Paleoenvironment And Paleoceanography Of The North Icelandic Shelf Since The Last Deglaciation

The North Atlantic has been the focus of paleoclimate and paleoceanographic study in recent years, following increasingly becoming the hotspot of research with different scales. A high-resolution diatom record from core MD99-2271 reveals a series of palaeoceanographic change on the North Icelandic shelf during 14600-3000 cal. yr BP.A total of 170 taxa were identified from 120 sediment samples of core MD99-2271. The main species include Thalassiosira nordenskioeldii, Thalassiosira oestrupii,Rhizosolenia borealis, Rhizosolenia hebetata, Fragilariopsis cylindrus, Thalassiosira bulbosa, Bacterosira bathyomphala, Fragilariopsis oceanica, Thalassiosira hyalina, Thalassiosira antarctica var.brorealis resting spore, Thalassionema nitzschioides, Par alia sulcata, Odontella aurita et al.The sustaining increase of warm diatoms and the continuing reduction of cold taxa in core MD99-2271 on the North Iceland shelf reveal a warming trend of climate in this area during 14600～3000 cal. yr BP. The periodic counter-balance of these two types of diatoms in the diatom assemblages indicates the process of temperature variation in the context of climate warming. The reconstructed paleoenvironment of the North Iceland shelf by the Rw/wc, which may indicate the temperature changes of seawater, can roughly be divided into five stages since the last deglaciation.The interval 14600-12800 cal. yr BP is the warm B(?)lling-Aller(?)d period and relatively high abundance of warm-water species T. nitzschioides suggests that Atlantic water, presumably related to the strength of the Irminger Current had a stronger influence on the North Icelandic shelf. Increased abundance of sea-ice diatom species (F. cylindrus and T. bulbosa) indicates a significant increase in the influence of the East Greenland Current during the 12800～11500 cal. yr BP. The interval 11500～10200 cal. yr BP is characterized by the coldest climate since the last deglaciation (Younger Dryas event). The present-day oceanographic current system in this area had been established at the transition to the Holocene. Between 10200-6000 cal. yr BP, there were a significant increase in warm-water species (T. nitzschioides and T. oestrupii), and a marked decline of sea-ice species and cold water species. This suggests a period of enhanced influence of the Irminger Current on the North Icelandic shelf, corresponding in time to the Holocene climatic optimum. Finally, during 6000～3000 cal. yr BP, the influence of the East Greenland Current became stronger at the end of the Holocene Climate Optimum, which led to the sea water temperature reduced.The machenism for changes in palaeoclimate and palaeoceanography on the North Iceland shelf since the last deglaciation are also discussed in this thesis. A general warming trend together with periodic changes in sea water temperatures and some cold events during 14600～3000 cal. yr BP may result from the interaction of cold and warm water masses, e.g. variations in strength of the cold East Greenland Current and the warm Irminger Current. Furthermore, the reason of periodic rapid cooling events and regional climate in a wider range may be due to solar insolation in the Nothern Hemisphere and the North Atlantic deep water circulation and the thermohaline circulation may have magnified these change.