Lunar fortnightly modulation of tidal mixing near Kashevarov Bank, Sea of Okhotsk, and its impacts on biota and sea ice

Here we examine the consequences of strong tidal mixing on spatial and temporal distributions of biota and sea ice above Kashevarov Bank, Sea of Okhotsk, using data from field surveys (hydrography, pressure gauge and current meter moorings, and bio-acoustic soundings) and remote sensing (NOAA AVHRR). Fortnightly variations in the amplitude of diurnal tidal currents, primarily resulting from the K₁–O₁ interaction, are shown to dominate water motion over the bank. These currents (with maximum velocities 2 m s⁻¹) create a sharp tidally-mixed front that separates well-mixed water above the bank from stratified water along its flanks. Such mixing draws water upward from the cold dichothermal layer (100–150 m) into the surface layer, and thus serves to ventilate the intermediate layers of the Sea of Okhotsk. In summer, fortnightly modulation of the tidal mixing creates temporal variations in water column stratification, a critical factor in the joint supply of nutrients and light required to sustain phytoplankton growth. As such, chlorophyll-a and oxygen values vary in response to the fortnightly cycle, and zooplankton likewise form dense aggregations within the tidally-mixed front in response to the phytoplankton production. It is further noted that the brood cycle of dominant zooplankton species on the bank matches the fortnightly modulation of the tidal currents. In winter, tidal mixing draws relatively warm water upward from mid-depth to maintain a polynya that cyclically opens and closes in response to fortnightly variation in vertical heat flux.     

Microwave signatures of the sea ice in the east Greenland current

Airborne microwave radiometer measurements at 5, 17, and 34 GHz have been carried out over the East Greenland Current. Sea ice signatures have been established for some of the basic ice types like first-year ice and multiyear ice. Other signatures have been experienced like that of presumably very old arctic ice and signatures associated more with the snow cover on the ice than with the ice itself. During MIZEX-83 measurements of total ice concentration were carried out.     

2017年夏季北冰洋浮冰区海雾特征分析

首先利用中国第八次北极考察队期间获取的走航观测数据分析了环北极考察的海雾特征。接下来利用在北冰洋密集浮冰区海雾加密观测实验期间获取的GPS探空观测数据和NCEP再分析资料,研究了北冰洋浮冰区海雾生成的气象要素特征、边界层特征和大气环流形势特征,发现浮冰区冰雪面之上的冷空气穹丘使得大气易于达到饱和,为北冰洋不同种类海雾的出现造了有利条件。平流雾、辐射雾和蒸汽雾生消的机理和影响期间边界层气象特征各不相同,并且根据特定环流形势对3种海雾进行预报是可行的。     

北极巴伦支海和拉普捷夫海海冰中细菌和微藻的垂直分布

通过计算机图像测定系统测定、计算获得海冰细菌的大小、面积和碳含量,研究了北极巴伦支海和拉普捷夫海的浮冰中细菌大小、丰度和生物量的垂直分布及其与海冰微藻生物量的关系.细菌在冰心中是非均匀分布的,至少有两种不同分布类型:第一类有单一的丰度峰值,在冰心底部或在冰心中部;第二类有两个丰度峰值.海冰中细菌的丰度为0.4×105～36.7×105个/cm3.不同类型海冰中的细菌大小变化极大,在多年冰中,最大的细菌与叶绿素a最大值出现在同一层,而在一年冰中,细菌大小几乎没有垂直变化.整柱冰心的细菌生物量变化为19.2～79.2mg/cm2,细菌与海冰微藻生物量之比为0.43～10.00.对固定冰比较和研究的结果发现,海冰冰心中细菌大小、丰度和生物量的垂直分布差别极大.据此,分析了对目前海冰研究采样方法的局限性,并提出了规范采样方法的设想.     

Seasonal distribution of primary production,phytoplankton biomass and size distribution in the Greenland Sea

The study establishes an annual estimate for annual primary production of 81 g C m⁻² for the open Greenland Sea based on data from five cruises and literature data. This estimate agrees well with a model estimate based on nutrient utilisation but is a factor of 2–5 less than published primary production estimates made by remote sensing of this area. The seasonal distribution of particulate primary production in open Greenland Sea waters followed the seasonal distribution of surface irradiance with a peak in June, indicating that light is the primary factor governing primary production in the area. At stations along the ice edge, blooms were recorded in both June and August, suggesting a pattern of repeated blooms during the summer season at the ice edge. Subsurface phytoplankton peaks were a persistent feature in the open Greenland Sea from May to August. These peaks were consisted of actively photosynthesising phytoplankton and up to 90% of total water column particulate primary production was estimated to occur in association with these peaks. Diatoms dominated the phytoplankton community during the spring bloom and in the Polar Water during August. Size distribution analyses of the phytoplankton communities indicated that the relative abundance of large cells compared to small cells was greatest in May as compared to June and August. No significant differences were noted between June and August in the slope of the phytoplankton size distribution spectra. Inorganic nitrogen and phosphorus nutrients were measurable in surface waters on all cruises. Only in August were there some indications (altered Redfield ratios and higher nutrient concentrations in subsurface chlorophyll peaks than at the surface) of nutrient depletion of surface waters. Implications for food web structure and carbon flux of these patterns in phytoplankton activity and distribution are discussed.     

南海北部深海小型底栖动物丰度和生物量

2010年9月在南海北部5个深海站位和1个浅海站位进行了小型底栖动物和环境因子采样,对小型底栖动物的丰度和生物量进行了定量研究。本次调查中,共鉴定出10个小型底栖动物类群,分别是线虫、桡足类、多毛类、介形类、甲壳类幼体、异足类、寡毛类、涡虫、无板类和等足类。从丰度来看,线虫是绝对的优势类群,占总丰度百分比为94.72%;桡足类次之,占2.70%;多毛类再次,占1.62%;其他类群之和仅占0.96%。从生物量来看,线虫的生物量最大,占总生物量的53.83%;其次是多毛类,占32.17%;居生物量第三位的是桡足类,占7.14%;其他类群之和占6.85%。小型底栖动物的丰度和干重生物量分别为566.12±635.61个·(10cm2)-1和398.43±431.98μg·(10cm 2)-1,线虫的丰度和干重生物量分别为536.21±593.48个·(10cm 2)-1和214.48±237.39μg·(10cm 2)-1。研究站位线虫、桡足类、多毛类和小型底栖动物丰度,小型底栖动物生物量与环境因子的相关分析表明,影响线虫丰度、小型底栖动物丰度、小型底栖生物生物量的主要环境因子包括底层水pH值、沉积物粉砂黏土含量和有机质含量。单因素方差分析(One-way ANVOA)结果表明,线虫丰度、桡足类丰度、小型底栖动物丰度和生物量在不同站位均有显著差异。与渤海、北黄海、南黄海、长江口、芽庄湾(越南)、大亚湾、北部湾、南海近海等海域相比,本研究海域的小型底栖动物丰度和生物量偏低。     

Springtime coupling between chlorophyll a, sea ice and sea surface temperature in Disko Bay, West Greenland

Alterations in sea ice and primary production are expected to have cascading influences on the food web in high Arctic marine ecosystems. This study spanned four years and examined the spring phytoplankton production bloom in Disko Bay, West Greenland (69°N, 53°W) (using chlorophyll a concentrations as a proxy) under contrasting sea ice conditions in 2001 and 2003 (heavy sea ice) and 2002 and 2004 (light sea ice). Satellite-based observations of chlorophyll a, sea ice and sea surface temperature were used together with in situ depth profiles of chlorophyll a fluorescence collected at 24 sampling stations along the south coast of Disko Island (5-30 km offshore) in May 2003 and 2004. Chlorophyll a and sea surface temperatures were also obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS: EOS-Terra and AQUA satellites) between March 2001 and July 2004. Daily SMMR/SSMI sea ice data were obtained in the same years. An empirical regional algorithm was developed to calibrate ratios of remotely sensed measurements of water leaving radiance with in situ chlorophyll a fluorescence. The optimal integration depth was 0-4 m, explaining between 70% and 91% of the variance. The spatial development of the phytoplankton bloom showed that the southwestern corner of the study area had the earliest and the largest spring phytoplankton bloom. The eastern part of Disko Bay, influenced by meltwater outflow from the glaciers, shows no signs of an early phytoplankton bloom and followed the general pattern of an accelerated bloom soon after the disappearance of sea ice. In all four years the coupling between phytoplankton and sea ice was bounded by average open water between 50% and 80%, likely due to the combined availability of light and stable open water. The daily incremental growth in both mean chlorophyll a density (chlorophyll a per volume water, μg l⁻¹) and abundance (density of chlorophyll a extrapolated to ice free areas, tons) estimated by linear regression (chlorophyll a vs. day) between 1 April and 15 May was highest in 2002 and 2004 (light ice years) and lowest in 2001 and 2003 (heavy ice years). In years with late sea ice retreat the chlorophyll a attained only slightly lower densities than in years with early sea ice retreat. However, the abundance of chlorophyll a in light ice years was considerably larger than in heavy ice years, and there was an obvious effect of more open water for light-induced stimulation of primary production. This observation demonstrates the importance of estimating chlorophyll a abundance rather than density in sea ice covered areas. This study also presents the first regional calibration of MODIS chlorophyll a data for Arctic waters.     

Abundance,biomass and species composition of nearshore fish assemblages in Ghana,West Africa

Many of the world's fish populations are overexploited, including Ghana's fish resources. This study examines spatio-temporal trends in fish species composition in relation to biotic, abiotic and anthropogenic factors, towards achieving better-informed management of the beach-seine fisheries. Fishery-dependent data were collected between November 1999 and October 2001 from 94 beach-seine hauls fished at two stations along the Ghanaian coast. The catch consisted of fish, crustaceans, other invertebrates, and macroalgae. Generally, juveniles of species that are exploited by offshore fisheries were found in the catches. Species abundance and their occurrence generally peaked between November and January. Duration of solar radiation and tide level appeared to be important predictors of fish biomass. It is important to exploit the nearshore fish assemblage sustainably because of its nursery role. A co-managed (fishers and government) three-month ban on beach-seining (between May and July) is recommended as the most appropriate control measure towards the sustainability of Ghanaian fish stocks.     

渤海海冰季节演变的数值模拟

MM5数值产品作为大气强迫,利用冰-海洋耦合模式模拟2003～2004冬季渤海海冰演变过程。与海冰遥感、海洋站监测资料等实测资料相比,初冰日和终冰日和观测数据比较接近,模拟海冰各个发展阶段主要分布特征和MODIS遥感图像相似,但模拟的海冰厚度与辽东湾93平台、202平台的冰厚观测数据相比存在较大出入,说明该模型还有待改善。总体上看,冰-海洋耦合模式基本具备模拟渤海海冰季节演变过程的能力。     

渤海和北极海冰组构及晶体结构特征分析

渤海一年冰的组构和晶体结构表现出的冰的非连续生长速率使得冰层底部具有气泡含量不同的许多分层;静水生长的灰冰具有典型的粒状冰和柱状冰;融化-重冻结冰和重叠冰具有特定的晶体结构.位于北冰洋72°24.037'N,153°33.994'W,长2.2m的冰心样为三年冰,并且发现其内有一种新的晶体类型,定义为碎屑凝聚冰.由位于北冰洋74°58.614'N,160°31.830'W,长4.86m的冰心样的晶体结构分析发现它过去为冰脊,后经融化-冻结改造形成冰丘的证据.     

渤海及黄海北部冰情长期变化趋势分析

统计分析上世纪50年代—2010年渤海及黄海北部海冰资料,对其年代际变化特征进行分析。上世纪50年代—90年代冰情总体呈缓解的趋势,2000年以来冰情略有加重。研究发现太阳活动与渤海及黄海北部冰情变化关系密切,太阳活动可能是渤海及黄海北部冰情长期变化重要影响因素。如果太阳黑子的周期长度比上一个周期长,那么周期内冰情较上一个周期严重。反之亦然。     

渤海海冰特征厚度分析

通过海冰生消机理和数值试验,讨论了渤海海冰特征厚度的存在条件;对不同厚度的海冰表面温度、冰面热量收支、冰面下热传导和太阳辐射透射量进行了对比分析,分析了渤海海冰向特征冰厚的动态演化过程;在不同气温、风速、相对湿度和海洋热通量等气象和水文条件下,对渤海特征冰厚进行了计算;讨论了海冰生消的动态平衡过程,分析了1997/1998年冬季辽东湾JZ20-2海域实测冰厚与特征冰厚的相互关系。对渤海特征冰厚分析将有助于渤海海冰数值模拟工作的开展和对不同重现期设计冰厚的推算。     

Distribution of chlorophyll a and diatom in the sea ice of the Weddell Sea, Antarctica

Diatoms are major primary producers of microbial biomass in the Antarctica. They are found in the water and sea ice. The distribution, abundance of the ice diatoms and their relation to the environmental factors inside and outside the ice have been studied for its special role in the Antarctic Ocean ecology. In this paper we describe the abundance, distribution and composition of diatom assemblages in     

渤海海冰微波散射特性研究

Microwave remote sensing has become the primary means for sea-ice research, and has been supported by a great deal of field experiments and theoretical studies regarding sea-ice microwave scattering. However, these studies have been barely carried in the Bohai Sea. The sea-ice microwave scattering mechanism was first developed for the thin sea ice with slight roughness in the Bohai Sea in the winter of 2012, and included the backscattering coefficients which were measured on the different conditions of three bands(L, C and X), two polarizations(HH and VV), and incident angles of 20° to 60°, using a ground-based scatterometer and the synchronous physical parameters of the sea-ice temperature, density, thickness, salinity, and so on. The theoretical model of the sea-ice electromagnetic scattering is obtained based on these physical parameters. The research regarding the sea-ice microwave scattering mechanism is carried out through two means, which includes the comparison between the field microwave scattering data and the simulation results of the theoretical model, as well as the feature analysis of the four components of the sea-ice electromagnetic scattering. It is revealed that the sea-ice microwave scattering data and the theoretical simulation results vary in the same trend with the incident angles. Also, there is a visible variant in the sensitivity of every component to the different bands.For example, the C and X bands are sensitive to the top surface, the X band is sensitive to the scatterers, and the L and C bands are sensitive to the bottom surface, and so on. It is suggested that the features of the sea-ice surfaces and scatterers can be retrieved by the further research in the future. This experiment can provide an experimental and theoretical foundation for research regarding the sea-ice microwave scattering characteristics in the Bohai Sea.     

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.     

Geophysics of sea ice in the Baltic Sea: A review

With improved observation methods, increased winter navigation, and increased awareness of the climate and environmental changes, research on the Baltic Sea ice conditions has become increasingly active. Sea ice has been recognized as a sensitive indicator for changes in climate. Although the inter-annual variability in the ice conditions is large, a change towards milder ice winters has been detected from the time series of the maximum annual extent of sea ice and the length of the ice season. On the basis of the ice extent, the shift towards a warmer climate took place in the latter half of the 19th century. On the other hand, data on the ice thickness, which are mostly limited to the land-fast ice zone, basically do not show clear trends during the 20th century, except that during the last 20 years the thickness of land-fast ice has decreased. Due to difficulties in measuring the pack-ice thickness, the total mass of sea ice in the Baltic Sea is, however, still poorly known. The ice extent and length of the ice season depend on the indices of the Arctic Oscillation and North Atlantic Oscillation. Sea ice dynamics, thermodynamics, structure, and properties strongly interact with each other, as well as with the atmosphere and the sea. The surface conditions over the ice-covered Baltic Sea show high spatial variability, which cannot be described by two surface types (such as ice and open water) only. The variability is strongly reflected to the radiative and turbulent surface fluxes. The Baltic Sea has served as a testbed for several developments in the theory of sea ice dynamics. Experiences with advanced models have increased our understanding on sea ice dynamics, which depends on the ice thickness distribution, and in turn redistributes the ice thickness. During the latest decade, advance has been made in studies on sea ice structure, surface albedo, penetration of solar radiation, sub-surface melting, and formation of superimposed ice and snow ice. A high vertical resolution has been found as a prerequisite to successfully model thermodynamic processes during the spring melt period. A few observations have demonstrated how the river discharge and ice melt affect the stratification of the oceanic boundary layer below the ice and the oceanic heat flux to the ice bottom. In general, process studies on ice–ocean interaction have been rare. In the future, increasingly multidisciplinary studies are needed with close links between sea ice physics, geochemistry and biology.     

渤海冬季海冰反照率变化

渤海海冰对于大尺度气候变化比较敏感,基于CLARA-A1-SAL数据分析了1992~2008年冬季（12、1、2月）渤海海冰区域反照率的时空变化,同时分析了海冰密集度、海冰外延线面积和海水表面温度的变化与海冰反照率的相互关系。渤海海冰区域反照率随时间波动变化且变化趋势不明显,趋势线斜率仅为0.0388%。年际变化在9.93%~14.5%之间,平均值为11.79%。海冰反照率在1999,2000和2005等重冰年的值明显高于其他年份,在1994,1998,2001和2006等轻冰年的值较低。从单个月份反照率来看,12月海冰反照率的增加趋势（趋势线斜率0.0988%）明显高于1月和2月,1月的海冰反照率平均值（12.9%）高于另外两个月份。海冰反照率和海冰密集度呈明显的正相关关系;和海表面温度呈负相关关系（显著性水平90%）。     

Properties of sea ice and overlying snow in the Southern Sea of Okhotsk

The general properties of sea ice and overlying snow in the southern Sea of Okhotsk were examined during early February of 2003 to 2005 with the P/V “Soya”. Thin section analysis of crystal structure revealed that frazil ice (48% of total core length) was more prevalent than columnar ice (39%) and that stratigraphic layering was prominent with a mean layer thickness of 12 cm, indicating that dynamic processes are essential to ice growth. The mean thickness of ice blocks and visual observations suggest that ridging dominates the deformation process above thicknesses of 30 to 40 cm. As for snow, it was found that faceted crystals and depth hoar are dominant (78%), as which is also common in the Antarctic sea ice, and is indicative of the strong vertical temperature gradients within the snow. Stable isotope measurements (δ¹⁸O) indicate that snow ice occupies 9% of total core length and that the mass fraction of meteoric ice accounts for 1 to 2% of total ice volume, which is lower than the Antarctic sea ice. Associated with this, the effective fractionation coefficient during the freezing of seawater was also derived. Snow ice was characterized by lower density, higher salinity, and nearly twice the gas content of ice of seawater origin. In addition, it is shown that the surface brine volume fraction and freeboard are well correlated with ice thickness, indicating some promise for remote sensing approaches to the estimation of ice thickness.     

Full-scale flexural strength of sea ice and freshwater ice in Spitsbergen Fjords and North-West Barents Sea

The present paper describes the results of a rather long series of full–scale, flexural–strength tests on ice beams (over 70 tests) performed in–situ in seawater and freshwater ice at and near Svalbard archipelago during the period 2010–2018. Ice thickness varied in the range of 0.2–0.8 m. Based on a comprehensive analysis of the test data, characteristic plots of ice flexural strength and effective elastic modulus versus the liquid–brine–volume fraction, which varied over a large range of 0–0.2 and were obtained specifically for the geographic region under consideration. The observed range in flexural strength for seawater ice was 0.109–0.415 MPa, and the same for freshwater ice was 0.275–0.807 MPa. The test results with cantilever beams did not show a dependence of the ice flexural strength on the direction of bending force applied to the free end of a beam. Experiments complemented with numerical analysis have demonstrated that stress concentrations in root sections of cantilever ice beams have significant impact on the accuracy of measurement of flexural strength of freshwater ice. It is noted that modifications have to be introduced in the methodology that is used to measure the effective elastic modulus of ice based on the free–end deflection of cantilever ice beams.