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Air-Sea CO 2 Exchange in the Northern South China Sea

Air-Sea CO 2 Exchange in the Northern South China Sea. C.-M.Tseng. Thanks to: W.C. Chou ; C.T.A. Chen; C . C . Chen; S . W . Chung; K . T . Jiann; B . S . Lee; Y . H . Li; I.I. Lin; K.K. Liu ; D.D. Sheu ; F . K . Shiah; G.T.F. Wong ; L . S . Wen; Y . Y ang……. Talk outline.

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Air-Sea CO 2 Exchange in the Northern South China Sea

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  1. Air-Sea CO2 Exchangein the Northern South China Sea C.-M.Tseng Thanks to: W.C. Chou;C.T.A. Chen; C.C. Chen; S.W. Chung; K.T. Jiann; B.S. Lee; Y.H. Li; I.I. Lin;K.K. Liu;D.D. Sheu; F.K. Shiah; G.T.F. Wong;L.S. Wen; Y. Yang……

  2. Talk outline • Introduction & Overview • Annual & inter-annual variability of Ocean CO2 • Physical and biogeochemical processes affecting variability • Magnitude and variability of Air-sea exchange CO2 flux relative to global scales • Increasing magnitudes of TCO2 and fCO2 • Future study (e.g., El-Niño, Typhoon)

  3. key indicators of global change Sea level • Atmo. CO2, • Temp., • Sea ice. • Sea level Atmo. CO2 Temp. Sea ice.

  4. [CO2] year ppm y-1 2000 1.24 2001 1.85 2002 2.39 2003 2.21 2004 1.61 2005 2.41 2006 1.79 2007 2.17 2008 2.28 1850 1870 1890 1910 1930 1950 1970 1990 2010 • 1970 – 1979: 1.3 ppm y-1 1980 – 1989: 1.6 ppm y1 • 1990 – 1999: 1.5 ppm y-1 • 2000 - 2008: 2.0 ppm y-1 • 2008: 2.3 ppm y-1 Atmospheric CO2 Concentration Year 2008 Atmospheric CO2 concentration: 385 ppm 38% above pre-industrial NOAA 2007; Canadell et al. 2007, PNAS

  5. 4.2 Pg y-1 Atmosphere 46% 2.6 Pg y-1 + Land 29% 7.5 Pg C y-1 2.3 Pg y-1 Oceans 26% Fate of Anthropogenic CO2 Emissions (2000-2007) 1.5 Pg C y-1 Canadell et al. 2007, PNAS; Global Carbon Project 2008, update

  6. Mean Annual Air-Sea CO2 Flux Takahashi et al. (2002)

  7. J TS H RR LS PS A1 P C MS PR R KS Environmental Forcing Physical • Seasonal circulation • Kuroshio intrusion • Coastal diluted waters • Internal tides/waves • Upwelling Atmospheric • Winter and summer monsoons • Typhoons • Asian dusts • ENSO events • Climate variability (Shaw & Chao, 1994; Shaw et al., 1996)

  8. Distinctives of the South China Sea • Most of the sea is oligotrophic • Mixed-layer T is high (>22 oC) year round • Well stratified over the year (i.e., Effect of convective overturn is small) • Shallow thermocline (<40 m) • Higher atmospheric dust inputs and Fe fluxes • Seasonally alternative monsoons • Frequent occurrence of typhoons and tropical depressions (over 10 events/year)

  9. Annual Mean SST and SSS SST SSS Liu et. al 2009

  10. Composite Chl-a Distribution Summer (August) Winter (January) SEATS special issue, 2007

  11. Wind SST MLD TND EPZ SRP N+N S-chl I-chl IPP • Seasonal variations in wind speed – Higher in Winter; Lower in Summer (Monsoon) • Variations in T – never drops below 22oC. • Seasonal variations in mixed layer depth - <40 m in most of the year; approach 100 m in Winter. • Variations in nutrients – higher SRP, N+N in Winter • Higher wind speed correlates with lower T and higher Chl-a • Higher biomass and primary production in the Winter accompanies the higher nutrient concentrations. Tseng et. al 2005; 2007; 2009

  12. Air/sea gas exchange Air/sea gas exchange ΔF - - - + + + - - - + + + Photosyn Photosyn . . Δ B Temp. effect Δ Remineral Remineral . . T - - - + + + + + + + Δ Δ Δ Δ D E Mixing/upwelling Mixing/upwelling Factors affect the oceanic CO2 variability in the MLD Surface Mixed-Layer fCO2 Δ Δ C MLD ΔC = (ΔD +ΔE) + ΔF +ΔB +ΔT

  13. Estimating Air-Sea Exchange Fluxes of CO2 F = K DfCO2 = k s (fCO2sw- fCO2air) • Uncertainty:k- affected by wind, air bubble entrainment, sea surface conditions etc. Factors influencing CO2 flux estimates

  14. Zhai' paper: fCO2 in northern SCS Summer Fall Spring (Zhai et al., 2005)

  15. Chen' paper: • OR-I 508 • Nov 15-24 1997 • OR-I 546 • April 7-20 1999 • 15~28 stations • Wet season (sea-to-air): • ~0.006 Gt C per yr • Dry season (air-to-sea): • ~0.004 Gt C per yr (Chen et al., 2006) fCO2 in northern SCS

  16. fCO2=8.8 x T + 123.0; (or fCO2=184.9 x e0.025) r2= 0.81 SEATS: Mixed-layer fCO2 Temperature Effect fCO2 • Water fCO2 varies directly with T and inversely with chl-a – Low fCO2 in Winter (Solubility+Biological pump). • fCO2 water <fCO2 air in Winter -> invasion； fCO2 water >fCO2 air in Summer-> evasion Temp.

  17. Jun July Aug May Sept Oct Mar Nov Nov-Dec Dec Jan Feb-Mar

  18. Conceptual diagram of the contributing processes to the changes in salinity, temperature and the carbonate system in the mixed layer Tseng et al., 2007

  19. Comparison with Other Time-series Stations The relative importance of temp. & biological effect on seasonal fCO2 variability (Takahashi et al., 2002, DSRII) Location and Oceanic regime Temperature effect / Biological effect Temperature effect - Biological effect References 18º15’N , 115º35’E South China Sea,the largest subtropical marginal sea 2.0 (80/40 matm) +40 mtam SEATS This study 22º45’N, 158ºW North Pacific subtropical gyre 2.6 (59/23 matm) Calculated based on Winn et al. (1994) HOT +36 mtam 31º50’N, 64º10’W Western North Atlantic subtropical gyre Bates et al. (2001) Takahashi et al. (2002) BATS 2.7 (150/55 matm) +95 mtam 44ºN, 155ºE Northwestern subarctic Pacific Ocean Calculated based on Tsurushima et al. (2002) 0.8 (174/228 matm) -54 mtam KNOT Wong and Chan (1991) Takahashi et al. (2002) 50ºN, 145ºW Northeastern subarctic Pacific Ocean 0.9 (100/115 matm) -10 mtam OSP

  20. SEATS CO2 Flux (1999~2004) Seasons Fluxes (mol C m-2 y-1) Net ≈ -0.02 (Tseng et al., 2007) “+” denotes evasion to the atmosphere “-” denotes invasion to the ocean Months

  21. SEATS CO2 Flux (1999~2007) • Normally CO2 invasion in Winter ；CO2 evasion in Summer • CO2flux varies inter-annuallymarked in red dashed circle • Interannual anomaly may be linked to large-scale climate variability (e.g, ENSO, Pacific Decadal Oscillation etc.) Net evasion flux: + 0.1 ± 0.7

  22. Comparison with other time-series stations Annual sea-to-air flux References (molC m-2year-1) + 0.1 ± 0.7 This study SEATS (1999-2004) Tseng et al., 2007 -0.02 ± 1.06 SEATS (2002-2003) Chou et al. 2004 -0.1 to –0.2 SEATS (1990-2004) Chai et al., 2009 - 0.04 +0.33 Chai et al., 2009 Whole SCS -0.7 Winn et al., 1994 HOT BATS -0.3 to –0.8 Bates et al., 1996, 1998

  23. Interannual Trends of CO2 at SEATS NTCO2=(2.0 ± 1.4)X+ 1886.1; r2= 0.11, p=0.17 2004 1999 2000 2001 2002 2003 NfCO2=(2.6 ± 0.9)X+ 358.3; r2= 0.05, p<0.01 r2= 0.84 1999 2000 2001 2002 2003 2004 An increase of M-L fCO2 &NTCO2 Tseng et al., 2007

  24. Modeled Surface fCO2 Distributions Feb. May Nov. Aug. Chai et al., 2009 averaged +0.33 moles C m-2 year-1

  25. SCS CO2 Flux (1990~2004) La Niña El Niño Annual means (dash line) Chai et al., 2009

  26. Inter-annual trends of CO2 at SEATS NTCO2 fCO2 Chai et al., 2009

  27. References • Tseng C.-M., George T.F. Wong, I. I. Lin, Chou-Long Wu, KK liu (2005) A unique seasonal pattern in phytoplankton biomass in low-latitude waters in the South China Sea, Geophysical Research Letters, 32, L08608, doi:10.1029/2004GL022111. • Wen-Chen Chou, David D., Sheu, C.T. Arthur Chen, S. L. Wang and C.-M. Tseng (2005) Seasonal variability of carbon chemistry at the SEATS time-series site, northern South China Sea between 2002 and 2003. Terrestrial, Atmospheric and Oceanic Sciences, 16, 445-465. • Tseng C.-M., G.T.F. Wong, W.-C. Chou, B.-S. Lee, D.D. Sheu, K.-K. Liu (2007) Temporal Variations in the carbonate system in the upper layer at the SEATS station. Deep-Sea Research II, 54/14-15: 1448-1468. • Chai F., G. Liu1, H. Xue, L. Shi, Y. Chao, C.-M. Tseng, W.-C. Chou, K.-K. Liu (2009) Seasonal and Interannual Variability of Carbon Cycle in South China Sea: a Three- Dimensional Physical-Biogeochemical Modeling Study, Journal of Oceanography, 65, 703-720. • Liu, k.K., C.-M. Tseng, T.Y. Yeh, L.W. Wang, (2009) Elevated phytoplankton biomass in marginal seas in the low latitude ocean: A case study of the South China Sea, Advances in Geosciences (in press). • Tseng, C.-M., G.-C. Gong, L.-W. Wang, K.-K. Liu, and Y. Yang (2009), Anomalous biogeochemical conditions in the northern South China Sea during the El-Niño events between 1997 and 2003, Geophysical Research Letters, 36, L14611, doi:10.1029/ 2009GL038252. • Tseng, C.-M., K.-K. Liu, L.-W. Wang, and G.-C. Gong (2009), Anomalous hydrographic and biological conditions in the northern South China Sea during the 1997–1998 El Niño and comparisons with the equatorial Pacific. Deep-Sea Research I, doi:10.1016/ j.dsr.2009.09.004. • Liu, K.-K., C.-M. Tseng, C.-R. Wu, I-I Lin (2009) Biogeochemical fluxes of the South China Sea. In: Liu, K.-K., Atkinson, L., Quiñones, R., Talaue-McManus, L. (Eds.) Carbon and Nutrient Fluxes in Continental Margins: a Global Synthesis. IGBP Book Series, Springer, Berlin. Pp. 464-482.

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