Seasonal variations of the upper ocean in the western North Pacific observed by an Argo float

Naoto Iwasaka, Fumiaki Kobashi, Yosuke Kinoshita, and ,Yuko Ohno

Tokyo University of Marine Science and Technology
Faculty of Marine Technology
Etchujima 2-1-6, Koto-ku, Tokyo 135-8533, JAPAN
Tel 81-3-5245-7395 (direct line)
81-3-5245-7300 (main number)
Fax 81-3-5245-7395
e-mail iwasaka@e.kaiyodai.ac.jp

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 was gradually deepened in the first two months. It reached its maximum depth of about 130m in the end of January. Then the mixed layer varied largely and sometimes the pycnocline was very weakened until the summer mixed layer formed in late April. The thin surface mixed layer was maintained in the rest of the observation period. Heat content analysis suggested that the vertical heat advection was one of the most dominant terms in the heat balance in the upper layer. When subtracting the vertical heat advection term from the heat balance, monthly mean surface heat flux and the horizontal heat advection could account for the residual. It was discussed that the vertical motions that account for the major portion of the heat balance.