Boron isotope Ratio as a paleo pH proxy

1. Boron Isotopic study in marine carbonates: reconstruction of
paleo-pH and pCO2 records of Quaternary and Anthropocene
MOHD. TARIQUE
JRF
Date: 19/10/2015

2. Carbon cycle
Ocean-Atmosphere coupling

3. CO2 cycle vary in different time scale:
• Geological time (Quaternary, 2.5 to 0 Million year)
• Modern (Anthropocene)
What are controlling factors/forces and their time scale ?
Geological time
1. Ocean Stratification
2. Efficiency of biological pump
3. Orbital forcing
4. Volcanic eruption
Anthropocene(Manmade)
1. Industries
2. Burning fossil fuels
3. Deforestation
Sigman and Boyle 2000, Nature

4. Source: IPCC Report. 2014

5. Preindustrial
Today
Projection for Year 2100
PETIT et al. 1999, Nature & IPCC Report 2014

6. Atmospheric CO2
CO2 + H2O ⇒ H2CO3
H2CO3 ⇒ H+ + HCO3
–
Decreases pH of ocean
H+ + CO3
2– ⇒ HCO3
–
Reducing  CO3
2–  in ocean
CaCO3  Ca2+ + CO3
2-
Mineral Dissolution
 Mineral formation
Ocean
Acidification
Excess absorption of CO2 by
ocean reduces its pH, it is
called Ocean acidification

7. Future Ocean ?
• How the pH of the ocean is going to change in future ?
• How decrease in pH of ocean is going to affect marine organisms and their
ecosystem ?
• What are the cause of Variation in CO2 during glacial and interglacial
periods ?
• Does CO2 sink capacity of the ocean will change in future ?
• Foraminifera
• Corals
Archive
• Boron
Isotope Ratio
Proxy

8. Honisch & Hemming, 2005. Earth and Planetary Science Letters & Petit et al. 1999 Nature
pCO2 variation using Boron paleo-pH proxy and Antarctic ice core.
Ice core
boron pH proxy

9. 11B
80% 10B
20%
Atomic number = 5
Atomic mass = 10.81
Relative Abundance of isotopes

10. Boron in ocean water
[B] = 4.5 ppm
B(OH)3
Abundance(80%)
B(OH)4
-
Abundance(20%)
B(OH)3 + H2O = B(OH)4
- + H+
KB =
[H+] [B(OH)4
-]
[B(OH)3]
log
[B(OH)4
-]
[B(OH)3]
= pH - pKB
Hemming & Hanson 1992, Geochimica et Cosmochimica Acta

11. pH = pKB – log
δ11Bsw – δ11Bborate
δ11Bsw – 11-10KB δ11Bborate – 1000( 11-10KB – 1)
39.6‰
(Foster et al. 2010)
1.0272
(Klochko et al. 2006)
8.597 at 25 °C
(Dickson 1990)
Sample
Where:
δ11Bsw = Delta value of sea water
pKB = dissociation constant of boric acid
11-10KB = Fractionation factor between B(OH)4- and B(OH)3
δ11Bborate = delta value of Sample
FOSTER et al. 2010. Geochemistry Geophysics Geosystems; KLOCHKO 2006. Earth and Planetary Science Letters &
DICKSON 1990. Deep-Sea Research.
(11B/10B)Sample
(11B/10B)standard
11B = - 1  1000 ‰

13. Proposed Study Area
CO2
CO2
CO2
CO2
1. Southern Ocean
• Southern Ocean acts as CO2 sink.
• Strong influence on global climate.
• Polar regions are highly sensitive to CO2
variation.
Southern Ocean & tropical Indian Ocean
Martinez et al. 2015, Nature

14. 2. Indian Ocean
• Corals are highly Sensitive to climate change.
• Their growth layers record annual variation in pH.
• Changes in ocean chemistry due to Anthropogenic CO2
and their effects on coral ecosystem.
Proposed Study Area

15. Boron isotope measurements
• Chemical extraction of boron from samples
• Isotope measurements using mass spectrometer (MC-ICPMS)
• Boron Isotope Ratio will be
determined using MC-ICP-MS
facility at NCAOR

16. Thank You