Palaeoclimatic control of Upper Pliocene Discoaster assemblages in the North Atlantic

Abstract. Abundance variations of six Pliocene species of the nannofossil genus Discoaster were analyzed over the time interval 1.89–2.95 Ma at five sites in the North Atlantic; DSDP 552 (56°N), DSDP 607 (41°N), ODP 659 (18°N), ODP 658 (20°N) and ODP 662 (1°S). Individual species are compared between the five sites as a percentage of the total Discoaster assemblage, using age models based mainly on Discoaster datums (3 control points used at each site). The sampling interval is approximately 3 kyrs.

Discoaster brouweri, the only species covering the complete time interval became a less significant component of the assemblages with increasing latitude during the interval prior to 2.3 Ma. Discoaster triradiatus shows a distinct abundance acme at all sites between 1.89–2.7 Ma. Discoaster surculus increased in relative abundance with higher latitudes and upwelling conditions (ODP Site 658).

Discoaster pentaradiatus is an important component of the assemblages at all sites, but displays an inverse abundance relationship with D. surculus as a function of increasing latitude and upwelling conditions. Discoaster tamalis and Discoaster asymmetricus are reduced at low latitudes and in upwelling conditions and increase relative to D. brouweri at higher latitudes, where there is strong evidence for taxonomic affinity.