1. Isotope enable Community Earth System Model
Alexandra Jahn, Keith Lindsay, Esther Brady,
Synte Peacock, Jiaxu Zhang*, Bette Otto-Bliesner, Zhengyu Liu*
NCAR and University of Wisconsin Madison (*)
NCAR is sponsored by the National Science Foundation
The iCESM project is funded by DOE

2. AOMIP special edition Freshwater paper published
Thanks to AOMIP for travel funding and financial publication support!

3. Isotope enable Community Earth System Model
Alexandra Jahn, Keith Lindsay, Esther Brady,
Synte Peacock, Jiaxu Zhang*, Bette Otto-Bliesner, Zhengyu Liu*
NCAR and University of Wisconsin Madison (*)
NCAR is sponsored by the National Science Foundation
The iCESM project is funded by DOE

4. A Collaborative Proposal: Development of an Isotope-Enabled CESM
Objective: To enhance the CESM with the capability of simulating key isotopes and geotracers, including δ18O, δD, Pa/Th, δ14C, and δ13C, to allow for better comparisons with obervations
PIs: Bette Otto-Bliesner and Zhengyu Liu
Co-PIs: S. Peacock, M. Vertenstein, A. Gettelman
Funded by DOE (SciDAC BER ESM)
CLM4
W. Riley
C. Koven
T. Wong
J. Tang
F. Joos
A. Bozbiyik
CICE
D. Bailey
A. Jahn
POP2
J. Zhang
E. Brady
K. Lindsay
S. Peacock
CAM5
D. Noone
C. Bardeen
Gettelman
J. Nusbaumer
CPL7
M. Vertenstein

5. Why are isotopes useful?
Different masses lead to different reactions (called fractionation)  Ratio of rare to abundant isotopes can be used as tracer of origins/processes
Radioactive tracers act as clocks
Example: Water isotopes, where heavier oxygen isotope (18O) is more likely to stay in the phase where it is bounded more strongly  water vapor is depleted in 18O  high latitude precipitation is very depleted in 18O

6. Application example: Paleo
Climate proxies:
(d18O, dD, Pa/Th, d13C, etc.) are used to infer climate change signals like
DT, Dprecip, and Circulation changes
 Comparisons with simulated isotopes are more direct than comparisons with inferred climate

7. Examples of δ13C as ocean tracer
  Curry and Oppo (2005 )
δ13C is used to infer paleo ocean water masses (e.g., NADW)
δ13C can be used as tracers of carbon cycle processes  e.g., used to diagnose the oceanic uptake of anthropogenic CO2

8. Application example: Arctic FW
Identify meteoric water, using δ18O and salinity (e.g., Ostlung and Hut, 184, Schlosser et al. 1994):
 Having δ18O in models allows direct comparison with observational geochemical data
Schlosser et al., 2002

9. Water isotopes in POP2
Same δ18O as local precip
Currently run in ocean only mode, forced with isotopic atmospheric fluxes from previous isotope enabled model (isoCAM)
Courtesy of Jiaxu Zhang

10. Water isotopes in POP2
Courtesy of Jiaxu Zhang

11. Carbon isotopes in POP2 Solubility pump Biological pump
Abiotic 14C in DIC in POP2 (solubility pump only)
 follow OCMIP2 protocol
 Error by ignoring biological pump is ~10% (Fiadeiro 1982)
Biotic 14C and 13C in POP2 (solubility and biological pump)
 need ecosystem model to simulate
base code on 13C code from ETH (Gruber et al) for POP1
 Add biotic 14C
Source: S. Chisholm, Nature, 2000

12. Radiocarbon (abiotic)
Total surface ocean D14C
Corel data from: Benavides, and Druffel. 1986,, Druffel 1980/81/82/87/97, Hua, et al 2005, Guilderson et al. 2000, Druffel and Griffin 1999, Guilderson, and Schrag 1998
CESM
Corals

13. Radiocarbon (abiotic)
D14C at 500 m
Level of maximum deep convection: (annual mean)
Other biases in coupled x3 CCSM4:
Too weak AMOC strength (by 5-7 Sv)
About 1000 m too shallow NADW penetration depth
See Shields et al. (2012)

14. Future work Finish addition of 13C and 14C and test implementation
Finish water isotope implementation in sea ice model and test
 Look at freshwater ocean-ice isotope simulations under CORE forcing for last decades
Add tracers for Protactinium (Pa) and Thorium (Th) to the ecosystem model of the CESM
Couple water isotope tracer modules for atmosphere, ocean and ice and test
Include tracers in iTRACE fully-coupled simulation from LGM to present (1° Ocean/Ice, 2° atmosphere)
Compare simulations to observations, using the new tracers for more direct (but still not “apple to apple”) comparisons