Assessing anoxia, recovery and carbonate production setback in a hemipelagic Tethyan basin during the Toarcian Oceanic Anoxic Event (Western Carpathians)

Hardground, gap and thin black shale: spatial heterogeneity of arrested carbonate sedimentation during the Jenkyns Event (T-OAE) in a Tethyan pelagic Basin (Gerecse Mts, Hungary)

“…This is coherent with enhanced primary productivity occurring from the base of the Toarcian, followed by enhanced thermohaline stratification promoting anoxia in the core of the event (Bucefalo Palliani et al, 2002;Mattioli et al, 2009). A biocalcification crisis simultaneous with the Jenkyns Event severely affected both carbonate platforms and pelagic carbonate factories (Mattioli et al, 2009;Trecalli et al, 2012;Ettinger et al, 2021;Krencker et al, 2020;Müller et al, 2020b). Brachiopod δ 11 B-pH data imply that seawater pH started to drop, in multiple steps, already after the Pliensbachian/Toarcian boundary, reaching the minimum (~7.2; a total drop of 0.4-0.5 in pH values) immediately before and during the Jenkyns Event, that suggests a significant global lowering of seawater pH.…”

“…This negative CIE is well-represented at Peniche (Hesselbo et al, 2007), but it is stratigraphically not documented in the Gerecse sections. The Pliensbachian/Toarcian Event is followed by a broad positive δ 13 C excursion, likely related to enhanced organic production and carbon burial on a global scale in the Polymorphum (=Tenuicostatum) Zone preceding the pronounced negative CIE at the T-OAE (Hesselbo et al, 2007;Hermoso et al, 2012;Müller et al, 2020b). This positive excursion is also missing at both the Tölgyhát and Kisgerecse sections, only a highly condensed ~5 cm thick bed is assigned to the Tenuicostatum Zone (Géczy, 1984;1985;Kovács, 2012) (Fig.…”

“…Multiple studies have suggested a calcification crisis that spans the Jenkyns Event (Mattioli et al, 2009;Trecalli et al, 2012;Ettinger et al, 2021), although brachiopod shell-based δ 11 B-pH data and a carbonate saturation model imply that the development of triggering factors commenced earlier, already at the Pliensbachian/Toarcian Event (Krencker et al, 2020;Müller et al, 2020a). Shallow-water carbonate platforms, carbonate production in epicontinental basins and hemipelagic-pelagic settings open to the Tethys Ocean were all severely affected (Mattioli et al, 2009;Trecalli et al, 2012;Suan et al, 2018;Müller et al, 2020b). Several mechanisms have been postulated for interpreting this calcification crisis.…”

“…First, increasing global seawater temperature and associated acceleration of hydrological cycle and eutrophication of the water column (Suan et al, 2008a) or, alternatively, thermohaline stratification of surface waters triggered a decrease in nutrient levels of surface waters, adversely affecting the calcareous phytoplankton (Mattioli et al, 2009). Second, a eustatic sea-level rise may have resulted in the drowning of carbonate platforms and, as a consequence, also in carbonate shortage in epicontinental basinal settings (Bodin et al, 2010;Léonide et al, 2012;Pittet et al, 2014), which could also explain the carbonate shortage in hemipelagic-pelagic ocean-facing basins (Müller et al, 2020b). Third, ocean acidification could have developed due to the input of excess CO 2 into the ocean-atmosphere system, lowering both the seawater pH and calcite saturation level (Ω<1) (Trecalli et al, 2012;Ettinger et al, 2021;Müller et al, 2020a).…”

Impact of Seawater Inorganic Carbon Chemistry on Element Incorporation in Foraminiferal Shell Carbonate

“…Because of the ocean's large role in mitigating anthropogenic carbon, predicting the effects of future climate change relies on understanding the processes involved, such as the ocean uptake of CO 2 and its reaction with water, and this can be achieved through reconstructions of past atmospheric CO 2 levels and ocean chemistry. The complete marine inorganic carbon chemistry can be computed when at least two of its six parameters (pCO 2 , dissolved inorganic carbon concentration ([DIC]), [CO 3 2 ], [HCO 3 ], pH and total alkalinity) are known parameters of the ocean's carbonate system, both subrecent (e.g., Hönisch & Hemming, 2005;Raitzsch et al, 2018) and in deep time (e.g., Müller et al, 2020;Pagani et al, 2005). Commonly applied isotopic ratiobased proxies for past sea water carbon reconstructions include the boron isotopic composition of calcareous organisms (e.g., corals, foraminifera; Foster & Rae, 2016;Hemming & Hanson, 1992) and the carbon isotopic composition of alkenones (long-chained unsaturated methyl and ethyl n-ketones; Pagani, 2014;Pagani et al, 2002).…”