Sr-87/Sr-86 variation in north Pacific sediments: a record of the Milankovitch cycle in the past 3 million years

Temporal variations of Sr isotopic compositions in the detrital component o f north Pacific sediments have been precisely examined. The Sr isotopic com position is controlled by the flux of eolian material from the Asian contin ent with a high Sr-87/Sr-86 ratio (0.724-0.726) relative to volcanic materi al with a low ratio (0.703-0.705) from the Izu-Ogasawara-Mariana are and oc eanic islands such as the Hawaiian Islands. Assuming that the volcanic flux is constant, the temporal variation in Sr isotopic ratio reflects the amou nt of eolian input from the continent. The major characteristics of the tem poral variations and the interpretation of them are summarized as follows. (1) The Sr-87/Sr-86 records show cyclic fluctuations of 400 ky and 100 ky p eriodicities which are associated with the eccentricity of the earth's orbi t (Milankovitch cycle). (2) Between 3 and 0.8 Ma, the Sr-87/Sr-86 ratio in the north central Pacific sediment increases gradually. This reflects an in creased eolian input from the arid region in east Asia. The increase must b e related to aridification of the Asian continent. (3) The decreased Sr-87/ Sr-86 ratio during the past 0.8 m.y. implies a decreased eolian input. The age of 0.8 Ma may relate to the climatic event known as the Middle Pleistoc ene shift. All of these phenomena reflect a fluctuation of the eolian flux corresponding to the paleoclimatic cycle of aridity in the Asian continent. The Sr isotopic composition of pelagic sediment in the north pacific is se nsitive to changes in the eolian input reflecting to the aridity of the Asi an continent. (C) 1999 Elsevier Science B.V. Ail rights reserved.