Dissolved oxygen at the bottom boundary layer of the Ulleung Basin, East Sea

Abstract

General consensus on typical vertical profile of dissolved oxygen in the Ulleung Basin is that dissolved oxygen concentration beyond 300 m decreases with increasing depth. However, the results of our observations in 2005 and 2006 revealed three different dissolved oxygen distribution types in the deep layer of the Ulleung Basin. The first type showed oxygen concentration decreasing with increasing depth (Type- 1), the second showed oxygen concentration decreasing very sharply near the bottom boundary layer but constant in the bottom adiabatic layer (Type-2), the final was of the oxygen minimum layer above the bottom boundary layer (Type-3). Type-2 was the most common pattern in the Ulleung Basin. Type-1 was most common close to the Japan Basin, including the Ulleung Interplane Gap, while Type-3 was found around Dok do. Oxygen Consumption Rate (OCR) at surface sediment estimated using the dissolved oxygen distribution at the bottom boundary layer was 0.2~5.8 mmol·m-2 d-1, which coincided with OCR from direct sediment incubation. This implies that organic matter decomposition at surface sediment may play an important role in dissolved oxygen distribution patterns at the bottom boundary layer of the Ulleung Basin.