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)
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
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
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
Spatial structure – satellite view
Patch 1: freshly upwelled, followed for 9 days
Patch 3: ~10 days old, followed for 8 days
Spatial structure – in situ
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
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
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?
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
Daily δnDIC calculation
δnDIC day
δnDIC night
δnDIC day+night
nDIC
Time
depth integrated NCPt = Zeut (max DICt- max DICt-1) – Ft (– Vt)
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
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
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
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
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
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
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
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?)
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!
B. Sea-air CO2 fluxes
Units on time plots legend!!!
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