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.     

基于声学方法的南黄海浮游动物垂直迁移季节变化研究

为研究南黄海浮游动物垂直迁移的季节变化, 分析了2006 年至2007 年4 个季节布放潜标中声学测流仪的观测数据。结果是: 声学测流仪测量的后向散射强度呈现显著的日变化特征, 这是由浮游动物垂直迁移造成的; 在4 个季节中都出现这一凌晨向下、黄昏向上的垂直迁移, 但是垂直迁移发生的时间有季节变化。利用南黄海辐射通量的直接观测数据, 讨论了垂直迁移发生时间与光照的关系,结果表明垂直迁移的季节变化主要受光照的影响。这对于研究浮游动物垂直迁移机制有一定意义。     

A model of turbidity maximum maintenance in the Irish Sea

A two-dimensional model has been developed in order to improve understanding of the processes which interact to maintain the sediment concentrations at an isolated turbidity maximum in the Irish Sea throughout the year. The model comprises two interchangeable populations of particles with different diameters, one of fine cohesive material, the other made up of flocs. Both populations are slow settling, and subject to horizontal diffusion, resuspension, settling, aggregation and disaggregation.The equations used to describe the processes of aggregation and the break-up of flocs in response to sediment concentration and turbulent shear have been developed by the tuning of the model to observations. Due to high turbulent shear at the turbidity maximum, the particles are predominantly fine, while the sediment in the surrounding water is made up of larger flocs. Diffusion of small particles out of the turbidity maximum balanced by the diffusion of aggregated material towards it provides a mechanism for its maintenance. The modelled sediment concentrations at the turbidity maximum can be reproduced year-on-year, with no loss due to diffusive processes. This is achievable with a limited, exhaustible source of material which is not replenished once resuspended.Through comparison with satellite imagery the correlation of the modelled sediment concentrations with observations is investigated, both spatially and temporally. The seasonal cycle is reproduced well by the model with winter and summer concentrations matching those observed. Spatially the model also performs well in both turbid regions and those where the surface sediment load is low.     

厦门西港浮游动物生态研究

本文根据１９９４年７月和１２月于厦门西港所获得的调查资料,分析了浮游动物的丰度及其季节和年际变化,讨论了浮游动物的物种和生态类群多样性,结果表明,７月浮游动物湿重生物量月均值约为１２月的２．５６倍,与历史资料相比,呈逐年趋势;７月和１２月在西港共记录浮游动物５５种和多种浮游幼体,它们分别隶属于５个生态类群,文中还分析了潮汐地浮游动物分布的影响。     

基于声学仪器与粒径分析仪研究东海浮游动物昼夜垂直迁移过程

浮游动物的昼夜迁移活动与其种群变动和摄食节律紧密联系,浮游动物昼夜移动的研究已经成为种群动力学研究的一个重要组成部分。2013年夏季在浙江东部近海,结合声学多普勒流速剖面仪(ADCP)和激光粒径分析仪(LISST-100)等仪器进行了一次定点周日连续观测。通过声学反演方法,得到后向散射强度剖面的时间变化,结合LISST-100得到的水体悬浮物粒径谱,研究了浮游动物垂直迁移及其习性。分析发现了可能是精致真刺水蚤的一次昼夜垂直迁移过程,其在夜间进入跃层附近进食,白天蛰伏于底层低温高盐的台湾暖流水中,垂向迁移速度达到了0.05 m/s。LISST-100观测还发现在夜间跃层边界处大粒径颗粒聚集和100～150 μm大小的颗粒物的减少,水体中不同粒径的悬浮颗粒物有明显的昼夜变化节律,推测水体中不同层次生物群落结构存在昼夜差异。     

Relationships between particle-grazing zooplankton and vertical phytoplankton distributions on the Texas continental shelf

This study compares vertical distributions of Penilia avirostris and Temora turbinata with vertical distributions of chlorophyll a over short time periods at a station in the north-western Gulf of Mexico in the summer and early fall of 1978. In June and July 1978 chlorophyll a and turbidity increased below the thermocline. In September 1978 chlorophyll a was concentrated in the upper mixed layer while turbidity was greatest near the bottom.In June and July P. avirostris and copepodites of T. turbinata were concentrated within the subsurface chlorophyll a layer. Adult T. turbinata were more widely distributed than the copepodites in June but apparently migrated diurnally in July. In September, abundance of all animals generally decreased slightly with depth. This change in animal distribution reflected changes in biotic and abiotic varlables between this cruise and previous cruises. In all cruises, animal distributions were positively correlated with chlorophyll a suggesting that food was the primary influence on distributions of these animals.     

Non-conservative Nutrient Fluxes from Budgets for the Irish Sea

Budgets for conservative tracers are used to determine the flow through the Irish Sea and combined with available data on nutrient distributions and inputs to estimate non-conservative nutrient fluxes. Steady state salinity and caesium-137 balances yield consistent estimates of the flow through the Irish Sea of Φ≈6×10⁴ m³s⁻¹. Using both tracers together with a mass balance allows the inclusion of separate diffusive flux terms and results in a diffusivity estimate ofK≈450 m²s⁻¹and a reduced flow of Φ≈4×10⁴ m³s⁻¹. These values are, however, sensitive to the gradients of salinity and caesium-137 concentration, which are not well defined by the observations.Following the LOICZ procedures, salinity and mass balances were combined with analogous statements for dissolved inorganic phosphorus (DIP) and dissolved inorganic nitrogen (DIN), in order to assess the non-conservative process rates. With regard to phosphorus it was found that the Irish Sea is close to balance with a slight net uptake of dissolved inorganic phosphorus, but the implied excess of uptake over release is not significant on account of uncertainties in the observations of boundary values and inputs. The DIN budget is subject to comparable uncertainties in the input data but does, however, indicate a significant imbalance with an average rate of denitrification of the order 0·3 mol N m⁻²y⁻¹.The implications of these budget results and their limitations are considered in relation to the application of the budgeting approach to areas with sparse data coverage. While the application of box model disciplines to conservative tracers can lead to satisfactory estimates of advective transport, the extension to non-conservative components requires extensive data to adequately specify the boundary values and input parameters averaged over the seasonal cycle.     

Changes in Irish Sea Benthos: Possible Effects of 40 years of Dredging

From 1946 to 1951 Dr N. S. Jones sampled the benthos around the south of the Isle of Man from over 200 sites. Multivariate methods have been used here to compare subsets of this historical data with recent data from the same locations: of these locations some have been subject to heavy scallop dredging over the intervening 40 plus years and some to little dredging. Clear changes were apparent regardless of scallop dredging intensity. Some of the changes in the heavily dredged areas were those expected to result from extreme physical disturbance—an increased polychaete mollusc ratio, loss of some fragile species, and an increase in the predominance of scavenger/predator species. However, changes in the lightly dredged areas also included the loss of a number of species including some potentially fragile tube-dwellers. Reasons for these changes were not apparent.     

南黄海浮游动物群落结构研究

根据2014年春、秋季南黄海16个站位的生物样品进行了浮游动物群落结构研究。共鉴定出99种浮游动物,其中春季68种,秋季78种。除浮游幼虫外,种类较多的类群是桡足类(34种,占总种类数的34.3%)、水螅水母(13种,13.1%)和端足类(5种,5.0%)。春季优势种为夜光虫(Y=0.259 7)、桡足幼体(Y=0.135 3)、拟长腹剑水蚤(Y=0.060 8)和伪长腹剑水蚤(Y=0.022 4),秋季时桡足幼体(Y=0.335 9)、伪长腹剑水蚤(Y=0.115 7)、强额拟哲水蚤(Y=0.053 3)、桡足类无节幼虫(Y=0.051 4)和拟长腹剑水蚤(Y=0.041 0)是优势种。春季浮游动物平均生物量为1 555.1 mg/m~3,秋季为425.8 mg/m~3。春季平均丰度为9 551.4个/m~3,秋季为2 103.7个/m~3。秋季香农-威纳指数、丰富度和均匀度结果皆比春季的高。浮游动物生物量与温度和水深相关性更高;丰度和温度相关性最高,其次和水深相关。     

夏季南海西部中尺度物理过程对营养盐和叶绿素a分布特征的影响

通过对2014年8月31日-9月26日国家自然科学基金委南海西部综合航次的调查结果分析,发现在中南半岛沿岸海域存在具有低温高盐的冷涡和位于其东南部海域具有高温低盐的暖涡。相对于暖涡和其他海域,冷涡水团含有更高的营养盐,并在50 m、75 m和100 m层增加明显,DIP分别高0.21 μmol/L、0.39 μmol/L和0.23 μmol/L,DIN分别高4.94 μmol/L、7.56 μmol/L和3.76 μmol/L,DSi分别高2.55 μmol/L、5.25 μmol/L和3.46 μmol/L,说明冷涡对提高初级生产力具有明显的营养优势条件和巨大潜力;叶绿素a最大值均出现在50 m层,其中以海南岛近岸海域最大,冷涡在25 m层提高初级生产力明显,主要是受营养盐影响显著;而在75 m、100 m层可能受到冷涡带来的低温环境而导致叶绿素a含量不高。     

Water transport from the North-east Irish Sea to western Scottish coastal waters: Further observations from time-trend matching of Sellafield radiocaesium

Radiocaesium isotopes, discharged into the North-east Irish Sea from the Sellafield (formerly Windscale) nuclear fuel reprocessing plant in Cumbria, have been employed as flow monitors to update and extend the record of coastal water movement from the Irish Sea to the Clyde Sea area and, further north, to Loch Etive. The temporal trends in radiocaesium levels have been used to determine the extent of water mixing en route and to define mean advection rates. Flow conditions from the Irish Sea have changed considerably since the mid-1970s, the residence time of northern Irish Sea waters being ～12 months during 1978–1980 inclusive. Average transport times of four and six months are estimated for the Sellafield to Clyde and Sellafield to Etive transects respectively. Sellafield ¹³⁷Cs levels in seawater were diluted by factors of 27 and 50 respectively during current movement to the Clyde and Etive areas. The decrease in salinity-corrected ¹³⁷Cs concentrations between the Clyde and Etive suggests that dilution by Atlantic water occurs, the latter mainly entering the Firth of Lorne from the west. The majority (～94%) of the radiocaesium supply to Loch Etive enters the Firth of Lorne via the portion of the coastal current circulating west of Islay, only ～6% arriving via the Sound of Jura.     

北太平洋亚热带环流区与西太平洋暖池区浮游动物群落垂直分布的差异及其对碳通量的意义

The mesozooplankton in both epipelagic and mesopelagic zones is essentially important for the study of ecosystem and biological carbon pump. Previous studies showed that the diel vertical migration(DVM) pattern of mesozooplankton varied among ecosystems. However, that pattern was largely unknown in the Western Pacific Warm Pool(WPWP). The vertical distribution, DVM and community structure of mesozooplankton from the surface to 1 000 m were compared at Stas JL7K(WPWP) and MA(North Pacific Subtropical Gyre, NPSG). Two sites showed similarly low biomass in both epipelagic and mesopelagic zones, which were in accordance with oligotrophic conditions of these two ecosystems. Stronger DVM(night/day ratio) was found at JL7K(1.31) than that at MA(1.09) on surface 0–100 m, and an obvious night increase of mesopelagic biomass was observed at JL7K, which was probably due to migrators from bathypelagic zone. Active carbon flux by DVM of zooplankton was estimated to be 0.23 mmol/(m2·d) at JL7K and 0.16 mmol/(m~2·d) at MA. The community structure analysis showed that calanoid copepods, cnidarians and appendicularians were the main contributors to DVM of mesozooplankton at both sites. We also compared the present result with previous studies of the two ecosystems,and suggested that the DVM of mesozooplankton was more homogeneous within the WPWP and more variable within the NPSG, though both ecosystems showed typically extremely oligotrophic conditions. The different diel vertical migration strength of mesozooplankton between NPSG and WPWP implied different efficiency of carbon pump in these two ecosystems.     

2012年夏季楚科奇海浮游动物垂直迁移及上升流对其生物量的影响

The diel vertical migration(DVM) of zooplankton and the influence of upwelling on zooplankton biomass were examined using water column data of current velocity and mean volume backscattering strength(MVBS)collected by moored acoustic Doppler current profilers(ADCPs) deployed in the southeastern Chukchi Sea during the 5th Chinese National Arctic Research Expedition(CHINARE) in summer 2012, combined with the satellite observational data such as sea surface temperature(SST), wind, and chlorophyll a(Chl a). Hourly acoustic data were continuously collected for 49-d in the mooring site. Spectral analysis indicated that there were different migrating patterns of zooplankton, even though precisely classifying the zooplankton taxa was not available. The prevailing 24-h cycle corresponded to the normal DVM with zooplankton swimming upwards at sunrise and returning to deep waters at sunset. There was a clear DVM in the upper 17 m of the water column during the period with distinct day-night cycles, and no active DVM throughout the water column when the sun above the horizon(polar day), suggesting that light intensity was the trigger for DVM. Also there was a second migrating pattern with 12-h cycle. The upwelling event occurring in the northwest of Alaskan coastal area had important influence on zooplankton biomass at the mooring site. During the upwelling, the SST close to the mooring site dropped significantly from maximal 6.35°C to minimal 1.31°C within five days. Simultaneously, there was a rapid increase in the MVBS and Chl a level, suggesting the aggregation of zooplankton related to upwelling.     

Seasonal changes in the vertical distribution and community structure of Antarctic macrozooplankton and micronekton

The macrozooplankton and micronekton community of the Lazarev Sea (Southern Ocean) was investigated at 3 depth layers during austral summer, autumn and winter: (1) the surface layer (0–2 m); (2) the epipelagic layer (0–200 m); and (3) the deep layer (0–3000 m). Altogether, 132 species were identified. Species composition changed with depth from a euphausiid-dominated community in the surface layer, via a siphonophore-dominated community in the epipelagic layer, to a chaetognath-dominated community in the deep layer. The surface layer community predominantly changed along gradients of surface water temperature and sea ice parameters, whereas the epipelagic community mainly changed along hydrographical gradients. Although representing only 1% of the depth range of the epipelagic layer, mean per-area macrofauna densities in the surface layer ranged at 8% of corresponding epipelagic densities in summer, 6% in autumn, and 24% in winter. Seasonal shifts of these proportional densities in abundant species indicated different strategies in the use of the surface layer, including both hibernal downward and hibernal upward shift in the vertical distribution, as well as year-round surface layer use by Antarctic krill. These findings imply that the surface layer, especially when it is ice-covered, is an important functional node of the pelagic ecosystem that has been underestimated by conventional depth-integrated sampling in the past. The exposure of this key habitat to climate-driven forces most likely adds to the known susceptibility of Antarctic pelagic ecosystems to temperature rise and changing sea ice conditions.     

Physical and anthropogenic effects on observed long-term nutrient changes in the Irish Sea

The trend in Irish Sea nutrient concentrations over the last four decades has been considered to reflect changes in anthropogenic loading. Comparison of a long-term database for the Menai Strait, North Wales, with an established historic data set for the Cypris station, Isle of Man, indicates that climate also has a significant influence on observations of nutrient concentrations. Data are presented detailing long-term shifts in nitrate, phosphate and silicate measurements since the 1960s at these two fixed sampling sites in the Irish Sea. Broad systematic changes observed in all three nutrients over the decades show a rise from the 1960s through to the 1980s, followed generally by an overall decline in the 1990s. Decadal-scale salinity changes occur in the opposite sense to nutrient changes. Anthropogenic inputs from freshwater cannot fully account for observed nutrient trends, neither is there evidence for shifts in nutrient concentrations in oceanic waters over the past four decades. Climatically forced movement in the geographical position of the freshwater/seawater mixing zone over a decadal time scale could, however, give rise to the observed shifts in nutrient concentration and salinity. This cannot alter nutrient concentration and salinity per se, but causes the measurements taken at fixed sampling sites to fluctuate inversely over this time scale. It is concluded that there is complex interplay between anthropogenic loading and climate affecting the distribution of nutrients in the Irish Sea.