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

Latest Triassic and Early Jurassic Spiriferinida (Brachiopoda) of Zealandia(New Zealand and New Caledonia)

The Late Triassic spiriferinides of Zealandia include the endemic or Austral genera Rastelligera, Psioidea and Psioidiella, and the cosmopolitan Zugmayerella. Mentzelia kawhiana is revised and placed in Callospiriferina. It appears in the late Rhaetian and is found in the Téremba Terrane in New Caledonia and throughout the Murihiku Terrane in New Zealand. The spiriferinides were severely affected at the Triassic-Jurassic boundary in Zealandia as elsewhere, but a moderately diverse fauna developed in the Early Jurassic. This has strong links to South America, and affinities with southern Europe and North Africa. In this study, a total of six species of Jurassic spiriferinides are recognised. Callospiriferina ongley is present in middle and late Hettangian and Sinemurian faunas. It is succeeded in the Pliensbachian and early Toarcian by Callospiriferina radiata. Two species of Spiriferina are recognised. S. sophiaealbae n. sp. first appears in the Middle Hettangian and is present in the Southland and Kawhia Synclines until the early Toarcian. S. arakiwa n. sp. is found mainly on the southwest limb of the Southland Syncline in the Pliensbachian and early Toarcian. The non-costate European genus Cisnerospira is represented in Zealandia by the small C. antipoda n. sp. This species ranges from Hettangian to early Toarcian. Two specimens of a spiriferinide with a costate sulcus are tentatively identified as Dispiriferina sp. cf. D. chilensis. The highest stratigraphic level at which Zealandian spiriferinides have been found is that of the Dactylioceras band at Kawhia, which is correlated with the Crassum Subzone of the Bifrons Zone (highest Early Toarcian) and includes three species of spiriferinide. This suggests that the Zealandian spiriferinides survived the Toarcian Event, only to meet their demise slightly later.

Reduced plate motion controlled timing of Early Jurassic Karoo-Ferrar large igneous province volcanism

Past large igneous province (LIP) emplacement is commonly associated with mantle plume upwelling and led to major carbon emissions. One of Earth's largest past environmental perturbations, the Toarcian oceanic anoxic event (T-OAE; ~183 Ma), has been linked to Karoo-Ferrar LIP emplacement. However, the role of mantle plumes in controlling the onset and timing of LIP magmatism is poorly understood. Using global plate reconstruction models and Lower Toarcian sedimentary mercury (Hg) concentrations, we demonstrate (i) that the T-OAE occurred coevally with Karoo-Ferrar emplacement and (ii) that timing and duration of LIP emplacement was governed by reduced Pangean plate motion, associated with a reversal in plate movement direction. This new model mechanistically links Earth's interior and surficial processes, and the mechanism is consistent with the timing of several of the largest LIP volcanic events throughout Earth history and, thus, the timing of many of Earth's past global climate change and mass extinction events.

Enhanced phosphorus recycling during past oceanic anoxia amplified by low rates of apatite authigenesis

Enhanced recycling of phosphorus as ocean deoxygenation expanded under past greenhouse climates contributed to widespread organic carbon burial and drawdown of atmospheric CO2. Redox-dependent phosphorus recycling was more efficient in such ancient anoxic marine environments, compared to modern anoxic settings, for reasons that remain unclear. Here, we show that low rates of apatite authigenesis in organic-rich sediments can explain the amplified phosphorus recycling in ancient settings as reflected in highly elevated ratios of organic carbon to total phosphorus. We argue that the low rates may be partly the result of the reduced saturation state of sediment porewaters with respect to apatite linked to ocean warming and acidification and/or a decreased availability of calcium carbonate, which acts as a template for apatite formation. Future changes in temperature and ocean biogeochemistry, induced by elevated atmospheric CO2, may similarly increase phosphorus availability and accelerate ocean deoxygenation and organic carbon burial.

Marine temperatures underestimated for past greenhouse climate

Understanding the Earth's climate system during past periods of high atmospheric CO₂ is crucial for forecasting climate change under anthropogenically-elevated CO₂. The Mesozoic Era is believed to have coincided with a long-term Greenhouse climate, and many of our temperature reconstructions come from stable isotopes of marine biotic calcite, in particular from belemnites, an extinct group of molluscs with carbonate hard-parts. Yet, temperatures reconstructed from the oxygen isotope composition of belemnites are consistently colder than those derived from other temperature proxies, leading to large uncertainties around Mesozoic sea temperatures. Here we apply clumped isotope palaeothermometry to two distinct carbonate phases from exceptionally well-preserved belemnites in order to constrain their living habitat, and improve temperature reconstructions based on stable oxygen isotopes. We show that belemnites precipitated both aragonite and calcite in warm, open ocean surface waters, and demonstrate how previous low estimates of belemnite calcification temperatures has led to widespread underestimation of Mesozoic sea temperatures by ca. 12 °C, raising estimates of some of the lowest temperature estimates for the Jurassic period to values which approach modern mid-latitude sea surface temperatures. Our findings enable accurate recalculation of global Mesozoic belemnite temperatures, and will thus improve our understanding of Greenhouse climate dynamics.

Ocean warming affected faunal dynamics of benthic invertebrate assemblages across the Toarcian Oceanic Anoxic Event in the Iberian Basin (Spain)

The Toarcian Oceanic Anoxic Event (TOAE; Early Jurassic, ca. 182 Ma ago) represents one of the major environmental disturbances of the Mesozoic and is associated with global warming, widespread anoxia, and a severe perturbation of the global carbon cycle. Warming-related dysoxia-anoxia has long been considered the main cause of elevated marine extinction rates, although extinctions have been recorded also in environments without evidence for deoxygenation. We addressed the role of warming and disturbance of the carbon cycle in an oxygenated habitat in the Iberian Basin, Spain, by correlating high resolution quantitative faunal occurrences of early Toarcian benthic marine invertebrates with geochemical proxy data (δ18O and δ13C). We find that temperature, as derived from the δ18O record of shells, is significantly correlated with taxonomic and functional diversity and ecological composition, whereas we find no evidence to link carbon cycle variations to the faunal patterns. The local faunal assemblages before and after the TOAE are taxonomically and ecologically distinct. Most ecological change occurred at the onset of the TOAE, synchronous with an increase in water temperatures, and involved declines in multiple diversity metrics, abundance, and biomass. The TOAE interval experienced a complete turnover of brachiopods and a predominance of opportunistic species, which underscores the generality of this pattern recorded elsewhere in the western Tethys Ocean. Ecological instability during the TOAE is indicated by distinct fluctuations in diversity and in the relative abundance of individual modes of life. Local recovery to ecologically stable and diverse post-TOAE faunal assemblages occurred rapidly at the end of the TOAE, synchronous with decreasing water temperatures. Because oxygen-depleted conditions prevailed in many other regions during the TOAE, this study demonstrates that multiple mechanisms can be operating simultaneously with different relative contributions in different parts of the ocean.