Dong-Ha Min

The East Sea (Japan Sea) in change : A story of dissolved oxygen

Dissolved oxygen (DO) is one of the most important oceanographic parameters measured for understanding various physicochemical processes in the ocean. This situation has been particularly true for the East Sea study ever since the first extensive investigation in the area during the 1930s (Uda, 1934). Uda found very high and uniform concentrations of DO, around 250 μM (5.6 ml/l), for waters below a few hundred meters over entire basins, and assumed that a very fast ventilation system was operating in the East Sea. The Circulation Research of the East Asian Marginal Seas (CREAMS), Japan-Korea-Russia international cooperative studies on the East Sea have provided a unique opportunity to investigate the entire East Sea for the first time since Udas study. A spectrophotometrically modified Winkler method (Pai et al., 1993) and a DO sensor (Sea Bird Model SBE 13) were tested successfully during the CREAMS studies for improving the precision and accuracy of DO measurement. The study further confirmed an earlier observation by Gamo et al. (1986) that DO structures in the East Sea have been changing drastically in such a way that the DO minimum depths have deepened by more than 1000 meters during the last 30 years. While the causes for these changes are not known at the present time, the analysis of DO profiles strongly suggests that the mode of deep water ventilation system in the East Sea has shifted from bottom water formation in the past to intermediate water formation at the present time (Kim and Kim, 1996). Studies of precise and accurate DO monitoring, along with other chemical tracers, deserve the highest priority for future research in the East Sea.

Large accumulation of anthropogenic CO2 in the East (Japan) Sea and its significant impact on carbonate chemistry

Received 19 December 2005; revised 10 July 2006; accepted 26 July 2006; published 22 November 2006. [1] This paper reports on a basin-wide inventory of anthropogenic CO2 in the East (Japan) Sea determined from high-quality alkalinity, chlorofluorocarbon, and nutrient data collected during a summertime survey in 1999 and total dissolved inorganic carbon data calculated from pH and alkalinity measurements. The data set comprises measurements from 203 hydrographic stations and covers most of the East Sea with the exception of the northwestern boundary region. Anthropogenic CO2 concentrations are estimated by separating this value from total dissolved inorganic carbon using a tracerbased (chlorofluorocarbon) separation technique. Wintertime surface CFC-12 data collected in regions of deep water formation off Vladivostok, Russia, improve the accuracy of estimates of anthropogenic CO2 concentrations by providing improved airsea CO2 disequilibrium values for intermediate and deep waters. Our calculation yields a total anthropogenic CO2 inventory in the East Sea of 0.40 ± 0.06 petagrams of carbon as of 1999. Anthropogenic CO2 has already reached the bottom of the East Sea, largely owing to the effective transport of anthropogenic CO2 from the surface to the ocean interior via deep water formation in the waters off Vladivostok. The highest specific column inventory (vertically integrated inventory per square meter) of anthropogenic CO2 of 80 mol C m � 2 is found in the Japan Basin (40N� 44N). Comparison of this inventory with those for other major basins of the same latitude band reveal that the East Sea values are much higher than the inventory for the Pacific Ocean (20� 30 mol C m � 2 ) and are similar to the inventory for the North Atlantic (66� 72 mol C m � 2 ). The substantial accumulation of anthropogenic CO2 in the East Sea during the industrial era has caused the aragonite and calcite saturation horizons to move upward by 80� 220 m and 500� 700 m, respectively. These upward movements are approximately 5 times greater than those found in the North Pacific. Both the large accumulation of anthropogenic CO2 and its significant impact on carbonate chemistry in the East Sea suggest that this sea is an important site for monitoring the future impact of the oceanic invasion of anthropogenic CO2.