234 Th/ 238 U disequilibrium and particulate organic carbon export in the northwestern South China Sea
- PDF / 603,567 Bytes
- 8 Pages / 595 x 842 pts (A4) Page_size
- 115 Downloads / 161 Views
234
Th/238 U disequilibrium and particulate organic carbon
export in the northwestern South China Sea MA Hao1,3,4 , ZENG Zhi1,3,4 , YU Wen2 , HE Jianhua2 , CHEN Liqi2∗ , CHENG Jianping1,3,4 , YIN Mingduan2 , ZENG Shi1 1 2
3
4
Department of Engineering Physics, Tsinghua University, Beijing 100084, China Key Laboratory of Global Change and Marine-Atmospheric Chemistry, State Oceanic Administration, Xiamen 361005, China Key Laboratory of Particle & Radiation Imaging (Tsinghua University), Ministry of Education, Beijing 100084, China Key Laboratory of High Energy Radiation Imaging Fundamental Science for National Defense, Beijing 100084, China
Received 16 July 2010; accepted 29 December 2010 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2011
Abstract 234 Th 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 234 Th activities were measured in the upper 60 m, showing a significant deficit relative to 238 U over the investigated stations. A stratified structure of 234 Th– 238 U 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 234 Th fluxes in combination with the measurement of POC/234 Th 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. Key words: 234 Th–238 U disequilibrium, POC export, South China Sea (SCS)
1 Introduction Increasing evidence has revealed that continental margins may play a significant role in global ocean carbon cycling (Frankignoulle and Borges, 2001). Despite their comprising about 8% of surface area of world oceans, continental margins contribute about 28% of global ocean primary production (Eppley and Peterson, 1979), implying that continental margins may be potential carbon sinks. Among many other processes, the particulate organic carbon (POC) export from the euphotic zone to the deep ocean is regarded as a critical index of the efficiency of biological pump and it has often been used as a necessary measurement to determine the bioFoundation item: The National Natural Science Foundation scientific research foundation of the Ministry of Science and and International Cooperation Program No. 2009DFA22920; Atmospheric Chemistry, State Oceanic Administration under Research Program. ∗ Corresponding author, E-mail: [email protected]
geochemical cycling rates of particle-reactive elements and constituents in the ocean (Eppley and Peterson, 1979; Buesseler et al., 1998; Falkowski et al., 1998). 234 Th is a radioactive nuclide with very high particle reactivity, produced in situ from the
Data Loading...
