Global hydroclimate perturbations during the Toarcian oceanic anoxic event

An intensification of the hydrological cycle is an expected consequence of global warming, and this will likely lead to spatially variable precipitation and drought extremes, and more intense tropical storms. Deep time hyperthermal events, characterised by large-scale carbon release and transient global warming, have the potential to provide insights into the nature and magnitude of hydroclimate changes in response to warming. The Toarcian oceanic anoxic event (T-OAE, or Jenkyns Event, ∼183 Ma) was a severe hyperthermal, and is associated with evidence for marked changes in hydroclimate, including: intensified tropical cyclone activity, an increase in global chemical weathering rates, and elevated freshwater runoff and terrigenous sediment fluxes to basins. Nevertheless, key knowledge gaps exist regarding the scale, significance, distribution and interpretation of these changes. Here, we review the evidence for T-OAE hydroclimate changes based on published data from 109 sites. Although these sites are primarily concentrated in the northwest Tethys region, we show that evidence for T-OAE hydroclimate change was globally distributed, and that most sites (63 %) record evidence consistent with an intensification of hydrological cycling under hotter conditions likely characterised by weather/precipitation extremes. Evidence for enhanced storm activity is common; recorded at up to a third of sites from both low and middle latitudes. This evidence is consistent with climate model predictions of increased tropical cyclone intensity and a poleward shift in storm tracks under elevated atmospheric CO₂. Evidence for enhanced weathering and terrigenous fluxes is also common. This evidence, coupled with the evidence for increased storminess, may help explain increased turbidite deposition during the event recorded at some deep-water sites. Although affected by geographic and perhaps sedimentological biases, our findings underline how hydroclimate change was an inherent and perhaps defining characteristic of the T-OAE, potentially of equal paleoenvironmental significance to the seawater deoxygenation that originally defined the event.