Lusitanian/Mediterranean ostracods in the Holocene of Denmark: implications for the interpretation of winter temperatures during the postglacial temperature maximum

Two species of Lusitanian/Mediterranean ostracods, Aurila arborescens and Callistocythere badia, are reported from middle Holocene (Atlantic chronozone) localities in northern Jutland, Denmark. The two species occur in gyttja-rich, sandy deposits in association with shallow-water euryhaline mollusc and ostracod faunas. They are found in sediments from the Atlantic chronozone dated between 6790 ± 75 BP and 5900 ± 110 BP. A. arborescens is essentially a Mediterranean species with only two documented live occurrences outside the Mediterranean. It lives in shallow water with coldest-month temperatures of at least 6°C and warmest-month temperatures of at least 15-16°C. C. badia occurs in littoral marine environments in the eastern Mediterranean and along the southern and western coasts of the British Isles. It is suggested that coldest-month sea-surface temperatures in northern Denmark between 6800 BP and 5900 BP were more than 5-6°C above present values. The temperature maximum of the Atlantic chronozone in southern Scandinavia was apparently strongly influenced by westerly winds that brought into the North Sea area warm Atlantic air- and watermasses of the type presently found southwest of the British Isles.