The Diatom Assemblages And Environmental Change In Western Greenland Since6700Cal. A BP

Being located in the high latitudes, adjacent to the Greenland ice sheet, the North Atlantic has been the focus of paleoclimate and ancient environmental reconstruction in recent years, following increasingly becoming the hotspot of research with different scales. Based on the ocean drilling GA306-GC3in West Greenland waters, by means of study of the bottom portion of the hole, when it comes to diatoms found in the core can directly reflect paleoclimatic change since the mid-late Holocene in West Greenland waters as well as main influencing factors.A total of107taxa were identified from89sediment samples of core GA306-GC3. The main species include Bacterosira bathyomphala, Fragilariopsis cylindrus, Fragilariopsis oceanica, Thalassionema nitzschioides, Thalassiosira antarctica var. boreal resting spore, Thalassiosira nordenskioeldii, Thalassiosira oestrupii, Rhizosolenia hebetata f. semispina, Rhizosolenia borealis and Thalassiosira hyaline et al.Using the special paleoenvironmental analysis softwares (Tilia and C2) on diatom cluster analysis and principal component analysis from the gravity core GC3, revealed a good consistency between the results. It can be divided into the same diatom assemblage zones from top to bottom, mutual reflecting the region climate gradually cooling process since6700cal. a BP, specific changes include the following three stages:The interval6650-3950cal. a BP is characterized by relatively high abundance of the warm-water species, corresponding to the Late Holocene Thermal Maximum. Declining slightly in warm-water species and increased fluctuation in cold water species indicate decrease impacts of Atlantic waters during the later stage.The content of warm species volatility increases from3950a. BP to3000cal. a BP, After3000cal. a BP the warm-water species return to relatively lower, and there is a clear increasing trend in the abundances of Arctic and sea-ice species, indicating a cold sea-surface conditions with high influence of East Greenland Current.The influence of the cold water might have increased on the West Greenland since warm species reach minimum from1650cal. a BP to130cal. a BP. A major change in diatom assemblages at around1000cal. a BP indicates a significant palaeoceanographic shift on the West Greenland shelf in the mid to late Holocene, which is demonstrated by the Medieval Warm Period.The variation tendency based on the diatom record from core GA306-GC3is consistent with other proxy-based palaeoclimatic and palaeoceanographic records in the North Atlantic region (i.e. the reconstructed GISP2ice core temperature record), being accordant with other information from adjacent regions, recording the Holocene Megathermal, Dark Ages Cold Period, the Medieval Warm Period the Little Ice Age and other ancient climate events.