Tides and short-term variabilities in the Kuroshio west of Yonakuni-jima

INTRODUCFIONTheKuroshioeastofTaiwanIslandflowsnorthwardandenterstheEastChinaalgathroughapaSSagebetweenTaiwanIslandandlriomote-shima.TOstudyfurthertheKuroshiothereandestimateitstransPOrt,itisnecessarytoobservetheKuroshioCurrentdirectly.Therehavebeen*ThisstudywassupportedbytheNationalNaturalaudienceFoundationofChinaundercontractNo.49476278.severaldirectobservationsoftheKuroshionearTaiwanIsland.Forexample,thedirectcurrentmeasurementat(24'24'N1123'35'E)byinabaetal.(1981)showedtheapp…     

Role of metal-organic complexes in the marine environment: A comparison of the copper and ligand titration methods

The differences in quality of the conditional stability constants deduced from ligand titration and metal titration methods are theoretically examined. The ecological role of the metal-organic complexes in seawater was considered on the basis of the concept of the metal buffering capacity index which is calculated from the conditional stability constant and the organic ligand concentration. The results of theoretical examination of the effect of metal contamination on the uptake of metals by phytoplankton indicate that the ecological significance of metal-organic complexes is essentially in the metal-buffering action. This means that the activities of free metal ions are maintained at a native constant level against relatively small perturbations by the addition or uptake of metals in the marine environment.     

Determination of conditional stability constants of organic copper and zinc complexes dissolved in seawater using ligand exchange method with EDTA

To clarify the nature of organic metal complexes dissolved in seawater, a ligand exchange reaction between ligands of natural origin and an aminopolycarboxylic acid (EDTA) was used to determine the conditional stability constants of organic metal complexes. The results indicate that more than two organic molecules complexed with copper and zinc exist in surface seawater. It is found that the conditional stability constants of these naturally-occurring organic metal complexes are 1–3 orders of magnitude higher than those of EDTA-Cu and EDTA-Zn complexes. These estimates of the conditional stability constants for the dominant species of organic copper and zinc complexes are 10^11.8 and 10^9.3, respectively, at pH 8.1. The results indicate that these naturally-occurring organic metal complexes are stable species and not easily dissociated or displaced with others in the marine environment.     

Dirunal variability and its quantification of subsurface sound scatterers in the western equatorial Pacific

A downwardf-looking acoustic Doppler current profiler (ADCP), suspended by a series of surface and subsurface floats and connecte to an anchroed ship, proided a quite stable platform to measure the, vertical profiles of backscatter strenght *BS) and three components of the velocith from 12 to 22 November 1992 at 1°30S and 156°15E, in the Intensive Flux Array (IFA) of TOGA/COARE. While the variability of the horizontal velocity was controlled by the semi-diurnal tide, BS and vertifal velocity were dominated by diurnal variability probably caused by the diel migration of zooplakton. The downward migration occurred early in the moring (0500–0700 in local time) and the upward one late in the afternoon (1700–1900). The average values of about 4 cm s^–1 for the sinking and rising speed were estimated from Doppler shift and BS isopleth displacement. The subsurface chlorophyll maximum (SCM) coincident with the top of the thermocline at 80–100 m was also detectable in the BS data during daytime when almost no migrating zooplankton remained in the upper 300 m. Backscatter signals from the SCM and thermocline were separated by corrlating the BS data with the chlorophylla and temperature data. The maximum contribution of the migrating zooplanktion, passively drifting phytoplankton and temperature gradient on BS was estimated to be 14.8, 7.0, 5.1 dB, respectively.     

Long-term measurement of temperature variabilities off Mindanao Island by the ocean acoustic tomography

Oceanic variabilities off Mindanao Island, Philippines where the North Equatorial Current branches into the Kuroshio and the Mindanao Current were measurerd for a period from 14 Feb.–1 Jun. 1992 by the oceean acoustic tomography (OAT). From the beginning of April, the travel time of acoustic rays propagating over a horizontal distance of about 250km, through the depth range of 80–4700 m around the underwater sound channel began to decrease, implying a warming of water. This variability was also confirmed with the results of temperature measurement at the sites where a sound source and receiver were located. The TOGA/TAO array data show that the OAT experiment was done when the 1991–1992 El Nino was at a decaying stage and the resulting warming-up of water occurred at the western Pacific. This study provides us a first evidence of ENSO-related variabilities detected by the OAT.     

Thorium concentration and the activity ratios230Th/232Th and228Th/232Th in sea water in the western North Pacific

The concentration of thorium isotopes and the activity ratios of²³⁰Th/²³²Th and²²⁸Th/²³²Th in sea water collected in the Kuroshio region, the mixing area of Oyashio and Kuroshio, the Japan Sea and the East China Sea in the western North Pacific were determined. Thorium isotopes were analyzed by α-ray spectrometry after separating them with an anion exchange resin. The average content of thorium (²³²Th) of 2.2×10⁻⁹ g/l was obtained in the open Pacific waters. The ratio of²³⁰Th/²³²Th is in accord with that of the top layer of the sediment in the same area. The high values of²²⁸Th/²³²Th ratio up to 36 were observed in sea water. The excess²²⁸Th in sea water may be due to the migration of²²⁸Ra through the water-sediment interface. Thorium content in suspended matter was 10 to 20% of the total thorium content in the Pacific water.     

Surface currents around Hokkaido in the late fall of 1981 obtained from analysis of satellite images

This paper describes the characteristics of currents around Hokkaido using a current vector map compiled by chasing the displacement of sea marks on a pair of successive thermal infrared images taken from a satellite, NOAA-6. The points of some sea surface patterns showing distinctive features which can be commonly identified in both images are called Sea Marks≓. This sea mark chase method≓ has a great advantage over velocity measurements by boats or buoys, in that it gives a synoptic view of the velocity distribution over a broad sea area extending for some hundreds of miles on a short time scale of half a day.In order to investigate the current in the late fall of 1981, we used the data taken at 19:05 JST on 30 October and at 7:20 JST on 31 October. With these data taken with a 12 hr difference, the measurement accuracy of the speed of sea marks reached ±0.1 knot through geometrical correction. The velocity vectors of sea marks agreed with results of GEK measurements performed on those days, and also with the mean current pattern obtained in the past based on sea surface data.The most distinct features recognized were some cyclonic and anticyclonic eddies of the order of 100 km in diameter which dominated in the Kuril Basin of the Okhotsk Sea. They appeared clearly in the original NOAA images and their physical parameters were determined quantitatively from the vector map. These eddies were located in the region of decay of the Soya Warm Current and were rotating at a speed nearly as large as that of the current. The problems of what feeds energy to these eddies and how long they live remain to be solved in future studies.     

A catalytic oxidation method for the determination of total nitrogen dissolved in seawater

A detailed examination of a high-temperature catalytic oxidation method for liquid samples in the analysis of total nitrogen dissolved in seawater is reported. The nitrogenous compounds in liquid samples are oxidized on a platinum catalyzer at 680°C under oxygen atmosphere and the generated NO₂ is absorbed into a chromogenic reagent, followed by a spectrophotometric determination. The results of this method are much higher than those of wet oxidation methods. Molecular size dependency of the results clearly indicates that the above discrepancy is caused by the low oxidation capacity of the wet oxidation method against high-polymer organic matter dissolved in seawater. The results revealed that the concentration of total nitrogen in seawater is nearly constant from surface to bottom, ranging from 30 to 40 μM 1^?1, which organic nitrogen concentration higher in the surface layer, and a rapid decrease with depth. An examination of molecular size distribution indicates that the concentration of high-polymer organic nitrogen decreases rapidly from surface to deeper layers, with molecular sizes ranging from 5 × 10³ to 3 × 10⁴. Because of the well-defined principle of the oxidation process, its reliability, ease of sample handling and of analytical procedure on board or in the land laboratory, the present method is much more suitable for the marine analytical chemistry of total and organic nitrogen than the other previous methods.     

Observation of mixed Rossby-gravity waves in the Western equatorial Pacific

During the IOP (Intensive Observation Period) of TOGA/COARE (Tropical Ocean and Global Atmosphere/Coupled Ocean Atmosphere Response Experiment) from December 1992 to February 1993, four Japanese moored ADCPs (Acoustic Doppler Current Profilers) measured vertical profiles of three-component velocities at the stations 2S (2°S, 156°E), 2N (2°N, 156°E), 154E (0°N, 154°E) and 147E (0°N, 147°E). Power spectra of the surface current showed a pronounced peak having a period of around 14 days for both the zonal and meridional velocities at the stations 2S and 2N near the equator, and for only the meridional velocity at the equator. This 14-day phenomenon is considered to be a kind of equatorial wave of the first baroclinic mode, from a comparison of the result of the vertical mode analysis and the vertical distribution of the standard deviation of band-pass filtered velocity fluctuations. A dispersion relationship obtained from the horizontal mode analysis of this wave confirmed that the 14-day phenomenon is a mixed Rossby-gravity wave with the westward propagating phase speed and eastward propagating group velocity. From the cross-spectral analysis of velocity data, the average phase speed and wavelength of the wave were estimated as 3.64 m s⁻¹ and 3939 km, respectively, for station pair 2S∼147E. These values were in good agreement with the average phase speed and wavelength of 3.58 m s⁻¹ and 3836 km estimated from the dispersion curve and the observed period. A northerly wind burst blew over all the mooring sites during the middle of the observation period. The mixed Rossby-gravity wave, which is anti-symmetric for the zonal velocity about the equator, is likely to be forced by this northerly wind burst crossing the equator. Generation of the oceanic mixed Rossby-gravity wave of the first baroclinic mode is discussed in association with the atmospheric Rossby wave having the same period.