Incorporation of Leucine and Thymidine by Estuarine Phytoplankton: Implications for Bacterial Productivity Estimates

Leucine and thymidine incorporation were examined in size-fractionated estuarine communities and in cultures of phytoplankton known to use dissolved organic nitrogen (DON). Cultured phytoplankton species were used to establish that phytoplankton took up leucine and thymidine into protein and DNA, respectively. Subsequently, incorporation of leucine and thymidine was measured in size-fractionated populations collected from the Lafayette River, VA, a eutrophic estuary where resident populations contain bloom-forming phytoplankton known to take up DON, and the Gulf of Mexico during a bloom of the mixotrophic red tide dinoflagellate, Karenia brevis. We examined the efficacy of size fractionation for determining phytoplankton versus bacterial incorporation of leucine and thymidine under conditions employed during bacterial productivity bioassays, and antibiotics were used to distinguish between bacterial and phytoplankton incorporation in cultured and natural populations. Results suggest that cultures and natural assemblages of phytoplankton can take up both leucine and thymidine when supplied at low concentrations (10 and 12 nmol L⁻¹, respectively) and during short incubations (15 min to 1 h). In natural populations, up to 95% of the leucine and thymidine incorporation during short bioassays was recovered in the >5.0-μm size fraction that contained ≤4.2% of the bacterial biomass.     

海洋浮游植物对磷的响应研究进展

磷是海洋浮游植物赖以生存的一种必需营养元素.海洋浮游植物对磷的响应,与初级生产力、碳循环以及固氮作用密切相关.总结了浮游植物可利用的磷源:优先吸收溶解无机磷;在寡磷海域,可通过相关酶类协助利用溶解有机磷来抵御无机磷的缺乏.对比了不同种类浮游植物对不同形态磷源利用方式的差异并从浮游植物生理学角度阐述了存在差异的根本原因.探讨了浮游植物对低磷环境的响应机制.近期的研究发现浮游植物细胞表面可以吸附磷,该发现有利于更加准确地衡量浮游植物承受的营养盐限制问题,进一步完善对海洋磷储库及其生物地球化学循环的认识.最后提出了今后需进一步研究的关键科学问题:浮游植物细胞表面吸附磷的机制;对不同结构有机磷化物的利用机理;浮游植物对磷的海洋生物地球化学循环的响应及反馈作用.     

The Effects of Tidal Export from Salt Marsh Ditches on Estuarine Water Quality and Plankton Communities

Salt marshes are an important transition zone between terrestrial and marine ecosystems, and in their natural state, they often function to cycle or trap terrestrially derived nutrients and organic matter. Many US salt marshes were ditched during the twentieth century, potentially altering their functionality. The goal of this 4-year study was to assess the impact of water from ditches within seven salt marshes on estuarine water quality and plankton communities within four estuaries on Long Island, NY, USA. We found that concentrations of inorganic nutrients (ammonium, phosphate), dissolved and particulate organic nitrogen and carbon (POC, PON, DOC, DON), and total coliform bacteria were significantly enriched in salt marsh ditches compared to the estuaries they discharged into. In addition, concentrations of ammonium and DON became more enriched in ditches as tidal levels decreased, suggesting these constituents were generated in situ. Quantification of nitrogen sources in Flanders Bay, NY, suggested salt marsh ditches could represent a substantial source of N to this estuary during summer months. Experimental incubations demonstrated that water from salt marsh ditches was capable of significantly enhancing the growth of multiple classes of phytoplankton, with large diatoms and dinoflagellates displaying the most dramatic increases in growth. Experiments further demonstrated that salt marsh ditchwater was capable of significantly enhancing pelagic respiration rates, suggesting discharge from ditches could influence estuarine oxygen consumption. In summary, this study demonstrates that tidal draining of salt marsh ditches is capable of degrading multiple aspects of estuarine water quality.     

Halocarbon emissions from marine phytoplankton and climate change

Long-lived and short-lived halocarbons have long been known for their adverse effects on atmospheric chemistry, especially ozone depletion that may be directly or indirectly influenced by global climate change. Marine organisms including phytoplankton contribute shorter-lived halocarbon compounds to the atmosphere. Oceans cover more than 70% of the Earth’s surface making the marine phytoplankton a significant presence. Changes in the environment will inevitably affect this widely distributed group of organisms. Various predictions have been made about how phytoplankton will respond to climate change, but as yet little is known about the interactions between phytoplankton, climate change and halocarbon emissions. We provide a summary of studies on halocarbon emissions by marine phytoplankton isolated from different climatic zones that includes data from our recent studies on tropical marine phytoplankton. It is important to determine and characterize the contribution of the phytoplankton to the halocarbon load in the atmosphere to allow their interaction with the changing global climate to be understood. Using these data, we compare the range of halocarbons emitted by phytoplankton with halocarbon emission data for seaweeds, a well-known biogenic contributor of short-lived halocarbons. Sørensen’s coefficient of similarity of 0.50 was calculated, which suggests that half of the detected halocarbon species present in seaweeds are also present in phytoplankton.     

Inorganic and Organic Nitrogen Use by Phytoplankton Along Chesapeake Bay,Measured Using a Flow Cytometric Sorting Approach

Two different approaches to measuring phytoplankton nitrogen (N) use were compared in late summer 2004 along the main axis of Chesapeake Bay. Uptake of ¹⁵N-labeled ammonium and nitrate and dual-labeled (¹⁵N and ¹³C) urea and dissolved free amino acids (DFAA) were measured in surface water samples from upper, mid, and lower bay stations. Two distinct methods were used to assess the relative uptake of N substrates by phytoplankton and correct for bacterial artifacts: (1) traditional filtration using Whatman glass fiber (GF/F) filters and (2) flow cytometric (FCM) sorting of chlorophyll-containing cells. The concentration of dissolved inorganic N (DIN) decreased with distance south along the bay, whereas dissolved organic N (DON) concentrations were relatively constant. Absolute N uptake rates measured using the traditional approach exceeded those of FCM-sorted phytoplankton, thereby suggesting the possibility of bacterial “contamination.” Ammonium was the dominant N form used throughout the transect, although FCM-sorted phytoplankton relied more on urea and DFAA as the ratio of DON/DIN increased toward the bay mouth. Overall, ammonium comprised 74 ± 17%, urea 10 ± 9%, DFAA 9 ± 7%, and nitrate 7 ± 12% of total measured N uptake by phytoplankton. Results suggest that bacteria relied primarily on DFAA and ammonium for N nutrition but also used N from urea at a rate similar to that of phytoplankton, whereas bacterial nitrate uptake was insignificant. On average, phytoplankton uptake of ammonium, urea, and DFAA was overestimated by 61%, 53%, and 135%, respectively, as a result of bacterial retention on GF/F filters.     

Characteristics of dissolved organic nitrogen (DON) in the surface water of Beijing Olympic Forest Park

The characteristics of dissolved organic nitrogen (DON) in surface water from Beijing Olympic Forest Park (BOFP) were investigated in this study. Nanofiltration (NF) pretreatment procedure using two NF membranes (NF90 and NF270) was applied to increase the accuracy and precision of DON measurements in surface water samples with high dissolved inorganic nitrogen/total dissolved nitrogen (DIN/TDN) ratios. Compared to NF90, NF270 showed better performance in lowering the DIN/TDN ratio and retaining DOC in both the synthetic water and raw water samples. DON concentrations ranged from 0.01 to 0.83 mg N L^?1 in water samples collected over four different months and showed a seasonal variation. The DON increased in summer due to the higher activity of decomposers on recent litterfall or because of a higher production of biomass in the surface water body. The molecular weight (MW) fractions of <3 kDa accounted for more than 50 % of the total DOC concentration and the fractions of <3 kDa contributed to more than 48 % of the total DON concentration. It could be concluded that most of the DON present in surface water of BOFP was composed of small molecules, which were mainly composed of monomers such as amino acids and urea, readily available for the uptake by phytoplankton and heterotrophic bacteria.     

Isotopic biogeochemistry of dissolved organic nitrogen: A new technique and application

We present a new technique for isolating and isotopically characterizing dissolved organic nitrogen (DON) for non-marine waters, δ¹⁵N values for DON from lacustrine samples and data suggesting that this technique will be applicable to marine samples. Our technique involves preconcentration of DON via rotary evaporation and removal of dissolved inorganic nitrogen (DIN) via dialysis using a membrane that retains material above 100 Da. Results demonstrate quantitative removal of DIN, complete recovery of DON (95% or greater) and retention of isotopic integrity (isotope effect less than 0.4‰) for a solution containing a DON standard (tripeptide) and DIN in deionized water. Reproducibility of carbon and nitrogen isotope values and elemental concentrations is demonstrated for DOM from Chefswet Basin, Lake Superior and Grand Traverse Bay, Lake Michigan. The applicability of this technique to marine samples is suggested by demonstrating 99% removal of DIN from a sample of Gulf Stream water amended with ammonium and nitrate.     

Prehistoric nutrient inputs and productivity in Narragansett Bay

Calculations by others of the preindustrial deposition of inorganic nitrogen from the atmosphere in the area of Narragansett Bay compared with recent measurements suggest that this flux has increased almost 15 times over natural background. On the basis of modern studies of the export of nitrogen and phosphorus from temperate forests, the prehistoric watershed also probably contributed very little reactive N or P to the bay. New information from undisturbed old-growth forests suggests that most of the N that was exported from the watershed was probably associated with refractory dissolved organic matter and thus contributed little to the fertility of the bay. The largest source of reactive dissolved inorganic nitrogen (DIN) and phosphorus (DIP) for Narragansett Bay under prehistoric conditions was the coastal ocean water entrained in the bay in estuarine circulation. The total input of DIN to this estuary has increased about five-fold and the input of total DIP has approximately doubled as a result of human activities. Recent ecosystem-level experiments using large (13 m³, 5 m deep) mesocosms designed as living models of Narragansett Bay showed that the primary production of phytoplankton in the bay is limited by the supply of DIN and that annual phytoplankton production is strongly correlated with the rate of input of DIN. The relationship between DIN input and annual phytoplankton production in the mesocosms is consistent with observations published by others working in 10 different natural marine systems, and a functional regression of the field and experimental data provides a tool to calculate the rate of prehistoric phytoplankton production that would have been associated with the prehistoric DIN input estimates. The result of this calculation suggests that phytoplankton production in the bay has approximately doubled (from about 130 g C m^?2 yr^?1 to 290 g C m^?2 yr^?1 for a baywide average) since the time of European contact. It also seems likely that seagrasses and macroalgae once made a much larger contribution to total system production than they do today.     

Metal–organic matter interaction: Ecological roles of ligands in oceanic DOM

The ecological roles of dissolved organic matter (DOM) in seawater have not been well understood. One definite function of DOM stems from its complexation ability with trace metals under the conditions of seawater. A chemical complexation model of the marine system was introduced in order to clarify the ecological roles of strong organic ligands in DOM related to the acquisition of bioactive metals (Cu, Fe and Zn) by phytoplankton, assuming that two types of strong organic ligands coexist in oceanic DOM and complexes with bioactive metals. The results reveal that the weaker organic ligand, rather than the stronger one, plays a significant role in the reduction of Cu toxicity for phytoplankton growth. It is suggested that the presence of reactions with Cu that are competitive to the strong organic ligand causes extremely low Fe concentrations in seawater and leads to Fe deficiency for phytoplankton growth. Therefore, it is concluded that the strong ligands in DOM play a chemical role in controlling free ion concentration levels of bioactive metals in the marine environment.     

New observations on the relative sea level and deglacial history of Greenland from Innaarsuit, Disko Bugt

Relative sea level (RSL) data derived from isolation basins at Innaarsuit, a site on the south shores of the large marine embayment of Disko Bugt, West Greenland, record rapid RSL fall from the marine limit (ca. 108 m) at 10,300-9900 cal yr B.P. to reach the present sea level at 3500 cal yr B.P. Since 2000 cal yr B.P., RSL rose ca. 3 m to the present. When compared with data from elsewhere in Disko Bugt, our results suggest that the embayment was deglaciated later and more quickly than previously thought, at or slightly before 10,300 cal yr B.P. The northern part of Disko Bugt experienced less rebound (ca. 10 m at 6000 cal yr B.P.) compared with areas to the south. Submergence during the late Holocene supports a model of crustal down-warping as a result of renewed ice-sheet growth during the neoglacial. There is little evidence for west to east differences in crustal rebound across the southern shores of Disko Bugt.     

海洋浮游植物群落的比生长率

系统地介绍了海洋浮游植物群落比生长率(μ)及其相关概念。介绍和比较分析了研究μ的细胞分裂周期法、生物化学指示物法、模型法和去除摄食者稀释法这4类方法,推荐去除摄食者稀释法作为中国近海μ研究的重要方法。比较各海区μ的分布规律,初步发现：① μ与群落物种组成密切相关;② μ在大洋低于近岸;③ μ在近岸中等营养高于富营养水域;④ 小粒径浮游植物μ高于大粒径浮游植物。但还有很多未知的情况,尤其是在中国海区此类工作还很薄弱,需加强,为更深入了解海洋生态系统奠定基础。     

Variability in inorganic and organic nitrogen uptake associated with riverine nutrient input in the Gulf of Riga, Baltic Sea

Concentrations and rates of uptake of dissolved organic nitrogen (DON, free amino acids, and urea) and inorganic nitrogen (DIN, nitrate, and ammonium) were measured along two transects in the Gulf of Riga, a sub-basin of the Baltic Sea, during May and July 1996. Concentrations of total dissolved nitrogen (TDN) were 23±3 μg-at N 1⁻¹ in the northern region (mouth) and 41±5 μg-at N 1⁻¹ in the southern region (head) of the Gulf. Rates of nitrogen uptake, determined with¹⁵N-labeled substrates, reflected differences in TDN concentration between the regions. In May, uptake of DIN+DON measured 0.17 and 0.43 μg-at N 1⁻¹ h⁻¹ in the northern and southern parts of the Gulf, respectively. In July, DIN+DON uptake measured 0.38 and 0.68 μg-at N 1⁻¹ h⁻¹ in the north and south, respectively. Most of the variability in total nitrogen flux between the northern and southern regions was due to heterogeneity of DON utilization. Uptake of urea and dissolved free amino acid were up to 6 and 3 times greater in the south compared to the north. As evidenced by size-fractionation, plankton size structure appeared to play a role in the uptake of DON. The community in the southern part was largely composed of cells <5 μm, while up to 67% of the community in the northern part was composed of cells >5 μm. Our results indicate that DON was a major source of nitrogen to phytoplankton, particularly in the southern part of the Gulf.     

Nutrient enrichments and phytoplankton growth in the surface waters of the Louisiana Bight

Nitrate concentrations have increased twofold in the Mississippi River during the past three decades. The increased nitrogen loading to the Louisiana shelf has been postulated as a factor leading to eutrophication and the subsequent development of hypoxia west of the Mississippi River delta. While ratios of nitrogen:phosphorus and nitrogen:silica are relatively high in surface waters on the western Louisiana shelf, nitrogen has been posed as the ‘limiting’ nutrient in this region. Bioassays were performed with nutrient additions to surface waters collected from the Louisiana shelf to examine the potential for specific nutrient limitation. Experiments were conducted in March and September 1991, and May 1992. The growth responses of natural and cultured phytoplankton populations were determined by measuring the time course of in vivo and 3-(3,4 dichlorophenyl)-1, 1-dimethylurea (DCMU)-induced fluorescence, as well as initial and final chlorophylla concentrations. The results suggest that phosphate and silicate potentially limit phytoplankton growth during the winter-spring, particularly at low salinities. In late summer, in contrast, nitrogen limitation may be prominent at higher salinities.     

Algal activity of dissolved organic nitrogen (DON) in the sediments of Lake Taihu,Eastern China

Understanding the contents and reactivity of dissolved organic nitrogen (DON) is important for illustrating its productivity contribution in aquatic ecosystem. The primary objective of this study was to investigate the characteristics and algal activity of DON in the sediments of Lake Taihu. A series of experiments were carried out to evaluate the algal bioavailability of DON fractions in the sediments of Lake Taihu, Eastern China. DON extracted in the lake sediments was separated into hydrophilic and hydrophobic forms by DAX-8 resin, and ammonia nitrogen in raw sample and hydrophilic fraction was removed by cation exchange resin. 77.42–109.18% DON recovery rates were obtained after DON fractionation at ZSW and DPG stations. The hydrophilic DON was the main DON form contributing 62.74–76.33% of total DON concentrations. Selenastrum capricornutum was incubated for 15 days with different nitrogen forms (raw sample, hydrophilic and hydrophobic fractions). Approximately 33.69–79.23% DON of the three fractions was available for algal uptake in the incubation. The order of DON bioavailability was ranked as follows: raw sample > hydrophilic fraction > hydrophobic fraction, indicating that hydrophilic fractions and raw samples exhibited higher DON bioavailability for algae. Parallel factor analysis resulted in identification of tryptophan-like proteins, tyrosine-like proteins and humic acid (HA)-like substances during the incubation periods. During the growth phase, the relative fluorescent intensities of tryptophan-like proteins, tyrosine-like substance and HA-like substance accumulated greatly with 24.84–26.38, 27.82–62.73 and 0–28.92%, respectively.     

Nutrient and phytoplankton dynamics in a sewage-impacted Gulf coast estuary: A field test of the PEG-model and equilibrium resource competition theory

Eutrophication and noxious bloom events are becoming more prevalent with increasing anthropogenic activities. To lessen ecological damage, there is a need to develop phytoplankton management programs aimed at enhancing growth of beneficial algae. The success of such management schemes with be dependent on the predictability of phytoplankton succession within the target system to a controlled perturbation. Freshwater lakes appear to exhibit a degree of predictability as described by the PEG-model and Equilibrium Resource Competition theory. We investigated whether these concepts could be applied to a marine system, the Nueces River estuary, Texas. The PEG-model predicted nicely the initial occurrence of edible phytoplankton forms after a favorable nutrient perturbation. Equilibrium Resource Competition theory, however, only successfully predicted the occurrence of major phytoplankton taxa immediately after a nutrient perturbation. Systemwide correlations between N:P and cyanobacteria, green algae, and diatoms were poor. In the Nueces River estuary, succession within the phytoplankton community showed a degree of predictability to nutrient perturbations. Therefore, management of the phytoplankton community composition may be possible. The PEG-model appears to be a useful guide for a phytoplankton management scheme, while the utility of Equilibrium Resource Competition may be limited.     

Taphonomy at two contiguous coastal rockshelters in Panama: Preliminary observations focusing on fishing and curing fish

The scarcity of animal products negatively influences nutrition in tropical inland areas, which lack large rivers. Consuming cured marine fish mitigates this deficiency. In Panama, trading cured fish from coastal to inland sites is documented ethnohistorically and can be inferred from the current archaeozoological record. Very large numbers of marine fish remains have been recovered at pre-Columbian sites located on and around Parita Bay, a mangrove-fringed estuary on the central Pacific coast. At Sitio Sierra, a farming village 12 km inland from the active marine shore, more than 70% of fish remains deposited between ca. 1800 and 1500 uncalibrated radiocarbon years BP proved to be of marine origin. Two small rock-shelters located downriver from Sitio Sierra and now 2.6 km from the marine shore (Vampiros-1 and Vampiros-2) show evidence for having been used intensively for fishing and preparing fish between ca. 2200 and 1900 BP. A prior model based on air photograph interpretation and sedimentological analyses of marine and terrigenous sediments suggest that these shelters would have been on or very near the active marine shore at this time. A much earlier occupation at Vampiros-1 dating to ca. 11,500–7700 BP corresponds to pre-agricultural (Paleoindian) and early agricultural (Early Preceramic) people who camped occasionally in this shelter when the transgressing ocean was in the process of flooding Parita Bay. No shell or bone was recovered in this earlier cultural component. In the more recent (2200–1900 BP), component abundant remains of marine mollusks and crustaceans and vertebrate bones (mostly fish) are in excellent condition. A synopsis of the geological and cultural history of the Vampiros shelters is followed by preliminary observations on the relationship between pre-Columbian human activities and these sites’ formation processes, soil chemistry, bone integrity and animal species. Evidence is accruing for human impacts on fish skeletons resulting from the in situ preparation of fish (i.e., gutting, cutting and smoking) providing the opportunity to compare our archaeofaunal data with the results of Irit Zohar's ethno-archeological research, which identified how preparing fish for salting and sun-drying at present-day Panamanian fishing villages around Parita Bay affects the fish skeleton physically and proportionally. There is a strong possibility that the Vampiros shelters were used to provision inland sites like Sitio Sierra with inshore marine fish although we cannot yet ascertain the means by which coastal foodstuffs may have arrived at the latter site.     

海洋次表层叶绿素最大值的特征因子及其影响因素

在多数情况下,海水中叶绿素垂直分布是不均匀的。次表层叶绿素最大值是其中较为常见的一种形式,普遍存在于大洋及沿岸海域。次表层叶绿素最大值层(SCML)的深度、厚度与强度是表征海洋次表层叶绿素最大值(SCM)现象的主要特征因子,受海洋水文环境、营养盐分布以及浮游植物种类等因素共同影响,在不同季节不同海区的分布有较大差异。总体上,相对近海,大洋中SCML特征因子的季节变化较小,SCML深度较大,厚度较大,强度较小。寡营养盐海区SCML深度及强度的影响因素研究已有较明确结论,SCML深度主要受物理因素(光照条件及水体混合程度)影响,而强度则受物理、生物因素(光照条件、水体混合程度或浮游动物摄食等)共同影响。近海富营养盐海区,SCML特征因子的影响因素研究较为薄弱。长时间序列、高分辨率观测站在相应海区的建立,对推进海洋SCM,尤其是近海SCM的研究有重要意义。卫星观测、现场观测和数学模型相结合,定量研究SCML特征因子与各物理、生物、化学因子的普适性关系,是进一步研究SCML特征因子的重要方向之一。     

Pre-salt to salt stratigraphic architecture in a rift basin: insights from a basin-scale study of the Gulf of Suez (Egypt)

We propose a basin-scale (～300 × 100 km) study of the pre-salt to salt sedimentary fill from the Suez rift based on outcrop and subsurface data. This study is a new synthesis of existing and newly acquired data using an integrated approach with (1) basin-scale synthesis of the structural framework, (2) stratigraphic architecture characterization of the entire Suez rift using sequence stratigraphy concepts, (3) lithologic maps reconstruction and interpretation, (4) isopach/depocenter maps interpolation to quantify sedimentary volumes, and (5) quantification of the sediment supply, mean carbonate and evaporite accumulation rates, and their integration into the rift dynamic. The Gulf of Suez is ca. 300-km-long and up to 80-km-wide rift structure, resulting from the late Oligocene to early Miocene rifting of the African and Arabian plates. The stratigraphic architecture has recorded five main stages of rift evolution, from rift initiation to finally tectonic quiescence characterized by salt deposits. Rift initiation (ca. 1–4 Myr duration): the Suez rift was initiated at the end of the Oligocene along the NNW-SSE trend of the Red Sea with evidences of active volcanism. Continental to lacustrine deposits only occurred in isolated depocenters. Sediment supply was relatively low. Rift widening (ca. 3 Myr duration): the rift propagated from south to north (Aquitanian), with first marine incursions from the Mediterranean Sea. The rift was subdivided into numerous depocenters controlled by active faults. Sedimentation was characterized by small carbonate platforms and associated sabkha deposits to the south and shallow open marine condition to the north with mixed sedimentation organized into an overall transgressive trend. Rift climax (ca. 5 Myr duration): the rift was then flooded during Burdigalian times recording the connection between the Mediterranean Sea and the Red Sea. The faults were gradually connected and reliefs on the rift shoulders were high as evidenced by a strong increase of the uplift/subsidence rates and sediment supply. Three main depocenters were then individualized across the rift and correspond to the Darag, Central, and Southern basins. Sedimentation was characterized by very large Gilbert-type deltas along the eastern margin and associated submarine fans and turbidite systems along the basin axis. Isolated carbonate platforms and reefs mainly occurred in the Southern basin and along tilted block crests. Late syn-rift to rift narrowing (ca. 4 Myr duration): during the Langhian, the basin recorded several falls of relative sea level and bathymetry in the rift axis was progressively reduced. The former reliefs induced during the rift climax were quickly destroyed as evidenced by the drastic drop in sediment supply. Stratigraphic reconstruction indicates that the Central basin was restricted during lowstand period; meanwhile, open marine conditions prevailed to the north and south of the Suez rift. The Central basin, Zaafarana, and Morgan accommodation zones thus acted as a major divide between the Mediterranean Sea and the Red Sea. During Serravalian times, the Suez rift also recorded several disconnections between the Mediterranean and Red seas as evidenced by massive evaporites in major fault-controlled depocenters. The Suez rift was occasionally characterized by N–S paleogeographic gradient with restricted setting to the north and open marine setting to the south (Red Sea). Tectonic quiescence to latest syn-rift (ca. 7 Myr duration): the Tortonian was then characterized by the deposition of very thick salt series (>1000 m) which recorded a period of maximum restriction for the Suez rift. The basin was still subdivided into several sub-basins bounded by major faults. The basin with a N-S paleogeographic gradient was totally and permanently disconnected from the Mediterranean Sea and connected to open marine condition via the Red Sea. The Messinian was also characterized by a thick salt series, but the evaporite typology and sedimentary systems distribution suggest a more humid climate than during Tortonian times. Pre-salt to salt transition was not sharp and lasted for ca. 4 Myr (Langhian-Serravalian). It was initiated as the result of the combined effect of (1) climatic changes with aridization and low water input from the catchments and (2) rift dynamic induced by plate tectonic reorganization that controlled the interplay between sea level and accommodation zones constituting sills.     

海洋浮游生态系统中小型浮游动物的生态功能

小型浮游动物在海洋生态系统中的作用,主要指有多少能量通过小型浮游动物传递到桡足类,从而比较沿"浮游植物→中型浮游动物"和"浮游植物+细菌→小型浮游动物→中型浮游动物"两条食物链到达中型浮游动物的能流大小.为达到这个目的,需要研究各个能流路径的传递效率,即能量在各个营养级(初级生产--小型浮游动物,细菌生产--小型浮游动物,小型浮游动物的生长率,小型浮游动物--中型浮游动物)的传递效率.综述了国内外对上述营养级传递效率的研究现状,以期为我国的同类研究提供参考.浮游植物初级生产力被小型浮游动物摄食的比例平均为每天60%～75%,大大高于桡足类对浮游植物初级生产力的摄食压力每天10%.海洋浮游细茵的二次生产力相当于初级生产力的30%.其中80%～180%被小型浮游动物摄食.小型浮游动物的毛生长率为30%～40%,生产力是初级生产力的21%～34%.在西班牙西北部沿海,桡足类每天摄食2%～51%小型浮游动物生产力.因此,桡足类通过微食物网摄食的能量是初级生产力的0.4%～17%,与桡足类摄食初级生产的10%处于同一量级.不考虑碎屑提供的能流,小型浮游动物对桡足类饵料的贡献为20%以上,甚至可高达50%.     

Transformation of phosphorus in the Elbe estuary

The distribution of dissolved and particle-bound phosphorus (P) was investigated in the Elbe estuary during March 1995. The forms of particulate P were studied with a sequential extraction technique. Organic P dominated particle-bound P in the outer reaches of the estuary (52%), decreased to a minimum of 21% in the turbidity zone, and increased to 33% further upstream. Fe-bound P was the second most important P species in the outer reaches (27%) and dominated in the turbidity zone (up to 57%) and upstream of the turbidity zone (up to 48%). The P:Fe ratio increased with decreasing salinity, from 0.11 in the outer reaches to about 0.22 at zero salinity. Dissolved inorganic P release from reverine suspended matter was about two to three times larger than release, from marine suspended matter and was dominated by release of Fe-bound P. Dissolved inorganic P release from marine and from riverine organic matter were of equal importance. Because marine suspended matter dominates in the estuary, this suggests riverine organic matter is remineralized much faster than marine organic matter. This is in line with the refractory nature of marine organic matter (no phytoplankton bloom) and the easily degradable character of the riverine suspended matter (phytoplankton bloom) in the Elbe estuary during March 1995.