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Small particles and carbon export in the surface ocean Chin-Chang Hung* and Gwo-Ching Gong

Small particles and carbon export in the surface ocean Chin-Chang Hung* and Gwo-Ching Gong National Taiwan Ocean University. Acknowledgements Drs. Hui-Ling Lin, James Liu, David Sheu, Chih-An Huh, Wen-Chen Chou, Chih-Ching Chung

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Small particles and carbon export in the surface ocean Chin-Chang Hung* and Gwo-Ching Gong

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  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 4.1 ± 0.1 GtC/yr 7.2 ± 0.3 GtC/yr 7.2 ± 0.3 GtC/yr 0.9 ± 0.6 GtC/yr 2.2 ± 0.5 GtC/yr IPCC, 2007

  4. 6CO2＋6H2O  C6H12O6＋6O2 • 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 ofcarbon 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 • CO2 & Nutrient budget • 234Th/238U disequilibrium

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

  8. Carbon flux to depth relationship • Cflux(z) = Cpp / (0.0238z +0.212) • Suess (1980) • Cflux(z): carbon flux to depth (z) • Cflux(z) = Cexport 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 234Th = depth integrated 234Th flux Hung and Gong (2007)

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

  12. Upper ocean carbon flux POC flux = (POC/234Th)p x 234Th flux POC can be PIC, PAHs, PCB, Biogenic silica & Trace metals etc. 234Th flux: depth integrated 234Th 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)

  13. Assumptions of the empirical method • Steady state or non steady state conditions • POC and 234Th should be carried down by sinking particles • 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/234Th)p x 234Th flux • Henceforth, the POC/234Th 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. SuspendedParticles >50 m >10 m >1 m Measuring 234Th and POC on size-fractionated suspended particles 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.

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

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

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

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

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

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

  25. T7KP Lower trap

  26. T7KP Upper trap

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

  28. Summer 2007

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

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