Data report: Pleistocene diatoms from Sites U1302 and U1303, Orphan Knoll, northwestern Atlantic Ocean

Abstract

Downcore variations of total diatom concentration and diatom assemblages have been studied along the upper 48 meters composite depth (mcd) of the corrected spliced composite section at Integrated Ocean Drilling Program Expedition 303 Sites U1302 and U1303. Diatom concentration varies between 1.0 × 10 3 and 2.1 × 10 6 valves/g. The highest diatom values are seen in the lower part, mostly between 35 and 48 mcd. The highly diversified diatom community is composed of ~110 species. The fossil diatom assemblage reflects the complex oceanographic setting in surface waters overlying Sites U1302 and U1303. Arctic/Subarctic components dominate the diatom assemblage, such as Actinocyclus curvatulus, Rhizosolenia hebetata var. hiemalis Bailey, Thalassiosira antiqua (Grunow) Cleve-Euler, Thalassiosira angulata, the vegetative cell of Thalassiosira gravida Cleve, and Thalassiosira trifulta G. Fryxell. Moderate influence of coastal waters is reflected by the occurrence of several species of resting spores of Chaetoceros, Actinocyclus octonarius Ehrenberg, Coscinodiscus radiatus Ehrenberg, and Thalassionema nitzschioides var. nitzschioides (Grunow) Van Heurck. Transport from shallow waters into the hemipelagic realm is mirrored by the presence of Delphineis karstenii (Boden) G. Fryxell and Paralia sulcata (Ehrenberg) Cleve, whereas Alveus marinus (Grunow) Kaczmarska and G. Fryxell and Fragilariopsis doliolus (Wallich) Medlin and Sims mainly represent a lowlatitude Atlantic signal.