Trecalli, A., Spangenberg, J., Adatte, T., Föllmi, K.B., Parente, M. (2012)
Carbonate platform evidence of ocean acidification at the onset of the early Toarcian oceanic anoxic event.
Earth and Planetary. Science Letters, 357–358, 214–225
The early Toarcian oceanic anoxic event (Early Jurassic; 183 Myr ago) is associated with one of the largest negative carbon isotope excursion (CIE) in the whole Phanerozoic (3–7%). Estimates of the magnitude and rate of CO injection in the ocean–atmosphere system are compatible with a scenario of
ocean acidiﬁcation. Many carbonate platforms drowned in the Pliensbachian, well before the early Toarcian event. In this paper we test the hypothesis of surface water ocean acidiﬁcation by presenting data from a resilient carbonate platform: the Apennine Carbonate Platform of southern Italy.
The studied sections document a dramatic shift of the carbonate factory from massive biocalciﬁcation to chemical precipitation. Lithiotis bivalves and calcareous algae (Palaeodasycladus mediterraneus), which were the most proliﬁc carbonate producers of Pliensbachian carbonate platforms, disappear
during the ﬁrst phase of the early Toarcian CIE, before the most depleted values are reached. We discuss the local versus supraregional signiﬁcance of this shift and propose a scenario involving abrupt decline of carbonate saturation, forced by CO release at the beginning of the early Toarcian CIE, followed by a calciﬁcation overshoot, driven by the recovery of ocean alkalinity. Attribution of the demise of carbonate platform hypercalciﬁers to ocean acidiﬁcation is supported by palaeophysiology and reinforced by experimental data on the detrimental effects of ocean acidiﬁcation on recent shellﬁshes and calcareous algae.