Bomb-pulse radiocarbon dating as a method for verifying atmospheric CO2 uptake during carbonate precipitation

Dr Kari Finstad1, Dr Megan Smith1, Dr Gregory Dipple2, Dr Georges  Beaudoin3, Dr Naomi Marks1, Dr Roger Aines1

1Lawrence Livermore National Laboratory, Livermore, United States, 2University of British Columbia, Vancouver, Canada, 3Université Laval, Quebec City, Canada

Precipitation of carbonate minerals is one of the most stable methods for removing carbon dioxide (CO2) from the atmosphere. Carbon mineralization occurs passively during the alteration of ultramafic rocks as cations (Mg2+ and Ca2+) are released and react with dissolved bicarbonate (HCO3-) to precipitate carbonate minerals. This process has been observed occurring naturally in numerous ultramafic settings, and previous studies have confirmed that actively precipitating systems incorporate modern atmospheric CO2 by measuring F14C > 1. There is a lot of interest in harnessing carbon mineralization as a CO2 sequestration strategy, however a method to account for carbon uptake is necessary. Here we report on our efforts to determine if bomb-pulse radiocarbon dating can be used to quantify atmospheric carbon sequestration and determine rates of precipitation during carbon mineralization.

We first validated our method by analyzing carbonate samples with known dates of precipitation at three time-points along the bomb curve. Two out of the three samples produced results within one year of the known sample precipitation date. We hypothesize that the sample which did not produce the expected result had an additional biological influence, as indicated by the d13C value. Samples from a suite of different ultramafic environments were then analyzed to further explore the applicability of this method, including a banded travertine to determine if calculating a rate of precipitation was possible. We conclude that bomb-pulse radiocarbon dating can be used to quantify the incorporation of modern atmospheric carbon during precipitation in certain environments, but calculating a rate of precipitation will be challenging and requires additional study. Careful sample selection is required, as is an understanding of local carbon cycling at individual sites.


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Date

Nov 08 - 19 2021