All the proxies systems that are part of the Palaeo-CO2 Project are based on the utilisation of marine sediments.


Advantages of using marine-sediments

Map of ODP drill sites (from IODP)

Map of ODP drill sites (from IODP)

Joides Resolution Drill Ship (from IODP)

Joides Resolution Drill Ship (from IODP)

The deep ocean is blanketed by sediments that in some parts are almost exclusively made of the slow accumulations of the shelly and soft parts of ancient marine organisms. Thanks to many years of ocean drilling (see here, above left and right) and a remarkable community effort there is an excellent, near continuous coverage of well-dated sediment stretching back at least 65 million years. This allows high-resolution climate and CO2 records to be generated on the same material.


Disadvantages of using marine sediments

Delta pCO2 from the Takahashi dataset (here)

Delta pCO2 from the Takahashi dataset (here)

The image above shows the difference between the pCO2 of the surface ocean and the atmosphere (postive, hot colours = the ocean is a source of CO2 to the atm. and vice versa). As can be seen there are quite significant differences in places between atmosphere and ocean with respect to CO2 content. This means we need to be careful where we choose our sites and ideally use records from multiple locations to minimise the effect of changing CO2 disequilibrium.


Proxies we use (in alphabetic order):

The Boron Isotopic Composition of Foraminifera.

The boron isotopic composition of marine carbonates is expressed as δ11B is sensitive to the pH of the seawater in which they grew. pH is one variable of the ocean carbonate system and can be used to reconstruct atmospheric CO2. Click here to find out more.

Modern culture of coccolithus pelagicus – eachalga is ~14 µm across (photo credit: Samantha Gibbs).

Modern culture of coccolithus pelagicus – eachalga is ~14 µm across (photo credit: Samantha Gibbs).

The isotopic composition of marine carbon.

The isotopic composition of carbon of a number of substrates can be used to provide information about CO2. Established and emerging proxies in the marine-realm include:

  • δ13C of sedimentary alkenones is a function of the CO2 content of the seawater in which the alkenone producing phytoplankton grew. Click here to find out more.
  • δ13C of dinoflagellate cysts (click here) and δ13C of coccoliths (click here) are emerging proxy of CO2.