Seasonal variation of the Korea Strait Bottom Cold Water and its relation to the bottom current

Abstract

Analysis of high resolution hydrographic and current data revealed that the Korea Strait Bottom Cold Water (KSBCW) flowed into the Korea Strait from May to January and contained two temperature minimums, one in August/September and another in December/January. With the main current flows confined within 70 km of the Korean coast, maximum southwestward bottom currents corresponded with the temperature minimums. Time‐series of bottom current and temperature near the Korean coast clearly showed that the bottom temperature decreased as the bottom current strengthened. Seasonal variation of the KSBCW was linked to the combined effects of the barotropic and baroclinic current variations in the Korea Strait. The annual minimum bottom temperature of the KSBCW was associated with the maximum southwestward baroclinic component. The KSBCW had a secondary maximum southwestward bottom current and secondary minimum temperature in December/January when the Tsushima Warm Current (TWC), flowing into the East/Japan Sea (EJS), had the minimum volume transport.

Distinct characteristics of the intermediate water observed off the east coast of Korea during two contrasting years

“…Therefore, it is natural to expect significant interannual and decadal variations of intermediate water properties which may or may not be linked to the atmospheric condition in the northwestern EJS; yet no observation has supported this in spite of several works dedicated to the interannual as well as seasonal variability in circulation of the southwestern EJS and potential connection to the Korea Strait, e.g., KSBCW [ Kim et al ., ; Min et al ., ; Kim and Min , ; Na et al ., ; Ito et al ., ]. To clarify the interannual and decadal variations, we define them here as time scales from 16 to 36 month periods and periods longer than 36 months (several to 10 years), respectively.…”

“…When the Subpolar Gyre strengthens, the NKCC carrying the NKCW extends farther south, i.e., competition between EKWC and NKCC. The NKCW along the east coast of Korea reaches the Korea Strait, and forms the KSBCW [ Kim and Kim , ; Cho and Kim , ; Isobe , ; Kim et al ., ; Min et al ., ; Na et al ., ]. On the contrary, a significance of the local forcing was also suggested that the EKWC well develops along the east coast of Korea when the KSBCW, southernmost extension of the NKCW, occupies the lower layer in the Korea Strait in summer, while the weakening or the disappearance of the EKWC occurs in winter when the KSBCW is indistinct in the Korea Strait [ Cho and Kim , ; Isobe , ].…”

“…Part of the NKCW continues to be carried southward along the coast as an undercurrent beneath the northward flowing EKWC [ Chang et al ., ]. On its way to south along the coast, the NKCW experiences radical transformation until it reaches the Korea Strait to form water mass named the Korea Strait Bottom Cold Water (KSBCW) [ Kim and Kim , ; Cho and Kim , ; Isobe , ; Kim et al ., ; Min et al ., ; Na et al ., ]. The KSBCW is colder than 10°C but not as cold as NKCW or ESIW, which have a temperature range of 1–5°C.…”

“…In this study, the intermediate water refers to both the NKCW and ESIW with no distinction, and temporal variability in their properties is considered. The intermediate water is typically characterized by the salinity minimum layer (<34.05) underneath the saline TWW in the subtropical areas or south of the SF at a depth of about 100–400 m, with a core potential density ( σ θ ) of 27.1–27.2 kg m −3 [ Kim and Chung , ; Cho and Kim , ; Kim and Kim , ; Kim et al ., ; Yun et al ., ; Talley et al ., ; Kim et al ., ]. Its temperature ranges from 1.0 to 5.0°C and dissolved oxygen is typically higher than 250 μmol L −1 (or 6.5 mL L −1 ) (Table ).…”

Interannual variability of the Korea Strait Bottom Cold Water and its relationship with the upper water temperatures and atmospheric forcing in the Sea of Japan (East Sea)

“…The KSBCW usually intrudes through the bottom layer (∼50 m and deeper) of the western channel, while the intrusion characteristics vary temporally and spatially [ Isoda and Oomura , 1992; Cho and Kim , 1998; Johnson and Teague , 2002; Kim et al , 2006; Senjyu et al , 2008]. Simultaneous measurements of temperatures and currents in the Korea Strait showed that a temperature minimum occurs when the volume of the southwestward currents is at a maximum [ Johnson and Teague , 2002; Kim et al , 2006].…”