Isotopic excursions at period boundaries

Biotic extinctions of varying magnitudes are associated with many era boundaries (see Section 1.5.5), and there are often accompanying excursions in the carbon isotopic record. Such isotopic excursions reflect environmental events of sufficient size to have an impact on the global carbon cycle. However, it is not always easy to determine whether the excursion was the result of the extinction event (due to biotic collapse), is attributable to some other consequence of the event leading to the extinction or may even be largely unrelated to the extinction event. The problems associated with interpretation of isotopic excursions are demonstrated by three important boundary events in the following subsections. 

Perhaps the best known of these extinction events occurred at the Cretaceous—Tertiary boundary (KTB), which left a clear signature in the C isotopic record. As we have seen in Section 5.8, the preferential assimilation of 12C02 during photosynthesis leaves surface waters depleted in the lighter C isotope, but 

Although primary production recovered, few zooplankton appear to have been present, so bacterial 

Atmospheric pC02 is likely to have increased as a result of equilibration between the air and Strangelove ocean, and the terrestrial wild fires triggered by the bolide impact (Wolbach et al. 1988). However, the periodic phytoplanktonic blooms would have drawn down significant amounts of C02. Consequently, it is likely that there were dramatic climatic swings during the recovery phase, until atmospheric C02 levels stabilized (Wolfe Upchurch 1986). 

The climate spanning the end of the Palaeocene and the start of the Eocene was warmer than at any other time during the Cainozoic (Bains et al. 1999).Within this interval there was a dramatically rapid warming—the 

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