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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 Meeting
10-11 September 2012
Outline
1. 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 01
Activity [dpm/l]
De
pth
, m
0.0 1.0 2.0 3.0
400
300
200
100
0
JC068 Th-234JC068 U-238D357 Th-234
D357 Station 09
Activity [dpm/l]
Th-234U-238
0.0 1.0 2.0 3.0
400
300
200
100
0
D357/JC068 Station 03
Activity [dpm/l]
0.0 1.0 2.0 3.0
400
300
200
100
0
JC068 Th-234JC068 U-238D357 Th-234
D357 Station 11
Activity [dpm/l]
Th-234U-238
0.0 1.0 2.0 3.0
400
300
200
100
0
D357/JC068 Station 05
Activity [dpm/l]
0.0 1.0 2.0 3.0
400
300
200
100
0
JC068 Th-234JC068 U-238D357 Th-234
D357 Station 06
Activity [dpm/l]
Th-234U-238
0.0 1.0 2.0 3.0
400
300
200
100
0
JC068 Station 08
Activity [dpm/l]
Th-234U-238
0.0 1.0 2.0 3.0
400
300
200
100
0
JC068 Station 12
Activity [dpm/l]
De
pth
, m
Th-234U-238
0.0 1.0 2.0 3.0
400
300
200
100
0
JC068 Station 14
Activity [dpm/l]
Th-234U-238
0.0 1.0 2.0 3.0
400
300
200
100
0
JC068 Station 16
Activity [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 20
Activity [dpm/l]
Th-234U-238
0.0 1.0 2.0 3.0
400
300
200
100
0
JC068 Station 21
Activity [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]
De
pth
, 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 05
Activity [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_Flux400900
1600
2500
cruise01234
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
D357
D357 reoc
AMT14
AMT14 subs
CRUISE
Th-234 fluxdpm/m2/day
AMT14
AMT14
AMT14
*AMT14 data from Thomalla et al 2006
ug/L
AMT14 subsAMT14
D357 r
D357
JC068
Cruise
uM
Data: M. Woodward
AMT14 subs
AMT14D357 r
D357
JC068
Cruise
0 1 2 3 4
250
200
150
100
500
POC:Th-234
De
pth
, 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
De
pth
, 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
De
pth
, 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
De
pth
, 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!
