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

Air-Sea CO2 Exchange

in the Northern South China Sea

C.-M.TsengThanks 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 & OverviewIntroduction & Overview Annual & inter-annual variability of Annual & inter-annual variability of

Ocean COOcean CO22

Physical and biogeochemical Physical and biogeochemical processes affecting variabilityprocesses affecting variability

Magnitude and variability of Air-sea Magnitude and variability of Air-sea exchange COexchange CO2 2 flux relative to global flux relative to global

scalesscales

Increasing magnitudes of TCOIncreasing magnitudes of TCO22 and and

ffCOCO22

Future studyFuture study (e.g., El-Niño, Typhoon)

Talk outline

1. Atmo. CO2,2. Temp.,3. Sea ice. 4. Sea level

key indicators of

global changeAtmo. CO2

Temp.

Sea ice.

Sea level

NOAA 2007; Canadell et al. 2007, PNAS

Atmospheric CO2 Concentration 0

1

2

3

4

5

6

7

8

9

1850 1870 1890 1910 1930 1950 1970 1990 2010

280

300

320

340

360

380

400

1850 1870 1890 1910 1930 1950 1970 1990 2010

Atm

oap

her

ic [

CO

2]

(pp

mv)

[CO2]

2 ppm/year

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1850 1870 1890 1910 1930 1950 1970 1990 2010

1850 1870 1890 1910 1930 1950 1970 1990 2010

[CO2]Year 2008

Atmospheric CO2 concentration:

385 ppm38% above pre-industrial

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

year ppm y-1

2000 1.242001 1.852002 2.392003 2.212004 1.612005 2.412006 1.792007 2.172008 2.28

Fate of Anthropogenic CO2 Emissions (2000-2007)

Canadell et al. 2007, PNAS; Global Carbon Project 2008, update

1.5 Pg C y-1

+7.5 Pg C y-1

Atmosphere46%

4.2 Pg y-1

Land29%

2.6 Pg y-1

Oceans26%

2.3 Pg y-1

Takahashi et al. (2002)

Mean Annual Air-Sea COMean Annual Air-Sea CO22 Flux Flux

C

RR

H

J

PRR

P

TS

KS

PS

MS

A1LS

Environmental ForcingPhysical• 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 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)

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 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.

1997 1998 1999 2000 2001 2002 2003 2004

I-ch

l (m

g/m

2 )

10

15

20

25

30

IPP

(m

gC

/m2 /d

)

0

200

400

WS

, f-

WS

(m

/s)

0

5

10

15

20

N+

N (

M)

0.0

0.1

0.2

0.3

0.4

0.00

0.02

0.04

0.06

SS

T,

f-S

ST

(o C)

24

26

28

30

32

De

pth

(m

)

0

20

40

60

80

100

S-c

hl (

mg/m

3)

0.0

0.2

0.4

(b)

(d)

(f)

(a)

(c)

(e)

SR

P (

M)

Win

dS

ST

MLD

S-c

hl

EPZ

TND

N+N

IPP

SRP

I-ch

l

Factors affect the oceanic CO2

variability in the MLD

ΔC = (ΔD +ΔE) + ΔF +ΔB +ΔT

Surface

MLD

Δ C fCO2 Δ

-+

Photosyn.

Remineral.

-+

-+

Photosyn.Δ B

Remineral.

- +

Air/sea gas exchange

- +- +

Air/sea gas exchange

ΔF

Mixed-Layer

++

ΔD ΔE

Mixing/upwelling

++

Δ Δ

Mixing/upwelling

-

+

-

+

-

+

Temp. effect ΔT

F = K fCO2 = k s (fCO2sw- fCO2air) Uncertainty: k- affected by wind, air bubble entrainment, sea surface conditions etc.

Estimating Air-Sea Exchange Fluxes of CO2

Wind

k pCO2

Air-Sea CO2Flux

SST

Transport

BiologyWindWaves

BubblesSurfaceFilm

Near SurfaceTurbulence

Bock et al. (1999)

Wind

k pCO2

Air-Sea CO2Flux

SST

Transport

BiologyWindWaves

BubblesSurfaceFilm

Near SurfaceTurbulence

Bock et al. (1999)

Factors influencing CO2 flux estimates

fCO2 in northern SCS

(Zhai et al., 2005)

Spring

Summer

Fall

(Chen et al., 2006)

OR-I 508OR-I 508

Nov 15-24 1997Nov 15-24 1997

OR-I 546OR-I 546

April 7-20 1999April 7-20 1999

15~28 stations15~28 stations

fCO2 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 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

Wat

er

fCO

2 (

atm

)

340

350

360

370

380

390

400

Air fC

O2 (

atm)

CalculatedUnderway

1999 2000 2001 2002 2003 2004

fC

O2

(at

m)

-30

-20

-10

0

10

20

30

40

fCO2=8.8 x T + 123.0;(or fCO2=184.9 x e0.025)

r2= 0.81

Temperature Effect

Temp.

fCO 2

Temperature (oC)

22 24 26 28 30 32

fCO

2 ( a

tm)

340

360

380

400

Mar

May

Jun July

Aug

OctSept

Nov

Nov-DecDecJan

Feb-Mar

Year fCO2 change (μatm) per oC during

Spring-Summer Summer-Fall Winter

2000

2003

+8.8 (2.4%) -16.4 (4.4%) -2.7 (0.8%)

y = 8.78x + 125.56,

r2 = 0.98

y = 16.42x - 100.48,

r2 = 0.94

y = 2.73x + 275.44,

r2 = 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 andOceanic regime

Temperature effect /Biological effect

Temperature effect -Biological effect

References

SEATS

HOT

BATS

KNOT

OSP

18º15’N , 115º35’ESouth China Sea,the largest

subtropical marginal sea

22º45’N, 158ºWNorth Pacific subtropical gyre

31º50’N, 64º10’WWestern North Atlantic

subtropical gyre

44ºN, 155ºENorthwestern subarctic Pacific

Ocean

50ºN, 145ºWNortheastern 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 onWinn et al. (1994)

Bates et al. (2001)Takahashi et al. (2002)

Calculated based onTsurushima et al. (2002)

Wong and Chan (1991)Takahashi et al. (2002)

Comparison with Other Time-series StationsThe relative importance of temp. & biological effect on seasonal fCO2 variability

(Takahashi et al., 2002, DSRII)

SEATS CO2 Flux (1999~2004)

“+” denotes evasion to the atmosphere“-” denotes invasion to the ocean

Net ≈ -0.02(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 CO2 Flux (1999~2007)

Net evasion flux: + 0.1 ± 0.7

• Normally CO2 invasion in Winter ； CO2

evasion in Summer

• CO2 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(1999-2004)

HOT

BATS

ReferencesAnnual sea-to-air flux

(molC m-2 year-1)

This study

Winn et al., 1994

Bates et al., 1996, 1998

+ 0.1 ± 0.7

-0.7

-0.3 to –0.8

SEATS(2002-2003)

Chou et al. 2004-0.1 to –0.2

Whole SCS Chai et al., 2009+0.33SEATS

(1990-2004) Chai et al., 2009- 0.04

-0.02 ± 1.06 Tseng et al., 2007

An increase of M-L fCO2 &NTCO2

NTCO2=(2.0 ± 1.4)X+ 1886.1; r2= 0.11, p=0.17

1999 2000 2001 2002 2003 2004

1999 2000 2001 2002 2003 2004

NfCO2=(2.6 ± 0.9)X+ 358.3; r2= 0.05, p<0.01

r2= 0.84

Interannual Trends of CO2 at SEATS

Mixed Layer

NTCO2(µmoles kg-1

yr-1)

fCO2(µatm yr-1)

HOT +1.0 (0.72~1.37)

(1988-1996)(Winn et al.,

1994)

BATS +1.7 (1988-1993)

(Bats et al,1996)

+1.6 ± 5.8 (1988-1998)

(Bats et al,2001)

+1.2 ± 0.3 (r2= 0.37, 1988-

2001)(Bats et al,2002)

+1.4 ± 10.7 (1988-1998)

(Bats et al,2001)

SEATS 2.0 ± 1.4(1999-2004)

2.6 ± 0.9(1999-2004)Tseng et al.,

2007

Feb.

Aug. Nov.

May

Chai et al., 2009

Modeled Surface fCO2 Distributionsaveraged +0.33 moles C m-2 year-1

Annual means (dash line)

SCS CO2 Flux (1990~2004)

Chai et al., 2009

El Niño

La Niña

Inter-annual trends of

CO2 at SEATS

NTCO2 fCO2

Chai et al., 2009

References1. 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.

2. 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.

3. 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.

4. 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.

5. 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:10.1029/ 2009GL038252.

7. 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.

8. 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.