LONGITUDINAL VARIABILITY OF EXPORT FLUXES OF PARTICULATE MATTER

BASED ON 234TH BUDGETS IN THE ATLANTIC SECTOR OF THE SOUTHERN OCEAN ALONG

40S [GEOTRACES CRUISES D357 AND JC068]

By Katsiaryna Pabortsava, Dr. Patrick Martin, Dr. Richard Sanders, Prof. Richard Lampitt

JC068 Post-Cruise Meeting10-11 September 2012

Outline1. Background 2. Objectives 3. Methods: model rationale, on-board and

laboratory work4. D357/JC068: current results5. Conclusions/Summary 6. Future work

Global Carbon Budget

[IPCC Report 2007]

Biological Carbon Pump

[U.S. JGOFS]

Variability in Carbon Export Flux

[Lutz et al , 2007]0.05 1 10 500.01 Flux (g Corg m-2 yr-1)

80N

40N

0

40S

2. Objectives Verify Lutz et al 2007 Carbon Flux estimates in the

Southern Atlantic Ocean Quantify longitudinal variations in downward fluxes of

particulate organic Carbon (POC), Nitrogen (PON), inorganic Carbon (PIC), biogenic Silica (BSi) , and Micronutrient Metals based on the measured 234Th budgets and identify causes of those variations

Relate the 234Th derived particle fluxes with Micronutrients metal fluxes and their concentration

profiles Upward fluxes via mixing

Explore the relationships between nutrient cycling, phytoplankton community structure and variability of the 234Th-derived particle fluxes

3. Methods

3.1234Th Scavenging model 234Th is a good proxy for estimation of

particle formation, transport and dissolution decay-product of naturally occurring

conservative 238U (t1/2=4.5x109 yr)

short-lived isotope (t1/2=24.1 days)

particle reactive: removed from the surface with sinking particles creating 234Th : 238U disequilibrium

234Th : 238U activity ratio

Secular equilibrium if 234Th : 238U =1→ No particles

234Th-deficit if 234Th : 238U <1 → Uptake by particles

234Th-excess if 234Th : 238U >1 → Remineralization

234Th 238U

Activity, dpm L-1

Dep

th,

m

500

0

3.1234Th Scavenging model

Total 234Th activity, dpm l-1 d-1:

Net loss of 234Th via sinking particles:

Integrated 234Th flux from surface to depth z at steady state:

234Th (dpm.L-1)

238U

Dep

th(m

)

++

+ ++

++

+

Credits: F.A.C. Le Moigne

Flux

3.1234Th Scavenging model

234Th Scavenging model Chen et. al 1986

Uranium-salinity relationship :

Measure concentration of 234Th and POC on sinking particles:

234Th (dpm.L-1)

238U

Dep

th(m

)

++

+ ++

++

+

Credits: F.A.C. Le Moigne

Flux

3.2 Sample collection at sea Total 234Th – ‘small’ volume

technique From a CTD rosette: 4L water collected at

different horizons from surface to depth Higher sampling resolution in the upper 100m

Particulate 234Th, POC, PON, PIC, BSi Stand Alone Pumps (SAPS) 53um and 1um mesh size fractionation 3-7 depths below the base of the mixed layer

3.3 Sample processing

Th-234 co-precipitated with MnO2

SAPS Folsom Splitter

RISØ low level β-counter

3.3 Sample processing On-board

MnO2 co-precipitation of total 234Th; spiking with 230Th yield tracer

First 234Th activity count (total and particulate) on RISØ low level β-counter

Splitting and filtration of SAPS samples

Land Laboratory Background activity count after 234Th completely decayed (~

6 months) Purification and quantification of 234Th recovery via anion-

exchange chromatography and ICP-MS analysis POC/PON analysis PIC content from Ca measurements on ICP-OES BSi content from Si measurement via wet alkaline digestion

4. D357/JC068 Provisional results

D357: •4 SAPS deployments at 1-3 depth below MLD•6 CTD casts at 7-20 depths (0-400m) for total 234Th• 2 CTD casts are reoccupation stations •1 deep CTD cast at >1000m depth for counter calibration

JC068: •4 SAPS deployments at 3-7 depths below MLD•10 CTD casts at 10-14 depths (0-400m) for total 234Th•2 deep CTD casts at >1000m depth for counter calibration

D357

D357: All laboratory analyses and data processing were completed by Dr. Patrick Martin

JC068: First Th-234 activity count = complete Th-234 background activity count = in

progress Particulate (SAPS) samples are prepared for

analyses

Current state of the D357/JC068 data

D357/JC068 Th-234 Activity profiles

D357/JC068 Station 01Activity [dpm/l]

Dep

th, m

0.0 1.0 2.0 3.0

400

300

200

100

0

JC068 Th-234JC068 U-238D357 Th-234

D357 Station 09Activity [dpm/l]

Th-234U-238

0.0 1.0 2.0 3.0

400

300

200

100

0

D357/JC068 Station 03Activity [dpm/l]

0.0 1.0 2.0 3.0

400

300

200

100

0

JC068 Th-234JC068 U-238D357 Th-234

D357 Station 11Activity [dpm/l]

Th-234U-238

0.0 1.0 2.0 3.0

400

300

200

100

0

D357/JC068 Station 05Activity [dpm/l]

0.0 1.0 2.0 3.0

400

300

200

100

0

JC068 Th-234JC068 U-238D357 Th-234

D357 Station 06Activity [dpm/l]

Th-234U-238

0.0 1.0 2.0 3.0

400

300

200

100

0

JC068 Station 08Activity [dpm/l]

Th-234U-238

0.0 1.0 2.0 3.0

400

300

200

100

0

JC068 Station 12Activity [dpm/l]

Dep

th, m

Th-234U-238

0.0 1.0 2.0 3.0

400

300

200

100

0

JC068 Station 14Activity [dpm/l]

Th-234U-238

0.0 1.0 2.0 3.0

400

300

200

100

0

JC068 Station 16Activity [dpm/l]

Th-234U-238

0.0 1.0 2.0 3.0

400

300

200

100

0

JC068 Station 18

Activity [dpm/l]

Th-234U-238

0.0 1.0 2.0 3.0

400

300

200

100

0

JC068 Station 20Activity [dpm/l]

Th-234U-238

0.0 1.0 2.0 3.0

400

300

200

100

0

JC068 Station 21Activity [dpm/l]

Th-234U-238

0.0 1.0 2.0 3.0

400

300

200

100

0

East

West Mid-Ocean Ridge

JC068 DataBackground 234Th activity: 0.30±0.01cpmPrecipitation efficiency: 95±1%

D357/JC068 Th-234 Activity profiles at the reoccupied stations

D357/JC068 Station 01Activity [dpm/l]

Dep

th, m

0 1 2 3 4

400

300

200

100

0

JC068 Th-234JC068 U-238D357 Th-234D357 Th-234 reocc

D357/JC068 Station 03Activity [dpm/l]

0 1 2 3 4

400

300

200

100

0

JC068 Th-234JC068 U-238D357 Th-234D357 Th-234 reocc

D357/JC068 Station 05Activity [dpm/l]

0 1 2 3 4

400

300

200

100

0

JC068 Th-234JC068 U-238D357 Th-234

East West

0.0 0.2 0.4 0.6 0.8 1.0 1.2

500

400

300

200

100

0

Fluor, ug/l

Dep

th, m

D357/JC068 Station 01/r

0.0 0.2 0.4 0.6 0.8 1.0 1.2

500

400

300

200

100

0

Fluor, ug/l

Dep

th, m

D357/JC068 Station 03/r

0.0 0.2 0.4 0.6 0.8 1.0 1.2

500

400

300

200

100

0

Fluor, ug/l

Dep

th, m

D357/JC068 Station 05/r

JC068D357D357 reocc

0 5 10 15 20 25 30

500

400

300

200

100

0

Nitrate, uM

Dep

th, m

0 5 10 15 20 25 30

500

400

300

200

100

0

Nitrate, uM

Dep

th, m

0 5 10 15 20 25 30

500

400

300

200

100

0

Nitrate, uM

Dep

th, m

JC068D357D357 reocc

D357/JC068 Fluorescence and Nutrients profiles at the reoccupied stations

Data: M.Woodward

D357/JC068 Th-234 flux at 100m

LonE

LatN

-45

-40

-35

-30

-25

-20

-50 -40 -30 -20 -10 0 10

Th234_Flux

400

900

1600

2500

cruise

0

1

2

3

4

JC068

D357D357 reoc

AMT14AMT14 subs

CRUISE

Th-234 fluxdpm/m2/day

AMT14

AMT14

AMT14

*AMT14 data from Thomalla et al 2006

ug/L

AMT14 subsAMT14

D357 rD357 JC068

Cruise

uM

Data: M. Woodward

AMT14 subs

AMT14D357 rD357

JC068

Cruise

0 1 2 3 4

250

200

150

100

500

POC:Th-234

Dep

th, m

D357 SAPS_ST03D357 SAPS_ST06D357 SAPS_ST01 2nd reoccD357 SAPS_ST11

0.0 0.5 1.0 1.5

250

200

150

100

500

PON:Th-234

Dep

th, m

D357 SAPS_ST03D357 SAPS_ST06D357 SAPS_ST01 2nd reoccD357 SAPS_ST11

0.0 0.5 1.0 1.5

250

200

150

100

500

PIC:Th-234

Dep

th, m

D357 SAPS_ST03D357 SAPS_ST06D357 SAPS_ST01 2nd reoccD357 SAPS_ST11

0.00 0.05 0.10 0.15 0.20 0.25 0.30

250

200

150

100

500

BSi:Th-234

Dep

th, m

D357 SAPS_ST03D357 SAPS_ST06D357 SAPS_ST01 2nd reoccD357 SAPS_ST11

Mean POC:Th-234 @120m: 2.37±1.038

Mean PON:Th-234 @120m: 0.40±0.147

Mean PIC:Th-234 @120m: 0.39±0.134

Mean BSi:Th-234 @120m: 0.035±0.024

0 5 10 15 20

02

46

810

Longitude, deg E

mm

ol/m

2/d

D357 POC Flux

0 5 10 15 20

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Longitude, deg E

mm

ol/m

2/d

D357 PON Flux

0 5 10 15 20

0.0

0.2

0.4

0.6

0.8

1.0

Longitude, deg E

mm

ol/m

2/d

D357 PIC Flux

0 5 10 15 20

0.0

0.2

0.4

0.6

0.8

1.0

Longitude, deg E

mm

ol/m

2/d

D357 BSi Flux

D357 Th-234 based integrated elemental fluxes at 120m

Summary Variations in depth-integrated Th-234 fluxes (D357 and JC068) and particle

fluxes (D357) were observed along 40S transect

Depth-integrated Th-234 fluxes along 40S were significantly higher than the Th-234 fluxes measured to the North of the transect (in oligotrophic S. Atllantic (data from Thomalla et. al. 2006) ) Lutz et. al. 2007 carbon export model in the southern ocean is realistic

Th-234-derived depth-integrated particle fluxes at 120m during D357 decreased away from the African shore westwards.

Temporal variations in depth-integrated Th-234 fluxes were observed at the reoccupied stations

Elemental measurements of the JC068 data have to be completed and data thoroughly analyzed to identify the processes responsible for the observed spatial and temporal variations

Future work. Analytical procedures

Measure POC, PON, BSi, PIC content of the SAPS samples (end of October 2012)

Complete counting of 234Th background activity (mid-November, 2012)

Measure MnO2 precipitation efficiency: purify 230Th via anion-exchange chromatography and measure 229Th : 230Th ratio on ICP-MS (November-December, 2012)

Future work. D357/JC068 Data Analysis

Calculate vertical 234Th activity profiles and 234Th-derived downward biogenic and lithogenic fluxes of C, N, Si, Metals

Identify causes of spatial, temporal variability, and variability with depth (incorporate D357 data) in particle fluxes along 40S transect

Composition of fluxes – what drives the carbon export in the area?

Compare derived carbon exports along the transect with model outputs (Lutz et al 2007)

Acknowledgements Dr. Gideon Henderson Dr. Walter Geibert Dr. F.A.C. Le Moigne NMF technicians of JC068 Science crew of JC068 K. Kouvaris

THANK YOU FOR YOUR ATTENTION!