Decadal changes in fish assemblages in waters near the Ieodo ocean research station (East China Sea) in relation to climate change from 1984 to 2010

We compiled and analyzed past time-series data to evaluate changes in oceanographic conditions and marine ecosystems near the Ieodo ocean research station (IORS) in the East China Sea (N 31°15??C33°45??, E 124°15??C127°45??) in relation to longterm changes in climate and global warming. The environment data we used was a depth-specific time-series of temperature and salinity for the water columns at 175 fixed stations along 22 oceanographic lines in Korean waters, based on bimonthly measurements since 1961 taken by the National Fisheries Research & Development Institute. As an indicator for the ecosystem status of the waters off Ieodo, we analyzed species composition in biomass of fishes caught by Korean fishing vessels in the waters near the IORS (1984?C2010) and summarized the data in relation to the environmental changes using canonical correspondence analysis (CCA). To detect step changes in the time-series of environmental factors, we applied a sequential t-test analysis of regime shift. Correspondence analysis detected a major shift in fish assemblage structure between 1990 and 1993: the dominant species was filefish during 1981?C1992, but chub mackerel during 1992?C2007. This shift in fish assemblage structure seemed to be related to the well-established 1989 regime shift in the North Pacific, which was confirmed again with respect to temperature in the Yellow Sea and the Korea Strait (but not in the waters off the IORS). In overall from 1984 to 2010, salinity was more important than water temperature in CCA, implying that the fluctuation of the Tsushima warm current is a most important force driving the long-term changes in fish assemblage structure in the waters off the IORS. Further multidisciplinary researches are required to identify oceanographic and biological processes that link climate-driven physical changes to fish recruitment and habitat range fluctuations.     

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.     

Geotechnical properties of deep oceanic sediments recovered from the hydrate occurrence regions in the Ulleung Basin, East Sea, offshore Korea

This study presents comprehensive geotechnical data of the natural marine sediments cored from the hydrate occurrence regions during the Ulleung Basin Gas Hydrate Expedition 1 (UBGH1), East Sea, offshore Korea in 2007. Geotechnical soil index properties of the Ulleung Basin sediments, including grain size distribution, porosity, water content, Atterberg limits, specific gravity, and specific surface area, were experimentally determined. These soil index properties were correlated to geotechnical engineering parameters (e.g., shear strength and friction angle) by using well-known empirical relationships. By performing standard consolidation tests on both undisturbed specimens (as recovered from the original core liner after hydrate dissociation) and remolded specimens, stress-dependent mechanical and hydraulic properties (e.g., compressibility and hydraulic conductivity) were measured. The experimental results provide important engineering parameters, and demonstrate the effect of hydrate presence and consequential dissociation to index properties, engineering parameters, and innate sediment structures.     

Crustal analysis of the Ulleung Basin in the East Sea (Japan Sea) from enhanced gravity mapping

To facilitate geological analyses of the Ulleung Basin in the East Sea (Japan Sea) between Korea and Japan, shipborne and satellite altimetry-derived gravity data are combined to derive a regionally coherent anomaly field. The 2-min gridded satellite altimetry-based gravity predicted by Sandwell and Smith [Sandwell DT, Smith WHF (1997) J Geophys Res 102(B5):10,039–10,054] are used for making cross-over adjustments that reduce the errors between track segments and at the cross-over points of shipborne gravity profiles. Relative to the regionally more homogeneous satellite gravity anomalies, the longer wavelength components of the shipborne anomalies are significantly improved with minimal distortion of their shorter wavelength components. The resulting free-air gravity anomaly map yields a more coherent integration of short and long wavelength anomalies compared to that obtained from either the shipborne or satellite data sets separately. The derived free-air anomalies range over about 140 mGals or more in amplitude and regionally correspond with bathymetric undulations in the Ulleung Basin. The gravity lows and highs along the basin’s margin indicate the transition from continental to oceanic crust. However, in the northeastern and central Ulleung Basin, the negative regional correlation between the central gravity high and bathymetric low suggests the presence of shallow denser mantle beneath thinned oceanic crust. A series of gravity highs mark seamounts or volcanic terranes from the Korean Plateau to Oki Island. Gravity modeling suggests underplating by mafic igneous rocks of the northwestern margin of the Ulleung Basin and the transition between continental and oceanic crust. The crust of the central Ulleung Basin is about a 14–15 km thick with a 4–5 km thick sediment cover. It may also include a relatively weakly developed buried fossil spreading ridge with approximately 2 km of relief.     

Evidence of gas hydrate from downhole logging data in the Ulleung Basin, East Sea

The Gas Hydrate Research and Development Organization (GHDO) of Korea successfully accomplished both coring (hydraulic piston and pressure coring) and logging (logging-while-drilling, LWD, and wireline logging) to investigate the presence of gas hydrate during the first deep drilling expedition in the Ulleung Basin, East Sea of Korea (referred to as UBGH1) in 2007. The LWD data from two sites (UBGH1-9, UBGH1-10) showed elevated electrical resistivity (>80 Ω-m) and P-wave velocity (>2000 m/s) values indicating the presence of gas hydrate. During the coring period, the richest gas hydrate accumulation was discovered at these intervals. Based on log data, the occurrence of gas hydrate is primarily controlled by the presence of fractures. The gas hydrate saturation calculated using Archie’s relation shows greater than 60% (as high as ∼90%) of the pore space, although Archie’s equation typically overestimates gas hydrate saturation in near-vertical fractures. The saturation of gas hydrate is also estimated using the modified Biot-Gassmann theory (BGTL) by Lee and Collett (2006). The saturation values estimated rom BGTL are much lower than those calculated from Archie’s equation. Based on log data, the hydrate-bearing sediment section is approximately 70 m (UBGH1-9) to 130 m (UBGH1-10) in thickness at these two sites. This was further directly confirmed by the recovery of gas hydrate samples and pore water freshening collected from deep drilling core during the expedition. LWD data also strongly support the interpretation of the seismic gas hydrate indicators (e.g., vent or chimney structures and bottom-simulating reflectors), which imply the probability of widespread gas hydrate presence in the Ulleung Basin.     

Evidence of gas hydrate from downhole logging data in the Ulleung Basin,East Sea

The Gas Hydrate Research and Development Organization (GHDO) of Korea successfully accomplished both coring (hydraulic piston and pressure coring) and logging (logging-while-drilling, LWD, and wireline logging) to investigate the presence of gas hydrate during the first deep drilling expedition in the Ulleung Basin, East Sea of Korea (referred to as UBGH1) in 2007. The LWD data from two sites (UBGH1-9, UBGH1-10) showed elevated electrical resistivity (>80 Ω-m) and P-wave velocity (>2000 m/s) values indicating the presence of gas hydrate. During the coring period, the richest gas hydrate accumulation was discovered at these intervals. Based on log data, the occurrence of gas hydrate is primarily controlled by the presence of fractures. The gas hydrate saturation calculated using Archie’s relation shows greater than 60% (as high as ∼90%) of the pore space, although Archie’s equation typically overestimates gas hydrate saturation in near-vertical fractures. The saturation of gas hydrate is also estimated using the modified Biot-Gassmann theory (BGTL) by Lee and Collett (2006). The saturation values estimated rom BGTL are much lower than those calculated from Archie’s equation. Based on log data, the hydrate-bearing sediment section is approximately 70 m (UBGH1-9) to 130 m (UBGH1-10) in thickness at these two sites. This was further directly confirmed by the recovery of gas hydrate samples and pore water freshening collected from deep drilling core during the expedition. LWD data also strongly support the interpretation of the seismic gas hydrate indicators (e.g., vent or chimney structures and bottom-simulating reflectors), which imply the probability of widespread gas hydrate presence in the Ulleung Basin.     

Organic carbon accumulation and sulfate reduction rates in slope and basin sediments of the Ulleung Basin,East/Japan Sea

This study investigated the organic carbon accumulation rates (OCARs) and sulfate reduction rates (SRRs) in slope and basin sediments of the Ulleung Basin, East/Japan Sea. These sediments have high organic contents at depths greater than 2,000 m; this is rare for deep-sea sediments, except for those of the Black Sea and Chilean upwelling regions. The mean organic carbon to total nitrogen molar ratio was estimated to be 6.98 in the Ulleung Basin sediments, indicating that the organic matter is predominantly of marine origin. Strong organic carbon enrichment in the Ulleung Basin appears to result from high export production, and low dilution by inputs of terrestrial materials and calcium carbonate. Apparent sedimentation rates, calculated primarily from excess ²¹⁰Pb distribution below the zone of sediment mixing, varied from 0.033 to 0.116 cm year⁻¹, agreeing well with previous results for the basin. OCARs fluctuated strongly in the range of 2.06–12.5 g C m⁻² year⁻¹, these rates being four times higher at the slope sites than at the basin sites. Within the top 15 cm of the sediment, the integrated SRRs ranged from 0.72 to 1.89 mmol m⁻² day⁻¹, with rates approximately twice as high in the slope areas as in the basin areas. SRR values were consistently higher in areas of high sedimentation and of high organic carbon accumulation, correlating well with apparent sedimentation rates and OCARs. The sulfate reduction rates recorded in the basin and slope sediments of the Ulleung Basin are higher than those reported for other parts of the world, with the exception of the Peruvian and Chilean upwelling regions. This is consistent with the high organic carbon contents of surface sediments of the Ulleung Basin, suggesting enhanced organic matter fluxes.     

Fossil diatom assemblages as paleoecological indicators of paleo-water environmental change in the Ulleung Basin,East Sea,Republic of Korea

The fossil diatom assemblage record from two sediment cores obtained from the Ulleung Basin, East Sea, Republic of Korea, revealed changes in the diatom assemblage zones in PG1 and PD3 core samples. The two sediment cores were δC¹⁴ dated and approximately represented the late Pleistocene–Holocene. The analysis of age zones in the PG1 core and PD3 core was assessed based on the frequency of variations, and occurrences of biostratigraphical fossil diatom species. During the Last Glacial Maximum (LGM), the sea level was lower than that at present and the Ulleung Basin became isolated from the Pacific Ocean. As a result, there would have been a limited Tsushima Warm Current (TWC) influence, and salinity would have decreased resulting in increased freshwater and coastal diatoms. The distribution pattern of diatoms presented in the cores was associated with changes in water temperature and salinity and the adding of terrigenous material brought about by the input of freshwater. Changes in the abundance of a tychopelagic diatom, Paralia sulcata, reflected the effect of the water currents. Diatom temperature (Td) values and the ratio of centric/pennate diatoms provided evidence of limited influences of the TWC and freshwater inflow. It is thought that all assemblage zones were influenced by the TWC, which had an important effect on the distribution and composition of fossil diatoms.     

Decadal variation and trend of the upper layer salinity in the South China Sea from 1960 to 2010

Ocean salinity is an essential measurable indicator of water cycle and plays a crucial role in regulating ocean and climate change. Using Simple Ocean Data Assimilation(SODA) reanalysis product, substantial decadal variability of the salinity in the upper layer of the South China Sea(SCS) from 1960 to 2010 was examined. Results show that a decadal variation of the upper layer salinity is clear. The upper layer(100 m) waters are found to freshen from 1960, become saltier during 1975 to 1995, and ...     

黄海、东海表、上层实测流分析

根据迄今为止所获得的142套锚碇浮标和58套卫星跟踪漂流浮标的大范围测流资料，综合分析了黄海、东海表、上层环流。研究结果更加清晰、形象、直观地展示了黑潮及其向对马暖流的分支，台湾暖流的分叉，和黄海暖流、长江冲淡水及涡旋发达海区的若干主要特征。     

黄海、东海表、上二层实测流分析

根据迄今为止所获得的142套锚碇浮标和58套卫星跟踪漂流浮标的大范围测流资料,综合分析了黄海、东海表、上层环流.研究结果更加清晰、形象、直观地展示了黑潮及其向对马暖流的分支,台湾暖流的分叉,和黄海暖流、长江冲淡水及涡旋发达海区的若干主要特征.     

Thermal fluxes and stability of the upper boundary of deep near-bottom layer in the Black Sea

Experimentally-derived data are used to scrutinize structural peculiarities of the upper boundary of deep near-bottom layer in the Black Sea. Thermal fluxes through the layer’s upper boundary have been evaluated and compared with the geothermal fluxes. Although there is significant divergence between the individual evaluations, the quantities at issue generally agree with one another. It is shown that in evaluating thermal fluxes, it is necessary to consider fine structure of the differential-diffusive type. Stability of the upper boundary of the deep near-bottom layer has been examined, and diagrams of stability/instability resulting from the development of convection have been plotted. Translated by Vladimir A. Puchkin.     

Relationship between deep-sea fish distributions and oceanic conditions of the East China Sea

Ｒｅｌａｔｉｏｎｓｈｉｐｂｅｔｗｅｅｎｄｅｅｐ－ｓｅａｆｉｓｈｄｉｓｔｒｉｂｕｔｉｏｎｓａｎｄｏｃｅａｎｉｃｃｏｎｄｉｔｉｏｎｓｏｆｔｈｅＥａｓｔＣｈｉｎａＳｅａ￥ＳｈｅｎＪｉｎ＇ａｏ（ＲｅｃｅｉｖｅｄＮｏｖｅｍｂｅｒ１７，１９９３；ａｃｃｅｐｔｅｄ...     

Qualitative assessment of gas hydrate and gas concentrations from the AVO characteristics of the BSR in the Ulleung Basin, East Sea (Japan Sea)

The presence of gas hydrate in the Ulleung Basin, East Sea (Japan Sea), inferred by various seismic indicators, including the widespread bottom-simulating reflector (BSR), has been confirmed by coring and drilling. We applied the standard AVO technique to the BSRs in turbidite/hemipelagic sediments crosscutting the dipping beds and those in debris-flow deposits to qualitatively assess the gas hydrate and gas concentrations. These BSRs are not likely to be affected by thin-bed tuning which can significantly alter the AVO response of the BSR. The BSRs crosscutting the dipping beds in turbidite/hemipelagic sediments are of low-seismic amplitude and characterized by a small positive gradient, indicating a decrease in Poisson’s ratio in the gas-hydrate stability zone (GHSZ), which, in turn, suggests the presence of gas hydrate. The BSRs in debris-flow deposits are characterized by a negative gradient, indicating decreased Poisson’s ratio below the GHSZ, which is likely due to a few percent or greater gas saturations. The increase in the steepness of the AVO gradient and the magnitude of the intercept of the BSRs in debris-flow deposits with increasing seismic amplitude of the BSRs is probably due to an increase in gas saturations, as predicted by AVO model studies based on rock physics. The reflection strength of the BSRs in debris-flow deposits, therefore, can be a qualitative measure of gas saturations below the GHSZ.     

Biomarker-based Seawater Temperatures of Winter Sinking Particles and Core-top Sediment in the Ulleung Basin of the East Sea

Ocean Science Journal - This study evaluates the application of biomarkerbased temperature proxy data (alkenone with its resultant $$U_{37}^{K'}$$ index and glycerol dialkyl glycerol tetraether...     

Qualitative assessment of gas hydrate and gas concentrations from the AVO characteristics of the BSR in the Ulleung Basin,East Sea (Japan Sea)

The presence of gas hydrate in the Ulleung Basin, East Sea (Japan Sea), inferred by various seismic indicators, including the widespread bottom-simulating reflector (BSR), has been confirmed by coring and drilling. We applied the standard AVO technique to the BSRs in turbidite/hemipelagic sediments crosscutting the dipping beds and those in debris-flow deposits to qualitatively assess the gas hydrate and gas concentrations. These BSRs are not likely to be affected by thin-bed tuning which can significantly alter the AVO response of the BSR. The BSRs crosscutting the dipping beds in turbidite/hemipelagic sediments are of low-seismic amplitude and characterized by a small positive gradient, indicating a decrease in Poisson’s ratio in the gas-hydrate stability zone (GHSZ), which, in turn, suggests the presence of gas hydrate. The BSRs in debris-flow deposits are characterized by a negative gradient, indicating decreased Poisson’s ratio below the GHSZ, which is likely due to a few percent or greater gas saturations. The increase in the steepness of the AVO gradient and the magnitude of the intercept of the BSRs in debris-flow deposits with increasing seismic amplitude of the BSRs is probably due to an increase in gas saturations, as predicted by AVO model studies based on rock physics. The reflection strength of the BSRs in debris-flow deposits, therefore, can be a qualitative measure of gas saturations below the GHSZ.     

南海北部上层海洋变化的定点观测分析

对南海季风试验(CSMEX)加密观测期(IOP)“实验3”号船在南海北部获得的CTD温盐和声学多普勒流速剖面仪(ADCP)海流等观测资料进行分析,给出东沙群岛西南部大陆坡附近IOP两个阶段定点观测的海洋分量部分结果,通过分析海水的动力、热力学结构,描述夏季风暴发、维持期间该测站上层海洋的变化,讨论近表面水的温度、盐度和海流对海面风场的响应.     

南海西北部上层海洋对台风“杜苏芮”的响应分析

基于锚碇观测资料,本文分析了南海西北部陆坡区上层海洋对台风“杜苏芮”的动力学和热力学响应特征。在动力学响应方面,台风“杜苏芮”期间上层流速显著增强,混合层纬向流速可达1.20 m/s;“杜苏芮”经过后上层海水运动以近惯性振荡为主(流向顺时针旋转周期在36～40 h之间)。近惯性能量在垂向分布上存在两个高值中心,分别位于混合层和温跃层深度上。近惯性能量耗散过程的e折时间尺度约为3.7 d,我们认为能量的向下传播在局地近惯性能量衰减过程中起主要作用。对能量谱的分析表明,“杜苏芮”作用期间近惯性频率能量相对于其作用前增大了约29.4倍,而全日和半日频率(K₁和M₂)能量有所减弱。此外,能量谱显示近惯性频率存在明显的“蓝移”现象,即对于纬向和经向流速分量在400 m以浅平均的近惯性振荡频率分别为1.167 f₀和1.170 f₀(f₀为局地惯性频率)。蓝移与近惯性内波的向下传播及正的相对涡度的输入有关。在热力学响应方面,上层海洋在台风的搅拌作用下,40～250 m深度均出现较小增温,最大增温幅度接近1°C;此外70 m以浅盐度的降低可能与台风过境时的降水相关,而Ekman抽吸引起的上升流则可能对70～100 m深度盐度的升高具有重要作用。     

Distribution and origin of shallow gas in deep-sea sediments of the Ulleung Basin, East Sea (Sea of Japan)

A synthesis of high-resolution (Chirp, 2–7 kHz) subbottom profiles in the Ulleung Basin reveals patchy distribution of shallow (<90 m subbottom depth) gassy sediments in the eastern basin plain below 1,800-m water depth. The shallow gases in the sediments are associated with acoustic turbidities, columnar acoustic blankings, enhanced reflectors, dome structures, and pockmarks. Analyses of gas samples collected from a piston core in an earlier study suggest that the shallow gases are thermogenic in origin. Also, published data showing high amounts of organic matter in thick sections of marine shale (middle Miocene to lower Pliocene sequence) and high heat flow in the basin plain sediments are consistent with the formation of deep, thermogenic gas. In multi-channel deep seismic profiles, numerous acoustic chimneys and faults reflect that the deep, thermogenic gas would have migrated upwards from the deeper subsurface to the near-seafloor. The upward-migrating gases may have accumulated in porous debrites and turbidites (upper Pliocene sequence) overlain by impermeable hemipelagites (Quaternary sequence), resulting in the patchy distribution of shallow gases on the eastern basin plain.