Palaeoclimatic applications of large databases: developing and testing methods of palaeotemperature reconstruction using nonmarine ostracods

Abstract

Non-analogue methods for Quaternary palaeoclimatic reconstruction, such as the coleopteran Mutual Climate Range method and the Mutual Ostracod Temperature Range (MOTR) method, use large geographical databases combined with modern climate datasets to establish the modern climate/temperature ranges of species, which can then be applied to the interpretation of fossil assemblages. Such approaches have been criticized for their lack of attention to variation in the distributions of species within their climate ranges. The MOTR method, for example, assumes that a species has an equal probability of occurring anywhere within its temperature range (e.g. mean July air temperature range), but tests using calculated averages of all records (as opposed to just the two end-points that define the range) show this to be false. The MOTR method remains valid, nevertheless, as long as it is only used to estimate the temperature ranges within which a fossil assemblage could have existed. Analyses of the distributions of 65 species within European climate space show that most are not normal, but often skewed and sometimes polymodal. The factors influencing such variations are discussed and consideration is given to ways of taking them into account in palaeotemperature estimations based on ostracod assemblages. A revised calibration table is presented, showing the modern air temperature ranges of 65 species, for use with the MOTR method.