Modelling radiocarbon productiondistribution in GENIE

1
Modelling radiocarbon production/distribution in
GENIE

• Joy Singarayer
• P Valdes, A Ridgwell, D Richards

2
Background
Cosmic rays

• 14C depends on solar activity, geomagnetic
  intensity and climate
• Used for
• Dating
• Proxy for climate/ocean circulation
• Proxy for solar activity
• Has varied considerably over last 50ka

solar wind
Geomagnetic field
n
14N ?14C
14C O2 ?14CO O 14CO OH ? 14CO2 H
Photosynthesis
Dissolved 14CO2 Carbonates
3
IntCal04 calibration curve
14C atmospheric record
Beck et al, Hughen et al
Cariaco (GRIP ss09sea)Bahamas 25-3 (2006)
Model deconvolute records, investigate
sensitivity to sea-ice, wind-stress, geomagnetic
excursions, ocean biogeochemistry etc.
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Model development
Global mean 14C production rate - function of
solar/geomag
Global d14C prescription in EMBM
2D atmosphere EMBM
ATCHEM
2D sea ice
3D ocean GOLDSTEIN
2D land surface
ENTS
BIOGEM
SEDGEM
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Modern ocean distribution

• Prescribed d14CO2atm 38.4
• 8 level goldstein ocean

cb-goldstein
Atlantic DIC ?14C ()
Data (WOCE)
cbs-goldstein
Sediment burial 0.24 GtC yr-1
6
Modern ocean distribution

• Prescribed d14CO2atm 38.4
• cbs vs cbms

Atlantic DIC ?14C ()
cbs-goldstein
Data (WOCE)
cbms-goldstein (ENTS land included)
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Modern ocean distribution

• Prescribed d14CO2atm 38.4
• cbs vs. cbms

cbs-goldstein
cbms-goldstein (ENTS land included)
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Modern ocean distribution

• Prescribed d14CO2atm 38.4
• Cbms with goldstein vs. fixed annual mean sea-ice

Atlantic DIC ?14C ()
cbms-goldstein
Data (WOCE)
cbms-goldstein (fixed sea-ice)
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Balancing the modern 14C budget

• Global average 2.02 atoms cm-2 s-1 (Masarik and
  Beer, 1999)
• cbms-goldstein
• 10,000 year simulation after 30,000 year spin-up

Atlantic
Pacific
DIC ?14C ()
Model
Model
Data (WOCE)
Data (WOCE)
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Balancing the modern 14C budget

• Source atmospheric production
• Sink radioactive decay, ocean sediment burial

• Some other modelling studies
• Beck et al (2001) large ocean sedimentary sink
  of 1.85GtC yr-1 (Box model)
• Hughen et al (2004) specify additional
  sedimentation in long-lived reservoirs (Box
  model)
• Köhler et al (2005) lower production rate to
  1.68 atoms cm-2 s-1 (BICYCLE box model)
• Or specifying normalised production rate

Bahamas ?14C record Box model
11
Balancing the modern 14C budget

• Geomagnetic intensity during late Holocene was
  higher than present
• Lal et al (2005) solar activity increase
  12-16kyr BP and 16-22ka high lat. production
  lower by factor 1.5 (8.5-9.5ka higher by factor
  2)
• Uncertainty in modern production rate 1.8-2.4
  atoms cm-2 s-1

• Ocean sediment burial
• Modern CaCO3 0.2GtC year-1
• Holocene coral reef build-up Ridgwell et al
  (2003) 0.15 GtC year-1 for last 5ka equivalent?

Relative CaCO3 accumulation rate
Age (ka BP)
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Balancing the modern 14C budget

• 14C production rate modelled using a record of
  the last 10ka relative geomagnetic intensity
• CaCO3 accumulation rate 1.0 GtC yr-1

Atlantic
Pacific
DIC ?14C ()
Model
Model
Data (WOCE)
Data (WOCE)
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Marine records
West Scotland, N Atlantic

• Increase in age of surface water in N Atlantic
  during Younger Dryas (by 300-500 years)
• Why
• increased sea-ice cover?
• lower advection of surface waters into N
  Atlantic?
• Reasons for structure?

West Norway, N Atlantic
Austin et al, submitted Bondevik et al, Science
(2006)
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Idealised hosing experiments

• modern set-up cbs-goldstein
• prescribed d14C 38.4
• freshwater input (negative salinity flux) from
  2000 to 3000 years

N Atl. MOC max
Surface 14C age
Simulation time (years)
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Atlantic MOC
DIC D14C
Sea-ice
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Simulation time (years)
Freshwater flux
N Atl. max THC
14C age
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Next steps

• Hosing experiments
• Map out sensitivity to hosing, sea-ice etc.
• Compare to atmosphere and ocean records
• Model development
• IGCM 14C production and ocean/land fluxes
• Genie-land addition of carbon isotopes
• 16-level cbms-goldstein
• Further assessment of modern 14C budget

14C production in top layer of 22-level model
Year 12
Year 25
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• Aims of project
• Genie capabilities and cbs-goldstein
• Model development - ents, atchem (not on cvs
  needs tidying)
• Some results modern bomb c14?
• Balancing the budget difference with
  sedimentation
• Geomagnetic excursions
• Reservoir ages
• Dissolution homogeneous vs interface
• Next steps igcm
• 10Be more model development
• Issues with genie sedgem not in yet (when?),
  user manual and details about all the bits,
  16-level ocean version. What about carbon
  isotopes in genie-land (who is working on that
  and should I wait to then put in c14?), still not
  entirely sure what modules I can use with what.
  Improvements on fixedchem for carbon in
  atmosphere?. Lack of sea-ice in cbs-goldstein
  (some with cbms_goldstein) any better with EVP,
  higher resolution etc.