pCO2 dynamic and air-sea fluxes in the Scheldt plume (Southern North Sea) from 2001 to 2003

(1)

pCO

₂

dynamic and air-sea fluxes in the

Scheldt plume (Southern North Sea)

from 2001 to 2003

Laure-Sophie Schiettecatte

(1)

_{, Frédéric Gazeau}

(2)

_{, Michel Frankignoulle}

and Alberto Vieira Borges

(1)

Chemical Oceanography Unit, Université de Liège, B5, Belgium

(2)

NIOO-KNAW-CEME, The Netherlands

(2)

Inner Scheldt estuary:

Heterotrophic and a source of CO

₂

: 300 to 700

mmol C m

-2

_day

-1

_{(Frankignoulle et al. 1998).}

Scheldt plume:

•Well-mixed through the year

•Phytoplanktonic bloom during spring (dominated by Phaeocystis sp.)

37th_{International Liège Colloquium, Gas transfer at water surfaces, pCO} _{dynamic and air-sea fluxes in the Scheldt plume (Southern North Sea) from 2001 to 2003}

(3)

Objectives: Temporal v Spatial high resolution

Two approaches:

• One

sampling station (2 times a

week)

• Whole Plume Surface area =

6000 to 7000

data records (only

1-3 times a month)

Krigging interpolation

Data treatment (S<34)

Determination of the plume

surface area

2.4 2.6 2.8 3 3.2 3.4 3.6 Longitude (°E) 51.1 51.2 51.3 51.4 51.5 51.6 51.7 51.8 51.9 L a ti tu d e ( °N ) Zeebrugge 2.4 2.6 2.8 3 3.2 3.4 3.6 Longitude (°E) 51.1 51.2 51.3 51.4 51.5 51.6 51.7 51.8 51.9 L a ti tu d e ( °N )

(4)

Surface pCO

₂

measured from the equilibrator

technique

(Frankignoulle et al. 2001)

.

Equilibrator deployed on the R.V. Belgica since

September

2000 (over 50 campaigns). Data

acquisition

every

minutes.

Calibration

every

weeks.

(5)

Fluxes (F = α

.K.∆

pCO2)

computed from:

•Atmospheric pCO

₂

(Kollumerwaard)

•4 Wind speed stations (every

hours)

•K-wind relations from L&M, W,

W&McG and N&al.

2 2.5 3 3.5 4 4.5 5 5.5 6 50.5 51 51.5 52 52.5 53 53.5 Cadzand Europlatform Vlakte Vlissingen K

Atmospheric pCO2data from the Dutch National Air Quality Monitoring Network supplied by the

National Institute of Public Health and environment (RIVM)

Wind speed data provided by Royal Netherlands Meteorological Institute KONINKLIJK NEDERLANDS METEOROLOGISCH INSTITUUT

(6)

Fixed station approach: Zeebrugge

Processes involved in

the pCO

₂

dynamic:

Biology

Temperature

J M M J S N J M M J S N J M M J S N J

0

100

200

300

400

500

600

700

800

900 1000

pCO

₂

(mean T°C)

pCO

₂

sea

Month

p

C

O

2 (

µ

a

tm

)

T/B

2001

0.76 2002

0.72 2003

0.70 J M M J S N J M M J S N J M M J S N J

0

100

200

300

400

500

600

700

800

900 1000

0

5

10

15

20

25 Month

p

C

O

2 (

µ

a

tm

)

T

e

m

p

e

ra

tu

re

(

°C

)

Atmospheric equilibrium

(7)

2.4 2.6 2.8 3 3.2 3.4 3.6 Longitude (°East) 51.1 51.2 51.3 51.4 51.5 51.6 51.7 51.8 51.9 L a ti tu d e ( °N o rt h ) 30 Jan. - 08 Feb. 2002 2.4 2.6 2.8 3 3.2 3.4 3.6 Longitude (°East) 51.1 51.2 51.3 51.4 51.5 51.6 51.7 51.8 51.9 L a ti tu d e ( °N o rt h ) 08-12 April 2002 2.4 2.6 2.8 3 3.2 3.4 3.6 Longitude (°East) 51.1 51.2 51.3 51.4 51.5 51.6 51.7 51.8 51.9 L a ti tu d e ( °N o rt h ) 01- 07 July 2002 2.4 2.6 2.8 3 3.2 3.4 3.6 Longitude (°East) 51.1 51.2 51.3 51.4 51.5 51.6 51.7 51.8 51.9 L a ti tu d e ( °N o rt h ) 28-31 Oct. 2002

Oversaturated most of the year

(except during spring).

Large variations of the surface

plume (800 to 4600km²).

Highest pCO

₂

values close to the

Scheldt

mouth

and

near

Zeebrugge.

(8)

J M M J S N J M M J S N J M M J S N J

-100

-50

0

50

100

150 C

O

2

F

lu

x

e

s

(

m

o

l

C

m

-2

d

-1

)

CO

₂

air-sea fluxes computed for

2001-2003 with wind speed at Vlakte

J

F M

A M

J

A S O N D

J

-100

-50

0

50

100

150 2002

Plume

C

O

2

F

lu

x

e

s

(

m

o

l

C

m

-2

d

-1

)

J

F M

A M

J

A S O N D

J

-100

-50

0

50

100

150 2002

Plume

Zeebrugge

C

O

2

F

lu

x

e

s

(

m

o

l

C

m

-2

d

-1

)

J

F M

A M

J

A S O N D

J

0

5

10

15

20

0 1000

2000

3000

4000

5000

2002

Wind speed

Surface

M

e

a

n

w

in

d

s

p

e

d

(

m

s

-1

)

P

lu

m

e

s

u

rf

a

c

e

(

k

m

²)

Whole surface area approach: CO

₂

air-sea fluxes

(9)

Annual mean air-sea CO

₂

flux (mol C m

2 _yr

-1

_{) from spatially integrated pCO}

2 No data during

summer

heterotrophic period

No data during spring

L&M

W

W&McG

N&al

This study

2001

-1.51

-2.61

-2.32

-2.08

2002

0.95

1.43

1.90

1.10 2003

2.60

4.06

3.36

3.24 Borges and Frankignoulle (2002)

1996-1999

1.08

2.00

2.81

1.47

(10)

-2500

-2000

-1500

-1000

-500

0

500 1000

1500

2000

2500

3000

j f m a m j j a s o n d

N&al

W&Mc

W

L&M

Carbon emission (t C day

-1

_{) in 2002}

Emission of carbon from the inner estuary: 456 t C day

-1

_{(Frankignoulle et al. 1998)}

%/ Inner Scheldt estuary

L&M

W

W&McG

N&al.

6

7

23

4 Whole surface area approach: CO

₂

emissions

(11)

Inner Scheldt:

+ 141

(Frankignoulle et

al. 1998) data from

1993-1996

Southern North Sea:

-0.2 (Thomas et al. 2004)

Whole North Sea:

-1.8 (Thomas et al. 2004)

Outer Scheldt:

This study: + 0.9 to 1.9 mol C m

2 yr

-1

(2002)

(12)

• Dominance

of

biological

processes

over

temperature in the pCO

₂

dynamics in the present

case.

• pCO

₂

dynamics

at

one

station

can

be

representative of the whole system, but not in

terms of CO

₂

air-sea fluxes.

• In such heterogeneous and dynamics systems, we

need both high temporal and spatial resolutions.

Conclusions

(13)

• Thank to the crew of the R.V. Belgica and

Joan Backers from the BMM for their help.

• This presentation is dedicated to Michel

Frankignoulle, who left us much too soon.