Two-phased Mass Rarity and Extinction in Land Plants During the End-Triassic Climate Crisis

Abstract

Greenhouse gas emissions from large-scale volcanism in the Central Atlantic Magmatic Province is considered to have caused the end-Triassic mass extinction (201.5 million years ago), but the impact on land plants has been debated. Here, abundance changes in spores and pollen record the devastating effects this volcanic induced climate crisis had on coastal and near-coastal lowland mire vegetation around the European epicontinental sea and the European Tethys margin. Combined stress from rising air temperatures and changing climate at the onset of the crisis was exacerbated by a rapidly rising sea-level resulting in fragmentation and destruction of coastal and near-coastal lowland mire habitats, causing mass rarity and extinctions primarily in gymnosperm trees and shrubs adapted to these environments. The devastation of these habitats was further amplified by a subsequent sea-level fall leaving pioneering opportunists and herbaceous survivors to colonize disturbed areas in an environment stressed by increased wildfire activity and enhanced soil erosion. The pioneering flora was severely decimated in a second mass rarity phase and ultimately extirpated. The second mass rarity phase occurred just prior to and at the onset of a prominent negative excursion in δ13Corg. A subsequent sea-level rise appears to have restored some of the near-coastal mire habitats allowing some of the plants to recover. The supraregional mass rarity during the end-Triassic crisis affected both previously dominant as well as rare plants and this resonates with ongoing and future climate change and attests to the vulnerability of coastal and lowland vegetation, especially rare plant species, to climatic and environmental disturbances, where rising sea-level threatens entire ecosystems.

Volcanically-Induced Environmental and Floral Changes Across the Triassic-Jurassic (T-J) Transition

“…The younger CIE-II in the Jiyuan Basin succession is also widely known from marine and terrestrial records as the unnamed minor CIE in other areas (Hesselbo et al, 2002;Ruhl et al, 2009Ruhl et al, , 2010Ruhl et al, , 2020Percival et al, 2017;Pieńkowski et al, 2020;Wignall and Atkinson, 2020;Fang et al, 2021; Figure 6). Like CIE-I, CIE-II is accompanied by a significant reduction in plant diversity in which 44% of genera are lost, and similar losses are known from other terrestrial records near the TJB (e.g., Wignall and Atkinson, 2020;Lindström, 2021). CIE-II is also accompanied by a minor Hg/TOC peak (144.93 ppb/wt%, VA-II).…”

“…The second pulse of extinction caused another abrupt, palynological change, resulting in the loss of further pollen taxa and a brief proliferation of Classopollis pollen (Wignall and Atkinson, 2020). Our study also identifies a bimodal reduction in plant diversity, suggesting that the two-step extinction pattern is a globally widespread phenomenon (e.g., Wignall and Atkinson, 2020;Lindström, 2021). A rapid recovery of fern spores and their floral dominance (reaching 68.2% of all palynomorphs) (Figure 2) occurred in the interlude between ETME-I and ETME-II in the Jiyuan Basin.…”

“…However, the impact of this crisis on terrestrial plant diversity is poorly understood. Studies of plant macrofossils and palynological (spore-pollen) assemblages reveal that plant diversity and many dominant species suffered severe losses in the Tethys ocean domain of the northern hemisphere in Europe (McElwain et al, 1999(McElwain et al, , 2007Kuerschner et al, 2007;Bonis et al, 2009Bonis et al, , 2010Pieńkowski et al, 2012;Lindström, 2016Lindström, , 2021Lindström et al, 2019;Wignall and Atkinson, 2020), North America (Olsen et al, 2002), South China (Wang et al, 2010;Li et al, 2020;Zhou et al, 2021), and northwest (NW) China (Lu and Deng, 2005;Deng et al, 2010;Sha et al, 2015;Fang et al, 2021). Similar losses are known from southern hemisphere Australia and New Zealand (De Jersey and McKellar, 2013).…”

“…The timing and causal mechanism(s) of the ETME are controversial (e.g., van de Schootbrugge et al, 2009;Barbacka et al, 2017;Lindström et al, 2019;Wignall and Atkinson, 2020;Lindström, 2021;Lucas, 2021). Wignall and Atkinson (2020) document two pulses of extinction in marine and terrestrial settings, with pulses occurring during the initial and the minor (unnamed) negative CIEs during the T-J transition.…”

End-Triassic Extinction in a Carbonate Platform From Western Tethys: A Comparison Between Extinction Trends and Geochemical Variations

“…The biotic response to the environmental changes during the Late Triassic is recorded both in marine and terrestrial successions. Recent studies have demonstrated in detail two extinction pulses recorded by both marine and terrestrial realms (Wignall and Atkinson, 2020;Lindström, 2021). If on land the climatic changes led to a turnover of megaflora (McElwain et al, 1999;Lindstrom, 2021), in the marine realm high rates of extinction were recorded by benthic biocalcifiers such as bivalves, foraminifers, corals and sponges (e.g., Kiessling et al, 2007;Greene et al, 2012;Todaro et al, 2018).…”