Seasonal variation in the flux of planktonic foraminifera: time series sediment trap results from the Panama Basin

A mooring array with three automated sediment traps capable of collecting time series samples was deployed in the Panama Basin for one year beginning in December 1979. A series of six consecutive two-month long samples was collected at each of three depths (890, 2590 and 3560 m) in order to examine seasonal variation in the flux of planktonic foraminifera, and evaluate the contribution of foraminifera to the total carbonate flux.The flux of the larger planktonic foraminifera (250–500 μm and 500–1000 μm) is greatest during February–March when upwelling is most intense in the Panama Basin. In contrast, the maximum flux of the smaller foraminifera (125–250 μm) is associated with a phytoplankton bloom during the summer months (June through September). This size-dependent flux pattern appears to be a species specific effect. The flux of the larger foraminifera is dominated by non-spinose forms (i.e. Neogloboquadrina dutertrei and Globorotalia theyeri), while the flux of the smaller foraminifera consists predominantly of spinose species (i.e. Globigerinoides ruber, G. sacculifer and G. conglobatus). Although the magnitude of the flux varied throughout the year, the average weight of individual foraminiferal tests in different size fractions showed no seasonal variability.With the exception of the June–July period when there was a major coccolith bloom, planktonic foraminifera greater than 125 μm account for between 28 and 34% of the total carbonate flux at this location. During the coccolith bloom, planktonic foraminifera accounted for less than 2% of the total carbonate flux. Planktonic foraminifera in the 250–500 μm size range are the most significant contributors to the overall particulate flux, accounting for roughly 70–80% of the total foraminiferal fluxes measured at the three trap depths.     

Carbon isotopic compositions of Recent planktonic foraminifera of the Indian Ocean

Carbon and oxygen isotopic determinations have been made of 29 species of Recent Indian Ocean planktonic foraminifera. Fourteen core-top samples were used and as many as 18 species were chosen from a single core-top sample. The δ¹³C of the foraminifera was compared with that of total dissolved CO₂ (ΣCO₂) and of calcite precipitated in isotopic equilibrium with ΣCO₂. The foraminiferal calcite is always at least 1.2‰ less than the value estimated for equilibrium calcite. This carbon isotopic disequilibrium suggests the partial utilization of¹³C-depleted metabolic CO₂. The calcite tests of several species, however, have δ¹³C values which are similar to the δ¹³C of ΣCO₂ in seawater. This relationship suggests that important paleohydrographic information may be obtained from carbon isotope records based on analyses of several foraminiferal species from single deep-sea sediment samples.     

Quantity, composition, and source of sediment collected in sediment traps along the fringing coral reef off Molokai, Hawaii

Sediment traps were used to evaluate the frequency, cause, and relative intensity of sediment mobility/resuspension along the fringing coral reef off southern Molokai (February 2000-May 2002). Two storms with high rainfall, floods, and exceptionally high waves resulted in sediment collection rates>1000 times higher than during non-storm periods, primarily because of sediment resuspension by waves. Based on quantity and composition of trapped sediment, floods recharged the reef flat with land-derived sediment, but had a low potential for burying coral on the fore reef when accompanied by high waves. The trapped sediments have low concentrations of anthropogenic metals. The magnetic properties of trapped sediment may provide information about the sources of land-derived sediment reaching the fore reef. The high trapping rate and low sediment cover indicate that coral surfaces on the fore reef are exposed to transient resuspended sediment, and that the traps do not measure net sediment accumulation on the reef surface.     

Bacterial growth and the decomposition of particulate organic carbon collected in sediment traps

We have studied bacterial abundance and production in samples from sediment traps deployed for 1 and 100 days in several areas of the shelf and slope regions of the Middle Atlantic Bight, U.S.A. By making a series of assumptions about bacterial growth at the expense of POC in traps, we have estimated that the turnover time of organic particles collected in traps during long deployments is slow (mean 1500 ± 300 days), if only bacterial activity is considered. However the abundance and biomass of bacteria in traps is very high, ranging from 3 to 30 × 10¹¹ cells gC^?1, i.e., 0.3 to 3% of the POC is bacterial carbon. Fifteen to 88% of the particles in traps were colonized by bacteria, but usually about half the particles had only 0 to 1 cell attached. Growth of bacteria was observed at all scales relevant to these trap deployments; over periods ranging from hours to weeks, at rates of 0.01 to 0.3 d^?1. In spite of slow growth, bacteria appeared to be physiologically active in that [³H]adenine and [³H]thymidine were incorporated more rapidly into RNA and protein than into DNA. Total incorporation rates were high. We conclude that even relatively old (ca. 1 y) POC in sediment traps supports high levels of active bacterial biomass, but that POC decomposition is slow, so that bacteria may not be the principal agents of POC turnover following collection.     

Seasonal and ontogenetic changes of mycosporine-like amino acids in planktonic organisms from an alpine lake

We studied the quantitative and qualitative mycosporine-like amino acid (MAA) composition in phytoplankton and the copepod Cyclops abyssorum tatricus from an alpine lake over a 15-month period. Up to eight MAAs were identified in the samples, with shinorine being predominant. The MAAs occurred year round and showed a strong seasonal pattern. Compared with ice-cover periods, concentrations during the summer were on average 3.6 and 3.0 times higher in phytoplankton and C. abyssorum tatricus, respectively. During the summer, the contents of MAAs in phytoplankton decreased with depth, suggesting their photoprotective role. Chlorophyll a-specific concentrations of MAAs in phytoplankton correlated significantly with the incident solar radiation and ultraviolet (UV) water transparency (r(2) ≤ 0.36), however, the strongest relationship was found with water temperature (r(2) = 0.67). In zooplankton, highest contents of MAAs were found in eggs, nauplii, and young copepodids, presumably providing a high level of photoprotection for progeny. Proportions of the dominant MAAs in the copepod showed seasonal and ontogenetic variations, which were consistent with relative changes in the predominant MAA, but not other abundant MAAs, in phytoplankton. Considering a time lag of approximately 1 month between the synthesis and subsequent accumulation of these compounds, MAA concentrations in late copepodid to adult life stages were significantly correlated to those in phytoplankton. Annual patterns in MAAs with high concentrations during periods of elevated environmental stress are consistent with the idea that these compounds play an important role in protecting aquatic organisms against UV damage.     

The effects of oil exploration and production in the Fladen Ground: composition and concentration of hydrocarbons in sediment samples collected during 2001 and their comparison with sediment samples collected in 1989

Due to the potentially accumulative nature of the Fladen Ground, an area of intense oil activity in the North Sea, a survey was carried out in 1989 to map the distribution of contamination in relation to these oil activities. All the sediments collected were screened by ultraviolet fluorescence (UVF) for polycyclic aromatic hydrocarbons (PAHs) and selected samples were analysed for n-alkanes (by GC-FID), PAHs and biomarkers (by GC-MSD). This survey was repeated in 2001, with all the 1989 sites being resampled. All of these sediments were analysed for UVF oil equivalents, PAHs, n-alkanes and biomarkers. The concentrations of these parameters decreased between 1989 and 2001, with average decreases ranging from 43% to 88%. In addition, no significant difference was found, for all the parameters, between near field (<5 km from an oil installation) and far field (>5 km from an oil installation) sites in 2001 indicating that the Fladen Ground is approaching a 'steady state' or background concentration for contamination.     

Carbon isotopic composition and genetic types of natural gas in the Sichuan Basin,China

The origin and genetic types of natural gas in the Sichuan Basin are still disputed.To classify the origin and genetic types in different areas,the paper analyzes the carbon isotopic composition of gases and geologic features in the Sichuan Basin.The results showed that the gas sourced from terrestrial layers is typically characterized by terrestrial origin and was mainly accumulated nearby to form reservoir.The carbon isotopic composition of gas showed a normal combination sequence distribution,suggesting that natural gas in continental strata is not affected by secondary alteration or that this deformation is very weak.The gas source is singular,and only gas from the southern and northern Sichuan Basin shows the characteristic of mixed sources.However,marine gas presents the characteristics of an oil-formed gas.The carbon isotopic composition of natural gas in the western and central part of the basin mostly distributes in a normal combination sequence,and few of them showed an inversion,indicating that the gas perhaps had not experienced secondary alteration.The carbon isotopic composition of marine-origin gas in the southern,northern and eastern Sichuan Basin displays a completely different distribution pattern,which is probably caused by different mixing ratio of gas with multi-source and multi-period.     

Seasonal variations in the isotopic composition of leaf and stem water from an arid region of Southeast Asia

Abstract

Stable isotopes are powerful research tools in environmental sciences and their use in ecosystem research is increasing. Stable isotope measurements allow the study of evapotranspiration fluxes, soil evaporation and leaf transpiration phenomena. Soil water and leaf water are the sources of the evapotranspiration that transfers large quantities of water from land to the atmosphere; as a result the isotopic composition of water left in the leaves is modified towards enrichment. Evaporation also changes the isotopic composition of water bodies creating a natural isotopic signal. The isotopic identity of soil water affects the oxygen isotopic signature of leaf and stem water. In this paper we present the isotopic data of bulk leaf water, showing the enrichment in isotopic value of oxygen due to evapotranspiration from leaves in conjunction with the isotopic signal of rainwater and other environmental factors such as humidity and temperature. Results suggest that the variation in the values of δ¹⁸O of Eucalyptus citriodora, Dalbergia sissoo, Melia azedarach and Pinus roxburghii is due to the seasonal changes in the δ¹⁸O of the source water for plants, i. e. rain. It is further observed that leaf water δ¹⁸O values are depleted during the months of July, August and September. This occurs due to the following reasons: (a) the sampling areas receive about 50% of the average annual rain during these months, and (b) rainfalls during these months are isotopically depleted compared with winter rains.

Citation Butt, S., Ali, M., Fazil, M. & Latif, Z. (2010) Seasonal variations in the isotopic composition of leaf and stem water from an arid region of Southeast Asia. Hydrol. Sci. J. 55(5), 844–848.     

Stable carbon and nitrogen isotopic composition of gas hydrate-bearing sediment from Hydrate Ridge,Cascadia Margin

Serious interest has been directed toward natural gas hydrate as a potential energy resource; factor in global climate change, and submarine geohazard since naturally occurring gas-hydrate deposits were found in the 1960s. Hydrate Ridge, Cascadia convergent mar- gin, is characterized by abundant methane hydrates at and below the seafloor, active venting of fluids and gases, chemosynthetic communities, and some of the highest methane oxidation rates ever found in the ma-rine environment. All of…     

Large 14C age offsets between the fine fraction and coexisting planktonic foraminifera in shallow Caribbean sediments

Absolute chronologies in paleoceanographic records are often constructed using the ¹⁴C dating of coarse fraction foraminifera (>150 μm). However, due to processes such as changes in sediment sources or abundances, sedimentation rates, bioturbation, reworking, the adsorption of modern carbon, etc., several studies conducted in different environmental settings have shown time-lags between records obtained from various granulometric fractions. In this study, we examined temporal phasing between the coarse foraminifera and fine fractions by studying changes in the abundances of δ¹⁸O, the ¹⁴C ages of the planktonic foraminifera Globigerinoides ruber (G. ruber, 250–350 μm), and the sediment fine fraction (<63 μm) over the last 45 ka in a core obtained from the northern Caribbean Sea. All of the records were found to be in phase during part of the Holocene (at least for the last ≈6 ka). As determined from δ¹⁸O records and ¹⁴C ages, the fine fraction was younger than G. ruber during the Last Deglaciation (of 1.89 ka). The coupling between bioturbation and changes in the fine fraction, and G. ruber abundances, as tested using a numerical model of the bioturbation record within a mixed-layer depth of 8 cm, was sufficient to explain the results. ¹⁴C age discrepancies increased from 5.64 to 8.5 ka during Marine Isotopic Stages (MIS) 2 and 3, respectively. These chronological discrepancies could not be explained by only one process and seemed to result from the interplay between mechanisms: size-differentiated bioturbation (for 1.5 to 2.5 ka), the adsorption of modern atmospheric CO₂ (for 3.04 to 5.92 ka), and variations in sedimentological processes that influenced the fine carbonate fraction. However, even if variations in the mineralogical composition of the fine carbonate fraction were identified using scanning-electron microscopy observations, X-ray diffraction measurements, and geochemical analyses (the mol % MgCO₃ of magnesian calcite and the Sr/Ca ratio of the bulk fine fraction), they can not account for the observed age differences. The results presented for core MD03-2628 extend beyond this case study because they illustrate the need for a detailed characterization of the various size fractions prior to paleoclimate signal interpretations, especially for chronological studies.     

南京市两个小型富营养湖泊浮游硅藻的季节性变化

为研究浅水富营养湖泊硅藻季节演替的规律,选择南京两个城市湖泊(前湖和月牙湖)作为对象,对水体硅藻和水质进行逐月采样和实验分析,结合数理统计分析手段,对2006年硅藻浓度、种群组合变化及其与环境因子的关系进行了讨论,结果表明:两湖硅藻都呈现较明显的季节演替特点,冬季浮游硅藻组合主要由Cyclostephanos的种类为主,代表了冷水富营养种组合类型:夏季和秋季以Cyclotella atomus和C.meneghiniana暖水耐营养种优势组合为主,硅藻和环境指标月富营养湖泊,春季硅藻丰度增加对初级生产量的贡献很小;随着营养程度的不断提高,温度对浮游硅藻的限制更为突出.     

Eutrophication of lake lugano ‘read’ by means of planktonic remains in the sediment

The trophic evolution of Lake Lugano has been studied by examination of Cladoceran remains and P, N and C in the sediment. The frequency ofBosmina remains has increased in recent years andSida has gradually decreased; today it is completely eliminated.Acroperus harpac is influenced by man's activities in the littoral zone. A clear relationship between P concentration in the sediment and the ratios between the Cladoceran species is evident.     

Using a Lagrangian model to estimate source regions of particles in sediment traps

A Lagrangian model is used to evaluate source regions of particles collected in the sediment traps at the DYFAMED(Dynamique des Flux Atmosphériques en Méditerranée) station by tracking particles backwards from March 1 to August 31, 2001. The analysis suggests that source regions depend on the flow fields, the settling speed of the particles, and the deployment depths of the traps. Monthly variation is observed in the distribution patterns of source regions, which is caused by the currents. The source regions are located around the traps and up to hundreds of kilometers away. As the settling speed increases with the particle diameters, the distance to the source regions decreases. The vertical flux can be approximately estimated in 1D for the particles with diameters larger than 500 μm. Furthermore, traps moored at various depths at the DYFAMED can collect particles that originated from different regions in the Ligurian Sea.     

The isotopic composition of strontium in Central American ignimbrites

Voluminous sheets of rhyolitic ignimbrites were crupted during Miocene time in a region of Central America that is underlain by a thick sequence of middle Paleozoic and older metamorphic and plutonic rocks. Strontium isotopic ratios of fifteen ignimbrites range from 0.7035 to as high as 0.7175. These values are markedly higher than those measured for cale-alkaline lavas of the same province, but overlap the range found in basement rocks that may have served as source rocks for anateetic magmas. This relationship is in contrast to that found in the western United States where siliceous ignimbrites are not significantly richer in radiogenic strontium than are the basalt erupted through the same basement series. Several possible models for the origin of the large volumes of siliceous magma are examined in terms of major-element and isotopic relations, experimental studies of phase relations, and the thermal requirements of melting or assimilating basement rocks. A mathematical model for the effects of assimilation in open and closed systems permits a comparison of predicted chemical and isotopic compositions with those observed and places limits on the plausibility of various schemes of contamination with or without concurrent crystal fractionation. None of the models is without its flaws. Recent suggestions that large volumes of siliceous magma may be derived from the mantle or lower crust explain certain aspects of the Central American ignimbrites very well if one postulates that the high strontium ratios resulted from contamination of the magma with radiogenic strontium released by the break-down of mieas in basement rocks through which the magmas rose. Such a model fails to explain the apparent restriction of large rhyolitic ignimbrite cruptions to areas underlain by thick continental crust.     

Evolution of planktonic foraminifera and thermocline in the southern South China Sea since 12 Ma (ODP-184, Site 1143)

Down-core variation in planktonic foraminifera (PF) at Site 1143 (ODP 184) has disclosed the evolution of upper water-column structure over the last 12 Ma in the southern South China Sea. In the early Late Miocene (∽10.6–7.8 Ma), there existed a lower percentage of total deep-dwelling species, reflecting a water thermocline deeper than that in the Middle Miocene, which resulted from the closure of Indonesian seaway and relevant intensification of the equatorial warm current. After the increase in deep-dwelling PF and the rising of thermocline during the late Late Miocene (7.6–6.4 Ma), the total deep-dwelling species decreased gradually from late Late Miocene (6.4 Ma) to the Pliocene, implying the deepening of water thermocline. The evolution of thermocline depth in the southern South China Sea reflected by the PF at Site 1143 might be a good indicator of the change of west Pacific “warm pool”.     

Implications of dredging induced changes in sediment particle size composition for the structure and function of marine benthic macrofaunal communities

A meta-analysis approach was used to assess the effect of dredging induced changes in sediment composition, under different conditions of natural physical disturbance, for the structure and function of marine benthic macrofaunal communities. Results showed the sensitivity of macrofaunal communities increased as both the proportion of gravel increased and the level of natural physical disturbance decreased. These findings may be explained by the close association of certain taxa with the gravel fraction, and the influence of natural physical disturbance which, as it increases, tends to restrict the colonisation by these species. We conclude that maintaining the gravel content of surface sediments after dredging and, where practicable, locating extraction sites in areas of higher natural disturbance will minimise the potential for long-term negative impacts on the macrofauna.