Periodic Regime Shifts of ENSO Behavior Appeared in Alkenone SST Changes in Mid-latitude North Pacific During the Last 150,000 Years.

In order to examine the response of mid-latitude North Pacific to glacial-interglacial changes, we have generated the late Quaternary records of alkenone SST in California (ODP 1014 and 1016) and Japan (MD01-2421) margins during the last 150,000 years. SST changed from 9 degrees to 18 degrees centigrade at ODP 1016 and from 12 degrees to 19 degrees centigrade at ODP 1014, and the profiles are similar to SPECMAP oxygen isotope profile, although early warmings were observed at terminations I and II. At MD01-2421, SST changed from 13 degrees to 23 degrees centigrade. The lowest SST (6 degrees lower than Holocene) was observed during the late LGM, while SST during the early LGM is almost as same as that of Holocene. A comparison between California and Japan margins showed that the periods with high SST in California margin are the periods with low SST in Japan margin, and the reverse is also true. The out of phase change repeated with precession cycle, and it reflects the latitudinal displacement of the subarctic boundary in reverse between the eastern and western margins of N. Pacific like a seesaw. Such a seesaw-like displacement is attributed to the regime shift of ENSO behavior. In more El Nino-like conditions, subtropical circulation was weaker, and the subarctic boundary shifted southwards in the western margin. The timing and cyclicity of the change agree with the result of Zebiak-Cane ENSO model (Clement et al., 1999, Paleoceanogr., 14, 441). The SST change in mid-latitude North Pacific is an amplified signal of the climatic changes induced by the regime shift of ENSO behavior.