Global change and the biogeochemistry of the North Sea: the possible role of phytoplankton and phytoplankton grazing

Phytoplankton plays a dominant role in shelf biogeochemistry by producing the major part of organic matter. Part of the organic matter will reach the sediment where diagenetic processes like denitrification, apatite formation or burial will remove nutrients from the biogeochemical cycle. In this article current knowledge on the decadal plankton variability in the North Sea is summarized and possible implications of these changes for the biogeochemistry of the North Sea are discussed. Most of the observed interdecadal dynamics seem to be linked to large-scale oceanographic and atmospheric processes. Prominent changes in the North Sea ecosystem have taken place around 1979 and 1988. In general, the phytoplankton color (CPRS indicator of phytoplankton biomass) reached minimum values during the end of the 1970s and has increased especially since the mid 1980s. Changes with a similar timing have been identified in many time series from the North Sea through the entire ecosystem and are sometimes referred to as regime shifts. It is suggested that the impact of global change on the local biogeochemistry is largely driven by the phyto- and zooplankton dynamics during spring and early summer. At that time the extent of zooplankton–phytoplankton interaction either allows that a large part of the new production is settling to the sediment, or that a significant part of the new production including the fixed nutrients is kept within the pelagic system. The origin of the extent of the phytoplankton–zooplankton interaction in spring is probably set in the previous autumn and winter. In coastal areas, both large-scale atmospheric and oceanographic changes as well as anthropogenic factors influence the long-term dynamics. Due to eutrophication, local primary production nowadays still is up to five times higher than during pre-industrial conditions, despite a decreasing trend. Recently, introduced species have strengthened the filter feeder component of coastal ecosystems. Especially in shallow coastal seas like the Wadden Sea, this will enhance particle retention, shift organic matter degradation to the benthic compartment and enhance nutrient removal from the biogeochemical cycle by denitrification or apatite formation.     

An 810‐year history of cold season temperature variability for northern Poland

Scots pine (Pinus sylvestris L.) is a widely used tree species in European dendroclimatology studies due to its common distribution across much of the continent. Almost all studies find radial growth strongly related to summer temperature, a result reflecting site selection at high elevation/latitude environments where trees grow at their ecophysiological limits. Due to the amount of attention spent on these sites there is a geographical and seasonal bias in temperature reconstructions based upon tree‐ring proxies in Europe. To overcome the limited availability of tree‐ring data in temperate lowlands, we present a northern Poland ring‐width chronology developed from living and historic Scots pine material with a strong common growth signal going back to AD 1200. Investigations into climate‐growth relationships found year‐to‐year ring‐width variability to be more strongly correlated to cold season temperature (November to April) prior to the growing season than summer temperatures during tree‐ring formation. Based on this relationship it was possible to reconstruct cold season temperature conditions for the last 810 years. Spatial field correlations with gridded instrumental records indicated that the reconstruction provides relevant cold season temperature information across the land regions bordering the North Atlantic Ocean and Baltic Sea, lowlands and uplands of western and central Europe, and the eastern and central interior of Russia. Despite an unsuccessful attempt to find a stationary relationship with the North Atlantic Oscillation, comparisons with several cold season temperature reconstructions confirmed the long‐term connection between our reconstructed temperature series for northern Poland and the wider area.     

On the quantitative importance of heterotrophic microplankton in the northern German Wadden Sea

To assess the importance of heterotrophic microplankton in the Wadden Sea, seasonal distribution and biomass of the main subgroups, that is, heterotrophic dinoflagellates, (separated into thecate and athecate forms), tintinnids, and aloricate ciliates, were studied in 1989 and 1990 in a total of six surveys covering the whole area of the northern German Wadden Sea. Heterotrophic microplankton biomass exhibited high spatial and temporal variation, ranging from 0 μg Cl^?1 to 66 μg Cl^?1, with maximum concentrations in spring., Mean stocks were lowest in winter (1.6 μg Cl^?1) and highest in spring (11.7 μg Cl^?1); intermediate concentrations were found in summer (8.5 μg Cl^?1). In winter, the heterotrophic microplankton was dominated by tintinnids. In spring and summer, aloricate ciliates and dinoflagellates made up the largest part of the biomass. A pronounced feature was a shift within the dinoprotist group from athecate to thecate forms in summer. In spring, maxima of athecate dinoflagellate carbon were associated with blooms ofPhaeocystis globosa, indicating a close trophic relationship. From rough estimates of the daily grazing potential, based on microheterotrophic biomass and conversion factors from the literature, it may be concluded that heterotrophic microplankton temporarily share a main role in the transfer of food and energy to higher trophic levels within the pelagic system of the Wadden Sea.     

西菲律宾海硅藻席沉积中的多囊虫类放射虫记录及其环境意义

为了多角度理解海洋纹层沉积物的形成过程,利用在西菲律宾海采集到的含纹层硅藻席的XT47孔岩心样品,进行多囊虫类放射虫的组合变化与环境意义分析.研究表明XT47孔岩心上段260 cm厚硅藻席沉积中含有丰富的放射虫、丰度高于2×104个/克;中段260～460 cm出现5次放射虫丰度高峰与红粘土的交替旋回沉积;下段460～...     

Biomarkers in upper Holocene Eastern North Sea and Wadden Sea sediments

Total extracts of sediment cores from five different stations in the North Sea and Wadden Sea were analysed for their biomarker composition. Only sediments of the Skagerrak contained significant amounts of marine biomarkers (mainly alkenones), other sites contained predominantly terrestrial biomarkers. Bioturbation in the Skagerrak is, however, far too high to determine sea surface temperature (SST) changes within short time intervals. These results indicate that biomarkers contained in these sediments are not useful to reconstruct climate fluctuations during the upper Holocene. High amounts of α-, β- and ω-hydroxy fatty acids as well as small amounts of α, β-dihydroxy fatty acids were released from the insoluble organic material of the sediments from the Wadden Sea station, indicating a significant input of the eelgrass Zostera marina. This was confirmed by microscopic observations. This is the first time the α,β-dihydroxy fatty acids have been found in a sediment core and they have proven to be potential biomarkers for these seagrass species.     

Main Species Characteristics of Phytoplankton Spring Blooms in NE Atlantic and Arctic Waters (68–80° N)

A compilation of phytoplankton species abundance data from the spring bloom along the northern Norwegian coast and in the Barents Sea shows that the quantitatively most important species are the prymnesiophyte Phaeocystis pouchetii and the common cold water to temperate diatoms Chaetoceros socialis, Skeletonema costatum sensu lato, Fragilariopsis oceanica, Thalassiosira spp., Chaetoceros furcellatus, Chaetoceros compressus, Chaetoceros debilis and Bacterosira bathyomphala. The relative abundance of diatoms and Phaeocystis varied highly and apparently stochastically between years. P. pouchetii occurred during all stages of the spring bloom and sometimes completely dominated the phytoplankton community. Along the Norwegian coast, the importance of P. pouchetii increased northwards. The species composition in coastal fjords at 70° N is surprisingly similar to that of shelf waters in the Barents Sea (up to 80° N). An exception is S. costatum sensu lato which was seldom observed in Arctic waters. Small flagellates (<10 μm) other than dinoflagellates and P. pouchetii are also important among the Barents Sea spring phytoplankton. Associations of species seem rigid over time and are dominated by C. socialis and P. pouchetii in northern waters. Biogeographical categories of spring bloom species in relation to environmental conditions are discussed.     

2009/2010年我国西南秋冬春连旱特征及其大气环流异常分析

利用中国逐日站点降水资料、逐日季风监测指数及逐日副热带高压指数、74项环流指数及NCEP/NCAR再分析资料, 分析了2009年秋季至2010年春季的秋冬春西南特大干旱过程中各指数及大气环流异常特征.结果表明: 自2009年10月底东亚冬季风建立以来, 至2010年春季, 东亚冬季风强度持续偏强, 加之西太平洋副热带高压较常年偏西偏南, 西南地区长期受副高控制, 气温持续偏高, 加之冷空气虽然总体偏强, 但主要控制我国北方地区, 造成冷暖空气在西南地区少有交汇, 致使降水偏少, 干旱发生发展. 印缅槽强度较常年偏弱, 来自印度洋、孟加拉湾以及南海的水汽条件不足, 向西南地区输送的来自南海和孟加拉湾两条水汽通道的水汽通量均较常年偏弱很多, 加之西南地区、特别是云南地区自2009年秋季以来, 长期处于下沉运动的正距平区, 造成这段时间西南地区干旱少雨, 旱情持续. 2009年9月El Niño事件全面爆发, 南海-西太平洋地区形成异常反气旋流场, 该反气旋流场较常年偏西偏南, 造成副高位置偏西偏南, 从而使得云贵高原及其周边的印度季风区的降雨量明显偏少;高原地区及南海、菲律宾附近及热带辐合带地区OLR异常对西太平洋副热带高压的变化有一定影响, 进而影响西南地区降水, 其内在机制还有待深入研究.     

Seasonal Occurrence of Cownose Rays (Rhinoptera bonasus) in North Carolina’s Estuarine and Coastal Waters

The seasonal occurrence of cownose rays (Rhinoptera bonasus) within North Carolina’s estuarine and coastal waters was examined from aerial surveys conducted during 2004–2006. Generalized linear models were used to assess the influence of several variables (month, year, habitat type, sea surface temperature, and turbidity) on predicted counts of cownose rays. The spatial distributions of rays were compared by season, and differences in group size were tested as a function of season and habitat. Cownose ray data associated with the North Carolina Division of Marine Fisheries (NCDMF) fishery independent gill net sampling program in Pamlico Sound was also examined as a function of season and year, and compared with aerial observations. Rays immigrated into the region in mid-spring (April), dispersed throughout the estuary in the summer (June–August), and emigrated by late autumn (November). Predicted counts were highest in the spring (April, May) and autumn (September–November) for coastal habitats and highest in the summer for estuarine habitats. Predicted counts were also higher in the coastal region than estuarine and higher when sea surface temperatures were above average. Comparison of group size by habitat type revealed substantially larger group sizes in the coastal habitat than the estuarine. In addition, for the estuary, spring surveys had larger group sizes than summer surveys; for the coastal habitat, autumn group sizes were significantly larger than spring or summer group sizes. The NCDMF gill net sampling surveys indicated similar trends in monthly migration patterns as well as increased ray abundance in 2008 and 2009 compared with 2003–2007. These results suggest that North Carolina’s waters serve as important habitat during the seasonal migration of cownose rays, as well as during the summer when the species may utilize the estuarine region as a nursery and/or for foraging.     

Cycling of trace metals (Mn, Fe, Mo, U, V, Cr) in deep pore waters of intertidal flat sediments

Trace metals (Mn, Fe, Mo, U, Cr, V) were studied in pore waters of an intertidal flat located in the German Wadden Sea. The study system is an example of a permeable tidal flat system where pore water exchange is affected by tidal driven pressure gradients besides diffusion. Permanently installed in situ samplers were used to extract pore waters down to 5 m depth throughout one year. The samplers were either located close to the tidal flat margin or in central parts of the tidal flat. Despite dynamic sedimentological and hydrological conditions, the general trends with depth in deep tidal flat pore waters are remarkably similar to those observed in deep sea environments. Rates of trace metal cycling must be comparably large in order to maintain the observed pore water profiles. Trace metals further show similar general trends with depth close to the margin and in central parts of the tidal flat. Seasonal sampling revealed that V and Cr vary concurrent with seasonal changes in dissolved organic carbon (DOC) concentration. This effect is most notable close to the tidal flat margin where sulphate, DOC, and nutrients vary with season down to some metres depth. Seasonal variations of Mn, Fe, Mo, and U are by contrast limited to the upper decimetres of the sediment. Their seasonal patterns depend on organic matter supply, redox stratification, and particulate matter deposited on sediment surfaces. Pore water sampling within one tidal cycle provides evidence for pore water advection in margin sediments. During low tide pore water flow towards the creekbank is generated by a hydraulic gradient suggesting that deep pore waters may be seeping out of creekbank sediments. Owing to the enrichment of specific elements like Mn in pore water compared to sea water, seeping pore waters may have an impact on the chemistry of the open water column. Mass balance calculations reveal that the impact of deep pore waters on the Mn budget in the open water column is below 4%. Mn deep pore water discharge of the whole Wadden Sea is estimated to be about 9% of the total dissolved riverine Mn input into the Southern North Sea.     

南黄海悬浮体的垂直分布特性及其指示意义

重点研究了南黄海典型断面的悬浮体垂直分布特性及其指示意义。结果表明:四季南海黄海北部断面悬浮体分布的共同特征是西高东低,冬、春季鲁北沿岸流携带悬浮体向南输运和黄海暖流北上是南黄海与北黄海进行物质交换的重要方式和途径;夏半年南黄海中部断面深水域存在的表层云团状悬浮体高值区或"中层悬浮体最大值"现象与该海域的生物活动具有密切的联系;冬、春季苏北浅滩外侧海域近岸区的悬浮体含量显著高于夏、秋季,且冬半年近岸区的悬浮体具有向外海输运的趋势;长江口东北部断面各季节均存在2个悬浮体高值区,其中位于断面西部近岸海域的高值区与长江冲淡水(夏季)或苏北沿岸水(冬季)的影响有关,位于断面东部深水域处的悬浮体高值区是黄海西部沿岸流物质输运的结果,并与济州岛西南部海域的泥质区总体相对应,黄海与东海的物质交换过程主要通过夏季长江冲淡水东北向扩展与冬半年黄海西部沿岸流南下和黄海暖流北上进行。另外,水体层化和陆架锋也显著影响着南黄海悬浮体的垂直分布状况,锋面是控制夏季悬浮体向外海深水区输运的主要物理机制。     

Late Devensian ice‐marginal features in the central North Sea – processes and chronology

Palaeoglaciological reconstructions of the North Sea sector of the last British Ice Sheet have, as other shelf areas, suffered from a lack of dates directly related to ice‐front positions. In the present study new high‐resolution TOPAS seismic data, bathymetric records and sediment core data from the Witch Ground Basin, central North Sea, were compiled. This compilation made it possible to map out three ice‐marginal positions, partly through identification of terminal moraines and partly through location of glacial‐fed debrisflows. The interfingering of the distal parts of the glacial‐fed debrisflows with continuous marine sedimentation enabled the development of a chronology for glacial events based on previously published and some new radiocarbon dates on marine molluscs and foraminifera. From these data it is suggested that after the central Witch Ground Basin was deglaciated at c. 27 cal. ka BP, the eastern part was inundated by glacial ice from the east in the Tampen advance at c. 21 cal. ka BP. Subsequently, the basin was inundated by ice from northeast during the Fladen 1 (c. 17.5 cal. ka BP) and the Fladen 2 (16.2 cal. ka BP) events. It should be emphasized that the Fladen 1 and 2 events, individually, may represent dynamics of relatively small lobes of glacial ice at the margin of the British Ice Sheet and that the climatic significance of these may be questioned. However, the Fladen Events probably correlate in time with the Clogher Head and Killard Point re‐advances previously documented from Ireland and the Bremanger event from off western Norway, suggesting that the British and Fennoscandian ice sheets both had major advances in their northwestern parts, close to the northwestern European seaboard, at this time.     

Connection between South Mediterranean climate and North African atmospheric circulation during the last 50,000 yr BP North Atlantic cold events

High-resolution clay mineralogical analyses were performed on sediment deposited during the last 50,000 yr in the Alboran sea (ODP Site 976). The clay mineral record is compared with pollen assemblages and with annual precipitation (Pann) and mean temperatures of the coldest month (MTCO) reconstructed with the modern analog technique (MAT). Enhanced contribution of palygorskite, a typical wind-blown clay mineral, characterizes the North Atlantic cold climatic events. Coeval development of the semi-arid vegetation (Artemisia rich) associated with a drastic fall of reconstructed precipitations and temperatures, suggest cold and arid continental conditions in the West Mediterranean area during North Atlantic cold events. The clay mineral association, especially the palygorskite content and the illite-to-kaolinite ratio, indicate western Morocco as one of the major source of the clay-size fraction during the North Atlantic cold events. The maximum abundance of Artemisia associated with the presence of Argania pollen both indicate Morocco as the main origin for pollen during these cold periods. The comparison of these pollen and clay mineral-specific features allows us to pinpoint western Morocco as the dominant source of wind-blown particles during North Atlantic cold events. These specific mineralogical composition and palynological assemblages reveal enhanced aridity over North Africa and intensification of winds favouring dust erosion and transport from North Africa toward the Alboran Sea during the North Atlantic cold events. According to atmospheric models, such a meridian transport (1) likely results from the development of strong and stable anticyclonic conditions over the tropical Atlantic and North Africa, similar to today's summer meteorological configuration and (2) implies a northward position of the westerly winds during North Atlantic cold events. Finally the synoptic situation over the West Mediterranean during the North Atlantic cold events is compared with the North Atlantic Oscillation (NAO), suggesting that during the cold Atlantic events, weather regimes over Europe and North Africa may have been systematically shifted towards a positive NAO situation.     

Algal blooms in a shallow lake with a special reference to lake (Loch) Lindores: Scotland

Algal blooms are frequently observed in eutrophic lakes; a typical example of which is Lake Lindores, where two species of algal blooms were observed during the studied period. The first bloom of Asterionella formosa occured in spring, with a second occurence of the bloom observed in late winter and autumn when the water temperature was fairly low. At a higher water temperature, of more than 15°C, an unwanted blue-green algal bloom of Anabaena flosaquae occured. The blue-green algal bloom normally occured in summer and early autumn.     

Climatic Regionalization and the Spatio-Temporal Occurrence of Extreme Single-Year Drought Events (1500–1998) in the Interior Pacific Northwest, USA

Tree-ring records from western juniper (Juniperus occidentalis var. occidentalis Hook.) growing throughout the interior Pacific Northwest identify extreme climatic pointer years (CPYs) (i.e., severe single-year droughts) from 1500–1998. Widespread and extreme CPYs were concentrated in the 16th and early part of the 17th centuries and did not occur again until the early 20th century. The 217-yr absence of extreme CPYs may have occurred during an extended period of low variance in the Pacific Decadal Oscillation. We mapped climatic boundaries for the interior Pacific Northwest based on the location of sites with similar precipitation variability indices. Three regions, the Northwest (based on chronologies from nine sites), the Southwest (four sites), and the East (five sites) were identified. Our results suggest that western juniper radial growth indices have substantial interannual variability within the northwestern range of the species (central Oregon), particularly when compared with western juniper growing in its eastern range (eastern Oregon, southeastern Idaho, and northern Nevada) and southwestern range (southern Oregon and northeast California). We suspect that the substantial differences in the variability of western juniper radial growth indices are linked to the influence of ENSO events on winter/spring precipitation amounts.     

Fire Weather in Israel — Synoptic Climatological Analysis

The study examines the synoptic situations and weather conditions under which occurred Israel's largest forest fires between the years 1987–1995. Annual rainfall and maximum temperature were found to have a positive correlation with both the size of the burnt area and the frequency of fires. A negative correlation was found for the relative humidity at 12 UTC for the same parameters. The fire season in Israel starts in May and ends in November, the peak months being May, June and July. No large fires were observed during the rainy season, December–February, despite the relatively low precipitation characterizing the region. Atmospheric disturbances as well as quasi-stationary systems were found to be favorable for the development of forest fires in Israel: the North African (‘Sharav’) cyclone and the Red Sea trough, which are common during spring and autumn. These systems carry hot, dry air from the deserts and are responsible for 55% of the burnt area from major forest fires in Israel and up to 33% of the major forest fires. Sixty-five percent of the forest fires occurred during the summer all of them under the quasi-stationary system of the Persian Gulf trough. These fires did not spread as widely as those that occurred under the North African cyclone and the Red Sea trough systems. The role of weather in the propagation of fire is exemplified in the case study of the ‘Sha'ar ha Gai’ fire of July 1995 — the biggest forest fire in the history of Israel (1300 ha). This revised version was published online in July 2006 with corrections to the Cover Date.     

Water quality and phytoplankton as indicators of hurricane impacts on a large estuarine ecosystem

Three sequential hurricanes in the fall of 1999 provided the impetus for assessing multi-annual effects on water quality and phytoplankton dynamics in southwestern Pamlico Sound, North Carolina. Two and a half years of post-hurricane data were examined for short- and long-term impacts from the storms and >100 year flooding. Salinity decreased dramatically and did not recover until May 2000. Inorganic nitrogen and phosphorus concentrations were briefly elevated during the flooding, but later returned to background levels. Dissolved organic carbon concentrations declined through the whole study period, but did not appear to peak as was observed in the Neuse River estuary, a key tributary of the Sound. Light attenuation was highest in the fall to spring following the storms and was best correlated with chlorophylla concentrations. Phytoplankton biomass (chla) increased and remained elevated until late spring 2000 when concentrations returned to pre-storm levels and then cycled seasonally. Phytoplankton community composition varied throughout the study, reflecting the complex interaction between physiological optimal and combinations of salinity, residence time, nutrient availability, and possibly grazing activity. Floodwater advection or dilution from upstream maxima may have controlled the spatial heterogeneity in total and group-specific biomass. The storms produced areas of shortterm hypoxia, but hypoxic events continued during the following two summers, correlating strongly with water column stratification. Nitrogen loading to the southwestern sound was inferred from network analysis of previous nitrogen cycling studies in the Neuse River estuary. Based on these analyses, nutrient cycling and removal in the sub-estuaries would be decreased under high flow conditions, confirming observations from other estuaries. The inferred nitrogen load from the flood was 2–3 times the normal loading to the Sound; this estimate was supported by the substantial algal bloom. After 8-mos, the salinity and chla data indicated the Sound had returned to pre-hurricane conditions, yet phytoplankton community compositional changes continued through the multi-year study period. This is an example of long-term aspects of estuarine recovery that should be considered in the context of a predicted 10–40 yr period of elevated tropical storm activity in the western Atlantic Basin.     

Variability in temperature and geometry of the Norwegian Current over the past 600 yr; stable isotope and grain size evidence from the Norwegian margin

Core P1‐003MC was retrieved from 851 m water depth on the southern Norwegian continental margin, close to the boundary between the Norwegian Current (NC) and the underlying cold Norwegian Sea Deep Water. The core chronology was established by using ²¹⁰Pb measurements and ¹⁴C dates, suggesting a sampling resolution of between 2 and 9 yr. Sea‐surface temperature (SST) variations in the NC are reconstructed from stable oxygen isotope measurements in two planktonic Foraminifera species, Neogloboquadrina pachyderma (d.) and Globigerina bulloides. The high temporal resolution of the SST proxy records allows direct comparison with instrumental ocean temperature measurements from Ocean Weather Ship (OWS) Mike in the Norwegian Sea and an air temperature record from the coastal island Ona, western Norway. The comparison of the instrumental and the proxy SST data suggests that N. pachyderma (d.) calcify during summer, whereas G. bulloides calcify during spring. The δ¹⁸O records of both species suggest that the past 70 yr have been the warmest throughout the past 600 yr. The spring and summer proxy temperature data suggest differences in the duration of the cold period of the Little Ice Age. The spring temperature was 1–3°C colder throughout most of the period between ca. AD 1400 and 1700, and the summer temperature was 1–2°C colder throughout most of the period between ca. AD 1400 and 1920. Fluctuations in the depth of the lower boundary of the NC have been investigated by examining grain size data and benthic foraminiferal assemblages. The data show that the transition depth of the lower boundary of the NC was deeper between ca. AD 1400 and 1650 than after ca. AD 1750 until present. Copyright © 2003 John Wiley & Sons, Ltd.     

Tracing growing degree‐day changes in the cuticle morphology of Betula nana leaves: a new micro‐phenological palaeo‐proxy

Changing growing‐season properties in the northern latitudes are among the most obvious consequences of ongoing global change. Available techniques including satellite monitoring and phenological observations enable the detection of changes over the last few decades to centuries, but the full range of natural variability is still difficult to capture. Here we introduce a new approach to reconstruct growing season properties, by studying imprints of prolonged growing season on epidermal cell growth in Betula nana. A high correlation between cell expansion determined in annually collected B. nana leaves and subfossil leaf fragments collected from recent peat sections in northern Scandinavia, and climatic indices such as budburst date, growing‐season degree‐days and May–September mean temperatures, enable the establishment of a new micro‐phenological proxy for growing season characteristics. The applicability of the epidermal cell undulation index (UI) is tested by comparison with historical instrumental records of growing‐season degree‐days for the last 200 a. The results demonstrate the potential of the new leaf‐morphology‐based technique to reconstruct and quantify past changes in growing degree‐days beyond instrumental data series. Applied to abundant B. nana leaf remains from peat and lake sediments, the UI may enable a reconstruction of growing degree‐days throughout the Holocene and other parts of the late Quaternary. Copyright © 2010 John Wiley & Sons, Ltd.     

Numerical Modeling of the Long-Term Transport, Dispersion, and Accumulation of Black Sea Pollutants into the North Aegean Coastal Waters

This study investigates the long-term capacity of the North Aegean coastal systems to transport and store conservative pollutants that originate from the Black Sea. Emphasis is placed on modeling the dispersion and accumulation of a passive tracer that represents a Black Sea pollutant (BSP) substance that continuously discharges from the Dardanelles exit into the North Aegean, for a long period of time (16?years). The effects of the Black Sea water (BSW) inflows, meteorological forcing, and seasonal stratification are assessed with a 3D hydrodynamic model (Estuary, Lake and Coastal Ocean Model), after validation with available field data. The salinity, water temperature, and discharge from the Dardanelles Strait are taken to be seasonally varied. According to the authors' best knowledge, the present paper constitutes the first numerical modeling attempt in the literature that apart from the long-term hydrodynamic characteristics that have also been studied in previous works, a suitable tracer is introduced in order to predict the long-term fate, distribution, and accumulation of pollutants that originate from the Black Sea into the North Aegean coastal regions. The overall results of the present investigation indicate that the BSP concentration is very high at the coastal waters of Thassos, Samothraki, and Limnos islands, as well as along the mainland coastal waters between Alexandroupolis and Strymonikos Gulf, during summer and autumn when strong water column stratification occurs. In general, the BSP concentration in the North Aegean surface waters reaches considerable high values (47?C58?% of the initial pollutant concentration at Dardanelles inflow) within 16?years. Even for depths more than 500?m the BSP concentration is still remarkable, slightly increasing with time. The increase of the BSP concentration with respect to time at various depths (from free surface up to 750?m) is also investigated.     

基于标准化降水指数的内蒙古地区干旱时空变化特征

利用内蒙古及周边地区70个气象站1951~2014年降水数据,采用标准化降水指数等方法,对内蒙古近64年气候干旱时空变化进行分析。结果表明:研究区近64年来除西部年际、春、秋、冬季,中部春、秋季及东部春、冬季气候趋于湿润外,其他均趋于干旱。中、东部年际、植(作)物生长期SPI在2001年和1990年左右发生突变,东部突变后趋于干旱并在2006年左右又发生明显转折后趋于湿润。西部在1960s干旱严重,中、东部在1990s至2000s干旱严重。西部年际SPI由西北向东南、东部由南向北干旱趋势速率呈阶梯状下降,中部干旱趋势速率较西、东部快;植(作)物生长期SPI空间变化与年际一致,但西、中部干旱趋势明显的区域有所扩大。