A recent survey on the phytoplankton composition in the Arctic Ocean (70-80^oN, 160-180^oW) revealed that dinoflagellate comprises the highest percentage of phytoplankton in surface water. The situation is different from that in Bering Sea and Baffin Sea where diatoms and golden-brown algae are usually the most dominant species during summer time. Taxonomic analysis confirmed that Alexandrium catenella and A. tamarense appeared in very high concentration at 5 M to 15 M below the sea surface. Their concentrations might be as high as 1650 cell/ml-1 at certain sampling stations. The results coincided with events of PSP in Alaska in recent years and the presence of low level PSP toxins in shellfish samples collected from the northern Greenland. Instead of settling at the bottom sediments, cysts of Alexandrium Spp. often appeared in the water at 15-20 M below the sea surface of Arctic Ocean. Some of the cysts are found trapped beneath floating ices. The phenomenon is closely related to the special climatic characteristic of the Arctic Ocean where ices are formed and deformed in a relatively rapid rate. The nutrient levels in surface water are analysed, with discussions over the potential and implications of harmful algal bloom in the arctic waters near Alaska and the NW Territories of Canada.