Facies system of the Eastern Barents Sea since the last glaciation to present

Twenty-two sediment cores raised from the central and eastern parts of the Barents Sea have been studied to reconstruct the evolution of the facies system since the Late Weichselian glaciation. Multiproxy records reveal four lithostratigraphic units, which reflect major development stages of paleoenvironments. Age control is provided by 23 AMS ¹⁴C dates for Holocene sections of four cores. Continental moraine deposits of the last glaciation are overlain by proximal glaciomarine facies of the initial deglaciation phase. During this phase, the Barents Sea ice sheet detached from the ground resulting in seawater penetration into troughs, iceberg calving, deposition of IRD and fine-grained glacier meltwater load in newly formed marine basins. The main deglaciation phase is characterized by pulsed sedimentation from various gravity flows resulting in accumulation of distal glaciomarine facies comprising laminated clay and sand sequences with minor IRD. Redistribution of fine-grained suspended matter by bottom currents and brine-induced nepheloid flows combined with biogenic processes and minor ice rafting caused facies diversity of the Holocene marine sediments. The Holocene facies of shelf depressions reflect rather high, but variable productivity responding to climate changes and variations of Atlantic water inflow into the Barents Sea.     

Vertical structure of low-frequency currents in the southwestern East Sea (Sea of Japan)

The vertical structure of low-frequency flows in the central Ulleung Interplain Gap of the southwestern East Sea (Sea of Japan) is analyzed based on full-depth current measurement during November 2002–April 2004. Record-length mean flows are directed toward the Ulleung Basin (Tsushima Basin) throughout the entire water column. Upper current variability above the permanent thermocline with a dominant period of about 50–60 days is shown to be closely related to the displacement of an anticyclonic warm eddy associated with the westward meander of the Offshore Branch. Fluctuations of deep currents below the permanent thermocline have a dominant period of about 40 days. Coherence between the current near the seabed and shallower depths is statistically significant up to 360 m for a period range between 15 and 100 days, but less significantly correlated with currents in the upper 200 m. Data from the densely equipped mooring line reveal that mean and eddy kinetic energies are minima at 1000 m, where isotherm slopes are also relatively flat. Empirical orthogonal function (EOF) analyses suggest that more than 79% of total variances of upper and deep currents can be explained by their respective first EOF mode characterized by nearly depth-independent eigenvectors. Spectral and EOF analyses of observed currents suggest that most of the deep current variability is not directly related to local upper current variability during the observation period.     

Dynamics of planktonic foraminiferal community in the Sea of Japan during the last 2 My

Based on the analysis of the foraminiferal assemblages in 118 sediment samples from the 210-m-long core of ODP Hole 798 drilled near Honshu Island, it is shown that the structure of their tanathocoenoses experienced three large reorganizations during the last 1.9 My, namely 0.68, 1.21, and 1.36 My B.P. The first reorganization coincides with the Matuyama-Brunhes boundary marked by the magnetic polarity reversal. The second reorganization corresponds to the sharp and progressive temperature fall caused by general climate deterioration. The third event is poorly interpretable thus far. Using the K-average method, the assemblages were differentiated into two types differing in their taxonomic structures. The replacement of one type of community with another occurred simultaneously with the cooling onset 1.21 My B.P. Spectral analysis of the variations in the integral characteristics of the taxonomic structure revealed three groups of cycles with average periods of 136, 59, and 33 ky. These estimates are one-third higher as compared to the duration of the Milankovitch climatic cycles. The species structure of the foraminiferal community is shown to be well consistent with the rank model of geometric series.     

Temporal and spatial variations of radiocarbon in Japan Sea bottom water

In 1995 and 2000, the radiocarbon ratio (Δ¹⁴C) of total dissolved inorganic carbon was measured in the Japan Sea where deep and bottom waters are formed within the sea itself. We found that (1) since 1979, the Δ¹⁴C in bottom water below about 2000-m depth in the western Japan Basin (WJB) had increased by about 30‰ by 1995, and (2) the bottom Δ¹⁴C in the WJB did not change between 1995 and 2000. The former finding was due to penetration of surface bomb-produced radiocarbon into the bottom water owing to bottom ventilation, whereas the latter was caused by stagnation of the bottom ventilation there. In the eastern Japan Basin (EJB), the bottom Δ¹⁴C also increased by about 30‰ between 1979 and 2002. Recent stagnation of the bottom ventilation in the EJB is also suggested from analyses of constant bomb-produced tritium between 1984 and 1999. The temporal variations of Δ¹⁴C, tritium, and dissolved oxygen in the bottom waters indicate that: (1) new bottom water is formed south of Vladivostok in the WJB only in severe winters; and (2) the new bottom water then follows the path of a cyclonic abyssal circulation of the Japan Sea, which results in the increases in dissolved oxygen and the transient tracers in the bottom waters in the EJB and Yamato Basin with an approximate 3-to 6-year time lag. This process is consistent with the spatial variations of Δ¹⁴C, bomb-produced ¹³⁷Cs, and chlorofluorocarbon-11 in the bottom waters of the Japan Sea.     

Distributional characteristics of planktonic Amphipoda (Hyperiidea) in the South Huanghai Sea and East China Sea

Ｄｉｓｔｒｉｂｕｔｉｏｎａｌ　ｃｈａｒａｃｔｅｒｉｓｔｉｃｓ　ｏｆ　ｐｌａｎｋｔｏｎｉｃ　Ａｍｐｈｉｐｏｄａ（Ｈｙｐｅｒｉｉｄｅａ）　ｉｎ　ｔｈｅ　Ｓｏｕｔｈ　Ｈｕａｎｇｈａｉ　Ｓｅａ　ａｎｄ　Ｅａｓｔ　Ｃｈｉｎａ　ＳｅａＬｉｎＪｉｎｇｈｏｎｇａｎｄ...     

Water masses and decadal variability in the East Sea (Sea of Japan)

Water masses in the East Sea are newly defined based upon vertical structure and analysis of CTD data collected in 1993–1999 during Circulation Research of the East Asian Marginal Seas (CREAMS). A distinct salinity minimum layer was found at 1500 m for the first time in the East Sea, which divides the East Sea Central Water (ESCW) above the minimum layer and the East Sea Deep Water (ESDW) below the minimum layer. ESCW is characterized by a tight temperature–salinity relationship in the temperature range of 0.6–0.12 °C, occupying 400–1500 m. It is also high in dissolved oxygen, which has been increasing since 1969, unlike the decrease in the ESDW and East Sea Bottom Water (ESBW). In the eastern Japan Basin a new water with high salinity in the temperature range of 1–5 °C was found in the upper layer and named the High Salinity Intermediate Water (HSIW). The origin of the East Sea Intermediate Water (ESIW), whose characteristics were found near the Korea Strait in the southwestern part of the East Sea in 1981 [Kim, K., & Chung, J. Y. (1984) On the salinity-minimum and dissolved oxygen-maximum layer in the East Sea (Sea of Japan), In T. Ichiye (Ed.), Ocean Hydrodynamics of the Japan and East China Seas (pp. 55–65). Amsterdam: Elsevier Science Publishers], is traced by its low salinity and high dissolved oxygen in the western Japan Basin. CTD data collected in winters of 1995–1999 confirmed that the HSIW and ESIW are formed locally in the Eastern and Western Japan Basin. CREAMS CTD data reveal that overall structure and characteristics of water masses in the East Sea are as complicated as those of the open oceans, where minute variations of salinity in deep waters are carefully magnified to the limit of CTD resolution. Since the 1960s water mass characteristics in the East Sea have changed, as bottom water formation has stopped or slowed down and production of the ESCW has increased recently.     

Seasonal variations in the low-salinity intermediate water in the region south of sub-polar front of the East Sea (Sea of Japan)

Seasonal variations in the low-salinity intermediate water (ESIW) in the region south of the sub-polar front of the East Sea were investigated by using historical hydrographic data. The salinity of the representative density (sigma-0=27.2) of the ESIW was minimal in summer and maximal in winter in the region south of the sub-polar front. The selected four subregions showed different salinity variations. In the west of Oki Spur and the Yamato Basin, salinity fluctuated similarly, with a minimum during summer. In the Ulleung Basin and northwest of Sado Island, however, variations in salinity showed two minima, one is in winter and the other is in summer. These results imply differences in the flow path of the ESIW into the region south of the sub-polar front over time.     

The Air-Sea Exchange of CO2 in the East Sea (Japan Sea)

During CREAMS expeditions, fCO₂ for surface waters was measured continuously along the cruise tracks. The fCO₂ in surface waters in summer varied in the range 320–440 μatm, showing moderate supersaturation with respect to atmospheric CO₂. In winter, however, fCO₂ showed under-saturation of CO₂ in most of the area, while varying in a much wider range from 180 to 520 μatm. Some very high fCO₂ values observed in the northern East Sea (Japan Sea) appeared to be associated with the intensive convection system developed in the area. A gas-exchange model was developed for describing the annual variation of fCO₂ and for estimating the annual flux of CO₂ at the air-sea interface. The model incorporated annual variations in SST, the thickness of the mixed layer, gas exchange associated with wind velocity, biological activity and atmospheric concentration of CO₂. The model shows that the East Sea releases CO₂ into the atmosphere from June to September, and absorbs CO₂ during the rest of the year, from October through May. The net annual CO₂ flux at the air-sea interface was estimated to be 0.032 (±0.012) Gt-C per year from the atmosphere into the East Sea. Water column chemistry shows penetration of CO₂ into the whole water column, supporting a short turnover time for deep waters in the East Sea. This revised version was published online in August 2006 with corrections to the Cover Date.     

Fluctuations of the calcite compensation depth (CCD) in the East Sea (Sea of Japan)

Variations in the calcite compensation depth (CCD) in the East Sea (Sea of Japan) since the early middle Miocene were inferred from data on age-depth relationships, sediment carbonate, and benthic foraminifers from ODP sites 794, 795, and 797. The CCD remained relatively shallow during much of the middle Miocene–Pliocene, and deepened sharply at the beginning of the Pleistocene. Since then it has fluctuated rapidly, possibly in relation to the onset of the northern hemisphere glacial cycles in the late Pliocene. The average CCD has deepened since at least the early middle Miocene, coinciding with the long-term drop in eustatic sea level. Received: 5 November 1998 / Revision accepted: 2 February 2000     

Depositional environment in the southern Ulleung Basin, East Sea (Sea of Japan), during the last 48 000 years

The present study is based on the sedimentological data from a piston core KCES1 off the southern Ulleung Basin margin, the East Sea (Sea of Japan). The data include sediment color (L^*), X-ray radiographs, grain size distribution and AMS¹⁴C date. Four kinds of sediments (homogeneous, laminated, crudely laminated and hybrid sediments) are identified according to the characters of the sedimentary structures that were considered to reflect changes in bottom-water oxygenation. Alternations of dark laminated/crudely laminated sediments and light homogeneous sediments represent millennial-scale variations that are possibly associated with the high-resolution changes in the East Asian monsoon (EAM). The relative contributions of the East China Sea Coastal Water (ECSCW) and the Tsushima Warm Current (TWC) were likely the main reasons for the repetition of the anoxic and oxic depositional conditions in the East Sea since the last 48 ka BP. During the interstadial, the strengthen summer EAM was attributed to the expansion of the ECSCW because of more humid climate in central Asia, and then more strongly low-salinity, nutrient-enriched water was introduced into the East Sea. The ventilation of deep water was restricted and therefore the dark laminated layer deposited under the anoxic bottom water condition. During the lowest stand of sea level in the last glacial maximum (LGM), the isolated East Sea dominated by stratiˉed water masses and the euxinic depositional environment formed. The homogenous sediments have been predominating since 17.5 ka BP indicating that the TWC has intruded into the East Sea gradually with the stepwise rise of sea level and the bottom water oxygen level was high. During the late Younger Dryas (YD) period, the last dark laminated layer deposited because the ventilation of bottom water was restricted by stronger summer EAM. The TWC strengthened and the bottom water became oxic again from 10.5 ka BP.     

东海和黄海二甲基亚砜（DMSO）的季节和空间变化

Seasonal and spatial distributions of dissolved and particulate dimethylsulfoxide(DMSOd,DMSOp)were measured in the East China Sea and the Yellow Sea during March–April 2011 and October–November 2011.The concentrations of DMSOd and DMSOp in the surface water were 20.6(5.13–73.8)and 8.90(3.75–29.6)nmol/L in spring,and 13.4(4.17–42.7)and 8.18(3.44–22.6)nmol/L in autumn,respectively.Both DMSOd and DMSOp concentrations revealed similar seasonal changes with higher values occurring in spring,mainly because of the higher phytoplankton biomass observed in spring.Moreover,the ratios of DMSOp/chlorophyll a also exhibited an apparent seasonal change with higher values in autumn(35.7 mmol/g)and lower values in spring(23.4 mmol/g),thereby corresponding with the seasonal variation in the proportion of DMSO producers in the phytoplankton community between spring and autumn.In addition,DMSOd and DMSOp concentrations in the surface seawater revealed obvious diurnal variations with the maxima appearing in the afternoon.     

210Pb-derived sediment accumulation rates in the southwestern East Sea (Sea of Japan)

 Recent sediment accumulation rates are 18–230 mg cm^-2 yr^-1 (0.02–0.2 cm yr^-1) based on excess ²¹⁰Pb activity profiles in the southwestern part of the East Sea (Sea of Japan). Assuming no mixing beneath surface mixed layers, ²¹⁰Pb-derived sediment accumulation rates are 18–32 mg cm^-2 yr^-1 in the northern part of the Yamato Ridge and the Ulleung Basin, 29–136 mg cm^-2 yr^-1 in the Korea Plateau, and 230 mg cm^-2 yr^-1 in the southern shelf. These values generally agree with long-term sedimentation rates estimated from dated ash layers. Received: 6 October 1995 / Revision received: 31 May 1996     

Supply of Heat by Tsushima Warm Current in the East Sea (Japan Sea)

A significant surface net heat loss appears around the Kuroshio and the Tsushima Warm Current regions. The area where the surface heat loss occurs should require heat to be supplied by the current to maintain the long-term annual heat balance. Oceanic heat advection in these regions plays an important role in the heat budget. The spatial distribution of the heat supply by the Tsushima Warm Current near the surface was examined by calculating the horizontal heat supply in the surface layer of the East Sea (the Japan Sea) (ESJS), directly from historical sea surface temperature and current data. We have also found a simple estimation of the effective vertical scale of heat supply by the current to compensate net heat loss using the heat supplied by the current in the surface 10 m layer. The heat supplied by the current for the annual heat balance was large in the Korea/Tsushima Strait and along the Japanese Coast, and was small in the northwestern part of the ESJS. The amount of heat supplied by the current was large in the northwestern part and small in the south-eastern part of the ESJS. These features suggest that the heat supplied by the Tsushima Warm Current is restricted to near the surface around the northeastern part and extends to a deeper layer around the southeastern part of the ESJS. This revised version was published online in August 2006 with corrections to the Cover Date.     

Sinking fluxes of particulate U-Th radionuclides in the East Sea (Sea of Japan)

A record of radionuclide fluxes at a deep marginal sea of the Northwest Pacific Ocean (39°40′N 132°24′ E, Japan Basin, East Sea/Sea of Japan) was obtained from analysis of a 1-year continuous collection of sediment-trap samples. The trap was placed at a depth of 2800 m, 500 m above the sea floor, and the samples were recovered at the end of one year. Concentrations of ²³⁸U, ²³⁴U, ²³²Th, ²³⁰Th and ²²⁸Th were measured in the trapped material. All of the radionuclide fluxes showed seasonal variations that were in phase with the variations in total particle flux, which were shown in earlier work to be closely tied to the primary production in the surface water. The formation of authigenic ²³⁸U appears to be less than in other open ocean regimes. The residence time of particulate thorium isotopes were of the order of a year, resulting in an average settling rate of a meter per day. Comparison of the measured ²³⁰Th_ex flux with that of the theoretical production in the overlying water column yielded about 40% surplus of ²³⁰Th, indicating that lateral advection contributes ²³⁰Th to this sampling site.     

Bathymetry enhancement by altimetry-derived gravity anomalies in the East Sea (Sea of Japan)

The gravity-geologic method (GGM) was used to enhance the bathymetry of the East Sea (Sea of Japan) with satellite altimetry-derived free-air gravity anomalies and shipborne depth measurements. By comparison with the bathymetry model of Smith and Sandwell’s (SAS) approach (1994), GGM was found to have an advantage with short wavelength (≤12 km) components, while SAS better predicts longer wavelength (≥25 km) components, despite its dependency on density contrast. To mitigate this limitation, a tuning density contrast of 10.25 g/cm³ between seawater and the seafloor was primarily estimated by the downward continuation method and then validated by the check points method with GGM. Similarly, SAS is limited by the “A” value in low-pass part of the Wiener filter, which defines the effective range of the wavelength components on bathymetry. As a final result, we present an enhanced GGM bathymetry model by integrating all available data.     

48 ka以来日本海Ulleung海盆南部的海洋沉积环境演化

晚第四纪以来伴随底层水含氧量的剧烈变化,浅色和深色沉积层的交替出现是日本海半远洋沉积物的主要特征。沉积特征分析表明,日本海Ulleung海盆南部KCES1孔的沉积物具有四种不同的沉积构造:均质、纹层、纹层状和混杂构造。深色沉积层一般具有纹层和纹层状构造,并且与我国内陆的千年尺度东亚夏季风强弱变化记录有很好的对应关系,表明纹层沉积物也具有千年尺度的变化规律,从而进一步说明了冰川性海平面变化和东亚夏季风波动应该是Ulleung海盆南部底层水溶解氧含量变化的主要原因。在暖期,在东亚夏季风降水相对增强的影响下,低温、低盐的东海沿岸水对日本海表层水体的贡献要大于对马暖流的贡献,日本海水体间的交换减弱,最终造成缺氧的海底沉积环境。在冷期,夏季风强度的减弱(冬季风增强)加快了日本海西北部深层水的生成,Ulleung海盆南部的底层水含氧量高,相应地沉积了具均质构造的浅色沉积物;在末次盛冰期最低海平面时,日本海成为一个封闭的海盆,降雨量高于蒸发量,水体出现分层,底层水处于停滞缺氧状态。自距今17.5 ka(日历年,下同)以来底层水含氧量较高,对马暖流逐渐成为影响日本海海洋沉积环境的主要因素。Ulleung海盆南部底层水的含氧量在YD期间有一定程度的降低,东海沿岸水的短暂强盛制约了深层水的流通。自距今10.5 ka以来对马暖流强盛,日本海海底处于富氧的沉积环境。     

High primary productivity and f-ratio in summer in the Ulleung basin of the East/Japan Sea

To better understand the cause of high summer primary productivity in the Ulleung Basin located in the southwest part of the East/Japan Sea, the spatial dynamics of primary, new, and regenerated productivities (PP, NP, and RP) were examined along the path of the Tsushima Warm Current system in summer 2008. We compared hydrographic and chemical parameters in the Ulleung Basin with those of the Kuroshio Current in the Western Pacific Ocean and the East China Sea. In summer, integrated primary productivity (IPP, 0.37–0.96 g C m⁻² d⁻¹) and integrated new productivity (INP, 26–221 mg N m⁻² d⁻¹) within the euphotic zone in the Ulleung Basin were higher than those in the East China Sea and the Western Pacific Ocean (0.17–0.28 g C m⁻² d⁻¹, 2−5 mg N m⁻² d⁻¹, respectively). In contrast, there was no pronounced spatial variation in integrated regenerated productivity (IRP, 43–824 mg N m⁻² d⁻¹). Strong positive correlations between IPP and INP (also the f-ratio), and between nitrate uptake rate in the mixed layer and nitrate upward flux through the top of pycnocline in summer in the Ulleung Basin imply that the high IPP was mainly supported by supply of nitrate from the underlying water in the euphotic zone. Shallowing of the pycnocline depth as the current enters the East/Japan Sea facilitates nitrate supply from the nutrient-replete cold water immediately below the pycnocline through nitrate upward flux. A subsurface maximum in PP at or above the pycnocline and a high f-ratio further support the importance of this source of nitrate for maintaining the high summer PP in the Ulleung Basin. In comparison, the high PP layer was observed at the surface in the following fall and spring in the Ulleung Basin. Our results demonstrate the importance of hydrographic features in enhancing PP in this oligotrophic Tsushima Warm Current system.     

Notes Distribution of planktonic pyrrophyta in the East China Sea

ＮｏｔｅｓＤｉｓｔｒｉｂｕｔｉｏｎｏｆｐｌａｎｋｔｏｎｉｃｐｙｒｒｏｐｈｙｔａｉｎｔｈｅＥａｓｔＣｈｉｎａＳｅａ￥／／Ｔｈｅｓｐｅｃｉｅｓｃｏｍｐｏｓｉｔｉｏｎａｎｄｑｕａｎｔｉｔｙｏｆｐｙｒｒｏｐｈｙｔａａｒｅｔｈｅｓｅｃｏｎｄｏｎｌｙｔｏｄｉａｔ...     

Environmental changes in the Amur Bay (Japan/East Sea) during the last 150 years revealed by examination of diatoms and silicoflagellates

Siliceous unicellular microalgae — diatoms and silicoflagellates from sediments in Amur Bay were analyzed with high temporal resolution to examine changes over the last 150 years. The age of sediments was estimated from unsupported ²¹⁰Pb controlled by ¹³⁷Cs. Siliceous microalgae examined in each cm of two sediment cores demonstrated significant changes in the ecological structure of the assemblages that reflected changes in sedimentation conditions. During the years 1860–1910 the sediments accumulated under the great influence of river runoff. For about the next 50 years the number of freshwater species and marine benthic diatoms in sediments sharply declined, which is probably connected with the weakening of the effects of river runoff due to deforestation. Since the early 1960s the sedimentation conditions in the Amur Bay changed significantly. Marine planktonic diatoms and silicoflagellates began to prevail in sediments and this reflects increasing microphytoplankton productivity. One consequence of this was the formation of seasonal bottom hypoxia in Amur Bay. The ecological structure of diatom and silicoflagellate assemblages indicates that the sea level began to rise since the early 1960s and this corresponds to the water and air temperature increase in the area for that period. The obtained data suggest that the environmental changes over the last 150 years in Armur Bay are associated with the weakening of river runoff due to deforestation, sea level rise caused by global warming, and the increase of siliceous microplankton productivity that resulted in the formation of seasonal bottom hypoxia.

     

Basin-To-Basin and Year-To-Year Variation of Temperature and Salinity Characteristics in the East Sea (Sea of Japan)

Analysis of CTD data from four CREAMS expeditions carried out in summers of 1993–1996 produces distinct T-S relationships for the western and eastern Japan Basin, the Ulleung Basin and the Yamato Basin. T-S characteristics are mainly determined by salinity as it changes its horizontal pattern in three layers, which are divided by isotherms of 5°C and 1°C; upper warm water, intermediate water and deep cold water. Upper warm water is most saline in the Ulleung Basin and the Yamato Basin. Salinity of intermediate water is the highest in the eastern Japan Basin. Deep cold water has the highest salinity in the Japan Basin. T-S curves in the western Japan Basin are characterized by a salinity jump around 1.2–1.4°C in the T-S plane, which was previously found off the east coast of Korea associated with the East Sea Intermediate Water (Cho and Kim, 1994). T-S curves for the Japan Basin undergo a large year-to-year variation for water warmer than 0.6°C, which occupies upper 400 m. It is postulated that the year-to-year variation in the Japan Basin is caused by convective overturning in winter. This revised version was published online in August 2006 with corrections to the Cover Date.