ASHLANTIC: Volcano-climate interactions during the Palaeocene-Eocene Thermal Maximum (PETM)

The Earth?s climate is vitally important for life on Earth and over long time scales it is relatively stable. The continued evolution of life over the last 4 billion years indicates that the climate has stayed within the narrow range that allows life to exist. However, there have been times when there have been mass extinctions, which suggests that there are occasional events that rock the climate out of its normal stable state. We know that the climate varies on a range of time scales; from local weather phenomena over hours to days, to slow changes over millions of years. In extremely rare cases the climate can change very quickly, with the whole globe warming several degrees (°C) in just a few thousand years. These rapid climate change events coincide with the mass extinctions in the geological record, suggesting that they are a direct cause of environmental stress. One such event is the Palaeocene-Eocene Thermal Maximum (PETM), which occurred approximately 56 million years ago. We know from various pieces of evidence that there was an extreme (4-5 °C) global warming event in a short time period (<20,000 years, fast in geological time scales). This warming was caused by a huge release of carbon to the atmosphere increasing the greenhouse effect. What we do not know is where this carbon came from. Possibilities include the release from sea floor sediments, a meteorite impact, and volcanic eruptions. By improving our understanding of what may have caused the PETM and how the oceans and atmosphere reacted, we can improve our predictions and create better mitigation strategies now we are causing a rapid warming event of our own. The project ASHLANTIC focused on how large-scale volcanism may have affected the climate. The PETM occurred at the same time that huge volumes of lava were being erupted along the coast of Greenland and the UK, leading to the formation of the North Atlantic Ocean. These lavas emitted carbon directly as a magmatic gas, but they also heated up surrounding sediments as they moved through the crust. If these sediments were rich in organic material, such as oil, then this would have drastically increased the carbon emissions. ASHLANTIC used a variety of geological and analytical techniques to try and find out when the volcanoes were erupting and how this correlated with the changes in climate. We used novel geochemical methods to track the changes to climate in the North Sea area across PETM, including proxies for surface water temperatures, how oxygenated the water column was, how powerful the hydrological cycle was, and what types of rocks we being eroded and transported to the oceans. The Eastern North Sea warmed by over 10 °C at the start of the PETM, peaking at around 33 °C at the height of the event! There was a large increase in rainfall and river runoff, affected both old continents and new lava fields alike. This is one of the first times these methods have been combined for an individual section. Our research shows that there is strong evidence for increased volcanic activity in the few thousand years before the PETM starts, but is less obvious during the global warming event itself. This may mean that the volcanism was responsible for starting the global warming, but some other process, possibly as a feedback to the initial warming, kept the temperatures high for a long time. There are hundreds of volcanic ash layers after the PETM that originated huge explosive eruptions, the largest ever documented from basaltic volcanoes. However, we showed that instead of an increase in volcanic activity, these layers are evidence of a change in style of eruption to more explosive activity. This was likely to be caused by the volcanoes being submerged during the opening of the Northeast Atlantic Ocean. Ashlantic was a great success, both in terms of achieving its stated aims and providing a platform for further scientific endeavours. To follow on from this research, the Ashlantic team secured funding for two International drill cores that are scheduled for the coming years. The Integrated Ocean Discovery Program (IODP) Expedition 396 will collect samples from the Norwegian continental margin in 2021 and the International Continental Drilling Program (ICDP) will drill more Danish strata in 2022.

Objective A aimed to drill Danish sediments to define a new type locality for the PETM. The drilling was unsuccessful, but an ideal section was found by digging a 45 m long trench in the beach. The beach section is now one of the best preserved expanded PETM sections in the world. The results have laid the foundation for two drilling (IODP and ICDP) campaigns that are scheduled for the coming years. Objective B aimed to implement novel proxies for volcanic activity across the PETM. The use of Hg as a volcanic proxy was a great success, showing significant regional variations between sites. The cause(s) of these variations will be tested during the upcoming IODP and ICDP drilling campaigns. Geochemical fingerprinting and studies of volcanic ash morphologies in Danish sediments suggest that many eruptions occurred underwater. The results suggest that the Danish ash layers mark the transition of volcanic activity from subaerial to submarine as the ocean began to open.

Identifying the historical triggers and feedbacks of rapid changes to Earth's climate represents a major scientific challenge of our time, as these processes provide a valuable analogue for future environmental perturbations. A key and timely field of research is the role that volcanoes play in regulating, replenishing, and disturbing atmospheric and oceanic chemistry over time. In particular, periods when huge volumes of magma reached the Earth surface in a short time frame often coincide with major climate change, suggesting a causal relationship. However, given the complexity of the Earth system, the multiple effects of volcanism on the climate are poorly constrained. The primary aim of this project is to establish a precise temporal relationship between the Palaeocene-Eocene Thermal Maximum (PETM) and the 2nd major pulse of activity from the North Atlantic Igneous Province (NAIP). The PETM at 55.8 Ma is one of the most extreme global warming events in prehistorical times, which saw a rapid 5-6 °C warming due to the catastrophic release of carbon that affected marine and terrestrial ecosystems worldwide. To achieve this aim, this project will collect a borehole drill core through the Fur Formation in Denmark. This key locality provides a rare continuous sequence through the PETM on land, containing hundreds of tephra layers derived from the NAIP that are relatively unaltered. The analyses will combine high-precision stratigraphic scanning and radio-isotopic dating techniques to refine the timing of the onset, duration, and termination of the PETM. A range of novel geochemical techniques will then assess the role that the NAIP played in the start and/or end of this rapid climate change. The interdisciplinary nature and wide scope of this project will be of high impact and of great value to the scientific community. The project, based at a Norwegian Centre of Excellence at the University of Oslo, will foster excellent national and international collaboration.