Warm afterglow from the Toarcian Oceanic Anoxic Event drives the success of deep-adapted brachiopods

C V Ullmann,T Klein,T M Lenton,M Aberhan,S A Kasemann,S P Hesselbo,R Boyle,V Piazza,L V Duarte

doi:10.1038/s41598-020-63487-6

C V Ullmann, T Klein + Show 7 more

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Many aspects of the supposed hyperthermal Toarcian Oceanic Anoxic Event (T-OAE, Early Jurassic, c. 182 Ma) are well understood but a lack of robust palaeotemperature data severely limits reconstruction of the processes that drove the T-OAE and associated environmental and biotic changes. New oxygen isotope data from calcite shells of the benthic fauna suggest that bottom water temperatures in the western Tethys were elevated by c. 3.5 °C through the entire T-OAE. Modelling supports the idea that widespread marine anoxia was induced by a greenhouse-driven weathering pulse, and is compatible with the OAE duration being extended by limitation of the global silicate weathering flux. In the western Tethys Ocean, the later part of the T-OAE is characterized by abundant occurrences of the brachiopod Soaresirhynchia, which exhibits characteristics of slow-growing, deep sea brachiopods. The unlikely success of Soaresirhynchia in a hyperthermal event is attributed here to low metabolic rate, which put it at an advantage over other species from shallow epicontinental environments with higher metabolic demand.

Highlights

The Early Jurassic Toarcian Stage is characterized by possibly the largest global carbon cycle perturbation since the beginning of the Mesozoic (c. 250 Ma)[1,2]
The earliest Toarcian is marked by the recovery from a negative CIE at the Pliensbachian-Toarcian boundary[5,9] and linked to early magmatism of the Karoo-Ferrar large igneous province[10,11,12,13]
The most characteristic feature of the Toarcian Oceanic Anoxic Event (T-OAE) carbon cycle perturbation is a pronounced negative CIE of several permil in magnitude commencing in the uppermost tenuicostatum ammonite zone[1,3,4,7,13] (Fig. 2)

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Introduction

The Early Jurassic Toarcian Stage is characterized by possibly the largest global carbon cycle perturbation since the beginning of the Mesozoic (c. 250 Ma)[1,2]. After the peak of the negative CIE, carbon isotope ratios rose strongly with δ13C values reaching up to around +6‰ in belemnite calcite in the UK sections[6,17] and >+5‰ in brachiopod calcite in Portugal[5,18].

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