Strong regionalism in dinoflagellate cysts in recent sediments from the Chukchi-East Siberian Seas, Arctic Ocean

•Biogeography of dinoflagellate cysts in the Pacific Arctic Ocean were investigated.•Strong regionality infers a growing impact of southern waters on warming Arctic Ocean.•Toxic-Alexandrium cyst accumulations point to potential bloom initiation in Arctic Ocean.•Dinoflagellate cysts are useful indicators of Arctic marine conditions under global warming.