1. Small particles and carbon export in the surface ocean Chin-Chang Hung* and Gwo-Ching Gong National Taiwan Ocean University

2. Acknowledgements Drs. Hui-Ling Lin, James Liu, David Sheu, Chih-An Huh, Wen-Chen Chou, Chih-Ching Chung Wang-Chen Chung, Fang-Shi Kuo, Wei-Ting Kuo, Song- Lan Lee, Min-Lan Sheu, Jin-Seng Hsieh, Chin-Wei Tseng, Jin-Min Wu and crews of R/V OR-I and OR-II

3. Global carbon cycle 7.2 ± 0.3 GtC/yr 0.9 ± 0.6 GtC/yr 2.2 ± 0.5 GtC/yr 4.1 ± 0.1 GtC/yr IPCC, 2007

4. 6CO 2 ＋ 6H 2 O  C 6 H 12 O 6 ＋ 6O 2 photosynthesis  respiration uptake  release Particulate organic carbon flux, POC flux Modified from Chung 2008

5. The Joint Global Ocean Flux Study (JGOFS) The Operational Goal of JGOFS was to assess more accurately, and understand better the processes controlling, regional to global and seasonal to interannual fluxes of carbon between the atmosphere, surface ocean and ocean interior, and their sensitivity to climate changes.

6. Methods for measuring POC flux Sediment traps Primary production (f ratio) New production CO 2 & Nutrient budget 234 Th/ 238 U disequilibrium

7. Upper ocean carbon flux A sediment trap directly measures carbon flux in the ocean, but has problems: 1.Hydrodynamics 2.Swimmers 3.Solubilization of particles 4.Trapping efficiency

8. Carbon flux to depth relationship C flux(z) = Cpp / (0.0238z +0.212) Suess (1980) C flux(z) : carbon flux to depth (z) C flux(z) = C export x (Z/Zo) -0.858 (Martin et al., 1987)

9. Comments by Bishop (1989) Bishop (1989) suggested that if the downward POC flux at 100 m depth is known, then the POC flux to the deep ocean may be predicted more accurately than from the PP-based equation.

10. Deficiency of 234 Th = depth integrated 234 Th flux Hung and Gong (2007)

11. Schematic of the 234 Th flux approach (Buesseler et al., 2006)

12. POC flux = (POC/ 234 Th)p x 234 Th flux POC can be PIC, PAHs, PCB, Biogenic silica & Trace metals etc. 234 Th flux: depth integrated 234 Th flux. POC ( at least 50 papers) Particulate inorganic carbon (Bacon et al., 1996 ) Polycyclic aromatic hydrocarbons (Gustafsson et al, 1997) Polychlorinated biphenyles (Gustafsson et al., 1997b) Biogenic silica (Buesseler et al 2001, Rutgers et al., 2002) Trace metals (Gustafsson et al. 2000, Weinstein et al) Upper ocean carbon flux

13. Assumptions of the empirical method 1.Steady state or non steady state conditions 2.POC and 234 Th should be carried down by sinking particles 3.Large particles are representative of major carbon flux in the ocean

14. Previous research review Smayda, T.J. (1970) documented the trend of larger particles to sink faster (cited # 316). Fowler and Knauer (1986) proposed that “the rare large particles (>100  m) sinking through the water column are responsible for the majority of the downward vertical mass flux in the ocean (cited# 297)

15. POC flux = (POC/ 234 Th)p x 234 Th flux Henceforth, the POC/ 234 Th ratio on large particles (e.g. > 53 or 70  m) has been increasingly adopted to calculate the POC flux through the euphotic zone in different hydrographic settings including many research from the Joint Global Ocean Flux Study (Buesseler et al., 1995; Bacon et al., 1996; Cochran et al., 2000, and many scientists) Bacon et al. (1996) pointed out that “the filtered large particles are representative of the sinking particles” has not been proven (cited# 117)

16. Measuring 234 Th and POC on size- fractionated suspended particles Suspended Particles >50  m >10  m >1  m Re-filtration through QMA or GF/F filters

17. Moran et al. (2003) L&O, 48, 1018-1029.

18. Moran et al., 2003 The largest uncertainty of Th-234 method is on POC/Th-234 ratio.

20. Large Uncertainty in previous studies (Hung and Gong, in preparation)

21. Question Are the filtered large suspended particles really representative of major settling particles?

22. Sinking Particles Sediment traps GPS instrument Satellite POC, TC, 234 Th, TCHO etc.

23. Measuring POC, acidic polysaccharides Measuring 234 Th in size-fractionated sinking particles Sinking Particles >150  m >50  m >10  m >1  m

24. Summer and Winter, 2006~2008. East China Sea Taiwan

30. Status of T7KP Sediment Mooring (July 7-Sept. 11, 2008)

35. T7KP Lower trap

36. T7KP Upper trap

37. Conclusions 1.We found that small particles (1-10 and 10-50  m) likely represent a significant fraction of sinking particles in terms of carbon and 234 Th contents in the surface ocean. 2.The results suggest that small sinking particles dominating carbon flux in the surface ocean are beyond current dogma of biological oceanography. 3.Most importantly, our results also show that the previous 234 Th-derived carbon export, based on POC/ 234 Th ratios on large filtered particles (>50  m) times 234 Th flux, may be significantly biased because plenty of filtered large particles (formed by small particles) may be breakup during sequential filtration process.

41. Summer 2007

42. What kinds of organic compounds are involved in the scavenging of 234 Th in different marine environments? acidic polysaccharides (APS) and/or protein-sugar? Who is responsible for the production of APS (bacteria or phytoplankton)?