Paleoceanography and dinoflagellate cyst record of northwestern North Pacific ODP Site 882 during the Pliocene–Pleistocene transition

Abstract

A palynological study of the Pliocene–Pleistocene transition (2761 to 2497 ka) at Ocean Drilling Program Site 882, located on the Detroit Seamount in the western Subarctic Gyre of the northern North Pacific, provides a detailed record from 68 productive samples of dinoflagellate cysts (dinocysts) and acritarchs with preservation varying from good to moderate. Dinocyst assemblages are characterized by an overwhelming dominance of round brown cysts, scarcity of phototrophs including Impagidinium species, and low taxonomic richness (a total of 11 dinocyst taxa for the entire study), reflecting the elevated nutrient levels but harsh conditions and reduced salinities of the North Pacific Subarctic Gyre. Cool, saline surface waters characterize the interval from 2761 to 2.72 Ma, as indicated by relatively abundant Impagidinium species including I. pallidum. Following the establishment of the modern halocline at ~2.72 Ma, significant shifts are recorded in both dinocyst concentrations and abundances of the acritarch Cymatiosphaera? invaginata. Productivity evidently remained fairly high even during glacial cycles, including the intense glacial Marine Isotope Stage (MIS) G4 at 2.70 Ma marked by common Habibacysta tectata and Pyxidinopsis reticulata, implying ice-free conditions at least during the summer. Dinocyst concentrations, and by inference productivity, are at their lowest during MIS 104 (2.6 Ma) which is associated with pronounced cooling in the northern North Atlantic and across the higher latitudes of the Northern Hemisphere. Low abundances of Cymatiosphaera? invaginata throughout the interval 2600–2565 ka, which includes interglacial MIS 103, unusually suggest reduced precipitation and hence elevated salinities at this time. The interval 2558–2497 ka registers a return to sporadically abundant Cymatiosphaera? invaginata in glacial MIS 100 and interglacial MISs 101 and 99, suggesting the return of reduced salinities and perhaps enhanced nutrient levels. In general, productivity seems to remain relatively unchanged although with a peak in interglacial MIS 101. Most species recorded occur within their published stratigraphic ranges. However, this study extends the highest reported occurrence of Impagidinium detroitense Zorzi et al., 2020 from Upper Pliocene (2700 ka) to Lower Pleistocene (2544 ka).