An Early Cenozoic perspective on Greenhouse warming and carbon cycle dynamics

Department of Earth and Planetary Sciences, University of California at Santa Cruz, Santa Cruz, California 95060, USA.
Nature (Impact Factor: 41.46). 02/2008; 451(7176):279-83. DOI: 10.1038/nature06588
Source: PubMed


Past episodes of greenhouse warming provide insight into the coupling of climate and the carbon cycle and thus may help to predict the consequences of unabated carbon emissions in the future.


Available from: Gerald Dickens
  • Source
    • "The Eocene-Oligocene transition (EOT), ~34 million years ago (34 Ma), represents one of the major climatic transitions in the past 65 million years (Zachos et al., 2008). A steady decline in temperatures from ~50 to ~34 Ma culminated in the rapid expansion of permanent ice over Antarctica (Zachos et al., 2001; Katz et al., 2008; Lear et al., 2008). "
    [Show abstract] [Hide abstract]
    ABSTRACT: The glaciation of Antarctica at the Eocene-Oligocene transition (approx. 34 million years ago) was a major shift in the Earth's climate system, but the mechanisms that caused the glaciation, and its effects, remain highly debated. A number of recent studies have used coupled atmosphere-ocean climate models to assess the climatic effects of Antarctic glacial inception, with often contrasting results. Here, using the HadCM3L model, we show that the global atmosphere and ocean response to growth of the Antarctic ice sheet is sensitive to subtle variations in palaeogeography, using two reconstructions representing Eocene and Oligocene geological stages. The earlier stage (Eocene; Priabonian),which has a relatively constricted Tasman Seaway, shows a major increase in sea surface temperature over the Pacific sector of the Southern Ocean in response to the ice sheet. This response does not occur for the later stage (Oligocene; Rupelian), which has a more open Tasman Seaway. This difference in temperature response is attributed to reorganization of ocean currents between the stages. Following ice sheet expansion in the earlier stage, the large Ross Sea gyre circulation decreases in size. Stronger zonal flow through the Tasman Seaway allows salinities to increase in the Ross Sea, deepwater formation initiates and multiple feedbacks then occur amplifying the temperature response. This is potentially a model-dependent result, but it highlights the sensitive nature of model simulations to subtle variations in palaeogeography, and highlights the need for coupled ice sheet-climate simulations to properly represent and investigate feedback processes acting on these time scales. © 2015 The Author(s) Published by the Royal Society. All rights reserved.
    Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences 11/2015; 373(2054):20140419. DOI:10.1098/rsta.2014.0419 · 2.15 Impact Factor
  • Source
    • "According to our estimates, the two distantly related lichenicolous genera in Parmeliaceae originated around the same time (c. 25 Ma in the late Oligocene). In the late part of the Oligocene, the Earth experienced a warming period, after a long cooling period in the early Oligocene that resulted in growth of the Antarctic ice sheets (Zachos et al., 2008). This warming period, however, was interrupted by cooling periods, such as the Mi-1 glaciation (Zachos et al., 2001; Wilson et al., 2008) at the Oligocene–Miocene boundary c. 24 Ma. "
    [Show abstract] [Hide abstract]
    ABSTRACT: We studied the evolutionary history of the Parmeliaceae (Lecanoromycetes, Ascomycota), one of the largest families of lichen-forming fungi with complex and variable morphologies, also including several lichenicolous fungi. We assembled a six-locus data set including nuclear, mitochondrial and low-copy protein-coding genes from 293 operational taxonomic units (OTUs). The lichenicolous lifestyle originated independently three times in lichenized ancestors within Parmeliaceae, and a new generic name is introduced for one of these fungi. In all cases, the independent origins occurred c. 24 million yr ago. Further, we show that the Paleocene, Eocene and Oligocene were key periods when diversification of major lineages within Parmeliaceae occurred, with subsequent radiations occurring primarily during the Oligocene and Miocene. Our phylogenetic hypothesis supports the independent origin of lichenicolous fungi associated with climatic shifts at the Oligocene-Miocene boundary. Moreover, diversification bursts at different times may be crucial factors driving the diversification of Parmeliaceae. Additionally, our study provides novel insight into evolutionary relationships in this large and diverse family of lichen-forming ascomycetes. © 2015 The Authors. New Phytologist © 2015 New Phytologist Trust.
    New Phytologist 11/2015; 208:1217-1226. DOI:10.1111/nph.13553 · 7.67 Impact Factor
  • Source
    • "Using Eq. (1), calculated MAP were 457 ± 336 mm y −1 and 439 ± 314 mm y −1 for O. biroi and O. arcuatus, respectively. This indicates that similar arid climatic conditions prevailed during the Late Palaeocene and the Early Eocene in southeastern France whilst the aridity decreased during the Palaeocene Eocene Thermal Maximum (PETM) according to Zachos et al. (2008). By contrast, Schmitz and Pujalte (2007) have shown that the climate of northern Spain was characterized by very marked rainy seasons at the time of the PETM, which cannot be detected in the range of δ 13 C values of analyzed eggshells. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Abundant fragments from eggs laid by giant birds occur in the Palaeocene (Thanetian) and Eocene (Sparnacian) sedimentary deposits of southeastern France. In the Sparnacian, thick eggshell fragments, assigned to the oospecies Ornitholithus arcuatus, correspond to very large bird eggs that were most likely laid by Gastornis. The Thanetian thin eggshell fragments, assigned to Ornitholithus biroi, were presumably laid by a smaller, yet unidentified bird. In order to investigate ecology and environment of these egg-laying birds, stable carbon and oxygen isotope compositions of 125 fossil eggshell fragments were analyzed. After removing samples affected by diagenetic alteration of the calcitic shells, the measured range of δ13Cc values (-11‰ to -6‰ V-PDB) is interpreted as reflecting an herbivorous diet for these birds in a context of limited annual precipitation (≈500mmy-1). Stable oxygen isotope analysis of living ostrich eggshell calcite, along with that of the water extracted from their albumen and yolk, provided evidence to calculate isotopic fractionation factors between both calcite and body water (αcalcite-body water=1.03041) and between body water and meteoric water (αbw-mw=1.00399), using δ18O values of local meteoric waters identified as the source of the birds drinking water. Combined with the δ18O values of fossil eggshells, both isotopic fractionations provided calculated δ18O values of meteoric waters in the range -9.5‰ to -2.8‰ (V-SMOW) for the Thanetian, and in the range -8.9‰ to -1.7‰ (V-SMOW) for the Sparnacian. These large isotopic ranges likely reflect inter-annual temperature variations of the complete year, suggesting a year round egg-laying strategy. Corresponding Mean Air Temperatures (MAT) were comprised between 20±4°C and 22±4°C during the Thanetian, and between 23±3°C and 25±3°C during the Sparnacian. These giant birds likely lived under a warm and dry climate similar to that prevailing today in western Mediterranean islands.
    Palaeogeography Palaeoclimatology Palaeoecology 10/2015; 435. DOI:10.1016/j.palaeo.2015.06.011 · 2.34 Impact Factor
Show more