Climatically influenced distribution of Gymnodinium catenatum during the past 2000 years in coastal sediments of southern Norway
Abstract Dinoflagellate cyst analysis of cored late Holocene sediments from the Norwegian coast of the Skagerrak and northern North Sea confirms the conclusions of previous studies from the Kattegat that climate influenced the quantitative distribution of Gymnodinium catenatum Graham 1943. These studies provide some of the first data on the effect of small-scale climatic changes on one component of the phytoplankton during the past 2000 years. In core 9310 from the Skagerrak, as in previous cores from the Kattegat, G. catenatum cysts increase proportionally from about AD 0 to peak amounts at about AD 900, 1200 and 1450 corresponding to periods of relatively warmer climate. Proportional decreases in G. catenatum correspond to periods of cooler climate in the 900s and 1300s, and to the colder climate of the Little Ice Age climax in the 1600s. In the site of core 9307 from the North Sea coast higher proportions of G. catenatum (15%) were probably reached between 300 and 1000 years later than in the other cores, due to the location of this site being closer to the biogeographic limit for high proportions of the species. New results also suggest that high proportions of the species (2–58%) were confined to open coastal waters south of Bergen, Norway. Living and fossil cysts of G. catenatum in this region are small compared with reported sizes elsewhere (24–40 vs. 37–60 μm), and may not be conspecific with G. catenatum. Irrespective of their taxonomy, the quantitative distribution of these cysts is influenced by climatic changes, and they are a reliable indicator of warmer water in more open coastal waters of Scandinavia during the late Holocene.