I have analysed δ13C and δ18O values in CaCO3 from the peat sediments (age late glacial and Holocene):

1) With CaCO3 concentrations aver. 1-2‰, the results obtained: δ13C = -34 to -33‰; δ18O = mostly -12 to -16 ‰;

2) With CaCO3 concentrations aver. 20-25%: δ13C = -34 to -29‰; δ18O = -4 to 20‰;

3) With CaCO3 concentrations aver. 1-5‰, the results obtained: δ13C = -31 to -23‰; δ18O = -23 to -18 ‰;

In general (based on literature): Δ13C values in peats range between -34 and -24 ‰ (Faure 1986) - CO2 evolved from such peats dissolves in groundwater and δ13C values of CO2aq range between -35 and -25 ‰ (fractionation factor -1.1 ‰, Clark and Fritz 1997) – HCO3- should be between -26 and -16 ‰ (fractionation factor 9 ‰, Romanek 1992) and CaCO3 values are expected to range between -25 and -15 ‰ (fractionation factor 1 ‰, Romanek 1992) – MUCH HIGHER THAN LISTED ABOVE

In case of the samples I analysed: If CaCO3 -34 to -29‰ then DIC (HCO3-) should be between -35 and -30‰ (fractionation factor 1 ‰, Romanek 1992), and further – CO2aq is expected to be between -44 and -40 ‰ (fractionation factor 9 ‰, Romanek 1992).

What is the reason for such low values?

1) Is it the methodological issue? Samples were analysed in the conventional method (Gas Bench) using phosphorus acid. The acid should dissolve CaCO3. Is it possible that organic matter was also dissolved? I have different information in this case. Please note that CaCO3 content is some samples was very low, i.e. 1-2 % but much higher, i.e. 20-30 % in others.

2) Is it possible that CO2 (and later HCO3-) incorporated into carbonates originated from the degradation of methane (very low δ13C values), gas very common on the bogs?

3) What is the origin of low δ18O values? Is it possible that the values reflect δ18O composition of organic matter?

I will appreciate any constructive help.

Regards,

Karina Apolinarska