University of Derby, United Kingdom

In an attempt to document the paleoecological affinities of individual extant and extinct dinoflagellate cysts, late Pliocene and early Pleistocene dinoflagellate cyst assemblages have been compared with geochemical data from the same samples. Mg/Ca ratios of Globigerina bulloides were measured to estimate the spring-summer sea-surface temperatures from four North Atlantic IODP/DSDP sites. Currently, our Pliocene-Pleistocene database contains 204 dinoflagellate cyst samples calibrated to geochemical data. This palaeo-database is compared with modern North Atlantic and global datasets. The focus lies in the quantitative relationship between Mg/Ca-based (i.e. spring-summer) sea-surface temperatures (SST (sub Mg/Ca) ) and dinoflagellate cyst distributions. In general, extant species are shown to have comparable spring-summer SST ranges in the past (SST (sub Mg/Ca) ) and today (SST from World Ocean Atlas 2005, Locarnini et al., 2006), demonstrating that our new approach is valid for inferring spring-summer SST ranges for extinct species. For example, Habibacysta tectata represents SST (sub Mg/Ca) values between 10 and 15 degrees C when it exceeds 30% of the assemblage, and Invertocysta lacrymosa exceeds 15% when SST (sub Mg/Ca) values are between 18.6 and 23.5 degrees C. However, comparing Pliocene and Pleistocene SST (sub Mg/Ca) values with present day summer values for the extant Impagidinium pallidum suggests a greater tolerance of higher temperatures in the past. This species occupies more than 5% of the assemblage at SST (sub Mg/Ca) values of 11.6-17.9 degrees C in the Pliocene and Pleistocene, whereas present day summer SSTs are around -1.7 to 6.9 degrees C. This observation questions the value of Impagidinium pallidum as reliable indicator of cold waters in older deposits, and may explain its bipolar distribution. Abstract Copyright (2011) Elsevier, B.V.