1/30 is there a higher c ant storage in the indian ocean? estimating the storage of anthropogenic...
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IS THERE A HIGHER CIS THERE A HIGHER CANTANT STORAGE STORAGE
IN THE INDIAN OCEAN?IN THE INDIAN OCEAN?
Estimating the storage of anthropogenic carbon in the subtropical Indian Ocean: a comparison of five different approaches
M. Álvarez, C. Lo Monaco, T. Tanhua, A. Yool, A. Oschlies, J. L. Bullister, C. Goyet, N. Metzl, F. Touratier, E. McDonagh, and H. L. Bryden, Biogeosciences, 6, 681-703, 2009.
http://www.biogeosciences-discuss.net/6/729/2009/bgd-6-729-2009.html
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CANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN
44.5 5 Pg 44.8 6 Pg 20.3 3 Pg
Indian Ocean
Pacific Ocean Atlantic Ocean
(Sabine et al, Science 2004)
CCANTANT inventory referred to 1994 = 110 ± 13 Pg C inventory referred to 1994 = 110 ± 13 Pg C
Indian Ocean contains
- 21% of the total CANT inventory
- half of the Atlantic CANT inventory despite having only 20% less area
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CANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN
Indian Ocean CIndian Ocean CANTANT vertical distribution vertical distribution mol/kg mol/kg
(Sabine et al, Science 2004)
RedSea /Persian Gulf Intermediate Water
Antarctic Intermediate Water (AAIW)
AAIW marks the deepest CANT penetration in the Subtropical gyre
No CANT in deep and bottom waters
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CANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN
Hypothesis:
CANT penetrates deeper than 1000-1500 m
How to assess this question:
compare different CANT methods -> difficult: every method has high uncertainties
help: relation of CANT with tracers (CFC12, CCl4)
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CANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN
On board R/V Charles Darwin, CD139 cruise, 1/3 – 15/4/2002, from Durban to Freemantle
P.I.: Harry Bryden (National Oceanographic Centre, Southampton, UK)
Physics: temperature, salinity, ADCP, LADCP
Chemistry: oxygen, salinity, nutrients, CO2 (pH & TA, TIC), CFCs (11, 12, 113), CCl4.
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CANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN
Salinity (psu)Africa Australia
NADW
AAIW
SAMW
CDW
AABW
AAIW
SAMW
NADW
AAIW
SAMW
AABW
NADW
AAIW
SAMW
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CANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN
CFC-12 (pmol/kg)
CDW
AABW
NADW
AAIW
SAMW
CDW
Africa Australia
AAIW
SAMW
AABW
AAIW
SAMW
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CANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN
CANT TECHNIQUES
1. CANT SAB99: method by Sabine et al. (GBC,1999), using their CDis
2. CANT LM05: method by LoMonaco et al. (JGR, 2005)
3. CANT TrOCA: Touratier & Goyet (Tellus, 2007)
4. CANT TTD
5. CANT from OCCAM model
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CANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN
CANT = C* - CDis = C – AOU/RC – ½(TA + AOU/RN ) + 106/104 · N* - C280 – CDis
C is the current total inorganic carbon
TA = TA - TA0, current alkalinity - preformed alkalinity TA0= 378.1 + 55.22 · Sal + 0.0716 · PO - 1.236 · Tpot
AOU is the Apparent Oxygen Utilization, assuming oxygen saturation
C280 is the inorganic carbon in equilibrium with the preindustrial atmosphere. C280 = f (Tpot, Sal, TA0, pCO2280) from thermodynamic equations pCO2280 = CO2 fugacity at a 100% of water vapor pressure in uatm = f(Tpot, Sal, 280) C280 in GSS96 => constants by Goyet & Poisson (1989) & a constant pCO2280 = 280 uatm linearilized equation: C280 = 2072 - 8.982 · (Tpot - 9) - 4.931 · (Sal - 35) + 0.842 · (TA0- 2320)
N* = (0.87 · (NO3 - 16 · PO4 + 2.9)) term accounting for the denitrification
Back-calculation technique by Sabine et al. (GBC, 1999) to estimate CANT.
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CANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN
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CANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN
CDis is obtained with own CD139 data using CFC12 ages and limit at 40 years
a) Old deep waters, CANT = 0 => C* = CDis
b) In upper waters, having the age: CDis = C*t|σ=cte
C*t = C - CBio - C t where Ct = f (Tpot, Sal, TA0, pCO2t) pCO2 in the atmosphere at 2002 – age (t)
c) In between => weigthed mean C* and C*t|=cte
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-35
-30
-25
-20
-15
-10
-5
0
5
25.8 26.3 26.8 27.3 27.8q
C di
s um
ol/k
g
SAB99 own Tables
SAB99
Comb
Interpolated
C*t method C* & C*t means C* method
CANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN
Fig. 4. Air-sea CO2 disequilibrium (mol kg-1) by q density intervals. Blue points correspond to the values taken directly from SAB99 work, light blue and orange points correspond to the values estimated using the CD139 biogeochemical data, following SAB99 (orange) and combined (light blue) methods. Interpolated points are highlighted with black open circles.
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CANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN
Back-calculation technique by Lo Monaco et al. (JGR, 2005):
CANT = CT – CBio - CT0 obs – (CT– CBio – C0 obs) REF
CT = measured TIC
CBio = 0.73·(O20 – O2) + 0.5·(TA – TA0) => biological activity variation in TIC
TA0 => preformed TA
O20 = O2
sat – ··O2Sat => O2 = 12% undersaturation
K = > mixing ratio of ice-covered water (OMP)
C0 obs => preformed TIC currently observed in the formation area water masses
REF = reference water where no CANT should be detected.
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CANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN
mixing ratios of southern and northern waters:
k(S) + k(NADW) = 1 determined from OMP analysis
TA0 = k(S) TA0(S) + k(N) TA0(NADW)
C0,obs = k(S) C0,obs(S) + k(N) C0,obs(NADW)
southern relationships:
winter surface data from the Atlantic and Indian oceans (WOCE and OISO cruises)
TA0(S) = 0.0685 PO + 59.787 S - 1.448 q + 217.15 (± 5.5 µmol/kg, r2 = 0.96, n = 243)
C0,obs(S) = -0.0439 PO + 42.79 S - 12.019 q + 739.83 (± 6.3 µmol/kg, r2 = 0.99, n = 428)
northern relationships
subsurface data from the North Atlantic and Nordic Seas (WOCE and KNORR cruises)
TA0(N) = 42.711 S + 1.265 q + 804.6 (± 9.3 µmol/kg, r2 = 0.92, n = 297)
C0,obs(N) = 10.69 S + 0.306 NO + 1631.6 (± 9.2 µmol/kg, r2 = 0.79, n = 364)
Back-calculation technique by Lo Monaco et al. (JGR, 2005)
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CANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN
Back-calculation technique by Lo Monaco et al. (JGR, 2005):
OMP analysis modified from Lo Monaco et al. (JGR, 2005)Endmembers: AAIW, NADW-E, NIDW, Indian Water, WDS/CDW, ISW Weddell Variables: Sal, Tpot, SiO2 and NO
34.1 34.2 34.3 34.4 34.5 34.6 34.7 34.8 34.9-2
0
2
4
6
AAIW2 IW
NADW-E NIDW
WDW/CDW
ISW Wed
0 20 40 60 80 100 120 140 160 180-2
0
2
4
6
AAIW2 IW
NADW-E NIDW
WDW/CDW
ISW Wed
450 500 550 600-2
0
2
4
6
AAIW2 IW
NADW-E NIDW
WDW/CDW
ISW Wed
Salinity
SiO2
NO
Tpo
tT
pot
Tpo
t
16/30-2 -1 0 1 2
-5500
-5000
-4500
-4000
-3500
-3000
-2500
-2000
-1500
-1000
Med-Calc weighted & adim.-0.2 -0.1 0 0.1 0.2 0.3
-5500
-5000
-4500
-4000
-3500
-3000
-2500
-2000
-1500
-1000
Med-Calc Real-10 -5 0 5 10 15
-5500
-5000
-4500
-4000
-3500
-3000
-2500
-2000
-1500
-1000
Med-Calc Real
Tpot
Sal
SiO2NO
data5
Tpot
Sal SiO2
NO
CANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEANBack-calculation technique by Lo Monaco et al. (JGR, 2005): OMP
Tpot, Sal, SiO2 NO STD Res. 0.0481 0.0051 1.3 3R2 0.9979 0.9967 0.9973 0.9611 (n=1299)
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CANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN2. Back-calculation technique by Lo Monaco et al. (JGR, 2005): OMP
NADW contribution
Ice-covered SW contribution
Africa AustraliaAfrica Australia
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CANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN
REF = NADW= reference water where no CANT should be detected.
Applied to samples with more 50% NADW from OMP analysis
(CT – CBio – C0 obs) REF = - 54.4 ± 1.4 umol/kg
(LoMonaco JGR2005 -51 umol/kg)
Back-calculation technique by Lo Monaco et al. (JGR, 2005):
CANT = CT – CBio - CT0 obs – (CT– CBio – C0 obs) REF
CANT = CT – CBio - CT0 obs – (- 54.4)
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CANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN
CANT TrOCA, Touratier et al (Tellus B, 2007):
CANT = (O2 + 1.279 · (CT – 0.5 · TA) – exp (7.511-0.01087· θ -781000/TA2))/1.279)
CANT (TrOCA) = (TrOCA – TrOCA280) / a
TrOCA = O2 + a · (CT -1/2 ·TA) a = ψO2 / [ψCO2 + ½ ·( ψ H+ − ψHPO24−)]
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CANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN
4. CANT TTD (Waugh et al., 2004; 2006; Tanhua et al., 2008):
- each water sample has its own “age”, i.e. time since it was last in contact with the atmosphere. The sum of all these ages makes the TTD of a water sample
- the mean age ( ) and the width of the TTD () are assumed to be of equal magnitude: realistic assumption of the relation between advective and diffusive transport in the Ocean
- CANT is an inert passive tracer where air-sea disequilibrium hasn’t changed over time.
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CANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN
5. CANT OCCAM
- global, medium-resolution, primitive equation ocean general circulation model (Marsh et al., 2005).
- OCCAM's vertical resolution is 66 levels (5 m thickness at the surface, 200 m at depth), with a horizontal resolution of typically 1 degree.
- Advection is 4th order accurate, and the model is time-integrated using a forward leapfrog scheme with a 1 hour time-step.
- Surface fluxes of heat and freshwater not specified but are calculated empirically using NCEP-derived atmospheric boundary quantities (Large and Yeager, 2004).
- OCCAM incorporates a NPZD plankton ecosystem (Oschlies, 2001; Yool et al., 2007) which drives the biogeochemical cycles of nitrogen, carbon, oxygen and alkalinity.
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CANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN
CANT vertical distributions
pCFC12 & pCCl4 SAB99 LM05Troca TTD OCCAM
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CANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN
CANT mean profile differences
-10 0 10 20
-5000
-4000
-3000
-2000
-1000
0The whole section
-10 0 10 20
-5000
-4000
-3000
-2000
-1000
0Western section
-10 0 10 20
-5000
-4000
-3000
-2000
-1000
0Mid section
-10 0 10 20
-5000
-4000
-3000
-2000
-1000
0East section
Troca
LM05
TTDOCCAM
data5
a)
c) d)
b)
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CANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN
Neutral density layers & salinity
Africa Australia
Bottom
AAIW
SAMW
Deep
Surface
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0
2
4
6
8
10
12
Surface SAMW AAIW Deep Bottom
CA
NT
inve
ntor
y (m
olC
/m2)
Troca
LM05
SAB99
TTD
OCCAM
LMZero
0
5
10
15
20
25
30
35
Total SAMW AAIW Deep Bottom
CA
NT
inve
ntor
y (m
olC
/m2)
CANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN
CANT mean inventories
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Revelle = 10
CANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN
Surface, SAMW waters and upper AAIW
Revelle = 13
Fig. 10. Partial pressure of CFC-12 (ppt) and CANT estimates (mmol kg-1) for upper waters with potential temperature higher than 5ºC, pressure higher than 200 dbar and CFC-12 age less than 30 years. Also shown in black is the atmospheric evolution of CFC-12 and CANT using Revelle factors of 10 and 13 (see text for details), some time markers are shown.
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CANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN
Deep and bottom waters
Fig. 11. a) Partial pressure of CFC-12 (ppt) and b) partial pressure of CCl4 (ppt) versus CANT (mol kg-1) estimates for deep waters with potential temperature lower than 5ºC, pressure higher than 200 dbar and CFC-12 age higher than 40 years. In the case of CCl4, the temperature limit is 3ºC. Also shown in black are the atmospheric evolution of CFC-12, CCl4 and CANT using Revelle factors of 10 and 13 (see text for details), some time markers are shown.
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Table 1. Mean standard deviation CANT specific inventory (molC m-2) by water masses in the
subtropical Indian Ocean for the different methods here evaluated. Mean and standard deviation values were obtained randomly modifying the initially calculated single CANT values by 5
mol kg-1. A set of 100 perturbations were done for the five methods. The standard deviation for each layer is weighted by the layer contribution to the total section area. See text for the acronyms. N/D stands for not determined. Values between brackets correspond to the LM05 method assuming a 100% oxygen saturation in equation (7), =0.
Upper SAMW AAIW Deep Bottom Total*
SAB99 N/D 8.50.5 8.10.4 00.5 0.30.2 23.9 2
LM05 N/D 110.7 110.50.60.4
(0.50.4)1.20.3
(0.00.3)30.82.5
(29.52.5)
TrOCA N/D 8.40.5 9.40.5 1.90.5 1.40.3 28.12.2
TTD 7.2 0.7 9.30.6 9.30.5 20.4 1.30.2 28.92.3
OCCAM 6.91.5 9.30.8 7.60.5 0.50.1 00 24.4 2.8
* The total specific inventory is calculated as the sum of the SAMW, AAIW, Deep and Bottom contributions plus 7 molC m-2, i.e., the TTD and OCCAM mean specific inventory for the upper layer.
CANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN
Inventories
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This work investigates the CANT penetration and inventory in the subtropical Indian Ocean along 32ºS calculated with data collected in 2002. Five different methods are compared and discussed: three carbon-based methods (C*, LM05 and TrOCA), TTD and a simulation from the OCCAM global model.
Comparatively, the C* method seems to yield too shallow penetration of CANT, with no or very low CANT detected in deep or bottom waters, mainly due to the formulation and assumptions of CTdis.
Our results indicate that SAB99 CTdis values are inconsistent with the current air-sea CO2 disequilibrium found in current Indian Ocean winter CTdis values. Although this could also be misleading taking into account that water masses are usually formed in particular times and areas of the ocean.
Previous estimates of CANT inventory in the subtropical Indian Ocean with the C* method appear to be underestimates.
Considering the CANT estimates derived from those methods consistent with the tracer distributions and the knowledge about water masses, our best estimate for the mean CANT specific inventory is 282 molC m-2 which compares with 242 molC m-2 from C*, 17% higher.
CANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN
Conclusions
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CANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN
Hypothesis:
CANT penetrates deeper than 1000 m (Sabine et al 1999)
How to assess this question:
difficult: every method has uncertainties
help: relation of CANT with tracers (CFC12, CCl4)
seems to be hinted by any other method
absolutely true, no method is perfect
questions still arise, saturation, mixing, etc..
community should combine methods and time-evolution studies at specially
sensitive regions
OPEN DISCUSSION: KEY REGION ….. THE SO
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CANT ALONG CD139 CRUISE (2002) 32ºS INDIAN OCEAN
Discusión:
¿Cuáles son las asunciones de cada método?
¿nos creemos el desequilibrio?
¿Qué método os parece el más fiable?
¿Se os ocurre como evaluar los métodos de otra manera?