Northwestern Sea Of Japan Research Articles

Mortality of late juvenile and adult stages of the scallop Mizuhopecten yessoensis (Jay)

Age and size distributions of living populations of the Japanese scallop Mizuhopecten yessoensis (Jay) and accumulations of dead scallop shells were compared in two areas of Peter the Great Bay (northwestern Sea of Japan) to determine the life stages at which higher mortality occurs. The highest mortality was recorded in the juvenile and pre-mature stages, when scallops were less than 2 years of age, and for individuals 6–7 years of age (probably the beginning of the senile period of scallop development) and 9–10 years of age (transition to the old-aged stage). The possible seasons of death were determined by examining the microsculpture of the external shell surface. The seasons at which the highest mortality occurred differed in various localities and was dependent on the extent of deviation of environmental characteristics from the optimal values for the scallop.

Modeling of the wind-driven circulation in the Japan Sea using a reduced gravity model

The surface circulation in the Japan Sea is investigated using a 1.5 layer reduced gravity model. Historical observations suggest strongly that an anti-clockwise circulation is dominant in the subpolar region north of the Polar Front as a general feature. This anti-clockwise circulation as well as the branching of the Tsushima Warm Current was simulated well by incorporating the Naet al. (1992)'s wind stress. The positive curl of the wind stress in the northern and the northwestern Japan Sea was found to play an important role in the formation of the subpolar gyre and the separation of the western boundary current (the East Korean Warm Current) in the Japan Sea.

Interannual variation of the upper portion of the Japan Sea Proper Water and its probable cause

The long-term variation of water properties in the upper portion of the Japan Sea Proper Water (UJSPW) is examined on the basis of hydrographic data at PM10, located on the northwestern Japan Sea, and at PM05, in the Yamato Basin, taken from 1965 through 1982. At PM10, located at the southern boundary of the UJSPW formation region, dissolved oxygen fluctuations on the UJSPW core showed negative correlation with phosphate variations, but showed no signficant correlation with salinity variations. At PM05 water properties fluctuated with smaller amplitudes than those at PM10 except for salinity. Dissolved oxygen variations at PM10 lead those at PM05 by 12–15 months, suggesting that the UJSPW near PM10 circulates into the Yamato Basin spending 12–15 months. Increases of dissolved oxygen contents in summer on relevant isopycnal surfaces at PM10 occurred after cold and/or windy winters except for two of eight; this suggests that larger volume of the UJSPW is formed in severa winter. Rough estimations of the formation rate and existing volume of the UJSPW are made on the basis of a climatological dataset; 1.5×104 km3 yr−1 and 27.3×104 km3, respectively. The ventilation time of the UJSPW, 18.2 years, is about one tenth or less of residence time for the entire Japan Sea Proper Water. This indicates that the UJSPW is renewed about ten times as quick as the deeper water.

Deposition of90Sr and plutonium isotopes derived from the Chernobyl accident in Japan

To clarify environmental effects of the Chemobyl radionuclides, long-lived Chernobyl radioactivity (239,240Pu,238Pu,241Pu and90Sr) in deposition samples in May 1986 was measured at 11 stations in Japan. Temporal variation of weekly deposition of90Sr differed from that of volatile radionuclides such as131I and137Cs, which may reflect the released process at Chernobyl. On the other hand, the geographical distributions of the monthly deposition of long-lived radionuclides were similar to those of volatile radionuclides, in which maximum deposits of90Sr and plutonium were observed in Akita, a northwestern Japan Sea coast site of Honshu Island. Higher241Pu deposition in most of the stations, as well as high238Pu/239,240Pu activity ratios were observed. The241Pu/238Pu activity ratios in deposition samples were nearly equal to that in the total release, which is clear evidence that Chernobyl-derived plutonium was transported to Japan in May 1986 together with volatile radionuclides although the contribution of Chernobyl Pu was about three orders of magnitude lower than137Cs.

The study of intermittent hydrophysical fields in the vicinity of the frontal zone

CTD data provided by the MGI-4204 and MARK-III probes are used to study the quasistationary subpolar front structure in the north-western Sea of Japan. In order to provide further insights into the intermittent scalar hydrophysical fields, the method of inhomogeneity identification using temperature pulsations calculated by the moving interval is suggested. The experimentally-derived inhomogeneity distribution is satisfactorily approximated by the exponential law.

Trace Element Composition of Detrital Magnetite from Coastal Sediments of Northwestern Japan Sea for Provenance Study

ABSTRACT Typomorphic varieties of magnetite in coastal sediments of the NW Japan Sea were distinguished by their contents of 11 trace elements: Ti, Mn, Cr, V, Ni, Co, Zr, Sn, Zn, Pb, Cu. Magnetite from principal magmatic complexes differing in composition and crystallization conditions were used as standard samples. The trace elements show that magnetite in sediments of the inlets near river mouths corresponds to that in rocks occurring in the basin of the rivers flowing into these inlets. Magnetite corresponding to that in rocks exposed on the coast and forming active cliffs indicates that these rocks supply abrasion material in the coastal zone. Different magnetite composition in modern nearshore sediments from that of relict shelf deposits is due to the more extensive provenance at sea-leve low-stands during cold phases of the Late Pleistocene.

ON THE IDENTITY OF BRODSKY'S EPILABIDOCERA AMPHITRITES AND PONTELLA PULVINATA WILSON, 1950 WITH PONTELLA LONGIPEDATA SATO, 1913 (COPEPODA : CALANOIDA)

The calanoid copepod Epilabidocera amphitrites of the family Pontellidae was originally described by McMuRRICH (1916) as Paralabidocera amphitrites n. g., n. sp. from the west coast of Vancouver Island, British Columbia, Canada. However, since the generic name Paralabidocera had been preoccupied by WoLFENDEN (1908) for a far different generic group of copepods which is now classified in the family Acartiidae, WILSON ( 1932, p. 558) proposed a new name Epilabidocera as a substitute for McMuRRICH's Paralabidocera. Now, Epilabidocera amphitrites is recorded from the eastern North Pacific and the Arctic Sea, including the west coast of the United States north of San Francisco Bay, the Gulf of Alaska, the eastern Bering Sea, the Chukchi Sea and off Point Barrow, northern Alaska (WILLEY 1920; EsTERLY 1924; CAMPBELL 1929; JoHNSON 1932, 1953, 1956, 1958; DAvis 1949; BEKLEMISHEV 1961; OMORI 1965; etc.) It was BRODSKY ( 1948) that recorded Epilabidocera amphitrites for the first time in the western North Pacific from the west coast of Kamchatka and Furugelma Island near Vladivostok in the northwestern Japan Sea. The same author again referred to this pontellid under the same name in his monograph (BRODSKY 1950) on the Copepoda Calanoida of the Far-Eastern seas of the U.S.S.R. and the Polar basin, and mention­ ed that its distribution in the western North Pacific covered the both coasts of Kam­ chatka and the east coast of Sakhalin (Karafuto) as well as the northwestern Japan Sea. Since then, !£· amphitrites has been recorded repeatedly in the western North Pacific by the Russian authors as shown below: PoNOMAREVA (1954)-From the Soya (La Perouse) Straits. BRODSKY ( 195 7)-Possjet Bay south of Vladivostok; southwestern Sakhalin; the northern area of the Mamiya (Tartary) Straits; southern Kuriles; eastern Sakhalin (also, the eastern Bering Sea and the Chukchi Sea). BRODSKY (1959)-Terpenija (Patience) Bay, Sakhalin, where it occurs in dense