Journal of Oceanography, Vol. 62 (No. 4), pp. 481-492, 2006
Naoto Iwasaka1,2*, Fumiaki Kobashi2, Yosuke Kinoshita2 and Yuko Ohno2
1Institute of Observational Research for Global Change, JAMSTEC, Natsushima-cho, Yokosuka, Kanagawa 237-0061, Japan
2Department of Marine Technology, Tokyo University of Marine Science and Technology, Etchujima, Koto-ku, Tokyo 135-8533, Japan
(Received 28 June 2005; in revised form 10 February 2006; accepted 16 February 2006)
Abstract: A seasonal evolution of surface mixed layer in the western North Pacific around 24°N between 143°E and 150°E was observed by using an Argo float for more than 9 months, from December 2001 through August 2002. The result showed that the mixed layer deepened gradually in the first two months. It reached its maximum depth of about 130 m at the end of January, after which the mixed layer varied largely and sometimes the pycnocline below the mixed layer was much weakened until the summer mixed layer formed in late April. The thin surface mixed layer was maintained during the rest of the observation period. Heat budget analysis suggests that the vertical and horizontal temperature advections are the two most dominant terms in the heat balance in the upper layer on time scales from a few days to a month. The vertical motions that are possibly responsible for the vertical temperature advection are discussed.