Diatom-based reconstruction of palaeoceanographic changes on the North Icelandic shelf during the last millennium

摘要

Pronounced palaeoceanographic changes during the last millennium are revealed by high-resolution diatom records from site MD99-2275 on the North Icelandic shelf. There is a high degree of consistency between the reconstructed summer sea surface temperature (SST) record based on diatoms and the instrumental and documentary data during the last 100. years. This confirms the reliability of this proxy for the study of palaeoceanographic and palaeoclimatic changes on the North Icelandic shelf. The present diatom-based summer SST reconstruction shows that the last millennium was characterized by a general cooling trend, but with some fluctuations. Warm and stable conditions with relatively strong influence of the Irminger Current on the North Icelandic shelf are indicated during the interval AD 940-1300, corresponding in time to the Medieval Warm Period (MWP). A considerable cooling at ?. AD 1300 indicates the transition to the Little Ice Age (LIA) with increased influence of Polar and Arctic water masses deriving from the East Greenland and East Icelandic currents. An extended cooling period between AD 1300 and 1910 is characterized by approximately century-scale oscillations, with marked cold intervals at AD 1325-1375, AD 1460-1500, AD 1610-1670 and AD 1810-1910, separated by relatively mild spells. A two-step warming during the last 100. years is interrupted by three cool events around AD 1920, in the AD 1960s and in the late AD 1990s. In general, the diatom-based indication of palaeoceanographic changes on the North Icelandic shelf during the last millennium corresponds to other proxy-based palaeoclimatic and palaeoceanographic records in the North Atlantic region.