TaeKeun Rho

Metagenomic examination of diversity within eukaryotic plankton from the ulleung basin in the East Sea of Korea

We constructed planktonic 18S rDNA clone libraries for micro-organisms in the euphotic zone of the Ulleung Basin in the East Sea of Korea. They revealed the cryptic biodiversity of eukaryotic planktons and demonstrated specific phylogenetic affiliations at certain water depths. Dinoflagellate clones dominated at the surface and 75-m depth. Members of the Syndiniales order (Groups I and II), containing wellknown parasitic dinoflagellates, as well as one their prominent hosts, Polycystinea, were found exclusively at 75 m. These observations suggest that the presence of species from Groups I and II is closely related to the specific water mass. Therefore, their metagenomics information might be useful for delineating both water-mass and physico-chemical properties.

Dissolved Oxygen and Nutrients

Changing global temperatures may alter oceanic concentrations of both dissolved oxygen (DO), which reflects water quality, and nutrients, which are an essential factor for the growth and distribution of phytoplankton. The East Sea (Japan Sea) is often considered a “miniature ocean” and an ideal natural laboratory to estimate the impact of global climate change on the oceanic biogeochemical cycles, because of the East Sea’s physical dynamics. Thus, the monitoring of nutrients and DO concentrations in the East Sea may help predict the response of biogeochemical cycles in the global ocean to changing climate. We describe and discuss the history of studies on DO in the East Sea, the change in vertical structure of DO profiles, the trend of DO inventory in the bottom layer, and the controversy regarding future projections of DO in the bottom water mass. We also summarize the history of nutrient measurements in the region, the general structure of vertical nutrient profiles, the horizontal nutrient distribution pattern on isobaric surfaces, the seasonal nutrient flux through the Korea Strait, and the recent debate on nutrient dynamics in the East Sea. The results of the studies we examine suggest that the processes controlling the structures and inventories of DO and nutrients in the East Sea are very sensitive to global climate changes.

Re-initiation of bottom water formation in the East Sea (Japan Sea) in a warming world

The East Sea (Japan Sea), a small marginal sea in the northwestern Pacific, is ventilated deeply down to the bottom and sensitive to changing surface conditions. Addressing the response of this marginal sea to the hydrological cycle and atmospheric forcing would be helpful for better understanding present and future environmental changes in oceans at the global and regional scales. Here, we present an analysis of observations revealing a slowdown of the long-term deepening in water boundaries associated with changes of water formation rate. Our results indicate that bottom (central) water formation has been enhanced (reduced) with more (less) oxygen supply to the bottom (central) layer since the 2000s. This paper presents a new projection that allows a three-layered deep structure, which retains bottom water, at least until 2040, contrasting previous results. This projection considers recent increase of slope convections mainly due to the salt supply via air-sea freshwater exchange and sea ice formation and decrease of open-ocean convections evidenced by reduced mixed layer depth in the northern East Sea, resulting in more bottom water and less central water formations. Such vigorous changes in water formation and ventilation provide certain implications on future climate changes.

Optimization of Chemical Oxygen Demand Determination in Seawater Samples Using the Alkaline Potassium Permanganate Method

Chemical oxygen demand (COD) is a practical parameter that is used to estimate the amount of organic pollutants in aqueous systems. It is generally used as a guideline to control the quality of waste treatment effluent globally and is a management tool to evaluate the total pollution load in the highly developed coastal regions of Korea. It is a preferred method because of the speed and simplicity of the analysis and because there are fewer instrumentation requirements. The Ministry of Oceans and Fisheries (MOF) of the Republic of Korea developed a standard procedure for the measurement of COD. It has been revised several times, and the most recent revision was made in 2013 (MOF 2013–230). In this study, we modified the standard COD measurement procedure (MOF 2013–230), especially the sample digestion apparatus, to enhance analytical efficiency for a large sample number (batch), which is called a Korea Institute of Ocean Science and Technology (KIOST) modified MOF 2013–230. We examined uncertainty related to each experimental step and optimized laboratory conditions to reduce such uncertainties. The detection limit and estimated expanded uncertainty related to the KIOST modified MOF 2013–230 was 0.18 and 0.11 mg O2/L at a 95% confidence level (k = 2), respectively. This study also provides several tips to maintain consistent COD measurements in seawater using the alkaline potassium permanganate method.