Long-term displacement of intertidal seagrass and mussel beds by expanding large sandy bedforms in the northern Wadden Sea

On aerial photographs, sandy tidal flats display (1) large sandy bedforms (> 10 m long, > 3 m wide), indicating effects of strong hydrodynamics on sediment relief, and (2) beds of seagrass and mussels, indicating stable sediment conditions. These physical and biogenic structures have been mapped from aerial photographs taken in a back-barrier tidal basin of the North Sea coast at low tide between 1936 and 2005. Fields of large intertidal sandy bedforms show a consistent spatial distribution in the central part of the basin, and have increased in area from 7.2 to 12.8 km², corresponding now to 10% of the tidal flats. Areal expansion may be linked to a rise in average high tide level and an increase of the expansion rate from the 1960s to the mid 1990s might be traced back to an increased frequency of storm tides during this period. It is shown that expanding fields of large sandy bedforms have replaced mussel beds in the low tidal zone and displaced seagrass beds in the mid tidal zone. Fields of intertidal large sandy bedforms are expected to expand further with an accelerating rise in sea level, and it is recommended to monitor these physical indicators of sediment instability and disturbance of biogenic benthic structures by analysing aerial photographs.     

西北冰洋表层沉积物中的底栖有孔虫组合及其古环境意义

通过对中国第1~4次北极考察在西北冰洋采集的表层沉积物中底栖有孔虫丰度及其优势种分布特征与环境因素关系的综合研究发现,楚科奇海区低的底栖有孔虫丰度主要受较高的陆源物质输入的稀释作用影响;楚科奇海台和阿尔法脊较高的底栖有孔虫丰度主要受到暖而咸的大西洋中层水的影响;受碳酸钙溶解作用影响的门捷列夫深海平原和加拿大海盆底栖有孔虫丰度较低,并且水深3 597 m的站位出现了似瓷质壳的Pyrgo williamsoni和Quinqueloculina orientalis,说明该区的CCD深度大于3 600 m。根据底栖有孔虫7个优势属种的百分含量分布特征可以划分出5个区域组合:南楚科奇海陆架-白令海峡组合以优势种Elphidium excavatum和Buccella frigida为特征,可能反映受白令海陆架水影响的浅水环境;阿拉斯加沿岸-波弗特海组合以优势种Florilus scaphus和Elphidium albiumbilicatum为特征,可能反映受季节性海冰融化,低盐的阿拉斯加沿岸流以及河流淡水输入的低盐环境;大西洋中层水组合以优势种Cassidulina laevigata为特征,可能反映高温高盐的大西洋中层水影响的环境;北极深层水组合以优势种Cibicides wuellerstorfi为特征,可能反映水深大于1 500 m低温高盐的北极深层水环境;门捷列夫深海平原组合以优势种Oridorsalis umbonatus为特征,可能反映低营养的底层水环境。     

黄渤海底栖纤毛虫分子多样性和生物地理学研究

对中国渤海、北黄海和南黄海三个海域底栖纤毛虫的分子多样性与生物地理学进行了研究。从底栖真核微生物18S rDNA的焦磷酸测序数据中提取出隶属于纤毛门的序列,并在此基础上分析了纤毛虫群落的阿尔法多样性和贝塔多样性。结果表明,纤毛虫操作分类单元的丰富度在渤海比北黄海和南黄海都高,但夏冬两季无显著差异。在所有检测的环境因子中,水体深度与阿尔法多样性的相关性最强。就纤毛虫群落组成上看,总体上旋唇纲的序列及操作分类单元丰富度均占优势地位（占比分别为77.0%和66.5%）;旋唇纲主要由环毛亚纲以及未能进一步分类的类群组成。底栖纤毛虫群落结构在三个海域之间显著不同,但夏冬两季无显著差异。从各主要类群的相对比例来看,唯有侧口纲的序列比例在三个区域间呈现显著的不同。偏门特尔分析表明,相对于地理距离和环境因子而言,水体深度在调控底栖纤毛虫群落结构中扮演者更为重要的角色。本研究同时也发现,超过60%的操作分类单元未能被进一步分类到纲或目级水平,约45%的操作分类单元与GenBank数据库中已描述种类的序列相似度低于或等于97%,表明在近海沉积物中可能存在大量待发现的纤毛虫类群或物种。本研究发现底栖纤毛虫阿尔法多样性从北黄海到南黄海降低的趋势,这一点与之前基于形态学方法的调查结果相似。然而,测序数据显示旋唇纲是最主要类群,而形态学调查表明前口纲和核残迹纲是主要类群。本文也探讨了可能造成分子与形态学研究结果差异的一些潜在原因。     

Benthic mineralization rates at two locations in the southern North Sea

Benthic oxygen uptake, sulphate reduction and benthic bacterial production were measured at two contrasting locations in the southern North Sea: the shallow and turbulent Broad Fourteens area in the Southern Bight, and the deeper Oyster Grounds, a deposition area, where thermohaline stratification occurs during summer. Oxygen uptake and sulphate reduction showed a clear seasonal pattern in the Broad Fourteens area, indicating a supply of carbon to the benthic system that is closely related to the standing stock of carbon in the water column. This close benthic-pelagic coupling is probably due to the influence of the tide in this part of the North Sea, which keeps the water column permanently mixed. At the Oyster Grounds, no seasonal pattern was observed. Peaks in oxygen uptake and sulphate reduction were found in winter. Irregularly occurring events, such as storms and fishery-related activities, are likely to affect the benthic mineralization patterns in this area. Annual benthic carbon mineralization rates estimated from oxygen uptake rates were 44 gC·m⁻² at the Broad Fourteens, and 131 gC·m⁻² at the Oyster Grounds, of which 26 and 28%, respectively, could be attributed to sulphate reduction (assuming an annual sulphide reoxidation rate of 100%). Although sulphate reduction rates in the southern North Sea are higher than previously suggested, aerobic respiration is the most important pathway for benthic carbon mineralization at the stations visited. Production rates of benthic bacterial carbon measured with labelled leucine were much higher than carbon mineralization rates based on oxygen uptake or sulphate reduction. This may either imply a very high bacterial carbon conversion efficiency, or point to shortcomings in the accuracy of the techniques. A critical evaluation of the techniques is recommended.     

Surf zone fishes in an exposed sandy beach at Sanrimatsubara,Japan: Does fish assemblage structure differ among microhabitats?

To assess differences in fish assemblage structures among microhabitats within the surf zone of an exposed sandy beach, three microhabitats (onshore current, rip current, and river adjacent sites) were sampled at Sanrimatsubara Beach, western Japan, in May, August, and November 2002 and 2003. Although several physical variables (e.g. wave height, current speed, turbidity, salinity, and sand particle size) and major prey abundances (calanoid copepods and mysids) differed among the sites, no significant differences were apparent in the numbers of fish species and individuals among the sites in any month in either year. In addition, species and individual numbers of two dominant feeding groups (zooplankton feeders, and epiphytic and benthic crustacean feeders) did not show any significant responses to among-site differences in prey abundance. Cluster and ordination analysis confirmed the similarity in fish species composition among the three sites. These results indicated that the surf zone fish assemblage structures were similar among the microhabitats in spite of there being microhabitat-related differences in abiotic and biotic environments.     

东海中陆架晚第四纪底栖有孔虫定量分析

利用东海中陆架EY02-1孔的柱状样品对底栖有孔虫动物群进行了定量分析研究,结合Q型因子分析及AMS“C测年数据,对东海中陆架古水团演化进行了初步探讨。Q型因子分析得到5个主因子．方差累积贡献为84．9％,这5个有孔虫组合在钻孔相关层位上反映特定的古水团特征。主因子1为Elphidium magellanicum组合,代表低温低盐沿岸水团(5～10m);主因子2为Bolivina robusta组合,代表中陆架水团(50～100m);主因子3为Protelphidium tuberculatum组合,代表外延的古黄海冷水团;主因子4为Florilus decorus组合,代表内陆架水团(0～50m);主因子5为Epistominella naraensis组合,代表水体较凉的水深大于30m的内陆架水团。结果表明,冰后期以古长江冲淡水为主体的低温低盐沿岸水团、中陆架水团及内陆架水团交替影响EY02-1孔附近中陆架。在氧同位素3期以古长江冲淡水为主体的东海沿岸流与外延的古黄海冷水团控制着有孔虫组合。在氧同位素5a-5c期间,EY02-1孔附近中陆架可能已受到古黄海冷水团的影响。该孔顶部11．4m含大量贝壳的细砂沉积可能对应氧同位素1期U2层潮流沙脊脊部沉积,细砂平均沉积速率高达0.877mm／a。     

白令海和楚科奇海表层沉积中的有孔虫及其沉积环境

通过对白令海和北冰洋楚科奇海39个表层沉积样品中有孔虫的定量分析,发现表层沉积中浮游有孔虫稀少可能与该区表层生产力低、碳酸盐溶解作用较强有关,而底栖有孔虫的分布则主要受表层初级生产力以及与水深相关的碳酸盐溶解作用和水团性质所控制,其中北冰洋楚科奇海陆架区有孔虫以Elphidium spp.组合和Nonionella robusta组合为主,丰度和分异度低,受北冰洋沿岸水团控制;白令海陆坡区有孔虫以Uvigerina peregrina-Globobulimina affinis组合为主,含N.robusta较多,丰度和分异度相对高,受太平洋中层和深层水团控制,但该区碳酸盐溶跃层和补偿深度(CCD)相对浅,约分别位于2000和3800m处.此外,白令海陆坡上部表层沉积中含有北冰洋陆坡区典型深水底栖有孔虫种Stetsonia arctica,说明白令海峡两侧的海区曾有深部水交流.     

Deep-sea reef fish assemblage patterns on the Blake Plateau(Western North Atlantic Ocean)

Deep‐water coral habitats are scattered throughout slope depths (360–800 m) off the Southeastern United States (SEUS, Cape Lookout, North Carolina, to Cape Canaveral, Florida), contributing substantial structure and diversity to bottom habitats. In some areas (e.g. off North Carolina) deep corals form nearly monotypic (Lophelia pertusa) high profile mounds, and in other areas (e.g. off Florida) many species may colonize hard substrata. Deep coral and hard substrata ecosystems off the SEUS support a unique fish assemblage. Using the Johnson‐Sea‐Link submersible (in 2000–2005, 65 dives), and a remotely operated vehicle (in 2003, five dives), fishes were surveyed in nine deep reef study areas along the SEUS slope. Forty‐two benthic reef fish species occurred in deep reef habitats in these study areas. Species richness was greatest on the two coral banks off Cape Lookout, North Carolina (n = 23 and 27 species) and lowest on the two sites off Cape Canaveral, Florida (n = 7 and 8 species). Fish assemblages exhibited significantly (ANOSIM, Global R = 0.69, P = 0.001) different patterns among sites. Stations sampled off North Carolina (three study areas) formed a distinct group that differed from all dives conducted to the south. Although several species defined the fish assemblages at the North Carolina sites, Laemonema barbatulum, Laemonema melanurum, and Helicolenus dactylopterus generally had the most influence on the definition of the North Carolina group. Fish assemblages at three sites within the central survey area on the Blake Plateau were also similar to each other, and were dominated by Nezumia sclerorhynchus and L. melanurum. Synaphobranchus spp. and Neaumia sclerorhynchus differentiated the two southern sites off Cape Canaveral, Florida, from the other station groups. Combinations of depth and habitat type had the most influence on these station groups; however, explicit mechanisms contributing to the organization of these assemblages remain unclear.     

Long-term series in ichthyoplankton: sole and sprat at French coast of the North Sea from 1975 to 1994

The sampling of eggs and larvae of sole and sprat at Gravelines (French part of the North Sea coast) since 1975 has produced a long-term series showing major interannual changes. Comparison of the results obtained on two species, one benthic and the other one pelagic, suggests some events affecting the environment that are also revealed by the holoplanktonic (appendicularia, chaetognatha) and meroplanktonic (cirripeda larvae) compartment. This study attempts also to distinguish general variations from more closely species-related fluctuations.     

Mudflat surface morphology as a structuring agent of algae and associated macroepifauna communities: A case study in the Ria Formosa

Although mudflats seem relatively planar, closer inspection reveals a succession of meso-topographical features, including consecutive convex and concave meso- and micro-topographical features. The objective of this study was to determine the influence of meso-scale surface sediment morphology on the dynamics of the macroalgae Ulvales (Chlorophyta) and associated macroepifauna in the Ria Formosa tidal lagoon (southern coast of Portugal). Four sites in the Ria Formosa were sampled monthly. Two were located on convex sections (mounds) of the mudflat and the other two on concave sections (depressions). Macroalgae and related macroepifauna were sampled at each station. Biomass was quantified by determination of the ash-free dry weight (AFDW). Data were analysed using the software package ‘PRIMER’ (Plymouth Routines In Multivariate Ecological Research). Results show a clear distinction between convex and concave areas. In convex sections, Enteromorpha dominated, to the point of being the only algal species present during part of the year. Conversely, biomass and dynamics of Enteromorpha and Ulva were almost the same in concave sections. The associated macroepifauna was also different in protruding or depressed sections of the mudflat. In the convex areas, the macroepifauna population showed less diversity and was dominated by the snail Hydrobia ulvae. In concave areas, the species diversity was larger, but dominated in terms of biomass by the amphipod Melita palmata and the gastropod Nassarius pfeifferi. Results of the study indicate that the benthic communities associated with concave or convex features were different. No relevant differences in texture and sediment physico-chemical characteristics were found between convex and concave sections. The inference is that the morphological nature of the bottom in tidal mudflats can act as a structuring agent of benthic communities.     

Effect of biodeposits from mussel culture on macroinvertebrate assemblages at sites of different hydrodynamic regime

The present study examined for differences in macroinvertebrate assemblage composition inside and outside of mussel farm sites experiencing different hydrodynamic regimes. Multivariate analysis revealed that there were significant differences in macroinvertebrate assemblage composition (averaged across seasons) between samples taken inside and outside of the two relatively low energy sites, whilst no such difference was observed for the relatively high energy site. Taxa that best discriminated between the dissimilarities observed in macroinvertebrate assemblage composition inside and outside farms were principally polychaetes (more abundant inside) and ophiuroids (more abundant outside). Sediment total organic matter and number of mussel shells were the parameters that best explained the difference in macroinvertebrate assemblage observed at the two relatively sheltered farm study sites. No taxa or environmental variables were particularly good at discriminating or explaining differences observed inside and outside the relatively high energy farm site. The present study indicates there is a relationship between the hydrodynamic regime of a farm site, organic enrichment of seabed sediments by mussel biodeposits, and a subsequent modification of the macroinverebrate assemblages. This finding has implications for the site selection of mussel farms in coastal environments.     

Foraminifera in surface sediments of the Bering and Chukchi Seas and their sedimentary environment

Based on a quantitative analysis of foraminifera in 39 surface samples of the Bering andChukchi Seas, the nearly absence of planktonic foraminifera in the surface sediments can be related to the low surface primary productivity and strong carbonate dissolution in the study area. It has been revealed that the surface primary productivity, and carbonate dissolution and properties of water masses related to the water depth mainly control the distribution of benthic foraminifera. The shelf of the Chukchi Sea is dominated by the Elphidium spp. assemblage and Nonionella robusta assemblage with low foraminiferal abundance and diversity, which is controlled by the coastal water mass of the Arctic Ocean. The slope of the Bering Sea is dominated by the Uvigerina peregrina - Globobulimina affinis assemblage with abundant N. robusta, and relatively high foraminiferal abundance and diversity, which is controlled by the intermediate and deep water masses of the Pacific Ocean. However, the Bering Sea has relatively sha     

Diversity and abundance of mangrove fiddle crabs, genus Uca (Decapoda, Ocypodidae) at a mangrove in Kema, North Sulawesi, Indonesia

Mangrove ecosystems are sites with high biodiversity of benthic fauna, and fiddler crabs (genus Uca) are common benthic fauna in mangroves. The North Sulawesi in Indonesia has a good condition of mangrove while the information of the fiddler crabs is still limited. Manual samplings were conducted in wet, dry and transient seasons at a mangrove in Kema, North Sulawesi to investigate the species composition, density and distribution pattern of fiddler crabs. A total of 168 individuals, subjected to eight species of genus Uca crabs were collected at the mangrove, with U. triangularis having the highest abundance and U. annulipes having the lowest abundance. The densities of fiddle crabs were 27.56 ind./m², 32.89 ind./m² and 14.22 ind./m² at the seaward, middle and landward zones, respectively, and the density was higher in dry and wet seasons than in transient season.     

Long-term benthic responses to sustained disturbance by aggregate extraction in an area off the east coast of the United Kingdom

The temporal variability of benthic assemblages inhabiting offshore gravel deposits in the North Sea is poorly known, as purpose-collected long-term data sets have until recently been non-existent. It has therefore proved difficult to understand the stability and resilience of these benthic ecosystems after disturbance caused by the extraction of aggregates on an industrial scale. The present investigation examines an 8-year time series of data collected in and around an active commercial aggregate extraction site off the east coast of the United Kingdom. Both physical and biological data sets suggest a distinct yet localised effect after sustained gravel extraction, with impacted sediments generally appearing more physically homogeneous and faunistically impoverished than undisturbed sediments. Although inter-annual variability of selected assemblage metrics was reduced in disturbed sediments, differences in some assemblage metrics became significant between years. Despite such observations, significant impacts to the benthos in any given year were not sustained for long. However, the magnitude of impact in almost every year would be enough to merit remedial intervention based on an existing model of measuring acceptable levels of disturbance as a result of organic enrichment. Caution must be exercised in making any such recommendations, especially as there are presently no models specifically designed to assess the degree of acceptable disturbance from aggregate extraction. This study not only highlights the importance of and need for long-term data sets in order to better understand the difference between natural and human-induced variability in benthic assemblages, but also emphasises the need to develop more relevant monitoring tools to better manage the activities of the marine aggregate extraction industry.     

阿什河流域底栖硅藻群落特征及水环境健康评价

为探索黑龙江省阿什河流域底栖硅藻群落特征及环境相关性,并对阿什河流域进行水环境健康评价,本研究于2018年7月(丰水期)和2018年10月(枯水期)对阿什河流域8个典型采样点进行调查。基于相似性分析检验(analysisofsimilarities,ANOSIM)和相似百分比分析(similarity percentages,SIMPER)分析探索枯水期与丰水期之间底栖硅藻的群落差异,通过冗余分析(redundancyanalysis,RDA)对驱动底栖硅藻的关键环境因子进行筛选;使用硅藻生物指数(biological diatom index, IBD)、硅藻属指数(generic index of diatom, GI)和水体营养指数(trophic state index, TSI)对研究区域水体营养状态进行初步评价。结果表明,研究期间共鉴定底栖硅藻89种,其中丰水期80种、枯水期57种。独立样本T检验(T-test)表明阿什河流域物种丰富度丰水期显著高于枯水期(P0.05),Shannon-wiener指数变化不显著(P0.05)。ANOSIM结合SIMPER分析结果显示阿什河流域硅藻群落格局存在一定的时空异质性。RDA分析表明水的电导率是驱动阿什河流域底栖硅藻空间分布的环境因子,枯水期与丰水期之间高锰酸盐指数(COD_(Mn))含量的变化是影响硅藻群落演替的因素之一。IBD、GI和TSI指数结果显示阿什河流域受人为活动干扰区域营养状态较差, IBD指数较GI指数能更有效的反映阿什河流域水体营养状况。     

Impacts of temperature anomalies on mortality of benthic organisms in the Adriatic Sea

Recurrent climate‐induced mass mortality episodes have been recorded in the Mediterranean Sea over the past 15 years, affecting rocky benthic communities. In this study, we provide for the first time a report on the annual mortality events of benthic sessile invertebrates occurring in the eastern part of the Adriatic Sea. Over the course of 14 consecutive years, we studied the sea temperature gradient to a depth of 40 m and found an abnormal summer warming trend and an increased frequency of above‐average temperatures. Mortality events were recorded in the summers of 10 observed years, in particular in 2009, when the highest mortality rates were recorded. Late in summer 2009, extensive mass mortality of sessile invertebrates was observed in the entire Eastern Adriatic Sea. We performed an analysis of selected target benthic species associated with mass mortality events with inter‐regional differences in hydrological and temperature conditions. We were able to characterize the mortality event by studying five areas covering the northern, central and southern regions of the Eastern Adriatic Sea. The degree of impact on each study area was quantified at 28 sites by estimating the proportion of affected target species. According to the obtained data, the northern sites (Cres area) were the least affected, whereas sites in the Central and Southern Adriatic [Tela??ica and Lastovo Nature Parks, Mljet National Park (NP)] displayed the highest impact. In summer 2009, sea surface temperatures reached values of 28 °C in the Cres area and 30 °C in Mljet NP. These thermal conditions were concomitant with moderate to severe mass mortalities of benthic populations. Mass mortality events reached depths of 45 m in most parts of the affected areas. Amongst studied species, the scleractinian coral and gorgonian populations suffered the most extensive damage during the mass mortality events.     

Global latitudinal species diversity gradient in deep-sea benthic foraminifera

Global scale patterns of species diversity for modern deep-sea benthic foraminifera, an important component of the bathyal and abyssal meiofauna, are examined using comparable data from five studies in the Atlantic, ranging over 138° of latitude from the Norwegian Sea to the Weddell Sea. We show that a pattern of decreasing diversity with increasing latitude characterises both the North and South Atlantic. This pattern is confirmed for the northern hemisphere by independent data from the west-central North Atlantic and the Arctic basin. Species diversity in the North Atlantic northwards from the equator is variable until a sharp fall in the Norwegian Sea (ca. 65°N). In the South Atlantic species diversity drops from a maximum in latitudes less than 30°S and then decreases slightly from 40 to 70°S. For any given latitude, North Atlantic diversity is generally lower than in the South Atlantic. Both ecological and historical factors related to food supply are invoked to explain the formation and maintenance of the latitudinal gradient of deep-sea benthic foraminiferal species diversity. The gradient formed some 36 million years ago when global climatic cooling led to seasonally fluctuating food supply in higher latitudes.     

Distinctly variable mudscapes: Distribution gradients of intertidal macrofauna across the Dutch Wadden Sea

The Wadden Sea is a shallow coastal region, with a large area of sedimentary tidal flats that extends from The Netherlands to Denmark and has been declared a site of international importance in the Dutch and German parts (Ramsar status and UNESCO World Heritage Site). Benthic macrofauna are central to the ecosystem functioning of this area, as they recycle nutrients, decompose organic matter and are an important food source for many secondary consumers, like fish and waterbirds. Due to the environmental gradients characteristic of estuarine systems, it is expected that changes in assemblage composition will be observed across the physical and environmental gradients of the Wadden Sea. First, we explored the spatial variation in assemblage composition of benthic macrofauna across the intertidal part of the Dutch Wadden Sea using 3 years of biomass data. Then, we identified the relative importance of six environmental variables for explaining and predicting changes in assemblage composition across the intertidal areas of the Wadden Sea using generalised dissimilarity modelling (GDM). In accordance with the environmental gradients across this system, the biomass contributed by a few common species differed from west to east and were distinct in the Dollard. In the west, bivalves Mya arenaria, Cerastoderma edule and Ensis directus contributed a relatively large and equal share of the total biomass, whereas C. edule contributed the sole largest share of the total biomass towards the east. The polychaete Alitta succinea became a large share of the total biomass in the upper Ems and in the Dollard estuary, but contributed little elsewhere. Similar to the observed differences in species composition, the spatial patterns in assemblage composition, as predicted by the GDM models, identified the Dollard as distinct and that the prevalence of assemblage types in the west differed to the east. Median grain size, followed by microphytobenthic biomass, and exposure time were the most important variables describing differences in assemblage composition. That the Wadden Sea forms a heterogeneous landscape where assemblage composition varies across multiple gradients has repercussions for management and monitoring.     

Abyssal bedforms and sediment drifts effected by deep-sea flows

The investigation of abyssal bedforms and sediment drifts as a tool for understanding the deep flow characteristics allows us to interprete that a benthic storm is primarily related to sediment distribution, development of longitudinal ripple marks, and concentration of suspended particulate matter. There explicitly exists a strong and periodical bottom flow which is called the benthic storm having a current speed of over 15 cm sec^?1 and duration of more than two days. Hydrodynamic regime has been thought to affect underlying sediment textural natures which can be used to distinguish between bottom currents with different velocities. Therefore, concentration of medium silt mode (0.010–0.017 mm in size) delineates a high-velocity core of the benthic storm in the deep sea bottom. Bottom current measurements in most of the North Pacific Ocean indicate that present bottom current speeds are generally less than 10 cm sec^?1. It appears likely, therefore, that significant erosion is not taking place today. However, at current passages, bases of sea mounts, and other topographic obstructions locally accelerated current flows are recognized to affect bottom configuration. While, it is concluded from bottom echo-characteristics and bottom current measurements that widespread occurrences of echo type 3 (sediment-drift deposit facies) recognized at 22°N and 42°N in the Northwest Pacific are associated with the North Equatorial current and the North Pacific current respectively, and can best be interpreted to be originated from benthic storms, the source of which were come from those surface currents.     

南海神狐海域含水合物层底栖有孔虫群落结构与同位素组成

为评价水合物甲烷对底栖有孔虫群落结构和同位素的影响,对南海北部神狐海域获取天然气水合物的钻孔BY3岩心,进行底栖有孔虫群落结构和稳定同位素分析,发现含水合物层底栖有孔虫丰度、分异度下降,群落中以内生种占绝对优势,有孔虫破碎率增加;与不含水合物层中的底栖有孔虫相比,含水合物层的底栖有孔虫碳同位素值出现较明显的负偏移。含水合物层中的Uvigerinaspp.、Cibicidesspp.和Oridorsalisspp.的δ13C平均值分别为-1.61‰、-0.79‰和-1.80‰,而在不含水合物层它们的δ13C平均值分别为-0.88‰、-0.27‰和-1.04‰;其中Uvigerinaspp.和Oridorsalisspp.的δ13C最轻值均出现在含水合物层,分别为-1.83‰和-2.29‰。这些说明底栖有孔虫在生长和埋藏过程中可能受到沉积物中甲烷水合物形成和演化的影响。