Isono, D., Yamamoto, M., Irino, T., Oba, T., Murayama, M., Nakamura, T. and Kawahata, H. 2009. The 1500-year climate oscillation in the midlatitude North Pacific during the Holocene. Geology 37: 591-594.
Working with three sediment cores retrieved off the coast of central Japan in the northwestern Pacific Ocean (36°02'N, 141°47'E), Isono et al. generated a multidecadal-resolution record of alkenone-derived sea surface temperature (SST) that covers the full expanse of the Holocene, which they then analyzed in a number of different ways. This record, in their words, "showed centennial and millennial variability with an amplitude of ~1°C throughout the entire Holocene," and they state that "spectral analysis for SST variation revealed a statistically significant peak with 1470-year periodicity." At the latter end of the record, Isono et al. report that "SST minima centered at ca. 0.3 ka and ca. 1.5 ka are correlated with the Little Ice Age and the Dark Ages Cold Period in Europe, respectively, whereas the SST maximum centered at ca. 1.0 ka is correlated with the Medieval Warm Period." From data presented in the authors' Figure 2, we estimate that the MWP was about 1°C warmer than the Current Warm Period.