium-234. Journal of Geophysical Research, 106: 11553–11579
Chen Jianfang, Zheng Lianfu, Wiesner M, et al. 1998. Estimations of primary production and export production in the South China Sea based on sediment trap experiments. Chinese Science Bulletin, 43: 583–586
Chen Min, Huang Yipu, Chen Feizhou, et al. 1997. Particle dynamics in the euphotic zone VI. The utility of tracer 234Th for studying particle dynamics in the upper water column of the northeastern South China Sea. Tropic Oceanology, 2: 91–103
Chen Weifang, Cai Pinghe, Dai Minhan, et al. 2008. Th-234/U-238 disequilibrium and particulate organic carbon export in the northern South China Sea. Journal of Oceanography, 64: 417–428
Chen Yuh-linglee. 2005. Spatial and seasonal variations of nitrate-based new production and primary production in the South China Sea. Deep-Sea Research Part I, 52: 319–340
Coale K H, Bruland K W. 1985. 234Th:238U disequilibria within the California Current. Limnology and Oceanography, 30: 22–33
Dugdale R C. 1967. Nutrient limitation in sea—dynamics identification and significance. Limnology and Oceanography, 12: 685–695
Eppley R W, Peterson B J. 1979. Particulate organic matter flux and planktonic new production in the deep ocean. Nature, 282: 677–680
Falkowski P G, Barber R T, Smetacek V. 1998. Biogeochemical controls and feedbacks on ocean primary production. Science, 281: 200–206
Frankignoulle M, Borges A V. 2001. European continental shelf as a significant sink for atmospheric carbon dioxide. Global Biogeochemical Cycle, 15: 569–576
Hung Chinchang, Wei Chingling. 1992. Th-234 scavenging in the water column off southwestern Taiwan. Terrestrial Atmospheric and Oceanic Sciences, 3: 183–197
Ku T L, Knauss K G, Mathieu G G. 1977. Uranium in open ocean: concentration and isotopic composition. Deep-Sea Research, 24: 1005–1017
Ma Hao, Zeng Zhi, He Jianhua, et al. 2008. Vertical flux of particulate organic carbon in the central South China Sea estimated from Th-234/U-238 disequilibria. Chinese Journal of Oceanology and Limnology, 26: 480–485
Savoye N, Benitez-Nelson C, Burd A B, et al. 2006. Th-234 sorption and export models in the water column: a review. Marine Chemistry, 100: 234–249
Small L F, Knauer G A, Tuel M D. 1987. The role of sinking fecal pellets in stratified euphotic zones. Deep-Sea Research Part A-Oceanographic Research Papers, 34: 1705–1712
Su Jilan. 2004. Overview of the South China Sea circulation and its influence on the coastal physical oceanography outside the Pearl River Estuary. Continental Shelf Research, 24: 1745–1760
Van der Loeff M R, Sarin M M, Baskaran M, et al. 2006. A review of present techniques and methodological advances in analyzing Th-234 in aquatic systems. Marine Chemistry, 100: 190–212
Waples J T, Benitez-Nelson C, Savoye N, et al. 2006. An introduction to the application and future use of 234Th in aquatic systems. Marine Chemistry, 100: 166–189
Yang Weifeng, Huang Yipu, Chen Min, et al. 2006. Disequilibria between Po-210 and Pb-210 in surface waters of the southern South China Sea and their implications. Science in China Series D, 49: 103–112
Zeng Xianzhang, Qiu Manhua, Yin Mingduan, et al. 2007. An in-situ analysis and measurement of thorium-234, uranium isotopes in seawater. Acta Oceanologica Sinica, 26: 73–83
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Foundation item: The National Natural Science Foundation of China under grant Nos 40531007, 40676062 and 10705019; the scientific research foundation of the Ministry of Science and Technology of China through commonweal grant No. 2007050228 and International Cooperation Program No. 2009DFA22920; Open Fund of the Key Laboratory of Global Change and Marine-Atmospheric Chemistry, State Oceanic Administration under grant Nos 0807 and 0902; Tsinghua University Initiative Scientific Research Program.
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Ma, H., Zeng, Z., Yu, W. et al. 234Th/238U disequilibrium and particulate organic carbon export in the northwestern South China Sea. Acta Oceanol. Sin. 30, 55–62 (2011). https://doi.org/10.1007/s13131-011-0119-2
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DOI: https://doi.org/10.1007/s13131-011-0119-2