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Early Mesozoic Biodiversity and Climate Change: marine ecosystem response to global warming and carbon dioxide rise

Final Report Summary - EMBICC (Early Mesozoic Biodiversity and Climate Change: marine ecosystem response to global warming and carbon dioxide rise)

The Early Mesozoic (from the Permian/Triassic boundary to the Middle Jurassic) is a critical, yet understudied, interval in the history of life. Three major extinction events (the Late Permian, Late Triassic and Early Toarcian events) occur within this interval of time. All of these biotic crises triggered major reorganization of marine ecosystems (McGhee et al., 2004), and taken together were largely responsible for the present structure and composition of marine ecosystems. They were also all intimately associated with evidence for dramatic global warming and increase in the atmospheric concentrations of CO2 (e.g. Kidder and Worsley, 2004). The global rise in temperature between the latest Permian and the earliest Triassic, for example, is estimated as some 5-6°C (Magaritz and Holser, 1991), which is within the upper range of estimates for temperature rise in the next century (e.g. Cox et al., 2000). This resulted in ocean stratification and expansion of the oxygen minimum zone (e.g. Wignall and Twitchett 1996; Hotinski et al., 2000) and the most profound biotic crisis in Earth history (e.g. Erwin, 1994; Benton and Twitchett, 2003).

There is a wide consensus that changes in atmospheric CO2 is a major driver of global temperature and climate change; a view that is supported by the GEOCARB III model (Berner & Kothavala, 2001) and geological archives of ancient pCO2 data such as fossil leaves and fossil soils (McElwain et al., 1999; Montanez et al., 2007). However, estimates of past temperatures, from isotopic analyses of calcitic fossils such as brachiopods and belemnites, show limited correlation with the estimates of past pCO2 (Veizer et al., 2000; Shaviv and Veizer, 2003). This apparent mismatch is particularly striking in the Early Mesozoic, where the GEOCARB III data indicate rising CO2 levels, but δ 18O analyses of fossil shells indicate falling temperatures (i.e. global cooling). Shaviv and Veizer (2003, and refs therein) have used this apparent negative relationship to infer that global temperatures are controlled by extraterrestrial factors, such as cosmic ray flux, rather than pCO2, with obvious implications for our understanding of past, present and future climate change.

Hence, despite the importance of the Early Mesozoic as a critical interval in Earth history, there are still some fundamental questions that need addressing and have relevance for the present-day.

The major aims of our project were to address the following two key questions:
1. What drives global temperature and climate in the Early Mesozoic?
2. What are the biotic responses associated with changes in temperature?