Violent release of thermogenic gases as a driver in the Paleogene climate & carbon cycle?

Ancient global warming events differ fundamentally from anthropogenic climate change, yet these events provide a unique opportunity to study how the climate and carbon cycle operate on timescales of centuries to millennia. We can learn much from the environmental consequences of ancient warming events, but detailed reconstructions of the causes of such ancient warming events are essential to validate their relevance for climate projections.

The global warming events that mark the Paleocene and Eocene provide valuable 'geological experiments' of climate and carbon cycle response to a runaway greenhouse climate. The most extreme of these events, the Paleocene-Eocene Thermal Maximum (ca. 56 Million years ago) is marked by 5 degree C of global warming within a few thousands of years. Intriguingly, around the same time, massive volcanic activity, forming a "large igneous province" or LIP, centered on present-day Iceland, led to the opening of the North Atlantic Ocean.

A total of ~10 million cubic kms erupted in this LIP over a span of several millions of years in the late Paleocene and early Eocene and CO2 brought up from deep within the Earth and emitted from these eruptions present a likely cause of a rise in atmospheric CO2 levels and global temperatures over that period. Moreover, seismic imaging of the seabed offshore Norway has revealed a second greenhouse gas release mechanism, in the form of 100s to 1000s of km-wide craters and chimneys on and below the ancient seabed. Brief phases of intense and widespread magma intrusion heated carbon-rich sediment layers deep below the seabed producing large volumes of gases, particularly methane, CO2, and water. The chimneys and craters formed when gases were released by violent venting. Each intrusive phase rapidly activated many chimneys and craters at once, emitting potentially large volumes of greenhouse gases. Yet, until recently the absence of suitable tools and material meant it was difficult to demonstrate the connection between the massive LIP volcanism and more rapid climate change, let alone quantify its impact.

We study the climatic influence of these vents, particularly with respect to the methane and CO2 generated around magmatic intrusions and released by violent venting. Expedition 396 will obtain two new drill cores from the center of one of the vents, and from just outside its crater rim. This unique material will allow us to reconstruct a detailed history of vent activity.

Age-diagnostic fossils and stable carbon isotopes will be used to reconstruct the time of crater formation, to date the sediment infill and the duration of activity. Sedimentary mercury concentration data has been developed as a tool over the past years to reconstruct past volcanic activity, and we will employ this tool to further understand the venting activity from outside the crater. These analyses are paired with other established tools to assess the effects of hot fluids on crater sediments, and utilize concentration spikes in elements that signal circulation of hydrothermal fluids, such as iron and manganese, to assess the influence of the hydrothermal plume on surrounding sea water.

Together, these new data will show when the crater formed, for how long it released gases and at what intensity. We use these new data in combination with existing data to reconstruct the potential contribution of venting on climate change. This will improve our understanding of ancient warming events, inform carbon cycle models and - (in)directly - (paleo)climate projections.