Article

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: 42.35). 02/2008; 451(7176):279-83. DOI: 10.1038/nature06588
Source: PubMed

ABSTRACT 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.

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Available from: Gerald Dickens, Aug 24, 2015
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    • "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. "
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    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 (≈ 500 mm y− 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 · 2.75 Impact Factor
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    • "Of interest here are long-term (>10 My) variations in Earth's climatic baseline. For example, Earth appears to vacillate between long (>50 My) warm intervals, where there are no significant continental ice sheets like the Cretaceous– Paleogene, to long cold intervals, where ice sheets are important, such as the mid-Cenozoic to present (Zachos et al., 2008). Compared to the Archean, when the sun was dimmer and there may http://dx.doi.org/10.1016/j.epsl.2015.05.045 0012-821X/© 2015 Elsevier B.V. All rights reserved. "
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    ABSTRACT: Continental arcs, such as the modern Andes or the Cretaceous Sierra Nevada batholith, are some of the highest topographic features on Earth. Continental arc volcanoes may produce more CO2 than most other types of volcanoes due to the interaction of magmas with sedimentary carbonates stored in the continental upper plate. As such, global flare-ups in continental arc magmatism may amplify atmospheric CO2 concentrations, leading to climatic warming. However, the high elevations of continental arcs may also enhance orographic precipitation and change global atmospheric circulation patterns, possibly increasing the efficiency of chemical weathering and drawdown of atmospheric CO2, which may subdue the climatic warming response to volcanic activity. To better evaluate the climatic response, we develop models that integrate magmatic crustal thickening, topographic uplift, isostasy and erosion. The topographic response is used to predict how soil formation rates, soil residence times, and chemical weathering rates vary during and after a magmatic episode. Although magmatism leads to crustal thickening, which requires topographic uplift, highest elevations peak ∼10 My after magmatism ends. Relatively high elevations, which enhance erosion and chemical weathering of the continental arc, persist for tens of million years after magmatism ends, depending on erosion kinetics. It has recently been suggested that the Cretaceous–Paleogene greenhouse (high atmospheric CO2 and warm climate) coincided with a global chain of continental arcs, whereas mid- to late Cenozoic icehouse conditions (low atmospheric CO2 and cold climate) coincided with a lull in continental arc activity after 50 Ma. Application of our models to the Sierra Nevada (California, USA) continental arc, which represents a segment of this global Cretaceous–Paleogene continental arc, reproduces the observed topographic and erosional response. Our models require that the newly formed continental arc crust remained high and continued to erode and weather well after (>50 My) the end of magmatism. Thus, in the aftermath of a global continental arc flare-up, both the total volcanic inputs of CO2 decline and the average weatherability of continents increases, the latter due to the increased proportion of widespread remnant topography available for weathering and erosion. This combination leads to a decrease in the long-term baseline of carbon in the ocean/atmosphere system, leading to cooling. Mid-Cenozoic cooling is often attributed solely to increased weathering rates associated with India–Eurasian collision and the Himalayan orogeny. However, the total area of now-extinct Cretaceous–Paleogene continental arcs is 1.3–2 times larger than that of the Himalayan range front and the Tibetan plateau combined, suggesting that weathering of these remnant volcanic arcs may also play a role in drawing down CO2 through silicate weathering and subsequent carbonate burial. In summary, if global continental arc flare-ups lead to greenhouse conditions, long-lived icehouse conditions should follow in the aftermath due to decreased CO2 inputs and an increase in regional weathering efficiency of remnant arc topography.
    Earth and Planetary Sciences Letters 09/2015; 425:105-119. DOI:10.1016/j.epsl.2015.05.045 · 4.35 Impact Factor
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    • "Fossils of Cedrelospermum were common from the Eocene of the middle latitudes in North America, while in the Oligocene they were found only in northwestern Gulf of Mexico and northwestern United States (Fig. 2). This suggests an overall southward retreat of the genus distribution in this continent from the Eocene to Oligocene, probably in response to the global cooling initiated during in the Eocene–Oligocene transition (Tiffney 1985; Graham 1999; Xiang and Soltis 2001; Zachos et al. 2008) (Fig. 2). Similar to the situation in North America, the genus also underwent an overall southward retreat from the Eocene to Oligocene in Europe, and even reached more southern latitudes in the Fig. 7 Cedrelospermum fruits from Asia, Europe and North America for comparison. "
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    ABSTRACT: Cedrelospermum (Ulmaceae) is an extinct genus with extensive fossil records in Europe and North America. However, no fossil of the genus has been reported from Asia. Here we describe Cedrelospermum asiaticum L.B. Jia, Y.J. Huang et Z.K. Zhou sp. nov. based on compressed fruits from the late Miocene of Yunnan, southwestern China. The fossil fruits are characterized by an ovate fruit body adjoined by double wings, with the veins on the primary wing converging toward a stigmatic area. According to the historical geographic distribution of the genus, we hypothesize that Cedrelospermum originated in North America where both single-winged and double-winged fruits were reported. The single-winged form subsequently spread into Europe via the North Atlantic land bridge and the double-winged form dispersed into Asia via the Bering land bridge. From the Eocene to Oligocene, a southward retreat of the genus distribution probably took place, which coincided with the global surface cooling initiated during the Eocene-Oligocene transition. The extinction of Cedrelospermum from Asia may be related to the intensification of the East Asian monsoon.
    Journal of Plant Research 07/2015; DOI:10.1007/s10265-015-0739-2 · 2.51 Impact Factor
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