GLOBAL OCEAN ACIDIFICATION IN THE AFTERMATH OF THE MARINOAN GLACIATION

During the Cryogenian-Ediacaran transition the Earth underwent substantial changes in its climatic, tectonic and bio-geochemical cycles. Within the Cryogenian at least two global-scale ice ages led to profound modifications in the interplay between oceans, atmosphere and continents (e.g. Hoffman et al., 1998). In this study, we investigate boron and carbonate carbon isotope patterns recorded in cap dolostones deposited in the direct aftermath of the younger Cryogenian glaciation (~635 Ma) on four different cratons.

Cap dolomites of the Yangtze Platform (South China block), Kazakhstan and Namibia (Kalahari and Congo craton) show similar B isotope and hence similar ocean-pH pattern although the nadir in ocean acidification differs between the investigated cratons/blocks. Of all blocks, the most pronounced negative excursions of -12‰ in δ¹¹B and down to -6‰ in δ¹³C, occur in Namibia (Congo Craton, Kasemann et al., 2010) and South China whereas a drop from 8.0 to 1.8‰ in δ¹¹B and down to ‑3‰ in δ¹³C is visible in Kazakhstan (Malyi Karatau range). Therefore, a transient decrease by >1 pH units down to a minimum ocean-pH of about 7 during deglaciation is indicated.

Our approach of a multi craton correlation provides evidence for a global ocean acidification event, potentially associated with enhanced atmospheric pCO2 during time of deglaciation.

[1] Hoffman et al. (1998) Science 281, 1342–1346.

[2] Kasemann et al. (2010) Geology 38, 775-778.