Pliocene climate of Japan and environs between 4.8 and 2.8 Ma: A joint pollen and marine faunal study

Joint analyses of siliceous fauna and pollen in sediment deposited in the Japan Sea (ODP Site 794A) and western Pacific (DSDP Sites 438 A and 440B) between ~4.8 to ~2.8 Ma provide stratigraphically-controlled, comprehensive data to reconstruct Pliocene northeast Asian/western Pacific climates. The marine (radiolarian) component of this study was used to develop new equations to quantify estimates of summer and winter sea surface temperatures. In this 2-Myr Pliocene interval, average sea surface temperatures were commonly below present values. Summer sea surface temperatures exceed present day values only during two intervals centered at ~3.95 and ~4.55 Ma. Environmental changes in northern Japan (inferred from diagnostic pollen assemblages in the same sediment samples), for the most part, reflect overall changes in marine surface temperatures offshore. Optimal conditions for the development of subtropical/warm temperate taxa in northern Japan occurred ~ 4.0 Ma, when winter SSTs offshore may have reached 2 °–4 °C above present. The continuous presence of now-extinct subtropical plants in Japan during early Pliocene (4.8- ~4.1 Ma) may have been sustained by equable conditions (lower seasonality) in the northwest Pacific. The upper part of our 2-Myr record (between ~3.4 −2.8 Ma) is characterized by increasingly lower sea surface temperature minima. These colder surface ocean conditions are associated with the predominance of boreal taxa across the northern Japanese archipelago, indicating substantially lower than observed temperatures.