Diatom response to the Holocene climatic optimum on the North Icelandic shelf

A diatom record from core MD992275 on the North Icelandic shelf reveals palaeoclimatic and palaeoceanographic changes during the time interval 9000 to 5600 cal. year BP. The study period includes the Holocene Climate Optimum (HCO), as widely known in the North Atlantic region. A comparison with data for the last 2000 years and with the present-day surface sediment diatom assemblages shows that there was considerably stronger influence of Atlantic water masses in the area during the HCO than in the late Holocene and today. The results of cluster analysis and principal component analysis divide the studied period into three intervals, each characterised by a specific diatom assemblage. The assemblages indicate changes in the interaction of the relatively warm Irminger Current (IC) and the cold East Greenland Current (EGC) and East Icelandic Current (EIC). The North Icelandic shelf was strongly affected by the IC during the interval 8000–6800 cal. year BP, which may be the warmest period of the Holocene. During the intervals 9000–8000 and 6800–5600 cal. year BP, the influence of the IC was relatively weak and that of the EGC and EIC increased correspondingly. The well-known 8200 cal. year BP cooling event, shown in many records from the North Atlantic, is reflected by a relatively strong influence of the EGC and EIC between about 8300 and 8100 cal. year BP in our record. However, the diatom assemblages show that the inferred circulation change did not bring the strength of the IC down to the levels seen at present and during the last two millennia.