Hi I have a number of δ13C (from AMS dating) values for the same species of freshwater gastropods in Indonesia, that show different δ13C values in the Holocene and Pleistocene and I want to understand why this is happening. I have tried to research what can cause changes in δ13C but I am turning up results about human diets and differences between terrestrial, freshwater, and marine plants. I have come across nothing to explain why the values would be changing in one species over time.
The results are uncorrected samples dated c. 9-10,000 BP with δ13C = -11, while uncorrected Pleistocene samples dated to between c. 17-25,000 BP have δ13C = -6.
These values do not correlate with how I understood δ13C values to behave. If freshwater plants are meant to have a general value between -35 and -25 then shouldn't a gastropod that lives 100% in that environment have a similar δ13C? and shouldn't that be broadly stable over time too?
I would really appreciate if someone could point out the obvious thing I am missing or point me towards an explanation as I would really like to understand why I am seeing these different results.
Hi Kim,
d13C value in organic matter (plants etc) is different (lighter) than the d13C in carbonates (heavier). Gastropod shells composed of calcium carbonate and the analyzed d13C value in gastropods depends on the isotopic fractionation of C isotopes during the formation of carbonate shells (habitat). And, the isotopic fraction in turn depends on other parameters (temp, salinity, etc). These could be the possible reason behind the temporal variation of d13C in gastropods.
All you need to do a little search to get more explanation on my point. (paleoenvironment/isotopic fractionation).
May this article help:
M. Wallace , G. Jones , M. Charles , R. Fraser , P. Halstead , T.H.E.
Heaton & A. Bogaard (2013) Stable carbon isotope analysis as a direct means of inferring
crop water status and water management practices, World Archaeology, 45:3, 388-409, DOI:
10.1080/00438243.2013.821671
To link to this article: https://doi.org/10.1080/00438243.2013.821671
Imprecision may relate to a similar process of pole reversals, magnetic breakdown and enrichment of 13C ~ 42,000 year ago, and the flux of ionizing radiation?
Cooper,, A., Turney, C.S. M., Palmer, J., Hogg, McGlone, M. Wilmshurst. J., 2021, A global environmental crisis 42,000 years ago., Science, Vol. 371, Issue 6531, p. 811-818. DOI: 10.1126/science.abb8677nrichment