1. Towards higher resolution, global-ocean, tracer simulations
Doctoral Thesis: Zouhair Lachkar
Contributors: J.-C. Dutay, P. Delecluse, J. C. Orr
LSCE/IPSL, Laboratoire des Sciences du Climat et de l’Environnement
CEA-CNRS-UVSQ Gif-sur-Yvette, France

2. Background:
Anthropogenic CO2 (1990):
Coarse-resolution ocean models (OCMIP-2)
Large differences
Generally underpredict storage
Eddy resolving global model (1/10°)
1st to give adequate Southern Extratropical CFC-11 inventory
model
data
range of OCMIP models
What horizontal resolution is needed to capture large-scale distributions?
Sasai et al., (2004, GRL)

3. Ocean spatiotemporal scales governing surface variability
Chelton et al. (2001). Satellite altimetry and earth sciences, Chap. on Satellite altimetry, 57–64. Academic Press, NY.

4. Thesis work of Zouhair Lachkar:
Part 1
Evaluate:
eddy-induced changes in simulated tracer distributions (model vs. model)
any improvement due to explicitly including eddies (model vs. data)?
Understand how eddies affect transient tracer uptake & storage
Part 2
Explore role of mesoscale eddies in AAIW ventilation (with CFC-11 as a diagnostic tool)
Part 3
Study role of eddies & temporal variability of meridional transport of heat, CFC-11, and anthropogenic CO2

5. Approach
2 versions of same model ORCA-LIM (Madec et al., 1998; Barnier et al., 2006)
(ORCA 05, ½° cos   ½°) mean res.  33 km
(ORCA 2, 2° cos   2°) mean res.  130 km
eddying
non-eddying
Eddy Kinetic Energy
Eddy Kinetic Energy
Tracers
Atmospheric levels (normalized)
Tracer
Air-sea equilibration time
CFC-11
 1 month
CO2
 1 yr
Bomb C14
 10 yr
14C
CFC-11
3 transient tracers:
- CFC-11
- Anthropogenic CO2
- Bomb 14C
CO2
Broecker and Peng, 1974
1950
Year
2000

6. Increasing resolution reduces CFC-11 uptake & storage
non-eddying
eddying
data
Inventory
Cumulative flux
Eddy-induced changes (model vs. model)
Global
Atlantic
Pacific
Indian
South of 20°s
flux
- 22%
-33,6%
-9,8%
-23,5%
-28%
inv
- 22%
-22,8%
-10,8%
-36,6%
-31%
Global inventory (106 mol) – (model vs. data)
non-eddying
eddying
Sasai et al (2004)
GLODAP (data)
648
506
510
540
Decrease of global uptake by 22% (28% in SO)
Largest flux decrease  Atlantic (>33%)
Largest inventory decrease  Indian (> 36%)
Eddying model generally agrees with data

7. Unlike explictlyGM alone brings little improvement, but not enough…
CFC-11 inventory
non-eddying
non-eddying
non-eddying + GM
eddying
eddying + GM
 non-eddying + GM
 eddying + GM
CFC-11 Zonal Integral (Mmol degree-1)

8. Increased resolution reduces CO2 uptake & storage
non-eddying
eddying
data
Cumulative flux
Inventory
Eddy-induced changes (model vs. model)
Global
Atlantic
Pacific
Indian
South of 20°s
Global inventory (PgC)
flux
- 18%
-21,3%
-12,5%
-23,8%
-25%
inv
- 18%
-17,9%
-14,3%
-24,8%
-26%
Global inventory (Pg C) – 1994 (model vs. data)
non-eddying
eddying
Sabine et al (2004)
GLODAP
120 98
106
Decrease of total uptake by 18% (25% in SO)
Largest air-sea flux decrease  Indian (>23%)
Largest inventory decrease  Indian (>24%)
Eddying model agrees with data

9. How do eddies affect Southern Ocean uptake?
Mixed Layer
Thermocline
60°S
40°S + =
Eulerian mean circulation
Eddy induced flow
Residual mean circulation
30 Sv
-10 Sv
20 Sv
Eddy-induced slow-down of the SO upper meridional circulation
4-year trajectories of set of particles launched at z=250 m, y=60°S, 110°E<x<120°E
depth (m)
Zonal mean CFC-11 saturation in the Atlantic
0 m
non-eddying
strong upwelling rapid northward transport
100 m
250 m
non-eddying
eddying
0 m
eddying
weak upwelling
slow northward transport
100 m
250 m

10. Effect of increasing horizontal resolution section I9S – CFC-11
Including mesoscale eddies:
reduces excessive penetration of CFC-11 in Southern Ocean
 yields a better agreement with data

11. Isopycnal meridional streamfunction
How do eddies affect AAIW ventilation?
LCDWAAIW
UCDWAAIW
SAMW
AAIW
UCDW
LCDW
NADW
Maximum of mixed layer depth
eddying
Isopycnal meridional streamfunction
non-eddying
30 Sv
CFC-11 inventory ( layer)
non-eddying
eddying
data
Including eddies leads to:
- increase of UCDWAAIW: +5 Sv
- decrease of LCDWAAIW (ML): -15 Sv
- reduction of excessive intermediate ocean ventilation (AAIW, - 42%)

12. Mesoscale eddies:
Decrease southern extratropical uptake (improve data-model agreement)
CFC-11: %;
Anthro. CO2: -25%;
Bomb C-14: negligible
Increase residence time of tracer-rich waters at the surface
Increase surface water saturation of rapid equilibrating tracers (CFC-11, anthropogenic CO2)
Reduce upwelling (LCDWAAIW)
Decrease formation & ventilation of AAIW
modify distribution of AAIW source regions (from circumpolar distribution along ACC to localized in the Pacific Ocean)
decrease vertical penetration of CFC-11 and CO2 (improve data-model agreement)
Need better parameterization or explicit representation of mesoscale eddies to properly simulate southern extratropical uptake & storage of CFC-11 & anthropogenic CO2

13. Future work: towards eddy-resolving transient tracer simulations
EGU 2006 General Assembly
Future work: towards eddy-resolving transient tracer simulations
ORCA2 (2° cos   2°) mean res.  130 km
ORCA05 (½° cos   ½°) mean res.  33 km
ORCA025 (¼° cos   ¼°) mean res.  17km
Surface current speed (5-day mean, Jan 1-5)
CFC-11 Inventory (1965) 
From European-led DRAKKAR project on high-resolution ocean modelling

15. Global 14C distribution is insensitive to horizontal resolution
non-eddying
eddying
data
Cumulative flux
Inventory
Eddy-induced changes (model vs. model)
Global
Atlantic
Pacific
Indian
South of 20°s
flux
- 4,6%
-4,7%
-4%
-6,1%
-8%
inv
- 4,6%
-5,7%
-1,8%
-7,3%
-7%
Global inventory (1028 atoms 14C) – 1994 (model vs. data)
non-eddying
eddying
GLODAP
Broeker et al 1995
3,07
2,94
3,13
3,29
Small decrease of uptake & inventory (<5%)
Good agreement with observation