Did high Neo-Tethys subduction rates contribute to early Cenozoic warming?
The 58–51 Ma interval was characterized by a long-term increase of global temperatures (+4 to +6 °C) up to the Early Eocene Climate Optimum (EECO, 52.9–50.7 Ma), the warmest interval of the Cenozoic. It was recently suggested that sustained high atmospheric <i>p</i>CO<sub>2</sub...
| Main Authors: | , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2015-12-01
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| Series: | Climate of the Past |
| Online Access: | http://www.clim-past.net/11/1751/2015/cp-11-1751-2015.pdf |
| Summary: | The 58–51 Ma interval was characterized by a long-term increase of global
temperatures (+4 to +6 °C) up to the Early Eocene Climate
Optimum (EECO, 52.9–50.7 Ma), the warmest interval of the Cenozoic. It was
recently suggested that sustained high atmospheric <i>p</i>CO<sub>2</sub>, controlling
warm early Cenozoic climate, may have been released during Neo-Tethys
closure through the subduction of large amounts of pelagic carbonates and
their recycling as CO<sub>2</sub> at arc volcanoes. To analyze the impact of
Neo-Tethys closure on early Cenozoic warming, we have modeled the volume of
subducted sediments and the amount of CO<sub>2</sub> emitted along the northern
Tethys margin. The impact of calculated CO<sub>2</sub> fluxes on global
temperature during the early Cenozoic have then been tested using a climate
carbon cycle model (GEOCLIM). We show that CO<sub>2</sub> production may have
reached up to 1.55 × 10<sup>18</sup> mol Ma<sup>−1</sup> specifically during the EECO,
~ 4 to 37 % higher that the modern global volcanic CO<sub>2</sub>
output, owing to a dramatic India-Asia plate convergence increase. The
subduction of thick Greater Indian continental margin carbonate sediments at
~ 55–50 Ma may also have led to additional CO<sub>2</sub> production
of 3.35 × 10<sup>18</sup> mol Ma<sup>−1</sup> during the EECO, making a total of 85 % of the
global volcanic CO<sub>2</sub> outgassed. However, climate modeling demonstrates
that timing of maximum CO<sub>2</sub> release only partially fits with the EECO,
and that corresponding maximum <i>p</i>CO<sub>2</sub> values (750 ppm) and surface warming
(+2 °C) do not reach values inferred from geochemical proxies, a
result consistent with conclusions arising from modeling based on other
published CO<sub>2</sub> fluxes. These results demonstrate that CO<sub>2</sub> derived
from decarbonation of Neo-Tethyan lithosphere may have possibly contributed
to, but certainly cannot account alone for early Cenozoic warming. Other
commonly cited sources of excess CO<sub>2</sub> such as enhanced igneous province
volcanism also appear to be up to 1 order of magnitude below fluxes
required by the model to fit with proxy data of <i>p</i>CO<sub>2</sub> and temperature at
that time. An alternate explanation may be that CO<sub>2</sub> consumption, a key
parameter of the long-term atmospheric <i>p</i>CO<sub>2</sub> balance, may have been
lower than suggested by modeling. These results call for a better
calibration of early Cenozoic weathering rates. |
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| ISSN: | 1814-9324 1814-9332 |