Early Paleogene wildfires in peat-forming environments at Schöningen, Germany

AbstractWildfire activity in early Paleogene greenhouse conditions can be used as an analogue to gauge the effect of future warming trends on wildfire in the current climate system. Inertinite (fossil charcoal in coal) from 11 autochthonous early Paleogene lignite seams from the Schöningen mine (Germany) was quantified using macerations, in situ pillars and industry standard crushed samples. A new three transect method was developed to quantify in situ charcoal. The combination of in situ pillars and crushed samples accounts for temporal and spatial variation in charcoal through a stratigraphically oriented pillar, whilst maintaining comparability with industry standards and previous work. Charcoal occurs as a range of randomly distributed particle sizes, indicating that fires were burning locally in the Schöningen peat-forming environment and in the surrounding areas, but according to petrological data, not in an episodic or periodic pattern. Although charcoal abundance is low (relative to previous high fire worlds such as the Cretaceous), three quantitative and semi-quantitative methods show increased wildfire activity (relative to the modern world) in the warmest parts of the early Paleogene. As atmospheric oxygen levels stabilised to modern values and precipitation and humidity became the main control on wildfire, increased rainfall followed by drier intervals would have created an environment rich in dry fuel in which wildfires could easily propagate if humidity was low enough. In the later part of the Early Eocene (Ypresian) charcoal abundance fell to levels similar to those found in modern peats. This indicates that the transition to the modern low fire world occurred within the Early Eocene, earlier than previous records suggest

Terrestrial environmental change across the onset of the PETM and the associated impact on biomarker proxies:A cautionary tale

The following supplementary information includes one dataset which contains 3 tables: Biomarker distributions and proxies at Cobham, UK Bulk and compound specific isotope data at Cobham (UK) Model-derived mean annual surface temperature and precipitation estimates as a function of CO2 at Cobham (UK)

Mid-latitude continental temperatures through the early Eocene in western Europe

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are increasingly used to reconstruct mean annual air temperature (MAAT) during the early Paleogene. However, the application of this proxy in coal deposits is limited and brGDGTs have only been detected in immature coals (i.e. lignites). Using samples recovered from Schöningen, Germany (∼48°N palaeolatitude), we provide the first detailed study into the occurrence and distribution of brGDGTs through a sequence of early Eocene lignites and associated interbeds. BrGDGTs are abundant and present in every sample. In comparison to modern studies, changes in vegetation type do not appear to significantly impact brGDGT distributions; however, there are subtle differences between lignites – representing peat-forming environments – and siliciclastic nearshore marine interbed depositional environments. Using the most recent brGDGT temperature calibration (MATmr) developed for soils, we generate the first continental temperature record from central-western continental Europe through the early Eocene. Lignite-derived MAAT estimates range from 23 to 26 °C while those derived from the nearshore marine interbeds exceed 20 °C. These estimates are consistent with other mid-latitude environments and model simulations, indicating enhanced mid-latitude, early Eocene warmth. In the basal part of the section studied, warming is recorded in both the lignites (∼2 °C) and nearshore marine interbeds (∼2–3 °C). This culminates in a long-term temperature maximum, likely including the Early Eocene Climatic Optimum (EECO). Although this long-term warming trend is relatively well established in the marine realm, it has rarely been shown in terrestrial settings. Using a suite of model simulations we show that the magnitude of warming at Schöningen is broadly consistent with a doubling of CO2, in agreement with late Paleocene and early Eocene pCO2 estimates

High temperatures in the terrestrial mid-latitudes during the early Palaeogene

The early Paleogene (56–48 Myr) provides valuable information about the Earth’s climate system in an equilibrium high pCO2 world. High ocean temperatures have been reconstructed for this greenhouse period, but land temperature estimates have been cooler than expected. This mismatch between marine and terrestrial temperatures has been difficult to reconcile. Here we present terrestrial temperature estimates from a newly calibrated branched glycerol dialkyl glycerol tetraether-based palaeothermometer in ancient lignites (fossilized peat). Our results suggest early Palaeogene mid-latitude mean annual air temperatures of 23–29 °C (with an uncertainty of ± 4.7 °C), 5–10 °C higher than most previous estimates. The identification of archaeal biomarkers in these same lignites, previously observed only in thermophiles and hyperthermophilic settings, support these high temperature estimates. These mid-latitude terrestrial temperature estimates are consistent with reconstructed ocean temperatures and indicate that the terrestrial realm was much warmer during the early Palaeogene than previously thought

Polyfunctionalised bio- and geohopanoids in the Eocene Cobham Lignite

We investigated the bacteriohopanepolyol (BHP) distribution in the Cobham Lignite sequence (SE England) deposited across the Palaeocene–Eocene boundary, including part of the Palaeocene–Eocene Thermal Maximum (PETM) as shown previously by a negative carbon isotope excursion (CIE). A variety of BHPs were identified, including the commonly occurring and non-source specific biohopanoid, bacteriohopanetetrol (BHT), and 32,35-anhydroBHT which was the most abundant polyfunctionalised geohopanoid in the majority of samples. BHPs with a terminal amine functionality, diagnostic biomarkers for methanotrophic bacteria, were found throughout the sequence, with similar distributions in both the lower laminated and upper blocky lignite except that 35-aminobacteriohopanepentol (aminopentol), indicative of Type I methanotrophs (gammaproteobacteria), was generally more abundant in the upper section within the CIE. The diagenetic fate of these compounds is currently poorly constrained; however, we also identified the recently reported N-containing transformation product, anhydroaminotriol, and several tentatively assigned novel N-containing structures potentially containing ketone functionalities. Although present throughout the section, there was a sharp peak in the occurrence of these novel compounds, which correlated with the onset of the CIE and highly isotopically depleted hopanes in the upper part of the laminated lignite, both also correlating well with aminopentol peak abundance. The significant abundance of these compounds suggests that 35-aminoBHPs have their own specific diagenetic pathway, potentially providing an alternative method allowing methanotroph activity to be traced in older samples even if the original biohopanoid markers are no longer present. At this time we cannot preclude the possibility that some or all of these BHPs have been produced by more recent subsurface activity, post deposition of the lignite; however, this would not be expected to generate the observed stratigraphic variability and we suggest that unprecedented observations of a range of highly functionalised biohopanoids in samples of this age could significantly extend the window of their known occurrence