Ferromanganese crusts from the Sea of Okhotsk

New data on the microstructures and the mineral and chemical compositions of ferromanganese crusts obtained from the western slope of the Kuril Island Arc in the Sea of Okhotsk during cruises of the R/V Vulkanolog are discussed. The study of the crusts using analytical electron microscopy methods revealed that their manganese phase is represented by vernadite, Fe-vernadite, todorokite, asbolane, and asbolane-buserite, while the iron phase consists of hematite, hydrohematite, ferroxyhite, and magnetite. The assemblage of lithic minerals includes apatite, quartz, epidote, and montmorillonite. According to the chemical analysis, most of the crusts contain a significant share of volcanogenic and hydrothermal material, which is evident from the elevated values of the Mn and Ti modules, the low concentrations of some trace elements, and the positive Eu anomaly in the rare earth elements composition.     

Geochemical features of the Okhotsk Sea Cenozoic volcanism

Cenozoic volcanic rocks were discovered on major rises of the inner Okhotsk Sea. In this paper, these rocks are geochemically typified, and the geodynamic conditions of their formation reconstructed. For this purpose, mineralogical and geochemical analyses as well as radioisotope age determinations were carried out. The radioisotope age determinations show that the Cenozoic volcanic rocks were formed during the Paleogene–Pleistocene. Within this period, Eocene and Plio-Pleistocene volcanic complexes are particularly prominent. Mineralogical and geochemical analyses show that the rocks belong to the calc-alkaline volcanic series. The Eocene volcanic rocks were formed under subaerial conditions, whereas the Plio-Pleistocene volcanics were formed under submarine conditions. The results of the study suggest that the Okhotsk Sea Basin was formed during the destruction of the Asian continental margin, the Eocene volcanism reflecting subaerial, the Plio-Pleistocene volcanism submarine stages of the Okhotsk Sea evolution.     

The Sea of Okhotsk: A Window on the Ice Age Ocean

The modern Sea of Okhotsk and the high-latitude glacial ocean share similar radiolarian faunas suggesting they also share environmental similarities. This sea favors deep- (>200 m) over shallow-living species as evidenced by collections of sediment traps set at 258 and 1061 m in the central part of the Sea. Of the twelve dominant polycystine radiolarian species, four live above and eight below 258 m. The shallow-living species’ productivity maxima coincide with spring and fall phytoplankton blooms while deep-living species’ annual production, nearly twice that of the shallow-living species, is concentrated in fall. Previous workers have shown that summer plankton tows collect higher concentrations of polycystine Radiolaria below than above 200 m and that Radiolaria, fish and zooplankton have unusual concentration maxima between 200 and 500 m. The paucity of Radiolaria and other consumers above 200 m coincides with an upper (0–150 m) cold (−1.5°C to 1.5°C), low salinity layer while higher concentrations below 200 m occur within warmer saltier water. This unusual biological structure must produce a lower ratio of shallow (<200 m) to deep carbon remineralization than elsewhere in the world ocean.Deep-living radiolarian species, similar to those of the modern Sea of Okhotsk, dominate glacial high-latitude deep-sea sediments. If the hydrographic and biological structures that produced these glacial faunas were like those of the modern Sea of Okhotsk, then glacial high-latitude oceans would have differed from today's in at least two respects. Surface waters were less saline and more stable enhancing the spread of winter sea ice. This stability, combined with a deepening of nutrient regeneration, reduced surface water nutrients contributing to a reduction of atmospheric carbon dioxide.     

New data on the cenozoic deformations of the West Kamchatka Peninsula and their implications for the recent tectonics of the Eastern Sea of Okhotsk region

The newly obtained data on the West Kamchatka complexes, together with the results published previously, allowed us to reach some conclusions regarding the Cenozoic kinematics in the eastern part of the Sea of Okhotsk region. The Cenozoic stress fields of submeridional-NW-SE trend were reconstructed. These results may provide independent evidence for the riftogenic opening model of the Sea of Okhotsk. On the other hand, the data might fit with the alternative concept of the effect of the collision process between the Indo-Australian and Eurasian plates concerning the Cenozoic structure of the Sea of Okhotsk region (including its eastern part). The stages of the principal regional phases of the structural development are shown. The NW-SE compression was the last and most essential stage of the structure formation and might, evidently, show a long-term response to the completion of the collision between the island arc of the Eastern peninsulas (Kronotskaya) and the Kamchatka Peninsula in the Middle-Late Miocene. In the recent and present-day intraplate geodynamic situation, the boundary between the hypothetic Sea of Okhotsk block and the Kamchatka Peninsula (the East Sea of Okhotsk fault zone) was mainly developed under the conditions of a left-side transpression and strike-slip setting. The comparison of the data obtained with the results of earlier detailed seismic surveys in the Sea of Okhotsk (the Deryugin Basin area) showed their general similarity.     

日本海、鄂霍次克海和白令海的古海洋学研究进展

边缘海的存在使大陆和大洋之间的物质和能量交换变得相当复杂。在构造运动和海平面升降的控制下,边缘海和大洋之间时而连通时而隔绝,各种古气候变化信号都在一定程度上被放大。基于近期有关西北太平洋边缘海的古海洋学研究成果,简要概述了日本海、鄂霍次克海、白令海以及北太平洋地区自中新世以来的古气候和古海洋环境演化特征,并认为它们与全球其它地区一样也受控于因地球轨道参数变化引起的太阳辐射率的变化,大尺度的气候变化具有与地球轨道偏心率周期相对应的100ka周期,而41ka的小尺度周期则受地球自转轴斜率变化的控制。一些突发性的气候变化则是由气候不稳定性、海峡的关闭与开启和其它一些地球气候系统的非线性活动所驱动。但同时作为中高纬度边缘海,它们的古海平面、古海水温度、古洋流等古海洋环境因子的变化特征还受到冰盖扩张和退缩、构造运动、冰川性地壳均衡补偿、东亚季风等因素的影响,具有一定的区域特点。     

The possibility of tsunami in the Sea of Okhotsk caused by deep-focus earthquakes

The earthquake that occurred on May 24, 2013, in the basin of the Sea of Okhotsk with a magnitude of 8.3 was the strongest in this region. We have modeled a possible tsunami caused by such an earthquake. The simulations confirm that the wave heights were sufficiently small because the earthquake epicenter depth was 640 km. We analyze the oscillations of the DART buoys in the vicinity of the earthquake source and show that they were not associated with the tsunami waves. Analysis of the available pressure gauge records at different points of the Sea of Okhotsk show that only in one case (Iturup Island) can the observed oscillations of the sea level with a height of approximately 4 cm be classified as tsunami waves.     

Biology and distribution of hyperiids in the Sea of Okhotsk

Long-term studies in the Sea of Okhotsk (1986–2012) demonstrated that hyperiids account for a small portion of zooplankton, making up only from 1.0 to 5.3% by weight. The minimum hyperiid biomass was observed in the coastal zone. The hyperiid biomass in the open water shelf community increased from spring to autumn. In the Sea of Okhotsk, hyperiids are represented by ten species, among which the most abundant in the northern regions (mainly in Shelikhov Gulf) is Themisto libellula, while the most abundant in other regions is T. pacifica. The distribution of T. pacifica in different seasons showed that the maximum biomass was concentrated in the deep-water zone. The range of T. libellula in the Sea of Okhotsk is mostly limited to the Shelikhov Gulf, but in certain years its habitation area can expand. In warm years with low ice coverage, the maximum expansion of T. libellula to the west in the shelf zone of the northern part of the Sea of Okhotsk was observed. Since variability of salinity and temperature in the northern part of the Sea of Okhotsk may be fatal for the cryophilic stenohaline T. libellula species, forecasted changes in thermohaline circulation will make it possible to predict the population dynamics of this important species.     

Barotropic Response of the Sea of Okhotsk to Wind Forcing

We have examined wind-induced circulation in the Sea of Okhotsk using a barotropic model that contains realistic topography with a resolution of 9.25 km. The monthly wind stress field calculated from daily European Centre for Medium-Range Weather Forecasting (ECMWF) Re-Analysis data is used as the forcing, and the integration is carried out for 20 days until the circulation attains an almost steady state. In the case of November (a representative for the winter season from October to March), southward currents of velocity 0.1–0.3 m s⁻¹ occur along the bottom contours off the east of Sakhalin Island. The currents are mostly confined to the shelf (shallower than 200 m) and extend as far south as the Hokkaido coast. In the July case (a representative for the summer season from April to September), significant currents do not occur, even in the shallow shelves. The simulated southward current over the east Sakhalin shelf appears to correspond to the near-shore branch of the East Sakhalin Current (ESC), which was observed with the surface drifters. These seasonal variations simulated in our experiments are consistent with the observations of the ESC. Dynamically, the simulated ESC is interpreted as the arrested topographic wave (ATW), which is the coastally trapped flow driven by steady alongshore wind stress. The volume transport of the simulated ESC over the shelf reaches about 1.0 Sv (1 Sv = 10⁶ m³s⁻¹) in the winter season, which is determined by the integrated onshore Ekman transport in the direction from which shelf waves propagate. This revised version was published online in July 2006 with corrections to the Cover Date.     

末次冰盛期以来鄂霍次克海北部陆架的海冰变化

本文通过高分辨率粒度分析,研究了鄂霍次克海北部陆架LV87-54-1岩芯记录的海冰活动历史。利用AnalySize程序对粒度数据进行端元分析,提取了3个端元,并将EM3作为海冰指标。EM3含量结果表明,末次冰盛期以来鄂霍次克海北部陆架以活动性海冰覆盖为主。末次冰盛期和海因里希冰阶1期（HS 1）时EM3含量最高,指示海冰活动强烈。冰期时北半球中高纬度气候变冷与北极涛动负相位是导致海冰大规模扩张的主要控制机制,东亚夏季风减弱与黑龙江入海径流量的减少促使鄂霍次克海生成更多的海冰。自波令−阿勒罗德间冰阶开始以来,鄂霍次克海北部陆架海冰生成急剧减少,在新仙女木时期海冰曾出现微弱峰值,随后又快速下降。自全新世以来,受北半球中高纬度气候变暖、秋季太阳辐射量升高、北极涛动正相位和东亚夏季风的增强共同影响,EM3含量一直稳定在较低水平,鄂霍次克海海冰的生成受到明显抑制。     

Simulation model of basic components of the Okhotsk Sea ecosystem

A simulation system which models the dynamics of major groups of plankton in the Okhotsk Sea, taking into account the most important abiotic environmental factors and the complex of external influence, is devised. A model study of the seasonal variability and spatial distribution of these groups has been carried out. The simulation complex consists of blocks which represent complete program algorithms of separate processes: the large-scale water circulation in the Okhotsk Sea, the formation of salinity, temperature conditions, spatial-temporal dynamics of phytoplankton, and the dynamics of macroplankton and mesoplankton.Translated by M. M. Trufanov.     

Mud volcanoes and gas vents in the Okhotsk Sea area

Gas emissions from mud volcanoes on Sakhalin Island and water-column gas flares arising from cold seeps in the Okhotsk Sea appear to be related. They are likely activated by tectonic movements along the transform plate boundary separating the Okhotsk Sea Plate from the Eurasian and Amur plates. Gas vents (flares) and methane anomalies occur in the waters offshore Sakhalin Island, along with NE-SW-trending mounds and fluid escape structures on the seafloor. The intersection of the NE-striking transverse faults on land with the Central Sakhalin and Hokkaido-Sakhalin shear zones apparently determines the sites of mud volcanoes, a pattern that continues offshore where the intersection with the East Sakhalin and West Derugin shear zones determines the sites of the submarine gas vents.     

Measurements of air-ice drag coefficient over the ice-covered Sea of Okhotsk

The air-ice drag coefficient under neutral stratification C _DN was measured with the eddy correlation method in the southern Sea of Okhotsk. The disturbance of the wind field caused by the ship’s structure was evaluated by computational fluid dynamics (CFD), and two types of correction methods were applied to estimate the error span of C _DN : one is based on the results of CFD, and the other is based on the parameterization of C _DN over open water suggested by Taylor and Yelland (2001). The C _DN × 10³ values finally obtained ranged from 1.9 to 5.4 with a mean value of 2.7 by the CFD correction and from 1.5 to 5.0 with a mean value of 3.1 by the other method. This is somewhat larger than the value of 2.5 suggested by Shirasawa (1981), and in the same range as 2.2–4.0 over rough ice and 3.1–5.0 over very rough ice, values which were complied by Guest and Davidson (1991) for first year ice. Most of the ice conditions were characterized by broken floes with a diameter less than 100 m and raised rims, which made the surface rougher than flat, level ice. The relation between C _DN and ice concentration was not clear, mainly because the contribution of the form drag caused at the freeboard was undetectable due to the great variation of ice surface condition. The roughness length z _M was also evaluated using the model developed for snow covered ice in a previous study.     

Simulated Pathways of the Northwestern Pacific Water in the Okhotsk Sea

Izvestiya, Atmospheric and Oceanic Physics - Water exchange between the Pacific Ocean and the Okhotsk Sea through the Kuril Straits and transport of Pacific waters into and from the Okhotsk Sea are...     

Distribution of alkalinity and dissolved calcium in the Sea of Okhotsk

During the summer seasons of 2002 and 2004, the total alkalinity (TA) and dissolved calcium (Ca) were studied at 41 stations in different areas of the Sea of Okhotsk: the Kuril depression, Deryugin Basin, the slopes of the Kamchatka Peninsula and Sakhalin Island, and in Sakhalin Bay. It was shown that the distributions of the TA and Ca in the water mass of deep sea areas are determined by the processes of CaCO₃ formation and dissolution according to the relation Δ Ca = 0.5 Δ TA (1). The variations of the TA and Ca values observed in the upper 10-m layer and in the near-bottom layers of local depressions in the Deryugin Basin do not satisfy relationship (1). Probable reasons for this discrepancy are considered: organic matter mineralization, mixing of water masses with different preform TA and Ca values, sea ice melting, runoff from land, and sea bottom effects. It is shown that the enrichment in the alkalinity and calcium is caused by the Amur River runoff in the desalinated sea surface layer and by the high geochemical activity in the Deryugin Basin in the near-bottom 200-m layer of local depressions.     

Volcanogenic complexes of the Sea of Okhotsk and the Sea of Japan (Comparative analysis)

Several coeval volcanogenic complexes indicating synchronous volcanic events in the Sea of Japan and the Sea of Okhotsk are defined. Volcanics from different-age complexes of the Sea of Okhotsk show many features in common and are attributed to the Pacific type of calc-alkaline series. They were formed in geodynamic settings of the active continental margin and point to its origination on the continental crust of the fragmented Asian continent margin. The volcanic rocks developed in the Sea of Japan reflect different rifting stages. The initial stage was marked by an eruption of calc-alkaline lavas (Paleocene-Eocene complex). At the stage of the marginal-sea spreading, erupted volcanics of the middle Miocene-Pliocene complex were melted from the depleted mantle and magmatism terminated by an eruption of postspreading Pliocene-Holocene volcanics melted from the enriched mantle EM I. Along with the differences, the magmatism in the Sea of Japan and Sea of Okhotsk has some features in common. In both cases, the sialic component of the lithosphere substantially influenced the magma generation.     

Seasonal Variations of Water Masses and Sea Level in the Southwestern Part of the Okhotsk Sea

A new grid data set for the southwestern part of the Okhotsk Sea was compiled by using all the available hydrographic data from the Japan Oceanographic Data Center, World Ocean Atlas 1994 and the other additional data sources with the resolution of about 10 km. We examine the seasonal variations of areas and volumes of Soya Warm Current Water (SWCW) and East Sakhalin Current Water (ESCW) and show that the exchanges of these water masses drastically occur in April and November. The peculiar variation of sea level in this region is also related with the water mass exchange. Sea level at the Hokkaido coast of the Okhotsk Sea reaches its minimum in April about two months later than in the case of ordinary mid-latitude ocean, and its maximum in December besides the summer peak. The winter peak of sea level in December is caused by the advent of fresh and cold ESCW which is accumulated at the subsurface layers (20–150 m) through the Ekman convergence by the prevailing northerly wind. Sea level minimum in April is caused by the release of the convergence and the recovery of dense SWCW that is saline and much colder than that in summer.     

A new climatology of the Okhotsk Sea derived from the FERHRI database

This paper introduces a new hydrographic climatology of the Okhotsk Sea; this climatology was constructed from the Far Eastern Regional Hydrometeorological Research Institute (FERHRI) database. The FERHRI database has a volume of data three to five times larger than the data used in previous studies because unpublished Russian observation data have been included in the FERHRI database. After removing erroneous data from the database by pertinent quality control methods, the climatology for 1/4°?×?1/4° grids is produced by applying objective analysis procedures. Features similar to those in previous studies are seen in the intermediate layers in the Okhotsk Sea, whereas our climatology provides values that fill in gaps in previous climatologies. It is obvious from the monthly climatologies that temperature and salinity distributions evolve in accordance with seasonal variations in the Eastern Sakhalin Current and inflow from the North Pacific. We also reconstructed climatologies for the winter mixed layer and dense shelf water from data obtained from the temperature minimum waters identified as the remnants of these two layers. Free access to the 1°?×?1° versions of all climatologies constructed in this study is available through the website.     

Improvement of short-term sea ice forecast in the southern Okhotsk Sea

In this study, a numerical model of 7-day forecast of sea ice produced by the Japan Meteorological Agency was improved by the following approaches. First, a new ice dynamic model was introduced: the distributed mass/discrete floe model. The model takes account of discrete characteristics of ice floes and well simulates the ice edge location at low computational cost. Secondly, the grid size was reduced to 5 × 5 km for the future high resolution forecasts. Next, the sea surface current data was examined because it significantly influences sea ice movement. We applied two new datasets of HINO and Okhotsk Ocean General Circulation Model (Okhotsk OGCM), which are estimated by numerical simulations, for the 7-day forecast of sea ice. Ice southward speed in January and the whorl formations in February and March were well reproduced with Okhotsk OGCM datasets. Finally, the ocean heat flux at the ice-ocean interface was refined. As a result, we achieved an ice edge error reduction from 30.8 km to 23.5 km.