Boron Isotopic study in marine carbonates: reconstruction of paleo-pH and pCO2 records of Quaternary and Anthropocene

MOHD. TARIQUE

JRF

Date: 19/10/2015

Carbon cycle

Ocean-Atmosphere coupling

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. DeforestationSigman and Boyle 2000, Nature

Source: IPCC Report. 2014

Preindustrial

Today

Projection for Year 2100

PETIT et al. 1999, Nature & IPCC Report 2014

Atmospheric CO2

CO2 + H2O ⇒ H2CO3

H2CO3⇒ H+ + HCO3–

Decreases pH of ocean

H+ + CO32– ⇒ HCO3

–

Reducing CO32– in ocean

CaCO3 Ca2+ + CO32-

Mineral Dissolution

Mineral formation

Ocean Acidification

Excess absorption of CO2 by

ocean reduces its pH, it is

called Ocean acidification

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

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

11B80%

10B20%

Atomic number = 5

Atomic mass = 10.81

Relative Abundance of isotopes

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

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 acid11-10KB = 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 ‰

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

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

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-MSfacility at NCAOR

Thank You