Sediment trap data. Constraining the seasonal particle flux in the eastern North Atlantic with Thorium isotopes M. Roy-Barman (1), R. El Hayek (1), I

Sediment trap data

0

500

1000

1500

2000

2500

1/2/01 3/3/01 2/4/01 2/5/01 1/6/01 1/7/01 31/7/01 30/8/01 29/9/01

1000 m

23

0T

hxs

flux

(fg

/m2/d

)

in situ production

0

500

1000

1500

2000

2500

1/2/01 3/3/01 2/4/01 2/5/01 1/6/01 1/7/01 31/7/01 30/8/01 29/9/01

230T

hxs fl

ux (f

g/m

2 /d)

400 m

in situ production

0,00E+00

1,00E-05

2,00E-05

3,00E-05

4,00E-05

5,00E-05

6,00E-05

1/2/01 3/3/01 2/4/01 2/5/01 1/6/01 1/7/01 31/7/01 30/8/01 29/9/01

230T

h/23

2T

h (a

tom

ic r

atio

)

400 m

1000 m

suspended particles collected between 400 m and 1000 m

Constraining the seasonal particle flux in the eastern North Atlantic with Thorium isotopes

M. Roy-Barman (1), R. El Hayek (1), I. Voege (2), M.Souhaut (3), N. Leblond (4), C. Jeandel (2).(1) LSCE, Avenue de la Terrasse, 91198 Gif sur Yvette, France, (2) AWI, PO Box 120161, 27515 Bremerhaven, Germany, (3) LEGOS, 14 Avenue E. Belin, 31400, Toulouse France, (4) LOV, BP 28, 06234 Villefranche sur mer, France

[email protected]

Poster Area Esplanade

poster board number P0600

Principle of the sediment trap calibration.

Problems … = trapping efficiency

230Th productionabove the trap

230Th trapped flux

230Th fixed on particles 234U 230Th

Problems … = trapping efficiency


230Th trapped flux


Problems… = trapping efficiency


230Th trapped flux


change of 230Th inventory in the water column

-Problems…

= trapping efficiency230Th productionabove the trap

230Th trapped flux



-

Time dependent of the sediment trap calibration.

T

H

H THT T

H

T

H

H TH THTHT

Eddy structure of the sampling area (M. Assenbaum et al., 2003)

Pomme 1 Pomme 2 Pomme 3 (winter) (spring) (Automn)

dissolved + particulate 230Thxs (fg/kg )

-1200

-1000

-800

-600

-400

-200

0

0 1 2 3 4 5 6 7

Dep

th (

m)

Pomme1 Pomme 2 Pomme 3

35,6

35,7

35,8

35,9

36

36,1

3 4 5 6 7

Pomme1

Pomme2

Pomme3


salin

ity

mixing trend

--> 230Thxs in not controlled

by production-scavenging only

1000 m samples

POMME 1 POMME 2 POMME 2 POMME 3 400 m 1000 m 400 m 1000 m

230Thxs flux in sediment trap (fg/m2/d)

744 935 195 439

in situ production above the trap (fg/m2/d)

592 1479 592

1479

apparent trapping efficiency

126 % 63 % 30 % 31 %

Change of 230Thxs inventory (fg/m2/d)

- 231 ± 1500 + 5830 ± 6674 + 755 ± 591 + 2737 ± 1647

corrected trapping efficiency (fg/m2/d)

> 23 %

> 40 % > 7 % > 100 %


-1200

-1000

-800

-600

-400

-200

0

0 1 2 3 4 5 6 7

Dep

th (

m)


T

H

H THT T

H

T

H

H TH THTHT



[email protected]: Constraining the present and past oceanic biological pump requires a good understanding of the marine particle dynamics and of their interaction with the surrounding water column. Particle fluxes are studied mainly with sediment traps, so that it is critical to evaluate their efficiency. The average efficiency of moored sediment traps is calibrated by the 230Th method. 230Th is produced uniformely in the ocean by radioactive decay of 238U and it is rapidely removed from the water column by scavenging on settling particles. The trapping efficiency is obtained by comparing the 230Thxs trapped flux with the 230Th production in the

overlying watercolumn. This was previously done with trap data obtained over a year in order to avoid the problem of estimating the change of 230Th inventory in the water column. The idea: Here we propose to extend this method to estimate the efficiency of moored traps on a seasonal scale. It requires high precision data to measure the change of 230Th inventory in the water column. By combining sediment trap data with the change of 230Th inventory, it is possible to obtain the trapping efficiency for a short time period.

Water column results: While the 230Thxs decreases in the surface waters from POMME 1 to

POMME 3, there is a significant increase of 230Thxs in the deep waters that cannot be solely due

to the remineralisation of the settling particles. The increasing rate of the 230Thxs inventory

from 0 to 400 or 1000 m in larger than the in situ production rate suggesting that advective inputs of 230Th are significant. The effect of water mass mixing is supported by the correlation between the 230Thxs content and the salinity of the water masses at 1000 m .

Trapping efficiency: For short periods, the flux/production ratio (apparent efficiency) may be different from the trapping efficiency. However during a high flux period, when particulate export must dominate over in situ production, it provides an upper bound of the trapping efficiency. The uncertainties on the change of 230Thxs inventory are large so that the corrected

efficiencies are not well constrained. Negative efficiencies are found when the 230Thxs

inventory increases faster than the in situ production. If we neglect the effect water mass mixing, we can obtain a lower bound for the corrected trapping efficiency.

Conclusion: By comparing apparent and corrected trapping efficiencies, a good braketing of the trapping efficiency can be obtained (eg. at 1000 m between P 1 and P 2 or at 400 m between P 2 and P 3). An explicit treatment of the mixing effect is required to improve the the method.


Sampling: During the POMME program, we have measured Thorium isotopes in seawater, small particles and large particles collected in early March 2001 (POMME 1), mid April 2001 (POMME 2) and September 2001 (POMME 3) in the eastern North Atlantic. Here, we report results obtained on large particles collected with moored sediment traps (at 400 and 1000 m) and dissolved and small particles samples collected between 10 and 1000 m in anticyclonic eddies closely associated to the sediment trap at the time of sampling. All these samples were analysed for 230Th and 232Th by ID-TIMS.

Trap results: During the spring bloom (from POMME 1 to POMME 2), strong variations of total mass flux and of the 230Thxs flux are recorded by the sediment traps. Over this period, the

trapped 230Thxs flux represents 125% of the overlying production at 400 m and 65% at 1000

m. From POMME 2 to POMME 3, the 230Thxs fluxes are more constant and they represent

30% of the overlying production only. Beside the trap calibration aspect, Th isotopes provide important information on the particle dynamics: the increase of 230Th/232Th ratio in the trapped material between 400 and 1000 m implies (independently of the flux data) that small particles have been aggregated to the sinking particles between these depths.

35,6

35,7

35,8

35,9

36

36,1

3 4 5 6 7

Pomme1

Pomme2

Pomme3


salin

ity

mixing trend

--> 230

Thxs in not controlled




230Th trapped flux



-Problems…


230Th trapped flux



-


Sediment trap data

Water column data



744 935 195 439


592 1479 592

1479


126 % 63 % 30 % 31 %


- 231 ± 1500 + 5830 ± 6674 + 755 ± 591 + 2737 ± 1647


> 23 %

> 40 % > 7 % > 100 %

0

500

1000

1500

2000

2500

1/2/01 3/3/01 2/4/01 2/5/01 1/6/01 1/7/01 31/7/01 30/8/01 29/9/01

1000 m

230 T

hxs

flux

(fg

/m2 /d

)

in situ production

0

500

1000

1500

2000

2500

1/2/01 3/3/01 2/4/01 2/5/01 1/6/01 1/7/01 31/7/01 30/8/01 29/9/01

230 T

hxs

flux

(fg/

m2 /d

)

400 m

in situ production

0,00E+00

1,00E-05

2,00E-05

3,00E-05

4,00E-05

5,00E-05

6,00E-05

1/2/01 3/3/01 2/4/01 2/5/01 1/6/01 1/7/01 31/7/01 30/8/01 29/9/01

23

0T

h/2

32T

h (a

tom

ic r

atio

)

400 m

1000 m



-1200

-1000

-800

-600

-400

-200

0

0 1 2 3 4 5 6 7

Dep

th (

m)


T

H

H THT T

H

T

H

H TH THTHT



[email protected]: Constraining the present and past oceanic biological pump requires a good understanding of the marine particle dynamics and of their interaction with the surrounding water column. Particle fluxes are studied mainly with sediment traps, so that it is critical to evaluate their efficiency. The average efficiency of moored sediment traps is calibrated by the 230Th method. 230Th is produced uniformely in the ocean by radioactive decay of 238U and it is rapidely removed from the water column by scavenging on settling particles. The trapping efficiency is obtained by comparing the 230Thxs trapped flux with the 230Th production in the

overlying watercolumn. This was previously done with trap data obtained over a year in order to avoid the problem of estimating the change of 230Th inventory in the water column. The idea: Here we propose to extend this method to estimate the efficiency of moored traps on a seasonal scale. It requires high precision data to measure the change of 230Th inventory in the water column. By combining sediment trap data with the change of 230Th inventory, it is possible to obtain the trapping efficiency for a short time period.

Water column results: While the 230Thxs decreases in the surface waters from POMME 1 to

POMME 3, there is a significant increase of 230Thxs in the deep waters that cannot be solely due

to the remineralisation of the settling particles. The increasing rate of the 230Thxs inventory

from 0 to 400 or 1000 m in larger than the in situ production rate suggesting that advective inputs of 230Th are significant. The effect of water mass mixing is supported by the correlation between the 230Thxs content and the salinity of the water masses at 1000 m .

Trapping efficiency: For short periods, the flux/production ratio (apparent efficiency) may be different from the trapping efficiency. However during a high flux period, when particulate export must dominate over in situ production, it provides an upper bound of the trapping efficiency. The uncertainties on the change of 230Thxs inventory are large so that the corrected

efficiencies are not well constrained. Negative efficiencies are found when the 230Thxs

inventory increases faster than the in situ production. If we neglect the effect water mass mixing, we can obtain a lower bound for the corrected trapping efficiency.

Conclusion: By comparing apparent and corrected trapping efficiencies, a good braketing of the trapping efficiency can be obtained (eg. at 1000 m between P 1 and P 2 or at 400 m between P 2 and P 3). An explicit treatment of the mixing effect is required to improve the the method.


Sampling: During the POMME program, we have measured Thorium isotopes in seawater, small particles and large particles collected in early March 2001 (POMME 1), mid April 2001 (POMME 2) and September 2001 (POMME 3) in the eastern North Atlantic. Here, we report results obtained on large particles collected with moored sediment traps (at 400 and 1000 m) and dissolved and small particles samples collected between 10 and 1000 m in anticyclonic eddies closely associated to the sediment trap at the time of sampling. All these samples were analysed for 230Th and 232Th by ID-TIMS.

Trap results: During the spring bloom (from POMME 1 to POMME 2), strong variations of total mass flux and of the 230Thxs flux are recorded by the sediment traps. Over this period, the

trapped 230Thxs flux represents 125% of the overlying production at 400 m and 65% at 1000

m. From POMME 2 to POMME 3, the 230Thxs fluxes are more constant and they represent

30% of the overlying production only. Beside the trap calibration aspect, Th isotopes provide important information on the particle dynamics: the increase of 230Th/232Th ratio in the trapped material between 400 and 1000 m implies (independently of the flux data) that small particles have been aggregated to the sinking particles between these depths.

35,6

35,7

35,8

35,9

36

36,1

3 4 5 6 7

Pomme1

Pomme2

Pomme3


salin

ity

mixing trend

--> 230

Thxs in not controlled




230Th trapped flux



-Problems…


230Th trapped flux



-


Sediment trap data

Water column data



744 935 195 439


592 1479 592

1479


126 % 63 % 30 % 31 %


- 231 ± 1500 + 5830 ± 6674 + 755 ± 591 + 2737 ± 1647


> 23 %

> 40 % > 7 % > 100 %

0

500

1000

1500

2000

2500

1/2/01 3/3/01 2/4/01 2/5/01 1/6/01 1/7/01 31/7/01 30/8/01 29/9/01

1000 m

230 T

hxs

flux

(fg

/m2 /d

)

in situ production

0

500

1000

1500

2000

2500

1/2/01 3/3/01 2/4/01 2/5/01 1/6/01 1/7/01 31/7/01 30/8/01 29/9/01

230 T

hxs

flux

(fg/

m2 /d

)

400 m

in situ production

0,00E+00

1,00E-05

2,00E-05

3,00E-05

4,00E-05

5,00E-05

6,00E-05

1/2/01 3/3/01 2/4/01 2/5/01 1/6/01 1/7/01 31/7/01 30/8/01 29/9/01

23

0T

h/2

32T

h (a

tom

ic r

atio

)

400 m

1000 m


Documents

Sediment trap data. Constraining the seasonal particle flux in the eastern North Atlantic with Thorium isotopes M. Roy-Barman (1), R. El Hayek (1), I