• Ocean and Polar Research
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• v.33 no.spc3
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• pp.371-383
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• 2011

To investigate the physical characteristics and variations of oceanic parameters in the tropical central North Pacific, oceanographic surveys were carried out in summer of 2006 and 2007. The survey periods were classified by Oceanic Ni$\tilde{n}$o Index as a weak El Ni$\tilde{n}$o in 2006 and a medium La Ni$\tilde{n}$a in 2007. The survey instruments were used to acquire data on CTD (Conductivity Temperature and Depth), XBT (Expendable Bathythermograph), and TSG (Thermosalinograph). The dominant temporal variation of surface temperature was diurnal. The diurnal variation in 2007, when the La Ni$\tilde{n}$a weather pattern was in place, was stronger than that in 2006. Surface salinity in 2006 was affected by a northwestward branch of North Equatorial Current, which implies that the El Ni$\tilde{n}$o affects surface properties in the North Equatorial Current region. Two salinity minimum layers existed at stations east of Chuuk in both year's observations. The climatological vertical salinity section along $180^{\circ}E$ shows that the two salinity minimum layers exist in $2^{\circ}N{\sim}12^{\circ}N$ region, consistent with our observations. Analysis of isopycnal lines over the salinity section implies that the upper salinity minimum layer is from intrusion of the upper part of North Pacific Intermediate Water into the lower part of South Pacific Subtropical Surface Water and the lower salinity minimum layer is from Antarctic Intermediate Water.

• Ocean and Polar Research
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• v.37 no.4
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• pp.265-278
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• 2015

We analyzed the North Pacific Intermediate Water (NPIW) that was simulated in 25 coupled general circulation models (CGCMs) using historical and Representative Concentration Pathway 4.5 (RCP4.5) scenario experiments of Coupled Model Intercomparison Project Phase 5 (CMIP5), focusing on the evaluation of the performance of HadGEM2-AO. A large inter-model diversity in salinity, density, and depth of the NPIW exists even though the multi-model ensemble mean (MME) is comparable to observations. It was found that the depth of the NPIW tends to be deeper in the models in which the NPIW is relatively saltier. HadGEM2-AO simulates the lightest NPIW having the lowest salinity at shallower depth, compared with other CGCMs. Future projections of the NPIW show that the temperature of the NPIW increases, but the density decreases in all CMIP5 models. It was shown that the salinity of the NPIW decreases in most models and the decrease tends to be larger in models simulating the lighter NPIW. The HadGEM2-AO projects moderate changes in the temperature and density of the NPIW out of the CMIP5 models.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.13 no.3
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• pp.190-199
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• 2008

To investigate hydrographic structure and characteristics of the tropical ocean in the eastern and the western Pacific, CTD(Conductivity-Temperature-Depth) data along $131^{\circ}W$ and $137^{\circ}-142^{\circ}E$ in July-August 2005 were analyzed. Sea surface temperature along $131.5^{\circ}W$ in summer is highest in the Equatorial Counter Current(ECC) because of the high-temperature water greater than $28^{\circ}C$ moving through the ECC from the western Pacific to the eastern Pacific in spring and summer. Based on the evidence of the presence of low salinity and high dissolved oxygen water in the North Equatorial Current(NEC), we suggested that the low salinity water moved from the Gulf of Panama to the east of Philippine along the North Equatorial Current(NEC). The South Equatorial Current(SEC) had the most saline water from surface to deep layer because the saline water from the Subtropical South Pacific Ocean moved to the north. The salinity minimum layer was observed at 500-1500 m depth along $131.5^{\circ}W$. The water mass with the salinity minimum layer in the north of $5^{\circ}N$ came from the North Pacific Intermediate Water(NPIW) and that in the south of $5^{\circ}N$ came from the Antarctic Intermediate Water(AAIW), which was more saline than the NPIW. Cyclonic cold eddy with a diameter of about 200km was found in $4-6^{\circ}N$. Sea surface temperature along $131.5^{\circ}W$ in the eastern Pacific was lower than along $137^{\circ}-142^{\circ}E$ in the western Pacific; on the other hand, sea surface salinity in the eastern Pacific was higher than in the western Pacific. Subsurface saline water from the Subtropical South Pacific Ocean was less saline in the eastern Pacific than in the western Pacific. Salinity and density(${\sigma}_{\theta}$) of the salinity minimum layer south of $14^{\circ}N$ was higher in the eastern Pacific than in the western Pacific.

• Journal of Environmental Science International
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• v.3 no.3
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• pp.229-239
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• 1994

By laying emphasis on the intermediate layer, water property distribution in the Northwest Pacific is studied using the hydrographic data obtained by Japan Meteorologica] Agency in the period from 1960 to 1986. The scattering of water type in T-S diagram is relatively small in the Kuroshio Region. Both the envelopes of saline side and of fresh side of the scattered data points shifts gradually from saline side to fresh side as the observation line moves from southwest to northeast. In the Mixed Water Region, the scattering of water type increases rapidly as the observation line moves north; The envelope of fresh cold side moves towards fresh cold side much faster than that of same side. The thermosteric anomaly value at the salinity minimum decreases as the observation line moves from north to south or southwest. This suggests that the water does not advect along the salinity minimum layer, but that the salinity minimun layer is understood as a boundary of two different waters aligned vertically. We defined the typical water masses for the Oyashio Water and the Kuroshio Water. The water mass below the salinity minimum layer may be created by isopycnal mixing of these two water masses with a fixed mixing rate. While, the water mass above the salinity minimum cannot be created simply by isopycnal mixing. The salinity minimum layer may be eroded from upper side due to active mixing processes in the surface layer, while the water of the salinity minimum layer moves gradually southward. This appears to give an explanation why the thermosteric anomaly value at salinity minimum decreases towards south.

• Journal of Environmental Science International
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• v.12 no.5
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• pp.521-527
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• 2003

To study the intruded phenomena of North Pacific Ocean around Boso peninsular, water property distribution in the adjacent seas to Japan is studied using the hydrographic data obtained by Japan Maritime Agency and Japan Fisheries Agency from 1973 to 1996, The scattering of water type in T-5 diagram is relatively small in the Kuroshio Region. Both the envelopes of saline side and of fresh side of the scattered data points shifts gradually from saline side to fresh side as the observation Line moves from southwest to northeast. In mixed water region, the scattering of water type increases rapidly as the observation line moves north; the envelope of fresh cold side moves towards fresh cold side much faster than that of saline side. This suggests that the water does not advect along the salinity minimum layer, but the salinity minimum layer can be understood as a boundary of two different waters aligned vertically, We defined the typical water masses as the Oyashio Water and the Kuroshio Water. The water mass below the salinity minimum layer may be created by isopycnal mixing of these two water masses with a fixed mixing rate. While the water mass above the salinity minimum cannot be created simply by isopycnal mixing. The salinity minimum layer may be eroded from upper side due to active minxing processes in the surface layer, while the water of the salinity minimum layer moves gradually southward. This appears to give an explanation why the thermosteric anomaly value at salinity minimun decereases towards south.

• Ocean and Polar Research
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• v.26 no.2
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• pp.299-309
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• 2004

Conductivity-temperature-depth (CTD) data obtained along a meridional section in the eastern tropical Pacific in July 2003 have been analyzed to identify various water masses, and to examine the hydrographic structure and zonal geostrophic currents in the upper 1000 m. Water mass analysis shows the existence of subtropical and intermediate waters, characterized by layers of subsurface salinity maximum and minimum, originating from both hemispheres of the Pacific. Vertical section of temperature in the upper 200 m shows the typical trough-ridge structure associated with the zonal current system for most of the tropical Pacific. Water with the lowest salinity of less than 33.6 was found in the upper 30 m between $8.5^{\circ}N$ and $10.5^{\circ}N$ in a boundary zone between the North Equatorial Current and North Equatorial Countercurrent. Temporal changes in water properties observed at $10.5^{\circ}N$ over a period of 9 days suggest both the local rainfall and horizontal advection is responsible for the presence of the low-salinity water. Development of a barrier layer was also observed at $10.5^{\circ}N$. In the North Equatorial Current region a local upwelling was observed at $15^{\circ}N$, which brings high salinity and cooler subtropical water to the sea surface. A band of countercurrent occurs in the upwelling region between $13^{\circ}N$ and $15^{\circ}N$.

• Ocean and Polar Research
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• v.26 no.2
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• pp.341-349
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• 2004

Hyrdography and deep currents were measured from 1997 to 1999 to investigate deep-sea environments in the KODOS (Korea Deep Ocean Study) area of the northeastern tropical Pacific. KODOS area is located meridionally from the North Equatorial Current to the boundary between the North Equatorial Current and the Equatorial Counter Current. Strong thermocline exists between 10 m and 120 m depths at the study area. Since that strong thermocline does hardly allow vertical mixing between surface and lower layer waters, vertical distributions of temperature, salinity, dissolved oxygen and nutrients drastically change near the thermocline. Salinity-minimum layer, which indicate the North Pacific Intermediate Water (NPIW) and the Antartic Intermediate Water (AAIW), vertically occupies vertically at the depths from 500 m down to 1400 m. The NPIW and the AAIW horizontally occur to the north and to the south of $7^{\circ}N$, respectively. The near-bottom water shows the physical characteristics of $1.05^{\circ}C$ and 34.70 psu at the depths of 10 m to 110 m above the bottom (approximately 4000-5000 m), which was originated from the Antarctic Circumpolar Water. It flows northeastwards for 2 to 4 months at the study area, and its mean velocity was 3.1-3.7 cm/s. Meanwhile, reverse (southwestward) currents appear for about 15 days with the average of 1.0-6.1 cm/s every 1 to 6 months. Dominant direction of the bottom currents obtained from the data for more than 6 months is northeastward with the average speeds of 1.7-2.1 cm/s. Therefore, it seems that deep waters from the Antarctica flow northwards passing through the KODOS area in the northeastern tropical Pacific.

• 한국해양학회지
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• v.20 no.1
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• pp.12-21
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• 1985

In this paper, the most important oceangraphic phenomena of the summer season in the East China Sea are reviewed. The hydrographic conditions in the suface layer above the seasonal thermocline are under great influence from solar heating, fresh water runoff mainly from the Yangtze River, and summer wind fields. In the lower layer below the thermocline, several distinct water masses e.g. the Kuroshio surface water, the Western North Pacific Central Water and the Yellow Sea Bottom Cold Water are intruded in response to the adjustment of the field of mass to the various dynamical processes. The frontal mixing between the intruded Yellow Sea Bottom Cold. Water and the Western North Pacific Central Water takes place in the bottom layer over the continental shelf south off Cheju Is. This mixed water probably has mush influence on the water properties of the intermediate and bottom layer around Cheju Is. and the south coast of Korea.

• Journal of the Korean Society for Marine Environment & Energy
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• v.18 no.3
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• pp.143-156
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• 2015

In order to understand the dynamic characteristics of water column environments in the Western Pacific seamount area (approximately $150.2^{\circ}E$, $20^{\circ}N$), we investigated the water mass and the behavior of water column parameters such as dissolved oxygen, inorganic nutrients (N, P), and chlorophyll-a. Physico-chemical properties of water column were obtained by CTD system at the nine stations which were selected along the east-west and south-north direction around the seamount (OSM14-2) in October 2014. From the temperature-salinity diagram, the main water masses were separated into North Pacific Tropical Water and Thermocline Water in the surface layer, North Pacific Intermediate Water in the intermediate layer, and North Pacific Deep Water in the bottom layer, respectively. Oxygen minimum zone (OMZ, mean $O_2$ $73.26{\mu}M$), known as dysoxic condition ($O_2<90{\mu}M$), was distributed in the depth range of 700~1,200 m throughout the study area. Inorganic nutrients typified by nitrite + nitrate and phosphate showed the lowest concentration in the surface mixed layer and then gradually increased downward with representing the maximum concentration in the OMZ, with lower N:P ratio (13.7), indicating that the nitrogen is regarded as limiting factor for primary production. Vertical distribution of water column parameters along the east-west and south-north station line around the seamount showed the effect of bottom water inflowing at around 500 m deep in the western and southern region, and concentrations of water column parameters in the bottom layer (below 2,500 m deep) of the western and southern region were differently distributed comparing to those of the other side regions (eastern and northern). The value of Excess N calculated from Redfield ratio (N:P=16:1) represented the negative value throughout the study area, which indicated the nitrogen sink dominant environments, and relative higher value of Excess N observed in the bottom layer of western and southern region. These observations suggest that the topographic features of a seamount influence the circulation of bottom current and its effects play a significant role in determining the behavior of water column environmental parameters.

• Ocean and Polar Research
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• v.34 no.3
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• pp.305-323
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• 2012

The ocean's response to the Pinatubo and 1259 volcanic eruptions was investigated using an ocean general circulation model equipped with an energy balance model. Volcanic eruptions release gases into the atmosphere which increases the aerosol optical depth and acts to reduce the incoming short-wave radiation. For example, there was a huge volcanic eruption (Pinatubo) in 1991 which reduced the global mean radiative forcing by about 3 W $m^{-2}$. Two numerical experiments were simulated. The first experiment features the Pinatubo eruption and the second experiment simulates the much larger volcanic eruption that occurred in 1259 when the radiative forcing was reduced by 7 times compared to the Pinatubo event. With the reduced radiative forcing due to the Pinatubo eruption at about 3 W $m^{-2}$ and 1259 eruption at about 21 W $m^{-2}$, the global mean sea surface temperature (SST) decreased to its lowest in the second year after each event by about $0.4^{\circ}C$ and $1.6^{\circ}C$, respectively. Sea surface salinity (SSS) increased substantially in the northern North Pacific, northern North Atlantic, and the Southern Ocean. The reduced SST together with SSS increased ocean convection, which yielded an increase in North Atlantic Deep Water, Antarctic Bottom Water, and North Pacific Intermediate Water production and their outflows. The increase in overturning circulation eventually increased the pole-ward ocean heat fluxes. In conclusion, huge volcanic eruptions perturb the ocean substantially and their hallmarks last for more than a decade, confirming the importance of volcanic eruptions in illustrating the decadal-climate variability recorded in the paleoclimate proxy data for the past million years.