11B and BCa

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?11B and B/Ca
Kat Allen
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Atmospheric CO2 (gas)
Ocean CO2 (aqueous)
HCO3- H
CO2 H2O
CO32- 2H
B(OH)4-
CaCO3
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Relative abundance of boric acid and borate
varies with pH.
?11B of the ocean is constant, but ?11B of
B(OH)3 and B(OH)4 varies with pH.
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Calibration
Offsets due to vital effects
Use SINGLE SPECIES
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?11B can be used to reconstruct
glacial-interglacial CO2 measured from ice cores.
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Longer time-scales 60 Myr
pCO2
pH
Pearson Palmer estimate really high pCO2 in the
Palaeocene! Values do not agree with stomatal
indexes (another CO2 proxy)
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Complication B and ?11B vary through time
Lemarchand et al, 2000
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Marine Boron

• SOURCES
• Continental detritus
• Hydrothermal vents
• Subduction zone fluids
• SINKS
• Clay absorption
• Ocean crust weathering
• Carbonate precipitation
• Residence Time Total B mass / influx
• Estimated between 3 - 16 Million years

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Challenges Potential

• Analytical accurate mass spec measurements, no
  internal fractionation
• Material need single species, no dissolution,
  narrow class size
• Calibration needed for each species
• Calculation many estimations involved, need to
  know T, S, Alk etc.
• Can reconstruct pCO2 past ice cores
• Can also be used to investigate upwelling

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B/Ca
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B/Ca as a proxy for pH
Higher pH
Higher B(OH)4-sw
Higher B(OH)4-carb
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KD
KD is temperature-dependent
Yu et al, 2007
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KD can be estimated using calibrated temperature
dependencies.
Yu et al, 2007
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Atmospheric CO2 (gas)
Why did we do all that work???
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Ocean CO2 (aqueous)
HCO3- H
CO2 H2O
CO32- 2H
Calculate pH
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B(OH)4-
CaCO3
B/Ca
Calculate B(OH)4-/HCO3-
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(Need to estimate salinity and alkalinity)
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PCO2 and pH calculated from B/Ca match Vostok ice
core CO2 trends!
LGM surface ocean 0.15 pH units PCO2 -95 uatm
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What about deep water?
B/Ca in benthic forams Strong relationship with
?CO32-
Carbon Compensation Depth (CCD)
Yu Elderfield, 2007
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Challenges

• Determining KD
• Understanding factors that influence B/Ca
• Estimating parameters used to calculate pH and
  CO2

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