Horizontal and vertical distribution of polycystine radiolarians in the western Arctic Ocean during the late summers of 2013 and 2015

Abstract

A drastic sea-ice reduction has been observed in the Pacific sector of the Arctic Ocean during the last few decades. However, it is still poorly understood how the future reduction in sea-ice cover will impact the microzooplankton communities within the Arctic marine ecosystems. To elucidate the relationship between hydrographic conditions and the horizontal and vertical distribution of polycystine radiolarians, we analyzed 84 plankton tow samples from 51 stations in the western Arctic Ocean. Radiolarians were commonly observed in the continental slope area and the deeper basin area but were scarce or absent on the continental shelf area during the late summers of 2013 and 2015. The horizontal distribution of radiolarians during this time interval was primarily related to the horizontal distribution of low salinity waters. Radiolarian abundances increased at the stations where the seasonally mixed layer, which was formed by sea-ice melt and river runoff, was observed. This result suggests that freshwater inputs would affect the distribution of radiolarians in the western Arctic, presumably via the modification of their food sources. Vertical distribution of radiolarian species was controlled by temperature and salinity characteristics of each water mass, but their abundance decreased in water masses with low dissolved oxygen.