Australia: The Land Where Time Began

A biography of the Australian continent 

Atmospheric Carbon Dioxide - A 300-Million-Year record from Plant Cuticles

According to the author1 geochemical proxies are used to reconstruct past atmospheric CO2 levels in order to better understand the link between atmospheric CO2 and climate over geological time (Berner, 1997; Pearson & Palmer, 2000; Ekart et al., 1999; Pagani, Freeman & Arthur, 1999). A broad picture of the variation of atmospheric CO2 throughout the Phanerozoic, that covers the last 544 My, has been provided by these records, though there are still some inconsistencies and gaps requiring attention. In this article the author1 presents evidence, based on stomatal abundance in fossil leaves from 4 plant genera closely related to the Ginkgo of the present, for a continuous record spanning 300 My. He reconstructed atmospheric CO2 concentrations based on the known relationship between the number of stomata on a leaf and CO2 concentrations in the growing season. The record he constructed indicated that over the last 300 My there were 2 episodes in which there were intervals when the atmospheric CO2 concentrations were low, less than 1,000 ppmv, and both of these intervals coincided with known ice ages occurring in the Neogene  8-1 Ma and Early Permian, 290-275 Ma. The levels of atmospheric CO2 were high, 1,000-2,000 ppmv, 250-65 Ma, most of the Mesozoic, though in this period there were intervals during which there were excursions in the atmospheric CO2 levels above 2,000 ppmv. The results of the author's study are consistent with some past CO2 record reconstructions (Berner, 1997; Pearson & Palmer, 2000), and palaeotemperature records (Veizer, Godderis & François, 2000), though they suggest the reconstructions based on carbon isotope proxies (Ekart et al., 1999; Pagani, Freeman & Arthur, 1999) may be compromised by isotopically light methane that was released as episodic outbursts (MacLeod & Wing, Krull et al., 2000). According to the author1 water vapour, CO2 and methane were involved in greenhouse climate warming over the last 300 My.


Sources & Further reading

  1. Retallack, G. J. "A 300-Million-Year Record of Atmospheric Carbon Dioxide from Fossil Plant Cuticles." Nature 411 (// 2001): 287-90.
Author: M. H. Monroe
Last updated 25/02/2013

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