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Quantifying competing carbon pathways in mesoscale upwelling filaments off NW Africa
Nick Hardman-Mountford (CSIRO), Carol Robinson (UEA), Ricardo Torres, Tim Smyth, Ian Brown, Vasilis Kitidis, P. Nightingale, C. Widdicombe (PML)
(or the pitfalls of seawater CO2 inversions)
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What is relative contribution of different CO2 pathways: air-sea flux vs. export production?
CoolHigh NHigh CO2
Warms
CO2 flux
Phytoplankton production
Respiration
Carbon export
NCP = E
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Lagrangian study: plume tracking with SF6 and drifters
• 3 patches seeded• P1 & P3 filaments tracked• P2 subducted
SOLAS-ICON+ (D338)
+The impact of coastal upwelling on the air-sea exchange of climatically important gases
Rees et al. 2011
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Sampling
Underway:T, S, fCO2, O2, Fl
Surface drifters:T, S, fCO2
Physics:CTD, MVP, ADCP, micro-turbulence, wirewalker, optics
Rosette bottle samples
Deck incubations
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Spatial structure – satellite view
Patch 1: freshly upwelled, followed for 9 days
Patch 3: ~10 days old, followed for 8 days
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Spatial structure – in situ
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Temporal variability
195
205
215
225
235
245
255
265380
400
420
440
460
480
500
520
22-Apr 23-Apr 24-Apr 25-Apr 26-Apr 27-Apr 28-Apr 29-Apr 30-Apr 01-May
O2
(µm
ol l-
1 )
fCO
2(μ
atm
)Patch 1 fCO2 O2
195
205
215
225
235
245
255
265380
400
420
440
460
480
500
520
540
14-May 15-May 16-May 17-May 18-May 19-May 20-May 21-May 22-May 23-May
O2
(µm
ol l-
1 )
fCO
2(μ
atm
)
Patch 3 fCO2 O2
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0
100
200
300
400
500
600
700
Sum of BIOMASS
0%10%20%30%40%50%60%70%80%90%
100%
Average of % FLAG
Average of % DINOS
Average of % DIATOMS
0
20
40
60
80
100
120
140
160
Sum of BIOMASS
0%10%20%30%40%50%60%70%80%90%
100%
Average of % FLAG
Average of % DINOS
Average of % DIATOMS
Phytoplankton community and primary productionPatch 1
Patch 3
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ncptrsptc
x
tc
JJDICDICth
hxxDICK
hzDICKz
hhF
tDIC
111
Daily DIC change
Sea-air Flux
Vertical diffusion flux
Horizontal diffusion flux
Vertical entrainment (ventilation)
Horizontal advection
NCP
• Assume advection/diffusion terms negligible because lagrangian expt, i.e. tracking water patch.
• Supported by lack of relationship between salinity and DIC within patch
• Salinity normalise DIC to make sure
2110.0
2120.0
2130.0
2140.0
2150.0
2160.0
2170.0
35.6 35.7 35.8 35.9 36 36.1 36.2 36.3 36.4
Patch 1
Patch 3
?Controls on CO2 dynamics
Shadwick et al. 2010
• Focus on NCP, F and V?
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y = 49.986x + 564.18R² = 0.8356
2330.0
2340.0
2350.0
2360.0
2370.0
2380.0
2390.0
35.6 35.7 35.8 35.9 36 36.1 36.2 36.3 36.4
TA (µ
mol
kg-1
)
Salinity
DIC calculations• Need continuous DIC
• Use discrete TA / S relationship to calculate continuous TAs
• Calculate DIC from TAs and measured underway fCO2 in CO2SYS
• Salinity normalise calculated DIC = nDIC
intint
SS
DICnDIC
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Daily δnDIC calculation
δnDIC day
δnDIC night
δnDIC day+night
nDIC
Time
depth integrated NCPt = Zeut (max DICt- max DICt-1) – Ft (– Vt)
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A. Daily nDIC change
-40
-30
-20
-10
0
10
20
30
40
22/04 23/04 24/04 25/04 26/04 27/04 28/04 29/04 30/04
µmol
l-1 dnDIC_day
dnDIC_night
Patch 1
-25
-20
-15
-10
-5
0
5
10
15
20
25
15/05 16/05 17/05 18/05 19/05 20/05 21/05 22/05
µmol
l-1
dnDIC_day
dnDIC_night
Patch 3
Daily DIC reduction
Night time DIC increase
production/respiration signal
Patch 1 has larger signals and is more variable than Patch 3
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B. Sea-air CO2 fluxes
0
5
10
15
20
25
30
35
22/04 23/04 24/04 25/04 26/04 27/04 28/04 29/04 30/04
mm
ol C
O2
m-2
d-1
Patch 1Patch 1
0
5
10
15
20
25
30
35
14/05 15/05 16/05 17/05 18/05 19/05 20/05 21/05 22/05
mm
ol C
O2
m-2
d-1
Patch 3Patch 3
Calculated using Nightingale et al. (2000)
Winds 6-14 m s-1 P1, 8-14 m s-1 P3
ΔpCO2 20-100 µatm P1, 60-110 µatm P3
Patch 1 sea-air flux starts high and reduces as seawater pCO2 reduces
Increase on 25-26/4 from ventilation?
Patch 3 sea-air flux higher on average, more gradual decline, driven by seawater pCO2 decline
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C. Depth Integrated NCP* vs. sea-air flux
-450
-400
-350
-300
-250
-200
-150
-100
-50
0
50
23/04 24/04 25/04 26/04 27/04 28/04 29/04 30/04
mm
ol C
m-2
d-1
- NCP_M
F_M N'00
Patch 1
-150
-100
-50
0
50
100
150
200
15/05 16/05 17/05 18/05 19/05 20/05 21/05 22/05
mm
ol C
m-2
d-1
- NCP_M
F_M N'00
Patch 3
y = -4.9816x + 921.34R² = 0.7242
350
370
390
410
430
450
470
490
510
530
550
80 90 100 110
NpC
O2
(µat
m)
%O2 Sat
y = -4.7253x + 949.31R² = 0.8301
350
370
390
410
430
450
470
490
510
530
550
90 100 110 120
NpC
O2
(µat
m)
%O2 Sat
Louicades et al. 2011
Patch 1
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C. Depth Integrated NCP* vs. sea-air flux
-450
-400
-350
-300
-250
-200
-150
-100
-50
0
50
23/04 24/04 25/04 26/04 27/04 28/04 29/04 30/04
mm
ol C
m-2
d-1
- NCP_M
F_M N'00
Patch 1
-150
-100
-50
0
50
100
150
200
15/05 16/05 17/05 18/05 19/05 20/05 21/05 22/05
mm
ol C
m-2
d-1
- NCP_M
F_M N'00
Patch 3
Patch 1 is net autotrophic and NCP* dominates over sea-air flux
Patch 3 shifts from autotrophic to heterotrophic between days
In ~trophic balance over all
NCP* dominates the signal but overall sea-air flux is greater
mmol C m-2 Patch 1 Patch 3
NCP* 1285 29
Sea-air flux 86 124
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NACW>50%Max(80%,75m)
SACW>50%Max(95%,300m)
SACW<50%Max(40%,150m)(NACW or BDA shelf water)
SACW>50%(Max 100%)
Patch 1
Patch 3
Water masses
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D. NCP vs. entrainment/ventilation vs. sea-air flux
-400-300-200-100
0100200300400500600
15/05 16/05 17/05 18/05 19/05 20/05 21/05 22/05
mm
ol C
m-2
d-1
- NCP_M
Vent_M
F_M N'00
-1500
-1000
-500
0
500
1000
23/04 24/04 25/04 26/04 27/04 28/04 29/04 30/04
mm
ol C
m-2
d-1
- NCP_M
Vent_M
F_M N'00
Use change in nutricline depth and DIC gradient over nutricline
NCP (residual) has to increase with ventilation
Accounting for ventilation increases estimate of autotrophy - Is it real?
mmol C m-2 Patch 1 Patch 3
NCP-V2823 715
Vent1537 687
Sea-air flux 86 124
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Preliminary conclusions
1. Biogeochemistry different between filaments:– phytoplankton, CO2 dynamics, [nutrients]
– Water masses or age?
2. Variable influence of NCP vs Sea-Air Flux– Patch 1: net autotrophic, NCP dominates; sea-air CO2 flux has minor
influence– Patch 3: trophic status looks neutral but depends on external sources of DIC;
sea-air CO2 flux may be dominant over time
3. Method– Ventilation calculation critical for determining NCP?– Method needs testing / refining for a lagrangian /sub-mesoscale
framework
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Next steps
• Consider sub-mesoscale physics to calculate ventilation fluxes
• Compare results with DOC, C14 PP, O18 R, N-flux estimates
• Look at heterotrophic dynamics (diurnal variability in grazing?)
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Acknowledgements: UK-SOLAS ICON team, National Marine Facilities staff, Captain and crew of RRS Discovery.
Funding: UK Natural Environment Research Council (NERC). Satellite images provided by NEODAAS, UK.
Thank you!
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B. Sea-air CO2 fluxes
Units on time plots legend!!!
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0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
4
4.5
5
5.5
6
6.5
7
7.5
8
8.5
9
21 23 25 27 29 01
Silic
ate
(μm
ol/l
)
Nitr
ate
+ N
itrite
(μm
ol/l
)
Apr '09
Filament 1
N+N
Si
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
9
9.5
10
10.5
11
11.5
12
12.5
13
15 17 19 21 23
Silic
ate
(μm
ol/l
)
Nitr
ate
+ N
itrite
(μm
ol/l
)
May '09
Filament 2
N+N
Si
Nutrients