Volcanically driven short-term, regional-scale cooling during the early Paleogene Greenhouse?

Sediment cores from the Mid-Norwegian Margin, IODP Expedition 396 recovered several glendonite (calcite) pseudomorphs after cold-water ikaite, CaCO₃•6H₂O, within sediments deposited during the Paleocene-Eocene Thermal Maximum hyperthermal and the early Eocene greenhouse. This presents an apparent climate paradox, since during this time interval, deep sea bottom water temperatures are not believed to have been lower than c. 10 °C anywhere on Earth, mostly much warmer (Meckler et al., 2022 and references therein), far above temperatures typical for natural ikaite formation (Vickers et al., 2022 and references therein). The glendonites are found in close association with ash horizons from the nearby North Atlantic large igneous province (NAIP), with some actually in the infill of a hydrothermal. This, coupled with the presence of glendonites in sediments of the same age from Svalbard and Denmark (Spielhagen and Tripati, 2009; Vickers et al., 2020), may point to volcanically-driven climate and environmental changes in this region, perhaps on temporal and spatial scales hitherto unresolved by global-scale datasets.

 

Here, we present reconstructed ikaite crystallisation temperatures from clumped isotope palaeothermometry and biomarker sea surface and air temperature reconstructions from glendonite-bearing horizons in ash-rich sediments at four IODP Expedition 396 sites. We find that the glendonites indicate bottom water temperatures considerably lower than the majority of other localities so far studied for this time interval (0 – 10 °C). The biomarker signals are harder to interpret, but may indicate sea surface and air temperatures significantly lower than many other studies across this time interval. We discuss possible causes and mechanisms for this cooling, and the conditions driving ikaite growth, focussing on whether these both may be linked to NAIP volcanism.