Multiple Proxy Estimates of pCO2 in the Hauterivian–Barremian of the Laiyang Basin, Eastern China
Abstract. In recent decades, several proxies have been developed to reconstruct atmospheric paleo-CO2 concentrations (pCO2). The confidence in paleo-CO2 estimates can be increased by comparing results from multiple proxies with multiple species at a single site. Here we present a new pCO2 record for the Hauterivian–Barremian using three methods based on two fossil coniferous species (Cupressinocladus sp. and Brachyphyllum obtusum) collected from Laiyang Basin, eastern China. The pCO2 values were approximately 579–663 ppmv (recent standardization) and 966–1106 ppmv (carboniferous standardization) based on the stomatal ratio (SR)-based method, and about 472–525 ppmv based on the mechanistic model. Both of these two methods were highly coincident with other SR-based and geochemical reconstructions for the early stage of the Early Cretaceous. The pCO2 value estimated using the carbon isotopes model was approximately 472–525 ppmv, which is generally lower than the pCO2 valueestimated using the other methods. The mechanistic model may be widely applied to more fossil taxa than the SR-based method and retains sensitivity at high pCO2. Furthermore, by comparing with other pCO2 records and Weissert event in the Early Cretaceous, the pCO2 values obtained from this study indicate a relatively low atmospheric CO2 concentration during the Hauterivian–Barremian, and reflect the cooling event in the last stage of the Weissert event.
This preprint has been withdrawn.
Peihong Jin et al.
Peihong Jin et al.
Peihong Jin et al.
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This is a good paper on an interesting question of international interest: reconstructing atmospheric carbon dioxide levels from several different models of stomatal index and plant isotopic composition for fossil plants of several levels from the Early Cretaceous period. The values are not wildly different from modern industrial atmosphere, which may surprise some who view the Cretaceous as a greenhouse period.
Can an age model of age for each stratigraphic level be constructed from the radiometric dates (l104)? This would put a more accurate age on the fossils studied here. It would be good to make the new data larger in Fig.6 so it is easier to see the new contribution, which seems to be only a few data points.
The estimates of Retallack 2001 used in Fig. 6 have been recently recalibrated by Retallack, G.J. and Conde, G.D., 2020. Deep time perspective on rising atmospheric CO2. Global and Planetary Change, 189, p.103177. Barremian and Aptian values calculated were 281-303 ppm, most like the isotopic model employed here. One spike of 969 ppm corresponds with OAE1 in the ocean and of 307 ppm with the Weissert event. These were not from USA as shown in Table 6 but from China, Australia and Argentina.
The Weissert event is here attributed to Parana-Etendeka flood basalt volcanism (l.465), but the marine signature is a positive isotopic excursion, which is the opposite of negative excursions found with other carbon dioxide greenhouse spikes at flood basalt events such as at the Permian-Triassic and Cretaceous-Tertiary events. Positive oceanic excursions are generally attributed to increased planktonic productivity and carbon burial in the ocean, and so reduced atmospheric carbon dioxide. Weathering of basalt (l.470) is a less convincing explanation for CO2 drawdown, as basalt is fine grained and more difficult to weather than loess and granite, which are weathered more during greenhouse spikes.
l.23, 206, 350, 437 Carboniferous should have capital “c”.
l.84 “One of the most desirable areas to study” is s curious way to introduce it without explanation why it is so desirable.
l.148 What is meant by ‘last second’ or ‘last third’? Secondary branches? Tertiary branches? Penultimate? Antipenultimate?
l.307 VPD standard is scarce nowadays: was it or Vienna PBD used?