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The marine microzooplankton radiolaria occur in seas from the Arctic to Antarctic. The siliceous Polycystine group are normally well preserved and frequently found in bottom sediments. They are very sensitive to environmental fluctuations and study of their present distribution is of crucial importance when attempting to reconstruct the ecological, climatic and oceanographic situations of the past.
Literature studies reveal that 26 polycystine species are present in the Arctic Ocean plankton but studies over the past decade has allowed us to identify 62 species in bottom sediments including those of the marginal seas. Following the last glaciation, biogenic opal first appears in the southern Norwegian Sea around 13.400 yrs BP. About 1000 years later, radiolaria spread to the Boreas Basin and probably entered the Arctic Ocean proper close to the Pleistocene/Holocene boundary.
Polycystine assemblages in the Arctic Ocean were orginally derived from the Atlantic fauna but within a very short time, about 10 ka, the Arctic fauna had become established and consists of arctic-boreal, cosmopolitan, and bipolar species. The majority of the Arctic Ocean species, excluding the endemics, also occur in surface sediments of the Arctic-Boreal, Atlantic, Pacific, Far East seas and in the Antarctic. However, the polycystine assemblages of the Arctic Ocean differ completely from those in the rest of the world with dominant key species and a different high rank taxa association reaching as high as 85-95%. Furthermore, the most abundant and widely distributed species in the Atlantic and Pacific (Lithomitra arachnea, Tholospyris borealis gr., Stylochlamidium venustum etc.), and similar but more diverse faunas from the Fram Strait and Chukchi Sea, do not occur in the high Arctic ocean basins. Actinomma leptoderma leptoderma, A. l. longispina and A. boreale are widely distributed in the Nordic Seas and the high Arctic basins and commonly in the Arctic Ocean. Two new species (Actinomma sp. A and B) have been recognized, showing strong morphological or transitional forms between them. We have studied the radiolarian faunas at more than 1000 stations in the northern hemisphere and so far we have only found the two new species in the central Arctic Ocean. Our available data support these species to be endemic to the Arctic Ocean and it is possible that speciation of the polycystines was extremely fast under the rigid regime present in the Arctic Ocean.
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