Impacts of Global Warming on Permo-Triassic Terrestrial Ecosystems
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Gondwana Research 25 (2014) 1308–1337 Contents lists available at ScienceDirect Gondwana Research journal homepage: www.elsevier.com/locate/gr GR Focus Review Impacts of global warming on Permo-Triassic terrestrial ecosystems Michael J. Benton a,⁎, Andrew J. Newell b a School of Earth Sciences, University of Bristol, Bristol, BS8 1RJ, UK b British Geological Survey, Maclean Building, Wallingford OX10 8BB, UK article info abstract Article history: Geologists and palaeontologists have expressed mixed views about the effects of the end-Permian mass Received 26 June 2012 extinction on continental habitats and on terrestrial life. Current work suggests that the effects on land Received in revised form 20 November 2012 were substantial, with massive erosion following the stripping of vegetation, associated with long-term Accepted 12 December 2012 aridification and short-term bursts of warming and acid rain. Wildfires at the Permo-Triassic boundary Available online 31 December 2012 contributed to the removal of forests and the prolonged absence of forests from the Earth's surface for up to 10 Myr. These physical crises on land impinged on the oceans, suggesting tight interlocking of terrestrial Keywords: Mass extinction and marine crises. Levels of extinction on land may well have been as high as in the sea, and this is certainly Permian the case for tetrapods. The mass extinction seems to have been less profound for plants and insects, but it is Triassic hard at present to disentangle issues of data quality from reductions in abundance and diversity. Several Continental killing agents have been proposed, and of these tetrapods may have succumbed primarily to acid rain, Terrestrial mass wasting, and aridification. Plants may have been more affected by the sudden effects of heating and Tetrapod wildfires, and the crisis for insects has yet to be explored. Plant © 2012 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. Insect Contents 1. Introduction ............................................................. 1309 2. The end-Permian mass extinction and loss of life on land ........................................ 1309 3. The first 10 million years of the Triassic ................................................ 1310 4. Reconstructing ancient climates ................................................... 1311 4.1. Sedimentological evidence for ancient climates ......................................... 1311 4.2. Palaeogeography and climate in the Permo-Triassic ....................................... 1312 4.3. Numerical climate models ................................................... 1312 5. Sedimentology of the terrestrial Permo-Triassic boundary interval ................................... 1313 5.1. Location and setting of key sections .............................................. 1313 5.2. General character of PTB terrestrial sections .......................................... 1313 6. Impact of PTr global warming on geomorphic processes ........................................ 1315 6.1. Weathering .......................................................... 1315 6.2. Erosion rates in the PTB interval ................................................ 1316 6.3. Wildfire........................................................... 1318 6.4. Changes in fluvial style .................................................... 1318 6.5. Changes to lacustrine systems ................................................. 1319 6.6. Desertification and aeolian activity ............................................... 1320 7. Evidence for atmospheric change ................................................... 1320 7.1. Carbon dioxide ........................................................ 1320 7.2. Oxygen ............................................................ 1321 7.3. Sulphur, chlorine, and fluorine ................................................. 1321 7.4. Destruction of the ozone layer (?) ............................................... 1321 8. Plant evolution through the Permo-Triassic crises ........................................... 1322 9. Insect evolution through the Permo-Triassic crises ........................................... 1323 ⁎ Corresponding author. E-mail addresses: [email protected] (M.J. Benton), [email protected] (A.J. Newell). 1342-937X/$ – see front matter © 2012 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.gr.2012.12.010 M.J. Benton, A.J. Newell / Gondwana Research 25 (2014) 1308–1337 1309 10. Vertebrate evolution through the Permo-Triassic crises ......................................... 1324 10.1. Changing opinions ....................................................... 1324 10.2. Scaling the vertebrate extinctions ................................................ 1324 10.3. Triassic recovery of vertebrates ................................................. 1325 10.4. Regional studies on vertebrate extinction and recovery ...................................... 1325 10.5. Vertebrate clades through the EPME crisis ............................................ 1327 11. Killing agents ............................................................. 1327 11.1. Introductory remarks: advocacy or science? ........................................... 1327 11.2. Hypoxia as the EPME killer ................................................... 1328 11.3. Hypercapnia and ocean acidification as the EPME killers ..................................... 1329 11.4. Global warming as the EPME killer ............................................... 1329 11.5. Aridity as the EPME killer .................................................... 1330 11.6. Acid rain and mass wasting as the EPME killers .......................................... 1331 11.7. Wildfires as the EPME killer ................................................... 1332 12. Death on land during the EPME .................................................... 1332 Acknowledgments .............................................................. 1333 References ................................................................. 1333 1. Introduction potential killing consequences of such long-term and short-term changes. Most work on the end-Permian mass extinction (EPME) has fo- cused on marine rather than terrestrial organisms. Killing agents in the oceans have generally been linked to increased CO2 concentra- 2. The end-Permian mass extinction and loss of life on land tions and global anoxia, associated with euxinia (anoxic and sulphidic conditions), hypercapnia (CO2 poisoning), and ocean acidification, al- The model for causation of the EPME has become focused on the though the relative importance of each aspect of this cocktail is debat- consequences of the Siberian Trap volcanic eruptions. The most widely ed (Wignall and Twitchett, 1996; Kump et al., 2005; Knoll et al., 2007; accepted model today (Wignall, 2001; Benton, 2003; Benton and Riccardi et al., 2007; Algeo et al., 2011). For life on land, many killing Twitchett, 2003; Erwin, 2006; Knoll et al., 2007; Algeo et al., 2011; mechanisms have been proposed, but dominant among these have S.-z. Shen et al., 2011; Payne and Clapham, 2012; Retallack, 2012) iden- been long-term and short-term changes in atmospheres and oceans, tifies consequences of the eruption of the Siberian flood basalts including global warming and reduction in the oxygen content of (Reichow et al., 2009) which over a peak eruptive period of around the atmosphere. Global warming could clearly have had an important 600 kyr generated large volumes of sulphate aerosols and carbon diox- role in killing land animals and plants, and the severity of the effects ide (Fig. 1). Methane was probably a major contributor towards a would depend on the amount and speed of the temperature rise, but runaway greenhouse effect through its release from destabilised isotopi- perhaps more importantly on related mass wasting and aridity. For cally light hydrate reservoirs (Berner, 2002) and the thermal metamor- oxygen reduction, only animals would obviously be affected, and sce- phism of Siberian coal measures and organic-rich shales (Retallack et al., narios for selective extinction through hypoxia have been proposed 2006; Grasby et al., 2011). for tetrapods at least (e.g. Huey and Ward, 2005). Decreases in the δ18O ratio of shallow marine biogenic carbonate Much of the evidence for a long-term rise in mean temperature and suggest that seawater temperature during the extinction event may fall in mean oxygen content of the atmosphere through the Permian have risen by 6–10 °C (Kearsey et al., 2009). Joachimski et al. Period, have come from global models, notably the Geocarbsulf model (2012) suggest low-latitude surface water warming of 8 °C based of Berner (2006, 2009). Further, the sharp increase in temperature on oxygen isotope records in south China, and these values are con- and the drop in oxygen across the Permo-Triassic boundary (PTB) firmed by palaeosol studies (Retallack, 2012). Temperatures at the have been based on evidence from stable isotopes, palaeosols, leaf sto- Equator are estimated at 32–35° in the earliest Triassic (Joachimski mata, and charcoal distribution (Glasspool and Scott, 2010; Retallack, et al., 2012), and up to 40° at the Smithian–Spathian boundary (Sun 2012). There are still many questions about the nature of the long- et al., 2012). term and short-term warming and oxygen reduction processes, and EPME killing models (Fig. 1) are based on the massive volumes