Showing papers by "Korean Ocean Research and Development Institute published in 2001"

The Role of Cabbeling and Double Diffusion in Setting the Density of the North Pacific Intermediate Water Salinity Minimum

Abstract: The top of the North Pacific Intermediate Water (NPIW) in the subtropical North Pacific is identified with the main salinity minimum in the density range σθ = 26.7–26.8. The most likely source of low salinity for the NPIW salinity minimum is the Oyashio winter mixed layer, of density σθ = 26.5–26.65. The Oyashio waters mix with Kuroshio waters in the broad region known as the Mixed Water Region (MWR), between the separated Kuroshio and Oyashio Fronts just east of Japan. It is shown that cabbeling during mixing of the cold, fresh Oyashio winter mixed layer water with the warm, saline Kuroshio water increases the density of the mixture by up to σθ = 0.07 at densities around σθ = 26.6–26.65, regardless of the mixing mechanism. Thus cabbeling accounts for about half of the observed density difference between the Oyashio winter mixed layer water and the top of the NPIW. Double diffusion during mixing of the interleaving layers of Oyashio and Kuroshio waters in the MWR can also change the density of th...

Post-World War II uranium changes in dated Mont Blanc ice and snow.

Abstract: Recent controversies concerning the possibility of environmental contamination due to the use of uranium in classical weaponry have led us to realize that there is a lack of time series for this metal from environmental archives. We have therefore performed analysis of a dated 140 m-long ice/snow core that was drilled in 1994 at a cold high altitude site (4250 m) near the summit of Mont Blanc in the French-Italian Alps. Ultraclean analytical procedures were employed in our analyses. Uranium concentrations were determined by inductively coupled plasma sector field mass spectrometry. In ice dating from before the 1940s, uranium concentrations are found to have remained fairly constant and can be explained simply by a crustal contribution. For the post-World War II layers, on the other hand, the data show large excesses above crustal contributions. These uranium excesses are attributed to tropospheric transport of dust emitted during extensive mining and milling operations which took place in the GDR and to a smaller extent in France at that time. There is no enhancement in uranium concentrations in the ice layer in which fallout from the 1986 Chernobyl accident was previously identified from a gross beta activity vs depth profile.

High density culture of the freshwater rotifer, Brachionus calyciflorus

Abstract: The freshwater rotifer, Brachionus calyciflorus is one of the live food organisms used for the mass production of larval fish. In this study possibility of obtaining high density cultures of the freshwater rotifer B. calyciflorus were investigated. The two culture systems used differed in their air and dissolved oxygen supplies using three temperatures in each case: 24, 28 and 32 °C. Rotifers were batch-cultured using 5 1-vessels and fed with the freshwater Chlorella. The growth rate of rotifers significantly increased with an increase in temperature. The maximum density of the rotifers with air-supply at 24 °C, 6500 ind. ml−1, was significantly lower than those cultured at 28 and 32 °C, i.e. 8600 and 8100 ind. ml−1, respectively. Dissolved oxygen levels decreased with time and ranged from 0.8 to 1.4 mg 1−1 when the density of freshwater rotifer was the highest at each temperature. The highest density (19 200 ind. ml−1) of freshwater rotifer was obtained in cultures with a supply of oxygen at 28 °C. Densities of 13 500 and 17 200 ind. ml−1 were found at 24 and 32 °C, respectively. Levels of NH3−N increased with time and a dramatic increase of NH3−N was observed at high temperatures. Levels of NH3−N at 24, 28 and 32 °C were 13.2, 18.5 and 24.5 mg 1−1, respectively. These levels coincided with the highest rotifer density at each of the three temperatures. When rotifers were cultured with an oxygen-supply and pH was adjusted to 7, the maximum density of rotifer reached 33 500 ind. ml−1 at 32 °C . These results suggested that high density culture of freshwater rotifer, B. calyciflorus could be achieved under optimal conditions with DO value of exceeding 5 mg 1−1 and NH3−N values of lower than 12.0 mg 1−1.

Single-cannister underwater stereocamera system with distance measurement function

Abstract: A single-canister underwater stereocamera system with a distance measurement function is disclosed. In the camera system, a camera drive unit, holding two cameras on its camera base, is set in a parallel space defined between two support plates, and is operable by a motor unit, thus being movable along with the two cameras to the front or back. A lens drive unit, holding two lenses on two lens bases, is set in the parallel space to be operable by the motor unit so as to laterally move the two lenses to the left or right under the guide of a linear guide bearing. The motor unit controls the focus length of each of the two cameras and the moving distance of the two lenses at the same time. In the camera system, the actual distance of an underwater target object from the system is measured by sensing a rotated position of the encoder of the motor unit, taking advantage of the fact that the actual distance of the target object has a functional relation of 1:1 with the focus length of each of the cameras. This camera system measures the actual distance of the target object while compensating for the refraction errors of light beams passing through both the window and water. The camera system is also encased within a waterproof and pressure-proof cylindrical canister having a transparent window at its front end wall. This camera system is thus effectively usable in deep sea.

An Assessment of HOx Chemistry in the Tropical Pacific Boundary Layer: Comparison of Model Simulations with Observations Recorded during PEM Tropics A

Abstract: Reported are the results from a comparison of OH, H2O2CH3OOH, and O3 observations with model predictions based on current HOx -CH4 reaction mechanisms. The field observations are those recorded during the NASA GTE field program, PEM-Tropics A. The major focus of this paper is on those data generated on the NASA P-3B aircraft during a mission flown in the marine boundary layer (MBL) near Christmas Island, a site located in the central equatorial Pacific (i.e., 2 N, 157 W). Taking advantage of the stability of the southeastern trade-winds, an air parcel was sampled in a Lagrangian mode over a significant fraction of a solar day. Analyses of these data revealed excellent agreement between model simulated and observed OH. In addition, the model simulations reproduced the major features in the observed diurnal profiles of H 2O2 and CH3OOH. In the case of O3, the model captured the key observational feature which involved an early morning maximum. An examination of the MBL HOx budget indicated that the O( 1 D)C H2O reaction is the major source of HOx while the major sinks involve both physical and chemical processes involving the peroxide species, H2O2 and CH3OOH. Overall, the generally good agreement between model and observations suggests that our current understanding of HOx -CH4 chemistry in the tropical MBL is quite good; however, there remains a need to critically examine this chemistry when both CH2 Oa nd HO 2 are added to the species measured.

A Detailed Comparison of a Range of Three-Dimensional Models of the M2 Tide in the Faeroe–Shetland Channel and Northern North Sea

Abstract: A three-dimensional hydrodynamic model of the Faeroe–Shetland Channel and northern North Sea is used to investigate the spatial variability of M2 tidal elevations and currents in the region. This area is chosen because it covers a range of water depths. Also, there is a significant database of tidal elevations (namely 41 gauges) and current meters (namely 89 observations) with which comparisons can be made. With the exception of a couple of measurements made at the shelf edge, which may be influenced by the internal tide, namely a 180° phase shift across the thermocline due to a first mode internal tide, the observations correspond to those of a barotropic tide. Two different approaches are used to represent the profile of tidal currents in the vertical. In the first a spectral/functional method is used, while in the second a finite difference grid is applied. A range of parameterizations of vertical eddy viscosity (suitable for deep water regions) are used, from ones in which viscosity is relate...

Respiration Rates of Free-Living Marine Nematodes in the Subtidal Coarse-Sand Habitat of Otsuchi Bay, Northeastern Honshu, Japan

Abstract: Respiration rates of six free-living nematode species dominant in the subtidal coarse-sand habitat of Otsuchi Bay, Northeastern Honshu, Japan, were measured discriminating sex and adult or juvenile. To measure the respiration rate, each nematode was put in a temperature-controlled microchamber of 45 μl in volume, and the dissolved oxygen concentration of the seawater was monitored for more than 3 hrs. Measurements were done at 5, 10, 15, and 20°C, covering the yearly temperature range of the habitat. Metabolic intensities (M.I.) of these species at 20°C were within the range of values previously reported for other nematode species. Juveniles of Mesacanthion sp. had the highest M.I. among the species measured, reflecting the carnivorous nature of the species. For Polygastrophora sp.., Mesacanthion sp., Metachromadora sp.. and Monoposthia sp.., M.I. decreased at lower temperature, and the Q10 value was close to 2. On the other hand, M.I. values of Symplocostoma sp.. and Theristus sp. were independe...

Comparison of Bottom Friction Formulations for Single-Constituent Tidal Simulations in Kyunggi Bay

Abstract: This paper investigates the influence of bottom friction on the tidal elevation in Kyunggi Bay, located west of Korea, by comparing the linear, linearized and quadratic bottom friction formulations, deducing an optimal bottom friction coefficient (BFC) for each formulation in single-constituent simulations. Model results are compared with observed tidal amplitudes and phases at 52 locations. The linear friction formulation with an optimal BFC produces the observed tidal elevation satisfactorily for all consitutents. However, the optimal linear BFC in Kyunggi Bay is one order smaller than that used in global tide calculations. The optimal BFC in the linearized formulation for the M2tide is identical to the theoretical value given by Pingree (1983). The optimal linearized BFCs for other constituents are approximately 90% of optimal quadratic BFC for the M2tide alone. Experiments with a range of quadratic BFCs show that the optimal BFCs for single-constituent tide are quite different from constituent by constituent, giving considerably large values of BFC except for the M2tide. The single-constituent simulation shows that the optimal quadratic BFC for S2(K1) only is about 4 (10) times larger than that for M2only. Multi-constituent simulation and single-constituent experiments with the force argument (Bowers et al., 1991) clearly show that the BFC in single-constituent simulations should be increased to incorporate the bulk effects of other constituents.

Trace element determination in polar snow and ice. An overview of the analytical process and application in environmental and paleoclimatic studies

Abstract: Publisher Summary This chapter emphasizes the study of trace element distribution in polar regions that provides information on the history of global scale atmospheric pollution caused by man. Lead concentration profiles in Greenland and Antarctic snow and ice contributes to a better knowledge of the worldwide dispersion of toxic substances emitted by several sources at mid latitudes and scavenged to the ground up to the polar ice caps. Together with Lead, other heavy metals, as cadmium, copper, and zinc, and platinum group elements (PGEs) have revealed their presence in the snow of the these environments, with concentrations above the natural background levels, pushing researchers to develop novel approaches for the determination of the analytes. The study of the occurrence of PGEs in polar snows constitutes an absolute novelty in terms of the effects for the use of gasoline of new formulation on the environment. The laboratories in the world that accepted this challenge use sophisticated sampling procedures in the field, and powerful analytical techniques such as double focusing magnetic sector Inductively Coupled Plasma Mass Spectrometry (ICP-MS), Laser Excited Atomic Fluorescence Spectrometry (LEAFS), and Thermal Ionisation Mass Spectrometry (TIMS), to produce a wealth of reliable data useful in the difficult task of deciphering snow and ice archives.

Calculation of fallout concentration in the Japan Sea

Abstract: A method was developed to calculate radionuclides concentration in the Japan Sea. The concentration of radioactive fallout (137Cs, 239'240Pu) due to atmospheric nuclear weapons tests was calculated to verify in the Japan Sea the method by comparison between calculated and observed values. The flow field was calculated by Japan Sea circulation model, which was improved in vertical resolution. We confirmed that influence of seasonal change of flow field was small on calculated results of fallout concentration. Therefore, annual mean flow field was adapted for this method. 137Cs and 239'240Pu concentrations were calculated by this method. Calculated 137Cs concentration agrees well with observed value. However, calculated 239'240Pu concentration was underestimated. This result suggests that 239'240Pu concentration in the Japan Sea might be affected by not only global fallout but also another source.