Volume transport from the Japan Basin to the Yamato Basin in the abyssal Japan Sea inferred from direct current observations
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The transport of Japan Basin Bottom Water (JBBW) into the Yamato Basin in the Japan Sea is an important boundary condition for the modification of the abyssal water mass in the Yamato Basin. To estimate the volume transport of JBBW, two year-long observations (October 2011–October 2012 and May 2014–May 2015) were carried out using current meters moored in the deep channel connecting the Japan Basin with the Yamato Basin. The mean transport toward the Yamato Basin from the Japan Basin was estimated to be 7.37 × 104 and 5.15 × 104 m3 s−1, consistent with previous estimates from box model analysis and lowered acoustic Doppler current profiler observations. The time series of JBBW transport showed significant variability. A cause of the variability was bottom-intensified flow fluctuations in the 3- to 15-day period band, which suggests bottom-trapped topographic Rossby waves in the deep channel. In addition, during August–October 2014, notable variation of JBBW transport accompanied significant decreases of potential temperature and dissolved oxygen concentration. Detailed examination of the episodic variations of flows, potential temperature, and dissolved oxygen concentration, together with consideration of sea surface height variations, suggested that rapid northward meandering of the surface subarctic front was another cause of the significant variation in JBBW transport.
KeywordsBottom water Moored current meters Volume transport Benthic front Topographic Rossby waves Subarctic front Dissolved oxygen concentration Japan Sea Yamato Basin Japan Basin
We would like to thank the captain and crew of the RT/V Nagasaki Maru and all the participants of the observation cruises for the deployment and recovery of the current meters. Thanks are also due to Prof. T. Matsuno and colleagues in the Regional Oceanography Section, RIAM, Kyushu University for their useful comments and discussions. Suggestions from two anonymous reviewers helped to revise the early version of the manuscript. The JMA hydrographic data were downloaded from http://www.jma.go.jp. The satellite infrared image was provided by the Japan Aerospace Exploration Agency (JAXA) from http://www.eorc.jaxa.jp. This work was supported by the Environment Research and Technology Development Fund of Ministry of the Environment, Japan (A-1002 and 2-1604) and JSPS KAKENHI Grant Number 26610151.
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