Assemblages of benthic foraminifers in the White Sea

Based upon the composition of the dominant species of benthic foraminifers in the bottom sediments sampled at 50 sampling stations in the White Sea, their six assemblages (communities) were defined and mapped. The ranges of these communities depend on the environmental factors determined by the bathymetric, latitudinal, and circum-continental sea zonalities, the sea currents, the bottom upwellings, the continental runoff, the productivity of the waters, and the CaCO₃ content in the near-bottom water layers and bottom sediments.     

Foraminifer communities of the atlantic continental margin of Europe

Based on an analysis of the structures of the populations of benthic foraminifers at 639 stations located on the Atlantic continental margin of Europe, 33 communities were distinguished and mapped with respect to the abundance of the dominating species. The habitats of the communities are formed under the influence of environmental factors, which depend on the latitudinal and bathymetric zonations of the basin, the currents, the near-bottom upwellings, coastal water runoff, and topography of the boundaries between water masses. The communities recognized are confined to certain water masses, which helps one to trace the boundaries between the water masses and the regions of near-bottom upwellings.     

Abundance ofBulimina exilis andMelonis barleeanum: Relationship to the quality of marine organic matter

Studies on diatoms showed that locations of Mauritanian coastal upwellings during the last glacial and deglaciation epochs were More westerly than present-day sites, i.e., off the continental shelf, rather than nearshore. Benthic foraminifera revealed a stratigraphic coverage from the present to the last glacial maximum (0 to 18000 yrs BP). Factor analysis produced four factor assemblages that account for 95.4 percent of the variance. Two factors are dominated by eitherBulimina exilis orMelonis barleeanum. The quantitative stratigraphic distribution of these two deep-sea species is related to the quality of marine organic matter derived from surface upwellings.B. exilis develops only when organic matter reaching the bottom is relatively unchanged;M. barleeanum prefers organic matter in a more altered form.     

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.

     

台湾海峡南部的海洋锋

通过近期水文观测,结合卫星遥感和历史水文资料,对台湾海峡南部海域的海洋锋现象进行了整体分析。结果表明,由于多种水系在此交汇,台湾海峡南部冬、夏季匀有明显锋面发育。受季风气候影响,锋面发育有显著的季节差异。夏季影响本海区的水系主要有韩江冲淡水、上升流、南海水、和黑潮水等。它们的交汇形成了韩江冲淡水羽状锋、台湾浅滩上升流锋、黑潮锋、以及陆架／陆坡锋等的三维锋结构。韩江冲淡水和上升汉对夏季海崃南部浅海峰     

Benthic foraminifera communities of the Andaman Sea (Indian Ocean)

Eleven communities of benthic foraminifera were distinguished on the basis of the results of a qualitative analysis of the structure the population at 94 stations at sea depths down to 4180 m in the Andaman Sea. The habitats of the communities are formed under the influence of the environmental factors, which are determined by the latitudinal and bathymetric zonality of the basin, the water masses, the currents, the upwellings, the coastal runoff, and the contents of calcium carbonate and oxygen in the near-bottom waters and organic carbon in the sediments.     

南海南部表层沉积物中生物硅的分布及其环境意义

对南海南部25个表层沉积样进行了生物硅的测定分析,试图揭示南海南部表层沉积生物硅的分布及其对现代海洋环境的指示意义,以便为古海洋学研究提供进一步的科学依据。研究发现,表层沉积物中生物硅含量与其所处水深呈显著正相关关系,相关系数达到0.782。陆架浅水区表层沉积物中生物硅含量非常低,不能反映表层水体中硅质生物生产力情况,这可能与沉积类型和陆源物质输入影响有关。深水区表层沉积物中生物硅的含量分布表明,其不仅能反映表层水体中硅质生物的古生产力水平,而且还能指示上升流的强弱,从而进一步证实了利用沉积物中生物硅含量来追踪上升流发育和变化的有效性与可信度。研究结果还显示,在研究区域中北部表层沉积生物硅中放射虫和海绵骨针较硅藻占有更大的比重,这可能是由于硅藻易被溶解并易被其他生物体摄食的缘故。在有上升流发育的海域,放射虫、硅藻和海绵骨针基本上表现出较高的丰度,这与高的生物硅含量相一致。     

Underway Measurement of Sea Surface Temperature and Salinity in the Taiwan Straits in August,1999

The distributional features of sea surface temperature and salinity(SST and SSS) in the Taiwan Straits have been analyzed using the SST and SSS underway measurements in August,1999.The characteristics of SST and SSS are summarized as foloows:There are several upwellings and diluted water in the Taiwan Straits.The upwellings are divided into two kinds:those along the western coast of the Taiwan Straits and those around the Taiwan Shoal.There are three sources of diluted water:diluted water of the Jiulongjiang River,diluted water of the Zhujiang River and diluted water of the Minjiang River.     

Seasonality of foraminiferal flux in sediment traps at Chatham Rise,SW Pacific: implications for paleotemperature estimates

Analysis of sediment traps located either side of the Subtropical Front east of New Zealand reveals a strong association between water masses and foraminiferal assemblages. The composition and timing of foraminiferal productivity is distinct between waters north and south of the front, and these differences are also reflected in the assemblages of nearby core-tops. The sediment trap data indicate highly seasonal flux patterns in this region, so sedimentary records may represent flux during a particular season, rather than throughout the annual cycle. This pronounced seasonality has implications for our estimates of the annual temperature range based on faunal assemblages. This study shows that despite strong flux seasonality the annual sea-surface temperature (SST) range is reliably estimated from the sediment trap foraminiferal assemblages by the modern analog technique. The successful estimation of the annual SST range also indicates that the annual flux obtained from these sediment traps is representative of the longer term flux preserved in surface sediments. Core-top assemblages from this region can therefore be directly related to modern sea-surface conditions, providing an analogue for interpreting past environmental change from fossil assemblages.     

Hydrological changes in the Laptev Sea during the Holocene inferred from the studies of aquatic palynomorphs

Based on the study of aquatic palynomorph assemblages in two Holocene sediment cores obtained from the eastern Laptev Sea shelf, the main stages in the postglacial transgression are reconstructed for the last 11.3 ky. During that period, the inner shelf of the Laptev Sea (sea depth of 51 m) was already flooded representing an area of intense freshwater sedimentation in the immediate proximity from the river mouth in the period of 11.3 to 10.3 ky B.P. Approximately 1.0–1.5 ky later, the inner shelf (sea depth of 32 m) was flooded, although it remained under the influence of the river runoff up to 7.4 ky B.P. The period of 10.3–7.4 ky B.P. was marked by the dominant dinoflagellate cysts Operculodinium centrocarpum among the aquatic palynomorphs, the appearance of more thermophilic dinoflagellate species, and elevated values of the AH ratio, which indicates an enhanced influx of relatively warm North Atlantic waters to the Laptev Sea shelf. The environment close to the present-day one became dominant on the outer and inner shelf of the Laptev Sea approximately 8.6 and 7.4 ky B.P., respectively.     

台湾海峡西部上升流的生成和长消原因分析

台湾海峡西部海域是上升流多发区,近年来已引起众多海洋学家的重视。我国海洋学家通过对台湾海峡区水团、海流和营养盐等的分析研究,不仅得出了台湾海峡西部海域上升流的分布范围和特征,并对其成因也作了探讨,取得了一些有价值的研究结果。由于这些研究都是采用间接方法,因此对上升流的主要成因尚存在不同的看法。本文通过对引起台湾海峡西部海域上升流的各驱动力因子量级的分析,进而判断出上升流的主要成因。     

Distributional patterns and variation of valve diameter of Paralia sulcata in surface sediments of Southern British Columbia Inlets

Paralia sulcata is one of 7 species out of 216 identified from 95 surface sediment samples which has a relative abundance of ≥2% of the total count. The relative abundance of P. sulcata in the surface sediments increases in the direction of increasing salinity in the surface waters, toward the mouth in high and medium runoff inlets, and toward the head in the low runoff inlets. The absolute abundance of P. sulcata in the surface sediments, and primary productivity, both increase toward the mouth in high and medium runoff inlets. Increasing valve diameter of P. sulcata is associated with both increasing salinity of the surface waters and increasing primary productivity.     

三峡工程对河口及邻近海域渔业影响的初步探讨

河口只是河流与海洋之间的一小部分水域,但对人类社会的发展和生物的进化起着重要的作用。它不仅是生物种群繁殖、育幼和栖息的场所,而且是溯河和降海鱼类洄游的必经之路,因此,河口对生物种群的繁衍延续和资源补充,以及保持生态平衡具有十分重要的意义。 然而,河口又是生态环境十分脆弱和敏感的水域,同时也是受人类干扰最为严重的区域。因此,河口的生态环境问题愈来愈引起人们的关注,其中包括长江三峡水库的兴建对长江口及其附近海域生态、环境的影响,特别是对位于河口两侧的我国著名两大渔场——舟山渔场和吕四渔场的影响问题。影响渔业资源的因子是多方面而且错综复杂的。本文主要通过长江径流的变化与环境因子变量的相关分析,并根据三峡水库不同蓄水方案,对河口近海渔业的影响问题进行初步探讨。     

西南季风不同阶段南海北部珠江口外断面水文调查分析

根据2000年7月及2001年5月南海北部珠江口外断面CTD调查资料、同期气象资料,并结合该海域历史资料,对调查断面珠江冲淡水扩展范围、跃层变动情况及上升流特征进行了分析,观察到对应于夏季西南季风的不同阶段,调查断面跃层分布与珠江冲淡水影响范围均发生明显变动,升降流的影响也呈现出不同特征：(1)西南季风较强时,断面陆架区上表层受冲淡水影响明显,海区的层化结构明显加强;(2)西南季风较强时．调查断面出现上升流和下降流。研究结果表明：(1)局地风应力与热通量的变化控制了调查断面跃层或混合层的温度和深度的变化,影响着珠江冲淡水的扩展范围,西南季风较强时珠江冲淡水扩展范围变大,调查断面跃层或混合层强度变大,深度变深;(2)夏季西南季风强时调查断面存在上升流,其形成机制为风产生的离岸水体Ekman输运的补偿效应,底地形的变化虽然也造成较弱的外海次表层水涌升,但可能只是加强了上升的速度或强度;(3)夏季西南季风强时调查断面上存在上升流区与下降流区毗邻的现象,下降流成因可能有二,一为近岸流和陆坡流呈相反方向运动形成弱的反气旋涡,二为“上升与下降因相互水体补充的需要而共生”。     

Effects of enhanced loads of nutrients on epiphytes on leaves and rhizomes of Posidonia oceanica

The increase of anthropogenic activities has severely altered both terrestrial and aquatic systems. Urbanisation, excessive use of agricultural fertilisers, organic runoff and climate change have caused an increase of nutrients in coastal waters, altering the diversity and food-web structure of benthic assemblages. The aims of the present paper were to text if an experimentally increased availability of nutrients, primarily nitrogen and phosphorous, in an oligotrophic basin, would affect epiphytic assemblages on leaves and rhizomes of P. oceanica and whether this could change rates of consumption of the plant by herbivores. In particular, we tested the hypothesis i) that changes to species composition and abundance of epiphytic assemblages generated by nutrients enrichment would vary between leaves and rhizomes and that ii) alterations to epiphytic assemblages on leaves might, in turn, modify feeding rates of herbivorous fish. After two years, the structure of both leaf and rhizome epiphytic assemblages responded to changes in nutrient concentrations before the occurrence of drastic alterations to the host plant, but only the former showed significant changes in terms of species composition. Moreover, a larger intensity of grazing on P. oceanica leaves was documented in experimentally enriched areas than in controls. The present findings and conclusions are applicable to other systems where patterns of biodiversity depend on changes in the availability of nutrients due to natural or anthropogenic events, likely interacting with biological processes, such as competition and grazing.     

Flow separation and vertical motions in a tidal flow interacting with a shallow-water island

This paper reports on the case study of Rattray Island (Great Barrier Reef, northeast Australia), lying perpendicular to tidal flow in shallow waters. At ebb and flood, attached (stable) eddies develop in the wake where swirls of turbidity suggest that sediment-laden waters are brought to the surface as a result of vertical transport. Both eddy and tip upwellings are encountered in the tidal flow around Rattray Island but there is currently no clear-cut answer as to which secondary flow generates upwelling with the largest intensity. This paper addresses this specific issue through idealized and realistic high-resolution numerical experiments. The analysis is supported by physical arguments based on the theory of flow separation. Given Rattray's geometry and surrounding bathymetry, the mechanism of flow separation in shallow waters helps explain the asymmetry in size of the eddies and their intensity. The results of idealized numerical experiments also suggest that eddy and tip upwellings may be of similar intensity at Rattray Island.     

Late Holocene marine productivity changes in Northern Patagonia-Chile inferred from a multi-proxy analysis of Jacaf channel sediments

A multi-proxy approach based on organic (organic carbon, alkenones, and C/N) and inorganic geochemical proxies (biogenic opal, inorganic carbon, Fe, Ti, and Ca) preserved in the sediments of the Jacaf channel (CF7-PC33; 44°21′S, 72°58′W, 510 m water depth), Chilean fjords, yields evidence of major past productivity fluctuations in accordance with climatic changes over the last ∼1800 years. The downcore record clearly shows two productivity/climate modes. The first period, prior to 900 cal yr BP, is characterized by decreased marine productivity and a reduced continental signal, pointing to diminished precipitation and runoff. In contrast, the second period between ∼750 cal yr BP and the late 1800s (top of core) is illustrated by elevated productivity and an increased continental signal, suggesting higher precipitation and runoff. Both time intervals are separated by a relatively abrupt transition of ∼150 years which roughly coincides with the beginning of the Little Ice Age. The increased content of freshwater diatoms and Chrysophyte cysts that characterize the last 200 years of the latter mode coincides with a significant decrease in the carbonate content of the sediment; together they further indicate increased terrigenous contributions and decreased marine carbonate productivity at the end of the Little Ice Age. The correspondence between our record and other paleoclimate studies carried out in South America and Antarctica demonstrates that the Chilean fjord area of Northern Patagonia is not just sensitive to local climatic variability but also to regional and possibly global variability.     

Abrupt changes of intermediate-water oxygen in the northwestern Pacific during the last 27 kyr

An oxygen minimum zone (OMZ) currently exists at intermediate water depths on the northern Japanese margin in the northwestern Pacific. The OMZ results largely from a combination of high surface–water productivity and poor ventilation of intermediate waters. We investigated the late Quaternary history (last 27 kyr) of the intensity of this OMZ using changes in benthic foraminiferal carbon isotopes and assemblages in a sediment core taken on the continental slope off Shimokita Peninsula, northern Japan, at a water depth of 975 m. The core was located well within the region of the present-day OMZ and high surface–water productivity. The benthic foraminiferal δ¹³C values, which indicate millennial-scale fluctuations of nutrient contents at the sediment–water interface, were 0.48‰ lower during the last glacial maximum (LGM) than during the late Holocene. These results do not indicate the formation of glacial intermediate waters of subarctic Pacific origin, but rather the large contribution of high-nutrient water masses such as the Antarctic Intermediate Water, implying that the regional circulation pattern during the LGM was similar to that of modern times. Benthic foraminiferal assemblages underwent major changes in response to changes in dissolved oxygen concentrations in ocean floor sediments. The lowest oxygen and highest nutrient conditions, marked by dysoxic taxa and negative values of benthic foraminiferal δ¹³C, occurred during the Bølling/Allerød (B/A) and Pre-Boreal warming events. Dysoxic conditions in this region during these intervals were possibly caused by high surface–water productivity at times of reduced intermediate–water ventilation in the northwestern Pacific. The benthic assemblages show dysoxic events on approx. 100- to 200-year cycles during the B/A, reflecting centennial-scale productivity changes related to freshwater cycles and surface–water circulation in the North Pacific.     

Intense localized productivity in the Irish Sea

The variability of primary productivity in surface waters was continuously recorded during spatial and sectional surveys of the Irish Sea in the summer of 1977. Localized patches of intense productivity were found, not in the frontal region of the western Irish Sea, but farther east. Subsurface distributions of physical, chemical and biological characteristics through a latitudinal section of the Irish Sea are reported. These data showed that the productivity peaks occurred at the boundaries of a water type exhibiting properties uncharacteristic of Irish Sea waters.     

Temporal variability of neustonic ichthyoplankton assemblages of the eastern Pacific warm pool: Can community structure be linked to climate variability?

Considerable evidence exists, showing an accelerated warming trend on earth during the past 40–50 years, attributed mainly to anthropogenic factors. Much of this excess heat is stored in the world's oceans, likely resulting in increased environmental variability felt by marine ecosystems. The long-term effects of this phenomenon on oceanic tropical ecosystems are largely unknown, and our understanding of its effects could be facilitated by long-term studies of how species compositions change with time. Ichthyoplankton, in particular, can integrate physical, environmental and ecological factors making them excellent model taxa to address this question. While on eight (1987–1990, 1992 and 1998–2000) NOAA Fisheries cruises to the eastern Pacific warm pool, we characterized the thermal and phytoplankton pigment structure of the water column, as well as the neustonic ichthyoplankton community using CTD casts and Manta (surface) net tows. Over the 13-year period, 852 CTD and Manta tow stations were completed. We divided the study area into three regions based on regional oceanography, thermocline depth and productivity, as well as a longitudinal gradient in species composition among stations. We then analyzed temporal trends of ichthyoplankton species composition within each region by pooling stations by region and year and making pairwise comparisons of community similarity between all combinations of the eight cruises within each region. We also identified environment-specific species assemblages and station groupings using hierarchical clustering and non-metric multi-dimensional scaling (MDS). Our analyses revealed a longitudinal gradient in community structure and temporal stability of ichthyoplankton species composition. Over the 13 years ichthyoplankton assemblages in the two westernmost regions varied less than in the eastern region. MDS and cluster analyses identified five ichthyoplankton assemblages that corresponded to oceanographic habitats and a gradient in community composition. We hypothesize that the changes in thermocline depth during the El Niños of 1987–1988, 1997–1998 and the extended period of warmth during 1990–1994 altered productivity sufficiently to cause a shift in the abundances of foundation species of the upwelling systems of the eastern Pacific warm pool. Our study suggests that ichthyoplankton assemblages in oligotrophic waters are more resilient to changes in the thermocline than assemblages in upwelling regions; or that oligotrophic regions simply have less physical variation compared to upwelling regions.