Dissolved Oxygen at the Bottom Boundary Layer of the Ulleung Basin, the East/Japan Sea

Abstract

Continuous observation of dissolved oxygen with the CTD system makes it possible to study the fine structures of dissolved oxygen. Dissolved oxygen distribution at the bottom boundary layer could have been understood using sonic altimeter which made it possible to approach the CTD system very close to the bottom. Typical vertical profile of dissolved oxygen in the Ulleung Basin has been believed that the dissolved oxygen concentration in deeper layer than 300 m decreases as the depth increases. However, the results of the observations carried out within less than 100 m above the bottom in 2005 and 2006 showed three different types of distribution patterns of dissolved oxygen in the deep layer of the Ulleung Basin. The first type was a pattern that oxygen concentration decreases as the depth increases (Type 1). The second one was a type that oxygen concentration decreases sharply near the bottom boundary layer and is kept constant in the bottom adiabatic layer (Type 2). The last one was that the oxygen minimum layer is found above the bottom boundary layer (Type 3). Most widely distributed pattern in the Ulleung Basin was Type 2. Type 1 distributed in the area close to the Japan Basin including the Ulleung Interplane Gap. Type 3 was found around Dok do. Oxygen consumption rate (OCR) at the surface sediment estimated using the dissolved oxygen distribution at the bottom boundary layer assuming organic matter decomposition at the sediment surface was 0.5 ?2.3 mmol m-2 d-1, which coincided with OCR from a direct sediment incubation. This implies that the organic matter decomposition at the sediment surface may play an important role in the dissolved oxygen distribution at the bottom boundary layer in the Ulleung Basin.