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 438A and 440B) between similar to 4.8 to similar to 2.8 Ma provide stratigraph ically-controlled, comprehensive data to reconstruct Pliocene northeas t Asian/western Pacific climates. The marine (radiolarian) component o f this study was used to develop new equations to quantify estimates o f summer and winter sea surface temperatures. In this 2-Myr Pliocene i nterval, average sea surface temperatures were commonly below present values. Summer sea surface temperatures exceed present day values only during two intervals centered at similar to 3.95 and similar to 4.55 Ma. Environmental changes in northern Japan (inferred from diagnostic pollen assemblages in the same sediment samples), for the most part, r eflect overall changes in marine surface temperatures offshore. Optima l conditions for the development of subtropical/warm temperate taxa in northern Japan occurred similar to 4.0 Ma, when winter SSTs offshore may have reached 2 degrees-4 degrees C above present. The continuous p resence of now-extinct subtropical plants in Japan during early Plioce ne (4.8-similar to 4.1 Ma) may have been sustained try equable conditi ons (lower seasonality) in the northwest Pacific. The upper part of ou r 2-Myr record (between similar to 3.4-2.8 Ma) is characterized by inc reasingly lower sea surface temperature minima. These colder surface o cean conditions are associated with the predominance of boreal taxa ac ross the northern Japanese archipelago, indicating substantially lower than observed temperatures.