Shallow-water hydrothermal venting linked to the Palaeocene–Eocene Thermal Maximum

Abstract

The Palaeocene–Eocene Thermal Maximum (PETM) was a global warming event of 5–6 °C around 56 million years ago caused by input of carbon into the ocean and atmosphere. Hydrothermal venting of greenhouse gases produced in contact aureoles surrounding magmatic intrusions in the North Atlantic Igneous Province have been proposed to play a key role in the PETM carbon-cycle perturbation, but the precise timing, magnitude and climatic impact of such venting remains uncertain. Here we present seismic data and the results of a five-borehole transect sampling the crater of a hydrothermal vent complex in the Northeast Atlantic. Stable carbon isotope stratigraphy and dinoflagellate cyst biostratigraphy reveal a negative carbon isotope excursion coincident with the appearance of the index taxon Apectodinium augustum in the vent crater, firmly tying the infill to the PETM. The shape of the crater and stratified sediments suggests large-scale explosive gas release during the initial phase of vent formation followed by rapid, but largely undisturbed, diatomite-rich infill. Moreover, we show that these vents erupted in very shallow water across the North Atlantic Igneous Province, such that volatile emissions would have entered the atmosphere almost directly without oxidation to CO2 and at the onset of the PETM.

Large Igneous Province Control on Ocean Anoxia and Eutrophication in the North Sea at the Paleocene–Eocene Thermal Maximum

“…Further evidence of a shallow and restricted northern North Atlantic comes from IODP Sites U1567 and U1568, where five holes through the Modgunn hydrothermal vent complex were drilled, and 3D seismic mapping was performed. The results suggest that the Modgunn vent complex formed a few thousand years before the PETM onset under shallow marine waters, whereas other hydrothermal vent complexes in the Modgunn Arch might have developed under short-lived subaerial settings (Berndt et al, 2023), supporting the assumption that the proto-Northeast Atlantic was possibly very susceptible to topographic changes. The interpretation of sedimentological, palynological and 2D seismic stratigraphic data propose that a complex fragmentation of both the northeastern North Atlantic (Norway-Greenland seaway) and the western North Atlantic (Greenland-Scotland Ridge) occurred at the Paleocene-Eocene, as a result of regional tectonic uplift (Hovikoski et al, 2021).…”

“…Although we are unable to correlate Sites U1567 and U1568 with the other records in Figure 5 as the CIEs are of slightly lower resolution in places (Berndt et al, 2023), we do note that these sites revert to unlaminated sedimentation during the PETM main phase which is consistent with their interpreted shallow marine water depth (Berndt et al, 2023). By contrast, the rapid infill of the Modgunn hydrothermal vent complex on the Norwegian continental margin means that the water depth of the lowermost-PETM strata may be considerably greater than at the top of the vent infill, which is still within the PETM, because Hole U1568A contains ∼80 m of syn-PETM infill (Berndt et al, 2023). Therefore, the potential effect of water depth on recording anoxia may be affected by the rapid infill of the vent crater that was initiated as a significant bathymetric depression.…”

“…Although we cannot accurately reconstruct paleo water depth, the sites with lower sedimentation rates appear to retain laminations for a longer period of time (e.g., E 8X) which may indicate that deeper sites were affected by anoxia/euxinia for longer as sedimentation rates tend to be highest in shallow and nearshore settings (e.g., Svalbard site BH9/05, where palynology interpretations indicate marginal marine conditions, Harding et al, 2011; Fur, which has been interpreted as outer neritic, Schoon et al, 2015). Although we are unable to correlate Sites U1567 and U1568 with the other records in Figure 5 as the CIEs are of slightly lower resolution in places (Berndt et al, 2023), we do note that these sites revert to unlaminated sedimentation during the PETM main phase which is consistent with their interpreted shallow marine water depth (Berndt et al, 2023). By contrast, the rapid infill of the Modgunn hydrothermal vent complex on the Norwegian continental margin means that the water depth of the lowermost-PETM strata may be considerably greater than at the top of the vent infill, which is still within the PETM, because Hole U1568A contains ∼80 m of syn-PETM infill (Berndt et al, 2023).…”

“…Regional tectonic uplift was primarily controlled by the upward movement of the Icelandic mantle plume between Greenland and Scotland during the opening of the Northeast Atlantic Ocean (Hartley et al, 2011;Jones, Hoggett, et al, 2019). The correlation between tectonic uplift and NAIP activity is well documented, with thousands of intruded sills recognized in 2D and 3D seismic stratigraphy in the Norwegian Sea and northwestern North Sea (Berndt et al, 2023;Conway-Jones & White, 2022;Hartley et al, 2011;Jones, Percival, et al, 2019;Svensen et al, 2004). Increased volcanic activity around the PETM onset is also documented by sedimentary mercury (Hg) and Hg isotopes in the North Sea, Spain, Svalbard, Denmark, and the Arctic Ocean (Jin et al, 2023;Jones, Percival, et al, 2019;Kender et al, 2021;Tremblin et al, 2022).…”

“…The North Sea and the northern Atlantic Ocean were connected by a shallow seaway, however this connection was possibly cut off by the NAIP uplift (Hartley et al., 2011; Zacke et al., 2009). NAIP emplacement not only modified the North Sea–North Atlantic connection, but also reorganized and narrowed the Norwegian–Greenland seaway, which became a shallow water strait around the PETM (Berndt et al., 2023; Hovikoski et al., 2021; Planke et al., 2023). Since the Norwegian–Greenland seaway was further connected to the Arctic Ocean (Prøis, 2015), the shallowing of the seaway would result in the partial isolation of the Arctic Ocean (Jones et al., 2023).…”