1
Claire Lo Monaco, Andrew Lenton and Nicolas Metzl
(LOCEAN-IPSL, Paris)
Natural and Anthropogenic Carbon Changes in the South Indian Ocean
Plan
•Ocean acidification
•Feedback on climate change
Carbon Budget 2007 (Global Carbon Project, 2008)
Conclusions:
“Anthropogenic CO2 emissions have been growing about four times faster since 2000 than during the previous decade, […]
Natural CO2 sinks are growing, but more slowly than atmospheric CO2, […]
All of these changes characterize a carbon cycle that is generating stronger climate forcing and sooner than expected.”
Scientific context
Plan
•Ocean acidification
•Feedback on climate change
I. Observations
Can we separate between anthropogenic and ‘natural’ carbon changes?
II. Model-Data comparison
Do coarse resolution Ocean-Carbon Models reproduce the observed changes?
III. On-going/future work
What drives DIC changes in the model? Would it be coherent with observations?
Scientific context
Measurements of Total Carbon and the associated parameters (temperature, salinity, oxygen, alkalinity, nutrients, …)
One cruise conducted in 1985
Six cruises conducted between 1998 and 2001(interannual variability)
Data (1)
OISO 1-6 :
INDIGO1 :
Mean position of hydrological fronts after Belkin and Gordon (1996)
I. Observations: sampling sites
Kerguelen Plateau
Data (2)
Large interannual variability can occur in the top 1000m of the ocean
- in the frontal region (associated with movement of the SAF)
- north of the SAF (mesoscale feature created by the Madagascar Current and the Agulhas Return Current
Mean position of hydrological fronts after Belkin and Gordon (1996)
I. Observations: sampling sites
Kerguelen Plateau
Rodgers et al. (subm!)
STMW
SAMW
AASW WW
Upper CDW
STSW
Water masses (1)
Mean position of hydrological fronts after Belkin and Gordon (1996)
I. Observations: water masses
Total carbon distribution (µmol/kg)
Kerguelen Plateau
STMW
SAMW
AASW WW
Upper CDW
STSW
Water masses (2)
Mean position of hydrological fronts after Belkin and Gordon (1996)
I. Observations: water masses
Total carbon distribution (µmol/kg)
Kerguelen Plateau
Deep winter mixing (down to ~500m)
Mode Waters formation
Cant
I. Observations : carbon changes
STMW
SAMW
WW
Upper CDW
Extended Multi-Linear Regression (eMLR) technique, Friis et al. (2005, DSR.I)
Anthropogenic carbon increased by 5-10 µmol/kg in Mode Waters (over 15 years)
~1/6 of the total accumulation of anthropogenic carbon (over 200 years)
Anthropogenic Carbon change over 15 years [µmol/kg]
STMW
SAMW
WW
Upper CDW
Anthropogenic Carbon distribution [µmol/kg]
Back-calculation (preformed carbon method), Lo Monaco et al. (2005, JGR)
TCO2 changes
I. Observation : carbon changes
STMW
SAMW
WW
Upper CDW
Total Carbon change over 15 years [µmol/kg]
+6±3 µmol/kg
no change
+15±5 µmol/kgNo changeAASW WW
Upper CDW
STMW
SAMW
STSW
-5±4 µmol/kg
No change
Total Carbon (µmol/kg) Total Carbon (µmol/kg)
35°S50°S
Extended Multi-Linear Regression (eMLR) technique
Only conservative tracers are used (Salinity, Temperature, NO)
50°S 35°S
eMLR results (1)
Total Carbon changes (TCO2) [µmol/kg]
STMW
SAMW
WW
Upper CDW
I. Observation : carbon changes
Anthropogenic Carbon changes (Canth) [µmol/kg]
STMW
SAMW
WW
Upper CDW
eMLR results (2)
I. Observation : carbon changes
Natural Carbon change (Cnat) [µmol/kg]
STMW
SAMW
WW
Upper CDW
STMW
SAMW
WW
Upper CDW
Anthropogenic Carbon changes (Canth) [µmol/kg]
STMW
SAMW
WW
Upper CDW
=
Total Carbon changes (TCO2) [µmol/kg]
+
MODEL description
Components:
Ocean Model OPA9 (GM90 and TKE mixed layer scheme),
Biogeochemical Model PISCES (NPZD model),
Ice Model LIM2
Resolution:
2°x 2° resolution (enhanced at the equator)
31 non -regular vertical levels (19 levels in the upper 500 meters)
Forgings:
ERA40 heat fluxes and winds
CORE freshwater fluxes (SST and SSS restored to Reynolds SST and Levitus SSS using bulk formulas)
CO2 scenario:
Pre-industrial run keeping atmospheric CO2 constant at 278 ppm
Anthropogenic run using the observed atmospheric CO2 values
II. Model-Data comparison: model description
Ocean Carbon Model NEMO2
DATA/MODEL: CANTII. Model-Data comparison: anthropogenic carbon
ANTHROPOGENIC CARBON DISTRIBUTION (µmol/kg)
MODEL (in 2000)DATA (late 1990’s)
500m
4030
2020
40
6030
DATA/MODEL changes (1)
DATA MODEL
Anthropogenic Carbon change (µmol/kg)
6
4
3
8
10
12
DATA
Total Carbon change (µmol/kg)
8 10
642
MODEL
8
II. Model-Data comparison: carbon changes
-20
DATA/MODEL nat C (1)
Natural Carbon change (µmol/kg)
MODEL (CO2atm = 278ppm)
-2
-4 -2
-4
DATA (TCO2-Cant)
2
-2
0
II. Model-Data comparison: carbon changes
-5
When the anthropogenic signal is removed, the remaining pattern shows
- a decrease in upper CDW,
but no significant change in sub-surface Antarctic waters
- a smaller decrease in SAMW,
but no significant change in STMW
DATA/MODEL nat C (2)
Natural Carbon change (µmol/kg)
MODEL (CO2atm = 278ppm)
-2
-4 -2
-4
DATA (TCO2-Cant)
2
-2
0
II. Model-Data comparison: carbon changes
-5
1000m
SummarySummary
Mode Waters transport anthropogenic CO2 from the surface down to ~1000m
STMW: The invasion of anthropogenic CO2 explains most of the TCO2 increase.
TCO2 increased by ~8 µmol/kg over 15 year
SAMW: The invasion of anthropogenic CO2 is compensated for by an equal decrease in natural carbon.
No change in TCO2.
South of the Polar Front: no significant change in anthropogenic carbon
upper CDW: TCO2 decreased by 9 (± 6) µmol/kg
II. MODEL
I. OBSERVATIONS
The observed changes are reasonably well reproduced in the model
The model suggests that the decrease in ocean carbon observed at mid-depths (~500-2000m), is a large scale feature representative of other regions in the
South Atlantic and South Pacific
Perspectives (2)Perspectives
CARINA+GLODAP merged dataset: Southern Indian sector
Ongoing/future work
What are the mechanisms driving the change in natural carbon in the model?Would it be coherent with observations?
XXXXXX END XXXXXX
To be continued…
CTOT +48 GtCCANTH +46 GtCCNAT +2 GtC
CTOT +21 GtCCANTH +25 GtCCNAT -4 GtC
CTOT +3 GtCCANTH +18 GtCCNAT -15 GtC
CTOT +24 GtCCANTH +3 GtCCNAT +21 GtC
Perspectives (1)PerspectivesChanges in ocean carbon inventories (Pg of Carbon)
500m-2000m below 2000m
Full water column 0-500m
CO2
Total Carbon
CLIMATE
OCEANIC CARBON CYCLE
OCEAN PROCESSE
S (photosynthe
sis, dynamics, ...)
CO2 emissio
ns
Anthropogenic CO2
Scientific context
Total Carbon
Scientific context
Water masses
Potential temperature [°C]
STMW
SAMWUpper CDW
WWAASW STSW
Mean position of hydrological fronts after Belkin and Gordon (1996)
I. Observations: water masses
Mode waters (1)
Eastern Subtropical Mode Waters
Subtropical Mode Waters
I. Observations: Mode waters
SAMW
Eastern STMW
STMW
Subpolar MW
STMW
Mode Waters distribution after Hanawa and Talley, 2000)
Mode Waters distribution after Hanawa and Talley, 2000)
Mode waters (2)
SAMW
Eastern STMW
STMW
Subpolar MW
STMW
Anthropogenic Carbon distribution [µmol/kg]
STMW
SAMWUpper CDW
WW
I. Observations: Mode Waters
OISO 1 to 3 (1998)
Cant 500m (1)
WOCE (1995-1996)
Large accumulation of anthropogenic carbon at mid-latitudes (20-40°S) in recently formed Mode Waters
Anthropogenic Carbon in Mode Waters
Observations :
Anthropogenic carbon distribution at 500m in the late 1990’s[µmol/kg]
500m
Anthropogenic carbon calculated from observations (TCO2, TA, O2 and
conservative tracers)
OISO 1 to 3 (1998)
Cant 500m (2)
WOCE (1995-1996)
Comparison of recent observations (1998-2001) with historical measurements (1985)
to evaluate the decadal change in ocean carbon
Anthropogenic Carbon in Mode Waters
Anthropogenic carbon calculated from observations (TCO2, TA, O2 and
conservative tracers)
Anthropogenic carbon distribution at 500m in the late 1990’s
Observations :
INDIGO 1 (1985)
[µmol/kg]
500m
Cant TCO2 distributions Total Carbon and Anthropogenic Carbon distributions
Anthropogenic Carbon distribution [µmol/kg]
STMW
SAMW
WW
Upper CDW
Total carbon distribution [µmol/kg]
STMW
SAMW
AASW WW
Upper CDW
STSW
Total Carbon changes (µmol/kg)
50°S 35°S
+6±3 µmol/kg
no change
+15±5 µmol/kgNo changeAASW WW
Upper CDW
STMW
SAMW
STSW
-5±4 µmol/kg
No change
Direct method
I. Observations
Anthropogenic carbon distribution [µmol/kg]
STMW
SAMW
AASW WW
Upper CDW
STSW
Total Carbon changes (µmol/kg)
TCO2 changes (2)
I. Observation : carbon changes
Physical and biogeochemical tracers (S, T, O2, Nut, Alk) are used to remove the effect of ocean variability (dynamics, biological activity).
Anthropogenic Carbon change over 15 years [µmol/kg]
STMW
SAMW
WW
Upper CDW
+6±3 µmol/kg
no change
+15±5 µmol/kgNo changeAASW WW
Upper CDW
STMW
SAMW
STSW
-5±4 µmol/kg
No change
Total Carbon (µmol/kg) Total Carbon (µmol/kg)
35°S50°S
eMLR method
Carbon changes : eMLR method
Extended Multi-Linear Regression (eMLR) technique
Friis et al. (2005, DSR.I)
Multi-Linear regressions of Total Carbon against selected tracers (A, B, C…) determined using observations collected at time t1 and t2.
t1 : INDIGO (1985) Total Carbon (t1) = a1.A1 + b1.B1 + c1.C1 + d1
t2 : OISO (1998-2001) Total Carbon (t2) = a2.A2 + b2.B2 + c2.C2 + d2
Coefficients determined for time t1 and t2 are then applied to the same set of tracers to evaluate the change in Total Carbon between t1 and t2:
Total Carbon change (t2 - t1) = (a2-a1).A2 + (b2-b1).B2 + (c2-c1).C2 + (d2-d1)
eMLR methods 1 & 2
Total Carbon changes (TCO2) [µmol/kg]
eMLR method 1: physical and BGC tracers TCO2 = eMRL (S, T, O2, Nut, Alk)
STMW
SAMW
WW
Upper CDW
eMLR method 2: using only conservative tracers TCO2 = eMRL (S, T, NO)
STMW
SAMW
WW
Upper CDW
I. Observation : carbon changes
Anthropogenic Carbon changes (Canth) [µmol/kg]
‘Natural’ C changes
Natural Carbon change (Cnat) [µmol/kg]
When the anthropogenic signal is removed from the total carbon change, the remaining pattern shows
- a large decrease in Upper Circumpolar Deep Water (6-12 µmol/kg), but no change in sub-surface Antarctic waters
- a small decrease in Subantarctic Mode Waters (4-6 µmol/kg), but no significant change in STMW (small increase in newly formed STMW?)
I. Observation : carbon changes
Difference between the 2 results:
CT (eMLR1) – Canth (eMLR2)
STMW
SAMW
WW
Upper CDW
DATA/MODEL changes (2)
DATA
Anthropogenic Carbon change (µmol/kg)
64
3
8
10
12
2
DATA
Total Carbon change (µmol/kg)
MODEL
II. Model-Data comparison: carbon changes
MODEL
DATA/MODEL OLD: CANT
DATA
11
9753
DATA / MODEL : Total and Anthropogenic Carbon changes
MODEL
Anthropogenic Carbon change (µmol/kg)
MODELDATA
Total Carbon change (µmol/kg)
-5
-3
3
5
7
9
11
MODEL: Natural Carbon changes at 700m [µmol/kg]
DATA/MODEL OLD: Nat C
Natural Carbon change (µmol/kg)
MODEL (CO2atm = 278ppm)
-11 -9-7
-5
-3
-7
-1
DATA / MODEL : ‘Natural’ Carbon changes
DATA (TCO2-Cant)
0
700m
Carbon decrease associated with
• Warming
• Oxygen increase
• Nutrients decrease
Natural Carbon changes at 700m [µmol/kg]
MODEL OLD: large scaleMODEL : Large scale changes
700m
Carbon decrease associated with
Nutrients decrease
Oxygen increase
Nitrate changes at 700m [µmol/kg]
Oxygen changes at 700m [µmol/kg]
Carbon decrease associated with
• Warming
• Oxygen increase
• Nutrients decrease