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. Yang……

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

1.Atmo. CO 2, 2. Temp., 3. Sea ice. 4.Sea level key indicators of global change Atmo. CO2 Temp. Sea ice. Sea level

NOAA 2007; Canadell et al. 2007, PNAS Atmospheric CO 2 Concentration [CO 2 ] Year 2008 Atmospheric CO 2 concentration: 385 ppm 38% above pre-industrial 1970 – 1979: 1.3 ppm y – 1989: 1.6 ppm y – 1999: 1.5 ppm y : 2.0 ppm y : 2.3 ppm y -1 year ppm y

Fate of Anthropogenic CO 2 Emissions ( ) Canadell et al. 2007, PNAS; Global Carbon Project 2008, update 1.5 Pg C y Pg C y -1 Atmosphere 46% 4.2 Pg y -1 Land 29% 2.6 Pg y -1 Oceans 26% 2.3 Pg y -1

Takahashi et al. (2002) Mean Annual Air-Sea CO 2 Flux

C RR H J PR R P TS KS PS MS A1 LS 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)

Distinctives of the South China Sea Most of the sea is oligotrophic Mixed-layer T is high (>22 o C) 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)

Annual Mean SST and SSS SSSSST Liu et. al 2009

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

Tseng et. al 2005; 2007; 2009 Seasonal variations in wind speed – Higher in Winter; Lower in Summer (Monsoon) Variations in T – never drops below 22 o C. 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. Wind SST MLD S-chl EPZ TND N+N IPP SRP I-chl

Factors affect the oceanic CO 2 variability in the MLD ΔC = (ΔD +ΔE) + ΔF +ΔB +ΔT Surface MLD Δ C fCO 2 Δ - + Photosyn. Remineral Photosyn. Δ B Remineral. - + Air/sea gas exchange ΔFΔF Mixed-Layer + + Δ D Δ E Mixing/upwelling + + ΔΔ Temp. effect Δ T

F = K  fCO 2 = k s ( f CO 2sw - f CO 2air )  Uncertainty: k- affected by wind, air bubble entrainment, sea surface conditions etc. Estimating Air-Sea Exchange Fluxes of CO 2 Factors influencing CO2 flux estimates

fCO 2 in northern SCS (Zhai et al., 2005) Spring Summer Fall

(Chen et al., 2006) OR-I 508 Nov Nov OR-I 546 April April ~28 stations 15~28 stations fCO 2 in northern SCS Wet season (sea-to-air): ~0.006 Gt C per yr Dry season (air-to-sea): ~0.004 Gt C per yr

SEATS: Mixed-layer fCO 2 Water fCO 2 varies directly with T and inversely with chl-a – Low fCO 2 in Winter (Solubility+Biological pump). fCO 2 water invasion ； fCO 2 water > fCO 2 air in Summer -> evasion fCO 2 =8.8 x T ; (or fCO 2 =184.9 x e ) r 2 = 0.81 Temperature Effect Temp. fCO 2

Mar May Jun July Aug Oct Sept Nov Nov-Dec Dec Jan Feb-Mar YearfCO 2 change (μatm) per o C during Spring-SummerSummer-FallWinter (2.4%)-16.4 (4.4%)-2.7 (0.8%) y = 8.78x , r 2 = 0.98 y = 16.42x , r 2 = 0.94 y = 2.73x , r 2 = 0.41

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

Location and Oceanic regime Temperature effect / Biological effect Temperature effect - Biological effect References SEATS HOT BATS KNOT OSP 18º15’N, 115º35’E South China Sea,the largest subtropical marginal sea 22º45’N, 158ºW North Pacific subtropical gyre 31º50’N, 64º10’W Western North Atlantic subtropical gyre 44ºN, 155ºE Northwestern subarctic Pacific Ocean 50ºN, 145ºW Northeastern subarctic Pacific Ocean 2.0 (80/40  atm) 2.6 (59/23  atm) 2.7 (150/55  atm) 0.8 (174/228  atm) 0.9 (100/115  atm) +40  tam +36  tam +95  tam -54  tam -10  tam This study Calculated based on Winn et al. (1994) Bates et al. (2001) Takahashi et al. (2002) Calculated based on Tsurushima et al. (2002) Wong and Chan (1991) Takahashi et al. (2002) Comparison with Other Time-series Stations The relative importance of temp. & biological effect on seasonal fCO 2 variability (Takahashi et al., 2002, DSRII)

SEATS CO 2 Flux (1999~2004) “+” denotes evasion to the atmosphere “-” denotes invasion to the ocean Net ≈ (Tseng et al., 2007) Spring 0.04±0.34 Summer 1.02±0.02 Autumn 0.10±0.66 Winter -1.21±0.43 Seasons Fluxes (mol C m -2 y -1 ) Months

SEATS CO 2 Flux (1999~2007) Net evasion flux: ± 0.7 Normally CO 2 invasion in Winter ； CO 2 evasion in Summer CO 2 flux varies inter- annually marked in red dashed circle Interannual anomaly may be linked to large- scale climate variability (e.g, ENSO, Pacific Decadal Oscillation etc.)

Comparison with other time- series stations SEATS ( ) HOT BATS References Annual sea-to-air flux (molC m - 2 year -1 ) This study Winn et al., 1994 Bates et al., 1996, ± to –0.8 SEATS ( ) Chou et al to –0.2 Whole SCS Chai et al., SEATS ( ) Chai et al., ± 1.06 Tseng et al., 2007

An increase of M-L fCO 2 &NTCO 2 NTCO 2 =(2.0 ± 1.4)X ; r 2 = 0.11, p= NfCO 2 =(2.6 ± 0.9)X ; r 2 = 0.05, p<0.01 r 2 = 0.84 Interannual Trends of CO 2 at SEATS Mixed Layer NTCO 2 (µmoles kg -1 yr -1 ) fCO 2 (µatm yr -1 ) HOT +1.0 (0.72~1.37) ( ) (Winn et al., 1994) BATS +1.7 ( ) (Bats et al,1996) +1.6 ± 5.8 ( ) (Bats et al,2001) +1.2 ± 0.3 (r 2 = 0.37, ) (Bats et al,2002) +1.4 ± 10.7 ( ) (Bats et al,2001) SEATS 2.0 ± 1.4 ( ) 2.6 ± 0.9 ( ) Tseng et al., 2007

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

Annual means (dash line) SCS CO 2 Flux (1990~2004) Chai et al., 2009 El Niño La Niña

Inter-annual trends of CO 2 at SEATS NTCO 2 fCO 2 Chai et al., 2009

References 1.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: /2004GL 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 Terrestrial, Atmospheric and Oceanic Sciences, 16, 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: 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, 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). 6.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: / 2009GL 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: / j.dsr 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