Increased fire activity at the Triassic/Jurassic boundary in Greenland due to climate-driven floral change

Abstract

Moisture content can be a dominant factor affecting combustion especially in live fuels due to the wide range of moisture content that can be encountered with vegetation. Laboratory experiments are used to study the fire dynamics of Mediterranean Pinus halepensis needles under a range of fuel and flow conditions. A set of 80 experiments with good repeatability were conducted in the Fire Propagation Apparatus (FPA) fire calorimeter. The burning behavior is measured in terms of the evolution of the mass loss rate and the heat release rate from ignition till burn out for different forced flow velocities. Recently collected live and dead needles are compared here for the first time. Additionally, live samples aged for 15 months after collection are presented as an alternative to study changes in live needles. Two different moisture conditions are considered, fresh and oven-dry. The most flammable samples are fresh dead and 15 months aged needles, followed by oven-dry dead, and oven-dry live needles. The least flammable is fresh live needles. Overall, the results show that fire physics and chemistry vary with the fuel and flow conditions, and that moisture content is not the only difference between live and dead fuels, but that the needle bed physicochemical mechanisms matters as well. The loss of volatiles and other changes induced during oven drying is seen to lead to significant differences in the burning behavior.

Episodic photic zone euxinia in the northeastern Panthalassic Ocean during the end-Triassic extinction

“…The expansion of OMZs during hothouse conditions may be aided by density stratification due to intense evaporation over epicontinental basins and/or a reduced latitudinal thermal gradient, suppressing high-latitude deep-water formation, thermohaline circulation, and ocean ventilation (Kidder and Worsley, 2010). Massive pulses of atmospheric CO 2 (to ~4400 ppm) from phases of Central Atlantic magmatic province volcanism (Schaller et al, 2011) are now more precisely dated to the ETE (Blackburn et al, 2013), and are synchronous with marine extinctions (e.g., Whiteside et al, 2010), fossil flora suggestive of increased CO 2 and extreme warming (McElwain et al, 1999), and enhanced wildfire activity (Belcher et al, 2010). The rise in pCO 2 was also coincident with a major disruption in biocalcification (van de Schootbrugge et al, 2007), possibly caused by ocean acidification, such as during the late Permian.…”

Charcoal Evidence That Rising Atmospheric Oxygen Terminated Early Jurassic Ocean Anoxia

“…Although, this sequence 31 preserves only the lower part of the negative CIE, and was conducted at a higher resolution than that captured here, a rise in global temperatures and drying of the regional climate is inferred due to increased abundance of thermophilic plant taxa immediately before the first negative d 13 C shift. Past Mesozoic global warming events have been shown to enhance fire activity 15 and warm, dry periods are commonly linked with increased fire probability and large fire events 32,33 , which tend to be enhanced when dry periods succeed wetter periods that are favourable to fuel accumulation. Thus the brief enhancement of fireactivity may have been influenced by climatic changes occurring over timescales of a few hundred to thousand years close to the onset of the OAE; either driven directly by the climate change or from a resulting change in vegetation, the fuel for fires.…”

“…Hence suppression of the rise in fire-activity throughout the negative CIE may be due to a significantly wetter climate, damping any pO 2 -fire response. Of significance however, is the ability of fire-activity to continue at background levels, which may indicate rising pO 2 enabling fuels with higher moisture contents to continue to burn at a similar level to before the event [13][14][15] .…”

On the reconstruction of plant photosynthetic and stress physiology across the Triassic–Jurassic boundary

“…The section at Astartekløft is composed of fluvial-lacustrine sediments, with the fossil plant beds occurring in crevasse splays that represent flooding events and coals deposited under swampy conditions (Figure 2) (Belcher et al, 2010). The paleoenvironmental setting of Astartekløft points to high levels of water availability during the Late Triassic to Early Jurassic (Dam and Surlyk, 1992), indicating that leaf expansion was unlikely to have been constrained by water availability.…”