Seasonal variation of the Sound scattering Layer (SSL) around Yellow Sea Bottom Cold Water (YABCW) in Korea region, 2011-2012

Abstract

The Yellow Sea Bottom Cold Water (YSBCW), defined as having a salinity of 32.0&#8211;33.0 psu and a temperature < 10°C, has a major influence on the oceanic environment of the Yellow Sea and is one of the main water masses in this sea in summer. The presence of the YSBCW has important effects on zooplankton, nekton, and other biological organisms in the Yellow Sea. For understanding the sound scattering layer (SSL) in the YSBCW region, this study presents results obtained from acoustic measurements taken in the YSBCW region in Korea region, in spring and summer of 2011 and 2012. For each survey, 13&#8211;27 hours of 200 kHz acoustic data were continuously collected at a stationary station. The acoustic volume scattering strength data (Sv) were analyzed with temperature profile data. In spring 2011/2012, the SSL migrated from surface layer at night to near the bottom at day time, due to the entire water column was well mixed with cool water. Then the descending and ascending speeds of the SSL were 0.7 m min-1 and 0.6 m min-1, respectively. In summer seasons, the SSL migrated from below thermocline at night to near the bottom at day time, due to the water column was divided in to two layer along strong thermocline. The SSL started to descend at a speed of 1.3 m min-1. Very high speed in summer 2011 was due to changes of the water column after typhoon (called Muifa). In addition to water temperature, suspended materials may be some influence on vertical migration of the SSL. It is concluded that the SSL patterns at the YSBCW site may be greatly influenced by water column changes during spring and summer season.