Low atmospheric CO ₂ levels during the Permo- Carboniferous glaciation inferred from fossil lycopsids

Abstract

Earth history was punctuated during the Permo-Carboniferous [300 -250 million years (Myr) ago] by the longest and most severe glaciation of the entire Phanerozoic Eon. But significant uncertainty surrounds the concentration of CO 2 in the atmosphere through this time interval and therefore its role in the evolution of this major prePleistocene glaciation. Here, I derive 24 Late Paleozoic CO 2 estimates from the fossil cuticle record of arborsecent lycopsids of the equatorial Carboniferous and Permian swamp communities. Quantitative calibration of Late Carboniferous (330 -300 Myr ago) and Permian (270 -260 Myr ago) lycopsid stomatal indices yield average atmospheric CO 2 concentrations of 344 ppm and 313 ppm, respectively. The reconstructions show a high degree of self-consistency and a degree of precision an order of magnitude greater than other approaches. Low CO 2 levels during the PermoCarboniferous glaciation are in agreement with glaciological evidence for the presence of continental ice and coupled models of climate and ice-sheet growth on Pangea. Moreover, the Permian data indicate atmospheric CO 2 levels were low 260 Myr ago, by which time continental deglaciation was already underway. Positive biotic feedbacks on climate, and geotectonic events, therefore are implicated as mechanisms underlying deglaciation.fossil plants ͉ paleoclimates ͉ stomata ͉ carbon isotopes P aleobotanical approaches for quantitatively estimating the pre-Quaternary CO 2 content of the Earth's atmosphere exploit the inverse relationship between leaf stomatal index (SI, fraction of epidermal cells that are stomata) and CO 2 shown by modern trees (1). However, their application has focused on the Cretaceous and Early Tertiary when extant species are represented in the fossil record (2). Attempts to extend this approach further back into the Paleozoic era with the genus Ginkgo are much less secure because of the need to switch to related taxa, such as pteridosperm genera, whose SIs lie outside the range of the calibration dataset (3). These considerations severely limit the utility of the plant fossil record for evaluating the role of CO 2 as a greenhouse gas during the Late Paleozoic glaciation (4), a time when quite large discrepancies are evident between geochemical modeling studies of the long-term carbon cycle (5), and paleobiological proxy CO 2 measurements (3, 6).Here, I report 24 quantitative Carboniferous and Permian atmospheric CO 2 estimates derived from the stomatal characteristics of fossil arborscent lycopsids, the spore-bearing vascular plant group dominating equatorial Euramerican and Cathaysian coal swamp floras during the Late Palaeozoic (7). The fossil lycopsid SIs were calibrated against the response to atmospheric CO 2 variations of three geographically distinct contemporary tropical Lycopodium cernuum populations, taken to be a reasonable nearest living equivalent (NLE) taxon among extant lycopsid species (8). Phylogenetically, Isoetes represents the nearest living relative to members of the Lepidodendron, Bothr...

Viewing leaf structure and evolution from a hydraulic perspective

“…For example, Gigantopteridales were probable seed plants from the Permian that produced astonishingly varied multi-vein reticulated vascular systems, with some closely approximating angiosperm leaves (Glasspool et al 2004). Moreover, giganopterids diversified continuously under low [CO 2 ] atm conditions for nearly 40 million years, before their termination at the Permian-Triassic boundary (Berner 1994;Beerling 2002). At this time, despite apparently appropriate environmental conditions and a gross-approximation of angiosperm venation architecture, there is no evidence that high D v evolved among the Gigantopterids (Glasspool et al 2004).…”

Palaeoecology of Macroneuropteris scheuchzeri, and its implications for resolving the paradox of ‘xeromorphic’ plants in Pennsylvanian wetlands

“…The late Palaeozoic was a time of very low CO 2 , b400 ppm (e.g., McElwain and Chaloner, 1995;Ekart et al, 1999;Beerling, 2002;Royer et al, 2007aRoyer et al, , 2007b) and very high O 2 (Scott and Glasspool, 2006;Berner, 2009;Glasspool and Scott, 2010), estimated by Scott and Glasspool (2006) to have been continuously above 26%. Under these atmospheric conditions, the high, saturating levels of light to which canopy and open-grown plants are exposed would have had potentially severe physiological consequences.…”

Plant Paleoecology in Deep Time1

“…Such studies of plants were among the biological patterns that lent strong support to the idea of continental drift, prior to the widespread acceptance of plate tectonics (see Chaloner [1959] for review), and, later, helped refine study of continental positions (e.g., Ziegler et al, 1996;Berthelin et al, 2003). Vegetational studies also are of importance in the ground-truthing of climatic models (e.g., Wing & Greenwood, 1993;Upchurch et al, 1999;Beerling & Woodward, 2001;Rees et al, 2002;Poulson et al, 2007). The resolution of paleobiogeographic studies is, of course, much better in younger rocks, something paralleled by paleogeographic reconstructions.…”

“…Some paleobotanical studies that have addressed Cretaceous climate, including plantclimate feedbacks, include those from Spicer et al (1994Spicer et al ( , 1996, Upchurch et al (1998Upchurch et al ( , 1999, DeConto et al (1999), and Beerling and Woodward (2001). Cretaceous plant productivity and biodiversity were broadly similar to those of the Jurassic in being highest at midlatitudes, where climates were most favorable (Spicer et al, 1993).…”

“…And, because living Ginkgo is monospecific (G. biloba L.) and there are no unequivocal natural stands today (unlike the recently discovered Wollemi Pine, Araucariaceae; Chambers et al, 1998), there is a high probability that Ginkgoaleans were adapted widely to a variety of habitats (see Rees et al, 2002). On the other hand, stomatal trends of fossil Ginkgo are believed to parallel those of the living taxon grown under varying atmospheric gas concentrations (Beerling & Royer, 2002a;see below).…”