Paleocene/Eocene carbon feedbacks triggered by volcanic activity

The Paleocene–Eocene Thermal Maximum (PETM) was a period of geologically-rapid carbon release and global warming ~56 million years ago. Although modelling, outcrop and proxy records suggest volcanic carbon release occurred, it has not yet been possible to identify the PETM trigger, or if multiple reservoirs of carbon were involved. Here we report elevated levels of mercury relative to organic carbon—a proxy for volcanism—directly preceding and within the early PETM from two North Sea sedimentary cores, signifying pulsed volcanism from the North Atlantic Igneous Province likely provided the trigger and subsequently sustained elevated CO2. However, the PETM onset coincides with a mercury low, suggesting at least one other carbon reservoir released significant greenhouse gases in response to initial warming. Our results support the existence of ‘tipping points’ in the Earth system, which can trigger release of additional carbon reservoirs and drive Earth’s climate into a hotter state.

Enhanced volcanism associated to the emplacement of the North Atlantic Igneous Province during the PETM evidenced by mercury anomalies in Pyrenean foreland sections

<p>The Paleocene-Eocene thermal maximum (PETM; ~55.6 Ma) is one of the most pronounced and the best known of the transient hyperthermal events of the Paleogene. The PETM is characterized by global warming, a significant perturbation of the carbon cycle, and a large perturbation of the biosphere. This extraordinary event is recorded by sharp negative carbon excursions (NCIE) in both oceanic and terrestrial carbonates. The sequence of events triggering this disturbance and the source of the <sup>13</sup>C-depleted carbon for the NCIE remains controversial. External perturbation such as volcanism, associated with the setup of the North Atlantic Igneous Province (NAIP), is suspected to be one of the mechanisms responsible for this abrupt climate upheaval. One proxy for investigating the possible link between the establishment of the NAIP and perturbation associated with the PETM is to study mercury (Hg) concentrations record in marine and continental sedimentary successions.</p><p>In this study, we present new high-resolution mercury and stable isotopic records from peripheral basins of the Pyrenean orogen across the PETM. The four studies sections vary from continental to bathyal deposit environment and offer the potential to evaluate how major climatic disturbances are associated with the PETM record through a continental to marine transect.</p><p>The data obtained reveal the occurrence of two main NCIEs. Based on biostratigraphy and similarity of shape and amplitude of the isotopic excursions with global records, the largest NCIE is interpreted as the PETM. This sharp excursion is preceded by another one that we interpreted as the Pre-Onset Excursion (POE), founded in some other profiles worldwide. These two NCIEs are systematically associated with important mercury anomalies, whatever the environment considered. Increase in Hg contents shows no correlation with clay or total organic carbon contents, suggesting that the influences of local processes or Hg scavenging by organic matter appear to be insignificant. These results show that multiple pulses of volcanism, probably associated with the emplacement of the NAIP, contributed to the onset and the long duration of the PETM. In addition, our study highlights the possibility to get reliable information about past extreme climate events from sedimentary successions even if deposited within active tectonic domains.</p><p>This work is financed and carried out within the framework of the BRGM-TOTAL Source-to-Sink project.</p>

Calcium isotope composition of Morozovella over the late Paleocene–early Eocene

Ocean acidification (OA) during the Paleocene-Eocene thermal maximum (PETM) likely caused a biocalcification crisis. The calcium isotope composition (δ44/40Ca) of primary carbonate producers may be sensitive to OA. To test this hypothesis, we constructed the first high-resolution, high-precision planktic foraminiferal δ44/40Ca records before and across the PETM. The records employ specimens of Morozovella spp. collected from Ocean Drilling Program Sites 1209 (Shatsky Rise, Pacific Ocean) and 1263 (Walvis Ridge, Atlantic Ocean). At Site 1209, δ44/40Ca values start at –1.33‰ during the Upper Paleocene and increase to a peak of –1.15‰ immediately before the negative carbon isotope excursion (CIE) that marks the PETM onset. Values remain elevated through the PETM interval and decrease into the earliest Eocene. A shorter-term record for Site 1263 shows a similar trend, although δ44/40Ca values are on average 0.22‰ lower and decrease shortly after the CIE onset. The trends support neither diagenetic overprinting, authigenic carbonate additions, nor changes in the δ44/40Ca value of seawater. Rather, they are consistent with a kinetic isotope effect, whereby calcite δ44/40Ca values inversely correlate with precipitation rate. Geologically rapid Ca isotope shifts appear to reflect the response of Morozovella to globally forced changes in the local carbonate geochemistry of seawater. All data combined suggest that the PETM-OA event occurred near the peak of a gradual reduction in seawater carbonate ion concentrations during a time of elevated atmospheric pCO2, potentially driven by North Atlantic igneous province emplacement.

Astronomical calibration of a key Early Eocene Boreal section: implications for the climate response to the North Atlantic Igneous Province

<p>Sections of the Fur formation exposed on the islands of Fur and Mors (N. Jutland, Denmark) expose well-preserved diatomites and over 140 interbedded ash layers spanning >1 Myr of the Early Eocene from the top part of the Paleocene-Eocene Thermal Maximum (PETM; 55.9 Ma). The Fur Formation is a Konzentrat-Lagerstätten with an extremely rich fish fauna as well as numerous exquisitely preserved invertebrates, vertebrates, plant material, and siliceous microfossils. Due to its peculiar bentonite record, the Fur formation also constitutes a reference for the North Sea area, recording phases of active North Atlantic Igneous Province (NAIP) volcanism. Recently, a sea-surface temperature (SST) record was derived from Tex<sub>86</sub> values for this formation, showing anomalously cool SSTs immediately after the PETM (~11–23°C, Stokke et al., 2020) while near-freezing bottom-water temperatures (BWTs) have been inferred from clumped isotopes analysis of giant glendonite crystals (Vickers et al., 2020). The section is constrained by three radiometric dates of ash layers but cyclostratigraphic analysis of the section has proved difficult due to the apparent homogeneity of the diatomite and multitude of interbedded ash layers. We performed a high-resolution analysis of the magnetic susceptibility and carbon isotopes on bulk organics (δ<sup>13</sup>C<sub>org</sub>) from across the top PETM to the top of the Silstrup Mb. The magnetic susceptibility depicts all the apparent ash layers as well as additional hidden ash layers with peaks of various heights, and thus constitutes an excellent stratigraphic tool for its potential of correlation to other sections and deep-sea sites of the North Atlantic. Our δ<sup>13</sup>C<sub>org </sub>record is characterized throughout by periodicities of 65 to 90 cm and 3.6 m that match well precession and short-eccentricity cycles. Long-term trends and filtered 100 kyr cycles from our record correlate very well to the recent benthic δ<sup>13</sup>C Cenozoic compilation, leading to an astronomical calibration of the section which spans ~1300 kyr from 55.88 to 54.6 Ma. Our calibration allows for a precise illustration of the drastic contrast between the post-PETM warm tropical SSTs/BWTs and the surprisingly cool SSTs/BWTs of the North Sea.</p><p>References</p><p>Stokke, E.W., et al., 2020, Earth and Planetary Science Letters 544, 116388.</p><p>Vickers, M.L., et al., 2020, Nature Communications 11, 4713.</p>

The spatial distribution of igneous centres along the Norwegian Atlantic Margin (Møre and Vøring) and their relationship to magmatic plumbing systems

A series of offshore intra-basinal igneous centres have been documented across the North Atlantic Igneous Province including the UK, Ireland and Greenland. However, inconsistent cross-border terminology implies that similar features are not present in the Norwegian offshore, which, in turns, leads to misperceptions of cross-border geological differences. This paper presents evidence for a series of Norwegian igneous centres and suggests a consistent non-genetic cross-border terminology. In the Møre Basin, several igneous centres sit close to the continent–ocean boundary (COB), which have previously been identified as seamounts and/or ‘outer highs’. To provide cross-border consistency these features are consolidated under umbrella terms: igneous centres or volcanic fissures. Further centres are probably present within the Møre Basin (east of the COB) where 3D seismic data were not available. In the Vøring Basin two new igneous centres, one intrusive and one extrusive, are identified within the continental domain. Additionally, a possible deep magmatic upwelling associated with the regionally significant T-Reflector is identified. These igneous centre end-members represent the complexity of the magmatic plumbing across the Norwegian margin. With further data it is likely that further igneous centres will be identified offshore mid-Norway.

Cold spells in the Nordic Seas during the early Eocene Greenhouse

The early Eocene (c. 56 - 48 million years ago) experienced some of the highest global temperatures in Earth’s history since the Mesozoic, with no polar ice. Reports of contradictory ice-rafted erratics and cold water glendonites in the higher latitudes have been largely dismissed due to ambiguity of the significance of these purported cold-climate indicators. Here we apply clumped isotope paleothermometry to a traditionally qualitative abiotic proxy, glendonite calcite, to generate quantitative temperature estimates for northern mid-latitude bottom waters. Our data show that the glendonites of the Danish Basin formed in waters below 5 °C, at water depths of <300 m. Such near-freezing temperatures have not previously been reconstructed from proxy data for anywhere on the early Eocene Earth, and these data therefore suggest that regionalised cool episodes punctuated the background warmth of the early Eocene, likely linked to eruptive phases of the North Atlantic Igneous Province.