Distribution of dinoflagellate cyst assemblages in surface sediments from the northern and western shelf of Iceland

In order to provide calibration for palaeoceanographic investigations, 54 surface sediment samples from the northern and western margin of Iceland and Greenland have been analysed for their dinoflagellate cyst assemblages. Relatively high diversity was observed with a total of 28 taxa. Cysts of Pentapharsodinium dalei are dominant accompanied by Operculodinium centrocarpum and Nematosphaeropsis labyrinthus. Three groups of assemblages have been recognised based on multivariate statistical analyses and these are related to surface water masses and currents. The first association, Group I, located west of Iceland, is characterised by high abundance of O. centrocarpum and N. labyrinthus accompanied by significant occurrence of the heterotrophic taxa Brigantedinium spp., Selenopemphix quanta, cysts of Polykrikos schwartzii and cysts of Protoperidinium americanum. This region is under the influence of the Irminger Current (IC) and contains the most productive waters around Iceland. The second association, Group II, comprising high relative abundance of cysts of P. dalei accompanied by significant occurrence of O. centrocarpum and a very high concentration (up to 256 920 cysts/g), is situated in the northern Icelandic shelf, in the Polar Front realm, i.e. the marginal zone between the East Icelandic Current (EIC) and the northern branch of the IC. The third group (Group III) is in the region influenced by the East Greenland Current and the EIC and characterised by the codominance of cysts of P. dalei and O. centrocarpum, relatively high representation of Impagidinium pallidum and low concentrations (from 370 to 56 220 cysts/g). This investigation demonstrates that dinocyst distribution is clearly related to upper water mass physical factors. Advection of temperate species around Iceland suggests significant transport by surface currents, especially the IC; however, the apparent boundaries between the associations and decreasing percentages related to environmental gradients indicate that dispersal by surface transport is limited by the ecological requirements of the dinoflagellate cells. Bottom currents may play a role in the accumulation rate of cysts.