Impact of shallow-living radiolarian flux variations on North Atlantic Cycladophora davisiana percentages

Abstract

The cause of high Cycladophora davisiana percentages, a deep-living (maximum abundance > 200 m) radiolarian species, in high-latitude (> 45°) late Pleistocene deep-sea sediments has been much debated. In this paper we show that in four subpolar North Atlantic cores these late Pleistocene high percentages (> 20%) result more from a reduction of other radiolarian flux, predominantly shallow-living species (< 200 m), than to an increase of C. davisiana flux relative to Holocene flux. These findings are similar to those reported from the North Pacific (Hays et al., 2013). In both oceans, the late Pleistocene to Holocene shallow-living species' flux increase is larger than the concomitant decrease of C. davisiana flux. Similarly, high C. davisiana percentages (> 20%) found today in Okhotsk Sea Holocene sediments (Kruglikova, 1975; Robertson, 1975; Morley and Hays, 1983) result from low radiolarian concentrations in the overlying dicothermal layer (20–150 m) where year round temperatures are near 0 °C. It is likely that the high C. davisiana percentages in North Atlantic late Pleistocene sediments were caused by a similar overlying stratification that had important biological consequences for radiolarians and other plankton. A more significant time transgressive increase in Shallow and Others radiolarian Assemblage flux occurs initially in the southernmost core in mid-Holocene, ultimately recorded at the northernmost site during the late Holocene. Here flux of the Deep Assemblage and C. davisiana also increases.