Thermogenic methane release as a cause for the long duration of the PETM

Abstract

The Paleocene-Eocene Thermal Maximum (PETM) (∼56 Ma) was a ∼170,000-y (∼170-kyr) period of global warming associated with rapid and massive injections of 13 C-depleted carbon into the ocean-atmosphere system, reflected in sedimentary components as a negative carbon isotope excursion (CIE). Carbon cycle modeling has indicated that the shape and magnitude of this CIE are generally explained by a large and rapid initial pulse, followed by ∼50 kyr of 13 C-depleted carbon injection. Suggested sources include submarine methane hydrates, terrigenous organic matter, and thermogenic methane and CO 2 from hydrothermal vent complexes. Here, we test for the contribution of carbon release associated with volcanic intrusions in the North Atlantic Igneous Province. We use dinoflagellate cyst and stable carbon isotope stratigraphy to date the active phase of a hydrothermal vent system and find it to postdate massive carbon release at the onset of the PETM. Crucially, however, it correlates to the period within the PETM of longer-term 13 C-depleted carbon release. This finding represents actual proof of PETM carbon release from a particular reservoir. Based on carbon cycle box model [i.e., Long-Term OceanAtmosphere-Sediment Carbon Cycle Reservoir (LOSCAR) model] experiments, we show that 4-12 pulses of carbon input from vent systems over 60 kyr with a total mass of 1,500 Pg of C, consistent with the vent literature, match the shape of the CIE and pattern of deep ocean carbonate dissolution as recorded in sediment records. We therefore conclude that CH 4 from the Norwegian Sea vent complexes was likely the main source of carbon during the PETM, following its dramatic onset.carbon cycle | thermogenic methane | volcanism | climate change | PETM

Tropical Atlantic climate and ecosystem regime shifts during the Paleocene–Eocene Thermal Maximum

“…The CIE has a distinct shape: a rapid "onset" (1-5 kyr;Kirtland Turner and Ridgwell, 2016;Zeebe et al, 2016) followed by a prolonged (50-100 kyr) period, the "body", of stable low 13 C values and a recovery that lasts 42-82 kyr (Röhl et al, 2007;Abdul Aziz et al, 2008;Murphy et al, 2010;Westerhold et al, 2017) to values that remain slightly 13 C-depleted (0.5-1 ‰) relative to the latest Paleocene. This pattern is best explained by massive ( 1500 Gt) carbon input from at least one but likely multiple reservoirs in the shape of CO 2 and/or CH 4 ; (Dickens et al, 1995;Panchuk et al, 2008;Zeebe et al, 2009;Dickens, 2011;Zeebe, 2013;Frieling et al, 2016;Luo et al, 2016).…”

3D structure and formation of hydrothermal vent complexes at the Paleocene-Eocene transition, the Møre Basin, mid-Norwegian margin

“…In addition, the venting process has been related to greenhouse gas expulsion to the atmosphere, thereby providing a link to the transient climatic shift during the Paleocene-Eocene Thermal Maximum (PETM) Berndt et al, 2016). The climatic records during this period are well documented from several sections worldwide (Zachos et al, 2001;Zachos et al, 2008), and recent results show that the only drilled HTVC in the Vøring Basin (borehole 6607/12-1) formed during the PETM plateau, thereby demonstrating a relationship between the long duration of the PETM and the gas venting (Frieling et al, 2016). Similar kilometer-scale hydrothermal vent structures have been described elsewhere in seismic data (Hansen et al, 2005;Planke et al, 2005;Grove, 2013;Berndt et al, 2016) and in outcrops (Svensen et al, 2006) in several basins.…”

“…Continental breakup was accompanied by large-scale igneous activity, forming kilometer-thick basaltic complexes on both sides of the continent-ocean boundary (Brekke, 2000). At the same time, extensive igneous sheet intrusions were emplaced in the Møre Basin, and hundreds of hydrothermal vent complexes were formed by pressure increase and devolatilization in the contact aureoles around the sills (Planke et al, 2005Svensen et al, 2004;Svensen and Jamtveit, 2010;Frieling et al, 2015). The Møre Basin subsequently subsided, leading to deposits of marine mud and ooze, and finally thick sequences of glacially derived sediments and slide material (Faleide et al, 2008).…”

“…The PETM is coeval with the initial opening of the northeast Atlantic Ocean (Storey et al, 2007), which has been linked to magma emplaced in the Møre Basin Frieling et al, 2016). Although no direct evidence for contact aureoles have been identified during the seismic interpretation, contact metamorphism around sills is well understood and led to the generation of CH 4 , CO 2 , and H 2 O from heating of organic-bearing sedimentary rocks (Aarnes et al, 2015).…”

Determining climate change impacts on ecosystems: the role of palaeontology

“…The cause of the rapid climate change leading to these transient events is still under debate (see Frieling et al . ); it is likely to be different for each given their different timing with regards to external forcing (Zeebe et al . ).…”