Coral Diversity and Temperature: a Palaeoclimatic Perspective for the Oligo-Miocene of the Mediterranean Region
Résumé
Zooxanthellate-coral (z-coral) generic richness values from 102 Oligocene-Miocene localities from the Mediterranean and adjacent areas are tested in this paper as a proxy for relative palaeotemperatures, essentially using the quantitative relationship between taxonomic richness and prevailing seawater temperature underlined by the so-called ‘energy hypothesis’. Patterns of generic richness and inferred palaeotemperatures are examined for each stage of the Oligocene-Miocene time interval and compared with some global palaeoclimatic curves based on oxygen stable-isotopes. Except for the Mid- Miocene Climatic Optimum, which is not recorded in the generic richness of the Mediterranean z-coral communities, the coral-richness-derived palaeotemperatures correlate well with the general palaeoclimatic trends shown by the isotope curves. Results also show: (1) a gradual increase of temperature from the early to the late Rupelian; and (2) a gradual widening of the temperature range after the Burdigalian. The latter indicates that z-coral communities were able to maintain themselves in the region by progressively adapting to a wider temperature range from the mid-Miocene onwards to the Messinian, as the Mediterranean was migrating northward. Although limitations and biases are underlined and discussed in the paper, the ‘energy hypothesis’ applied to fossil z-coral faunas appears to offer a powerful method when used at global or regional scales to estimate changes in palaeotemperatures. It holds particular promise for time intervals and regions where conventional isotopic data are lacking, such as the Oligocene and Miocene of the Mediterranean.