Kuh Kim

Argo profiling floats bring new era of in situ ocean observations

The Argo profiling float project will enable, for the first time, continuous global observations of the temperature, salinity, and velocity of the upper ocean in near-real time.This new capability will improve our understanding of the oceans role in climate, as well as spawn an enormous range of valuable ocean applications. Because over 90% of the observed increase in heat content of the air/land/sea climate system over the past 50 years occurred in the ocean [Leuitus et al., 2001], Argo will effectively monitor the pulse of the global heat balance.The end of 2003 was marked by two significant events for Argo. In mid-November 2003, over 200 scientists from 22 countries met at Argos first science workshop to discuss early results from the floats. Two weeks later, Argo had 1000 profiling floats—one-third of the target total—delivering data. As of 7 May that total was 1171.

Comparison of winter and summer hydrographic observations in the Yellow and East China Seas and adjacent Kuroshio during 1986

Abstract Two regional hydrographic surveys conducted in January and July 1986, aboard the R.V. Thompson and R.V. Washington illustrate the seasonal change in water properties from winter to summer in the Yellow and East China Seas (YECS) and adjacent Kuroshio. In January 1986, water over the shelf in the YECS was locally well mixed in the vertical, and the horizontal distribution of water properties was dominated by a large tongue or plume of relatively fresh Yellow Sea Cold Water (YSCW) flowing southeastward along the Chinese margin into the East China Sea. To the east of this plume, along the Korean margin, was found the more saline Yellow Sea Warm Water (YSWW). The Kuroshio front in the East China Sea was located at the shelf break, separating the warmer, more saline Kuroshio water from the relatively well-mixed cooler, less saline coastal water. Evidence of mixing between these two water masses was observed but limited to near the shelf break. In July 1986, water over the shelf in the YECS was strongly stratified everywhere except within tidally mixed areas near the coast. The surface water distribution in the YECS was dominated by a bubble or lens of Changjiang dilute water located to the northeast of the Changjiang mouth, and the bottom YSCW intensified and extended southward to the shelf break. The relatively fresh coastal water from the East China Sea shelf extended far past the shelf break over the Kuroshio near the surface, and in turn, Kuroshio water intruded onto the shelf near the bottom. Mixing between the Kuroshio and coastal water was found over much of the mid- and outer shelf and upper slope, spanning a cross-stream distance of 75 km. The seasonal freshening due to the Changjiang discharge contributed directly to the summer increase in freshwater transport in the upper Kuroshio. In addition, evidence of deep vertical mixing within the Kuroshio itself was found near 32.0°N, 128.2°E, most likely due to a mesoscale eddy found near there and internal tidal mixing over the slope.

Warming and structural changes in the east (Japan) Sea: A clue to future changes in global oceans?

The East (Japan) Sea has been in a warming trend during the last more than 40 years: a 0.1–0.5 degree of warming in the upper 1000 meters. The warming is accompanied by the deepening of the oxygen minimum layer by more than 1000 meters. The analysis of chemical tracers such as dissolved oxygen and CFCs clearly implies that the warming is associated with changes in deep water structures in the area, resulted from a replacement of the past bottom-water formation with an intermediate water formation in recent time. This shift has a remarkable resemblance to that anticipated to the ocean conveyor-belt system in coming century associated with recent global warming. In considering a rapid turn-over time of time scale less than 100 years, the East Sea may serve as a natural laboratory for global changes in the future.

Direct Measurements of Deep Currents in the Northern Japan Sea

Long-term current measurements by means of subsurface moorings were made for the first time at seven sites in the Japan Basin, the northern part of the Japan Sea. The objective was to directly explore the velocity field in the highly homogeneous deep water mass (the Japan Sea Proper Water) that occupies depths below 500 m. On each mooring three current meters were equipped at an approximately equal distance below about 1000 m depth. Duration of the measurements was 1 to 3 years depending on specific site. This paper describes the basic data set from the moored measurements. It is found that the deep water of the Japan Basin is very energetic with eddies and vertically coherent currents of the order of 0.1 m/s. Surprisingly, the currents and eddies exhibit strong seasonal dependence even in the deepest layers of the Basin. The observed new current features are discussed in comparison with conventional deep circulation pictures derived from hydrographic data.

Intermediate Waters in the East/Japan Sea

Properties of the intermediate layer in the East/Japan Sea are examined by using CREAMS data taken mainly in summer of 1995. Vertical profiles of potential temperature, salinity and dissolved oxygen and relationships between these physical and chemical properties show that the dissolved oxygen concentration of 250 µmol/l, roughly corresponding to 0.6°C at the depth of about 400 db, makes a boundary between intermediate and deep waters. Water colder than 0.6°C has a very stable relationship between potential temperature and salinity while salinity of the water warmer than 0.6°C is lower in the western Japan Basin than that in the eastern Japan Basin. The low salinity water with high oxygen corresponds to the East Sea Intermediate Water (ESIW; <34.06 psu, >250 µmol/l and >1.0°C) which was previously identified by Kim and Chung (1984) and the high salinity water with high oxygen found in eastern Japan Basin is named as the High Salinity Intermediate Water (HSIW; >34.07 psu, >250 µmol/l and >0.6°C). Spatial distribution of salinity and acceleration potential on the surface of σϑ = 27.2 kg/m3 shows that the ESIW prevailing in the western Japan Basin is transported eastward by a zonal flow along the polar front near 40°N and a cyclonic gyre in the eastern Japan Basin is closely related to the HSIW.

Mean flow and variability in the southwestern East Sea

Abstract The Ulleung Basin is one of three deep basins that are contained within the East/Japan Sea. Current meter moorings have been maintained in this basin beginning in 1996. The data from these moorings are used to investigate the mean circulation pattern, variability of deep flows, and volume transports of major water masses in the Ulleung Basin with supporting hydrographic data and help from a high-resolution numerical model. The bottom water within the Ulleung Basin, which must enter through a constricted passage from the north, is found to circulate cyclonically—a pattern that seems prevalent throughout the East Sea. A strong current of about 6 cm s −1 on average flows southward over the continental slope off the Korean coast underlying the northward East Korean Warm Current as part of the mean abyssal cyclonic circulation. Volume transports of the northward East Korean Warm Current, and southward flowing East Sea Intermediate Water and East Sea Proper Water are estimated to be 1.4 Sv (1 Sv =10 −6 m 3 s −1 ) , 0.8 Sv , and 3.0– 4.0 Sv , respectively. Deep flow variability involves a wide range of time scales with no apparent seasonal variations, whereas the deep currents in the northern East Sea are known to be strongly seasonal.

Branching Mechanism of the Tsushima Current in the Korea Strait

Abstract Hydrographic studies show the seasonal variation of the East Korean Warm Current (EKWC), which is a branch of the Tsushima Current along the Korean coast. To understand the dynamics of the branching mechanism of the TC in the Korea Strait, a hydraulic model with two active layers was investigated in a rectangular strait with varying depth. When the lower cold water flows southward in a shallow meridional channel from the deep northern basin, it separates from the eastern boundary because of the sloping bottom to conserve potential vorticity. After separation, the lower layer hugs the western boundary as the channel becomes shallow. In a region where the lower layer is absent due to separation, the northward flow in the upper layer has a positive relative vorticity to conserve potential vorticity because the bottom topography becomes deeper from south to north. The northward velocity has its maximum on the eastern boundary. This mechanism may explain the formation of the branch along the Japanese ...

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.

Absolute transport from the sea level difference across the Korea Strait

A strong linear relationship is found between the transport through the Korea Strait and the sea level difference (SLD) between Moji, Japan and Pusan, Korea after a correction is applied to SLD using cross-strait hydrographic sections to remove baroclinic effects, which lead to an overestimate of the transport by up to 40% in summer. The conversion factor from SLD to the transport is estimated as A = (10. 2 ± 1.1) x 10 6 m 2 s -1 with a reference value of SLD, Δ η0 = 197 ± 3 cm. Therefore, SLD provides a means to investigate long-term variations of the transport through the Korea Strait and their relation to changes in the Pacific Ocean, such as El Nino and decadal climate variations.

Global statistics of inertial motions

Statistics of inertial currents in the North Pacific, North Atlantic, and Southern Ocean are derived for the period 1997–2003 from surface trajectories of Argo profiling floats by employing a method developed recently by Park et al. (2004). The distribution of inertial amplitudes is non-Gaussian in the range 0~80 cm/sec with an average value of 13.7 cm/sec. The inertial amplitude in the mid-latitude (30°~45°N) band exceeds those in both the low (15°~30°N) and high (45°~60°N) latitude bands. In three basins, the amplitude in summer is greater than that in winter by 15%~25%. The inertial energy in the mixed layer reaches approximately 1100 J/m2~1165 J/m2 globally. The spatiotemporal patterns of inertial amplitudes in the North Atlantic mostly depend on the MLD, which exhibits strong meridional gradients. However, the small meridional gradient of the MLD in the North Pacific does not contribute significantly to the spatial distribution of inertial amplitudes. The total inertial energy estimated from the floats is consistent with the theory that inertial energy could contribute significantly to sustaining the meridional overturning circulation.