Yamada, K., Kamite, M., Saito-Kato, M., Okuno, M., Shinozuka, Y. and Yasuda, Y. 2010. Late Holocene monsoonal-climate change inferred from Lakes Ni-no-Megata and San-no-Megata, northeastern Japan. Quaternary International 220: 122-132.
Working with sediment cores they obtained in July of 2007 from Lakes Ni-no-Megata (39°57'N, 139°43'E) and San-no-Megata (39°56'N, 139°42'E) on the Oga Peninsula of northeastern Japan, the authors measured a number of sediment properties, among which were sulfur content and coarse mineral grains, the former of which served as a proxy for paleo-Asian summer monsoon activity and the latter of which served as a proxy for paleo-Asian winter monsoon activity. This work revealed the presence of a cold/dry interval stretching from AD 1 to 750, a warm/humid interval stretching from AD 750 to 1200, and another cold/dry interval stretching from AD 1200 to the present, which periods they associated, respectively, with "the Dark Ages Cold Period, the Medieval Warm Period and the Little Ice Age ." Thus, they identified the MWP as prevailing from AD 750 to 1200.