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1.
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2.
Large, mesopelagic teleost fishes have a potentially keystone position in the ecology of the pelagic water column, yet remain relatively unstudied when compared with large, commercially important, epipelagic fishes. Here, the ecological roles of four, large, vertically migrating teleosts were examined. Stomach content analyses were performed on 48 oilfish (Ruvettus pretiosis), 35 escolar (Lepidocybium flavobrunneum), 32 snake mackerel (Gempylus serpens) and seven lancetfish (Alepisaurus spp.) collected from pelagic longline gear in the Western North Atlantic Ocean from 2007 to 2010. Of these specimens, stable carbon and nitrogen isotope analyses were also performed on white dorsal muscle tissue from 33 oilfish, 16 escolar, 27 snake mackerel and seven lancetfish. Based on literature length‐at‐maturity values, all escolar, snake mackerel and lancetfish specimens were mature, while 13 of the 33 oilfish were juveniles. Crustaceans, annelids, salps, cephalopods and teleosts were present in the stomachs and were presumed to be prey items. A Kruskal–Wallis test showed the four species to be isotopically segregated in both δ13C and δ15N. Escolar were the most depleted in δ13C, followed by adult oilfish, juvenile oilfish and lancetfish, with snake mackerel the most enriched. The depletion in δ13C of adult oilfish and escolar may have been attributable to high C/N values, which were strongly correlated with length in oilfish, weakly correlated with length in escolar and moderately correlated with length in snake mackerel and lancetfish. The high C/N was likely due to the high lipid concentration of these fishes. Other factors that may have contributed to the depletion in δ13C may include spawning or a change in carbon source within the ecosystem. Large escolar occupied the highest trophic level (δ15N = 10.20), followed by snake mackerel (δ15N = 9.66), adult oilfish (δ15N = 9.32), lancetfish (δ15N = 9.05) and juvenile oilfish (δ15N = 7.83). A marked change in oilfish δ13C and C/N at 30–35 cm fork length coincided with a presumed length‐at‐maturity.  相似文献   

3.
Sinking particles were analyzed for their nitrogen isotopic ratio δ15N) of total particulate nitrogen (PN), stable carbon isotopic ratio (δ13C) and radioactive isotopic ratio (δ14C) of total particulate organic carbon (POC), at three different latitudinal (temperate, subpolar and equatorial) and geomorphological (trench, proximal abyssal plain and distal abyssal plain) sites in the western North Pacific Ocean using year-long time series sediment trap systems, to clarify the common vertical trends of the isotopic signals in deep water columns. Although the δ15N and δ13C values of sinking particulate organic matter (POM) were partly affected by the resuspension of sedimentary POM from the sea floor, especially in the trench, the changes in δ15N and δ13C values owing to the resuspension could be corrected by calculation of the isotopic mass balance from δ14C of sinking POC. After this correction, common downward decreasing trends in δ15N and δ13C values were obtained in the deep water columns, irrespective of the latitudes and depths. These coincidental isotopic signals between δ15N and δ13C values provide new constraints for the decomposition process of sinking POM, such as the preferential degradation of 15N- and 13C-rich compounds and the successive re-formation of the sinking particles by higher trophic level organisms in the deep water column.  相似文献   

4.
In this paper, we emphasize the importance of understanding the nesting ecology and nesting behaviour of green marine turtles (Chelonia mydas). Data were collected from 2007 until 2012 from nesting beaches at Setiu Terengganu, Malaysia. We focused on one of the beaches, Telaga Papan, based on data collected in 2012. We recorded the distribution of nesting areas, the emergence hour and the correlation between successful nesting attempts and false crawls. Telaga Papan had a significantly higher distribution of green marine turtle nesting compared with the other five beaches (ANOVA, F5,42 = 8.874, P < 0.01, mean = 36.750 ± 3.727). The highest number of successful nesting attempts was recorded in 2012 (mean = 28.714). A majority of the species landed between 22:00 and 23:59 h (25%). There was a strong correlation between successful nesting attempts and false crawls (rs = 0.883, P = 0.02). Based on these findings on the nesting ecology and nesting behaviour of green marine turtles, we suggest that scientific research, strict monitoring, awareness programs and policy implementation should be carried out proactively. Such activities are necessary to reduce the anthropogenic pressures at the nesting beaches as well as to ensure more successful nesting attempts of green marine turtles in Setiu.  相似文献   

5.
The Flemish Pass Basin is a deep-water basin located offshore on the continental passive margin of the Grand Banks, eastern Newfoundland, which is currently a hydrocarbon exploration target. The current study investigates the petrographic characteristics and origin of carbonate cements in the Ti-3 Member, a primary clastic reservoir interval of the Bodhrán Formation (Upper Jurassic) in the Flemish Pass Basin.The Ti-3 sandstones with average Q86.0F3.1R10.9 contain various diagenetic minerals, including calcite, pyrite, quartz overgrowth, dolomite and siderite. Based on the volume of calcite cement, the investigated sandstones can be classified into (1) calcite-cemented intervals (>20% calcite), and (2) poorly calcite-cemented intervals (porous). Petrographic analysis shows that the dominant cement is intergranular poikilotopic (300–500 μm) calcite, which stared to form extensively at early diagenesis. The precipitation of calcite occured after feldspar leaching and was followed by corrosion of quartz grains. Intergranular calcite cement hosts all-liquid inclusions mainly in the crystal core, but rare primary two-phase (liquid and vapor) fluid inclusions in the rims ((with mean homogenization temperature (Th) of 70.2 ± 4.9 °C and salinity estimates of 8.8 ± 1.2 eq. wt.% NaCl). The mean δ18O and δ13C isotopic compositions of the intergranular calcite are −8.3 ± 1.2‰, VPDB and −3.0 ± 1.3‰, VPDB, respectively; whereas, fracture-filling calcite has more depleted δ18O but similar δ13C values. The shale normalized rare earth element (REESN) patterns of calcite are generally parallel and exhibit slightly negative Ce anomalies and positive Eu anomalies. Fluid-inclusion gas ratios (CO2/CH4 and N2/Ar) of calcite cement further confirms that diagenetic fluids originated from modified seawater. Combined evidence from petrographic, microthermometric and geochemical analyses suggest that (1) the intergranular calcite cement precipitated from diagenetic fluids of mixed marine and meteoric (riverine) waters in suboxic conditions; (2)the cement was sourced from the oxidation of organic matters and the dissolution of biogenic marine carbonates within sandstone beds or adjacent silty mudstones; and (3) the late phases of the intergranular and fracture-filling calcite cements were deposited from hot circulated basinal fluids.Calcite cementation acts as a main controlling factor on the reservoir quality in the Flemish Pass reservoir sandstones. Over 75% of initial porosity was lost due to the early calcite cementation. The development of secondary porosity (mostly enlarged, moldic pores) and throats by later calcite dissolution due to maturation of organic matters (e.g., hydrocarbon and coals), was the key process in improving the reservoir quality.  相似文献   

6.
The trophodynamics of mesopelagic (macrozooplankton/micronekton) and benthic boundary layer (suprabenthos=hyperbenthos) faunas from the Algerian Basin were characterized on a seasonal scale through stable carbon and nitrogen isotopic analyses of a total of 34 species and two broad taxa (Copepoda and Cumacea). This is the first study simultaneously focused on trophodynamics of deep-sea zooplankton and suprabenthos. Samples were collected southeast of Mallorca (Algerian Basin, Western Mediterranean), on the continental slope close to Cabrera Archipelago, at 650–780 m depths, ca. bi-monthly between August 2003 and June 2004. Mean δ13C values of suprabenthos ranged from ?21.1‰ (Munnopsurus atlanticus) to ?16.7‰ (Cyclaspis longicaudata). Values of δ15N ranged from 2.8‰ (Lepechinella manco) to 9.9‰ (larvae of Gnathia sp.). The stable isotope ratios of suprabenthic fauna displayed a continuum of values, confirming a wide spectrum of feeding guilds (from filter feeders/surface deposit feeders to predators). According to the available information on diets for suprabenthic species, the highest annual mean δ15N values were found for the hematophagous isopod Gnathia sp. parasite on fish (represented by Praniza larvae) and carnivorous amphipods (e.g. Rhachotropis spp., Nicippe tumida) consuming copepods, and the lowest δ15N values were found for two cumaceans (Cyclaspis longicaudata and Platysympus typicus) feeding on detritus. Assuming a 15N-enrichment factor of 2.5‰ and deposit feeders as baseline, we found three trophic levels in suprabenthic food webs. δ13C ranges were particularly wide among deposit feeders (ranging from ?21.8% to ?17.3‰) and omnivores (from ?20.5% to ?18.8‰), suggesting exploitation of particulate organic matter (POM) of different characteristics. Our isotopic analyses revealed lower ranges of δ13C and δ15N for macrozooplankton/micronekton, compared with suprabenthos. δ13C values of zooplankton taxa ranged from ?21.1‰ (the hyperiid Phrosina semilunata) to ?19.9‰ (the decapod Pasiphaea multidentata), while δ15N values ranged from 3.9‰ (P. semilunata) to 7.5‰ (P. multidentata). Among zooplankton, more enriched δ15N values were found among carnivores (e.g. the fish Cyclothone spp. and Pasiphaea multidentata) preying on copepods, hyperiids, euphausiids and small fish. The lowest δ15N values were found for hyperiids that feed on the mucus nets of salps (e.g. Vibilia armata). After contrasting isotope analysis with dietary data, we conclude there were two trophic levels among zooplankton/micronekton. Strong correlation between the mean annual δ15N and δ13C values was found for zooplankton (R2=0.7), but not for suprabenthos, which suggests a single source of carbon for plankton. We found a general seasonal trend for δ13C enrichment from late autumn (November) to late winter–spring (February–April) for both suprabenthos and zooplankton. The δ13C enrichment in February–April was correlated in zooplankton with higher surface chlorophyll a concentration 1 month before sampling. As evidenced by δ13C–δ15N correlations, the response of zooplankton to the peak of surface primary production was almost immediate (an increase of δ13C–δ15N correlations in February), and stronger than for suprabenthos. The response among suprabenthos was weak, with slight increase in δ13C–δ15N relationships in April–June.  相似文献   

7.
Shark nets were established along the KwaZulu-Natal coast in 1952 to protect bathers against shark encounters. Sea turtle bycatch data for the period 1981–2008 in these shark nets indicated that loggerheads Caretta caretta were caught most frequently at 40.9 y–1 or 1.11 km-net–1 y–1, followed by green turtles Chelonia mydas at 0.32 km-net–1 y–1 and leatherbacks Dermochelys coriacea at 0.14 km-net–1 y–1. Catch rate of loggerheads increased throughout the study period, and was positively correlated with the increase in the number of nesting females from the recovering population in Maputaland, South Africa (r = 0.52, p < 0.05, n = 28). This increase is ascribed to successful nest conservation. Leatherback bycatch remained stable, following their nesting trends, although they receive similar conservation efforts on nesting beaches as loggerheads. Bycatch of green turtles, although not a nesting species in South Africa, was stable over time. Mortality varied between species (from 53.2% to 70.6%) with loggerheads being the most hardy, followed by leatherbacks and green turtles. Few hawksbills Eretmochelys imbricata and olive ridleys Lepidochelys olivacea were caught in the shark nets. Fewer sea turtles are caught by shark nets than by longlines and because the nesting populations of loggerheads, green turtles and leatherbacks are either stable or increasing in the South-West Indian Ocean, shark net bycatch was considered negligible and sustainable.  相似文献   

8.
We used the nitrogen isotope ratio of algae, suspended particles and nitrate in the water column to track spatial variations in the marine nitrogen cycle in the Mediterranean Sea. Surface PON (5–74 m) was more depleted in 15N in the eastern basin (−0.3±0.5‰) than in the western basin (+2.4±1.4‰), suggesting that nitrogen supplied by biological N2 fixation may be an important source of new nitrogen in the eastern basin, where preformed nitrate from the Atlantic Ocean could have been depleted during its transit eastward. The δ15N of nitrate in the deep Mediterranean (∼3‰ in the western-most Mediterranean and decreasing toward the east) is significantly lower than nitrate at similar depths from the North Atlantic (4.8–5‰), also suggesting an important role for N2 fixation. The eastward decrease in the δ15N of surface PON is greater than the eastward decrease in the δ15N of the subsurface nitrate, implying that the amount of N2 fixation in the eastern Mediterranean is great enough to cause a major divergence in the δ15N of phytoplankton biomass from the δ15N of the nitrate upwelled from below. Variations in productivity associated with frontal processes, including shoaling of the nitracline, did not lead to detectable variations in the δ15N of PON. This indicates that no differential fertilization or productivity gradient occurred in the Almerian/Oran area. Our results are consistent with a lack of gradient in chlorophyll-a (chl-a) and nitrate concentration in the Alboran Sea. 15N enrichment in particles below 500 m depth was detected in the Alboran Sea with respect to surface PON, reaching an average value of +7.4±0.7‰. The δ15N in sinking particles caught at 100 m depth (4.9–5.6‰) was intermediate between suspended surface and suspended deep particles. We found a consistent difference in the isotopic composition of nitrogen in PON compared with that of chlorophyll (Δδ15N[PON-chlorin]=+6.4±1.4‰) in the surface, similar to the offset reported earlier in cultures for cellular N and chl-a. This indicates that δ15N of phytoplankton biomass was retained in surface PON, and that alteration of the isotopic signal of PON at depth was due to heterotrophic activity.  相似文献   

9.
We analyzed the stable nitrogen isotope composition of an extensive set of samples of particulate matter (PM) and seawater nitrate collected during October/November 1997 along the Mexican coastline from 24° to 11.5°N. At the northern and southern end of our study area, the δ15N of PM ranged between 5 and 7‰ in the upper 200 m of the water column with higher values at intermediate depths. These data are very similar to those reported from other parts of the open ocean. In the oxygen minimum zone (OMZ), we found significantly higher δ15N values for suspended particles. Furthermore, the δ15N of nitrate (NO3) was elevated within the OMZ and we found a strong relationship between the oxygen concentration, nitrate deficit and the 15N content of the nitrate. The core of the OMZ between 22°N, 105°W and 15°N, 110°W coincided with higher nitrate deficits and δ15N values relative to the stations near the boundaries. The δ15N of nitrate was highest, with values up to 18.7‰, where oxygen concentrations were below 1–2 μmol/l. This pattern is consistent with an overall nitrogen isotopic enrichment factor of 22.5‰ for denitrification in the core of the OMZ using the Rayleigh equation (closed-system approach). Results from a diffusion model (open-system approach), however, gave a fractionation factor of 30±7.5‰, implying that the Rayleigh formula only gives a lower estimate of the fractionation factor ε. The vertical flux of particles collected in short-term deployments (ca. 35 h) of a drifting sediment trap was not significantly correlated with the water column nitrate deficit. The isotopic signature of the nitrate within the gradient is very similar to the δ15N value of sedimenting particles, suggesting that there might be a strong link between the production and sedimentation of particles. Upward flux of nitrate across the thermocline can account for less than half of the particle flux leaving the mixed layer. Mixing and transport of nitrate across the lower boundary of the OMZ can lead to significant enrichment in the 15N content of deep waters, and our isotopic data imply that at least 14% of the nitrate in the waters below the OMZ originates from this source.  相似文献   

10.
First direct evidence for ongoing gas seepage activity on the abandoned well site 22/4b (Northern North Sea, 57°55′ N, 01°38′ E) and discovery of neighboring seepage activity is provided from observations since 2005. A manned submersible dive in 2006 discovered several extraordinary intense seepage sites within a 60 m wide and 20 m deep crater cut into the flat 96 m deep seafloor. Capture and (isotope) chemical analyses of the gas bubbles near the seafloor revealed in situ concentrations of methane between 88 and 90%Vol. with δ13C–CH4 values around −74‰ VPDB, indicating a biogenic origin. Bulk methane concentrations throughout the water column were assessed by 120 Niskin water samples showing up to 400.000 nM CH4 in the crater at depth. In contrast, concentrations above the thermocline were orders of magnitude lower, with a median value of 20 nM. A dye tracer injection into the gas seeps revealed upwelling bubble and water motion with gas plume rise velocities up to ∼1 ms−1 (determined near the seabed). However, the dissolved dye did not pass the thermocline, but returned down to the seabed. Measurements of direct bubble-mediated atmospheric flux revealed low values of 0.7 ± 0.3 kty−1, much less than current state-of-the-art bubble dissolution models would predict for such a strong and upwelling in situ gas bubble flux at shallow water depths (i.e. ∼100 m).Acoustic multibeam water column imaging data indicate a pronounced 200 m lateral intrusion at the thermocline together with high methane concentration at this layer. A partly downward-orientated bubble plume motion is also visible in the acoustic data with potential short-circuiting in accordance to the dye experiment. This observation could partly explain the observed trapping of most of the released gas below the well-established thermocline in the North Sea. Moreover, 3D analyses of the multibeam water column data reveal that the upwelling plume transforms into a spiral expanding vortex while rising through the water column. Such a spiral vortex motion has never been reported before for marine gas seepage and might represent an important process with strong implication on plume dynamics, dissolution behavior, gas escape to the atmosphere, and is considered very important for respective modeling approaches.  相似文献   

11.
In Zakynthos Island (Greece), authigenic cementation of marine sediment has formed pipe-like, disc and doughnut-shaped concretions. The concretions are mostly composed of authigenic ferroan dolomite accompanied by pyrite. Samples with >80% dolomite, have stable isotope compositions in two groups. The more indurated concretions have δ18O around +4‰ and δ13C values between −8 and −29‰ indicating dolomite forming from anaerobic oxidation of thermogenic methane (hydrocarbon seep), in the sulphate-methane transition zone. The outer surfaces of some concretions, and the less-cemented concretions, typically have slightly heavier isotopic compositions and may indicate that concretion growth progressed from the outer margin in the ambient microbially-modified marine pore fluids, inward toward the central conduit where the isotopic compositions were more heavily influenced by the seep fluid. Sr isotope data suggest the concretions are fossil features, possibly of Pliocene age and represent an exhumed hydrocarbon seep plumbing system. Exposure on the modern seabed in the shallow subtidal zone has caused confusion, as concretion morphology resembles archaeological stonework of the Hellenic period.  相似文献   

12.
The food sources of aquacultured Apostichopus japonicus and the trophic levels of organisms in a sea cucumber(A. japonicus) and prawn(Penaeus japonica) polyculture system in a saltwater pond in Zhuanghe, Liaoning Province were examined using carbon and nitrogen stable isotopes. Across organisms, δ13C ranged from(–25.47±0.20)‰ to(–16.48±0.17)‰(mean±SD), and δ15N ranged from(4.23±0.49)‰ to(12.44±0.09)‰. The δ13C and δ15N contents of A. japonicus, P. japonica and Fenneropenaeus chinensis were comparatively higher than those of other organisms. Values of δ13C and δ15N revealed that P. japonica, Hemigrapsus sanguineus and Neomysis japonica comprised the largest component of the diet of A. japonicus. The mean trophic level of the organisms in this saltwater pond polyculture system was(2.75±0.08). P. japonica, A. japonicus, F. chinensis,Synechogobius hasta and Neomysis japonica were in the 3rd trophic level(2–3); jellyfish, H. sanguineus and zooplankton were in the 2nd trophic level(1–2); and Enteromorpha prolifera, benthic microalgae, periphyton and suspended matter primarily consisting of phytoplankton, bacteria and humus were in the primary trophic level(0–1).  相似文献   

13.
Deep-seafloor communities, especially those from the ice-covered Arctic, are subject to severe food limitation as the amount of particulate organic matter (POM) from the surface is attenuated with increasing depth. Here, we use naturally occurring stable isotope tracers (δ15N) to broaden our rudimentary knowledge of food web structure and the response of benthic organisms to decreasing food supplies along the bathymetric transect (～1300–5600 m water depth) of the deep-sea observatory HAUSGARTEN. Encompassing five trophic levels, the HAUSGARTEN food web is among the longest indicating continuous recycling of organic material typical of food-limited deep-sea ecosystems. The δ15N signatures ranged from 3.0‰ for Foraminifera to 21.4‰ (±0.4) for starfish (Poraniomorpha tumida). The majority of organisms occupied the second and third trophic level. Demersal fish fed at the third trophic level, consistent with results from stomach contents analysis. There were significant differences in the δ15N signatures of different functional groups with highest δ15N values in predators/scavengers (13.2±0.2‰) followed by suspension feeders (11.2±0.2‰) and deposit feeders (10.2±0.3‰). Depth (=increasing food limitation) affected functional groups in different ways. While the isotopic signatures of predators/scavengers did not change, those of suspension feeders increased with depth, and the reverse was found for deposit feeders. In contrast to the results of other studies, the δ15N signatures in POM samples obtained below 800 m did not vary significantly with depth indicating that changes in δ15N values are unlikely to be responsible for the depth-related δ15N signature changes observed for benthic consumers. However, the δ15N signatures of sediments decreased with increasing depth, which also explains the decrease found for deposit feeders. Suspension feeders may rely increasingly on particles trickling down the HAUSGARTEN slope and carrying higher δ15N signatures than the decreasing POM supplies, which elevates the δ15N value of their tissues. Our results imply that a depth-stratified approach should be taken to avoid a misinterpretation of data obtained at different depths.  相似文献   

14.
Nutrient inputs associated with coastal population growth threaten the integrity of coastal ecosystems around the globe. In order to assess the threat posed by rapid growth in tourism, we analyzed the nutrient concentrations as well as the δ15N of NO3− and macrophytes to detect wastewater nitrogen (N) at 6 locations along a groundwater-dominated coastal seagrass bed on the Caribbean coast of Mexico. We predicted that locations with greater coastal development would have higher concentrations of dissolved inorganic nitrogen (DIN) and phosphorus (P), as well as δ15N of NO3−, reflecting wastewater sources of N. However, concentrations of NO3− were not significantly different between developed (3.3 ± 5.3 μM NO3−) and undeveloped (1.1 ± 0.7 μM) marine embayments. The most important control on DIN concentration appeared to be mixing of fresh and salt water, with DIN concentrations negatively correlated with salinity. The δ15N of NO3− was elevated at an inland pond (7.0 ± 0.42‰) and a hydrologically-connected tide pool (7.6 ± 0.57‰) approximately 1 km downstream of the pond. The elevated δ15N of NO3− at the pond was paralleled by high δ15N values of Cladophora sp., a ubiquitous green alga (10 ± 1‰). We hypothesize that inputs of nitrogen rich (NO3− > 30 μM) groundwater, characterized by 15N enriched signatures, flow through localized submarine groundwater discharges (SGD) and contribute to the elevated δ15N signatures observed in many benthic macrophytes. However, changes in nitrogen concentrations and isotope values over the salinity gradient suggest that other processes (e.g. denitrification) could also be contributing to the 15N enrichments observed in primary producers. More measurements are needed to determine the relative importance of nitrogen transformation processes as a source of 15N to groundwaters; however, it is clear that continued inputs of anthropogenic N via SGD have the potential to severely impact ecologically and economically valuable seagrass meadows and coral reefs along the Caribbean coast of Mexico.  相似文献   

15.
Sediment cores from the REGAB pockmark, an active cold seep area in the southeast Atlantic, were analysed for their lipid biomarker distribution and associated stable carbon isotopic composition. Substantial amounts of diagnostic archaeal lipids were found, consisting mainly of archaeol, sn-2 hydroxyarchaeol and crocetane. All archaeal lipids were profoundly depleted in 13C with δ13C values as low as −133‰. Concurrently, abundant monoalkylglycerolethers (MAGE), assigned to sulphate-reducing bacteria, were identified and showed strong 13C-depletions (δ13C between −86‰ and −95‰). The structural and isotopic patterns of these microbial lipids provided compelling evidence for anaerobic oxidation of methane (AOM) occurring in REGAB sediments, mediated by archaea and sulphate reducing bacteria. Lipid fingerprints indicated that anaerobic methanotrophic archaea (ANME-2) and sulphate-reducing bacteria from the Desulfosarcina/Desulfococcus cluster are the dominant AOM assemblages. Depth profiles implied that highest AOM takes place below the upper 2 cm, mainly in the 6–12 cm depth interval. Significant abundances of 13C-depleted diploptene and 4α-methylsterols were found as well, inferring that aerobic methanotrophy occurs in the surface sediment interval. This first biomarker study at the recently investigated cold seeps in the SE Atlantic expand on existing work on AOM settings and add new evidence for aerobic and anaerobic methanotrophic communities occurring in close vicinity.  相似文献   

16.
The stable carbon isotope composition of particulate organic carbon (δ13CPOC) and naturally occurring long-lived radionuclide 226Ra (T1/2=1600 a) were applied to study the variations of upper ocean (<100 m) carbon dynamics in response to sea ice melting in Prydz Bay, East Antarctica during austral summer 2006. Surface δ13CPOC values ranged from −27.4‰ to −19.0‰ and generally decreased from inner bay (south of 67°S) toward the Antarctic Divergence. Surface water 226Ra activity concentration ranged from 0.92 to 2.09 Bq/m3 (average 1.65±0.32 Bq/m3, n=20) and increased toward the Antarctic Divergence, probably reflecting the influence of 226Ra-depleted meltwater and upwelled 226Ra-replete deep water. The fraction of meltwater, fi, was estimated from 226Ra activity concentration and salinity using a three-component (along with Antarctic Summer Surface Water, and Prydz Bay Deep Water) mixing model. Although the fraction of meltwater is relatively minor (1.6–11.9%, average 4.1±2.7%, n=20) for the surface waters (sampled at ~6 m), a positive correlation between surface δ13CPOC and fi (δ13CPOC=0.94×fi−28.44, n=20, r2=0.66, p<0.0001) was found, implying that sea ice melting may have contributed to elevated δ13CPOC values in the inner Prydz Bay compared to the open oceanic waters. This is the first time for a relationship between δ13CPOC and meltwater fraction to be reported in polar oceans to our knowledge. We propose that sea ice melting may have affected surface ocean δ13CPOC by enhancing water column stability and providing a more favorable light environment for phytoplankton photosynthesis, resulting in drawdown of seawater CO2 availability, likely reducing the magnitude of isotope fractionation during biological carbon fixation. Our results highlight the linkage of ice melting and δ13CPOC, providing insights into understanding the carbon cycling in the highly productive Antarctic waters.  相似文献   

17.
Gas occurrences consisting of carbon dioxide (CO2), hydrogen sulfide (H2S), and hydrocarbon (HC) gases and oil within the Dodan Field in southeastern Turkey are located in Cretaceous carbonate reservoir rocks in the Garzan and Mardin Formations. The aim of this study was to determine gas composition and to define the origin of gases in Dodan Field. For this purpose, gas samples were analyzed for their molecular and isotopic composition. The isotopic composition of CO2, with values of −1.5‰ and −2.8‰, suggested abiogenic origin from limestone. δ34S values of H2S ranged from +11.9 to +13.4‰. H2S is most likely formed from thermochemical sulfate reduction (TSR) and bacterial sulfate reduction (BSR) within the Bakuk Formation. The Bakuk Formation is composed of a dolomite dominated carbonate succession also containing anhydrite. TSR may occur within an evaporitic environment at temperatures of approximately 120–145 °C. Basin modeling revealed that these temperatures were reached within the Bakuk Formation at 10 Ma. Furthermore, sulfate reducing bacteria were found in oil–water phase samples from Dodan Field. As a result, the H2S in Dodan Field can be considered to have formed by BSR and TSR.As indicated by their isotopic composition, HC gases are of thermogenic origin and were generated within the Upper Permian Kas and Gomaniibrik Formations. As indicated by the heavier isotopic composition of methane and ethane, HC gases were later altered by TSR. Based on our results, the Dodan gas field may have formed as a result of the interaction of the following processes during the last 7–8 Ma: 1) thermogenic gas generation in Permian source rocks, 2) the formation of thrust faults, 3) the lateral-up dip migration of HC-gases due to thrust faults from the Kas Formation into the Bakuk Formation, 4) the formation of H2S and CO2 by TSR within the Bakuk Formation, 5) the vertical migration of gases into reservoirs through the thrust fault, and 6) lateral-up dip migration within reservoir rocks toward the Dodan structure.  相似文献   

18.
Isotopic patterns of biota across salinity gradients in man-made evaporative systems could assist in determining the use of these habitats by animals. Here we report δ13C, δ15N and δD measurements of a euryhaline fish, the Mediterranean toothcarp (Aphanius fasciatus), inhabiting a range of salinities in the Thyna saltworks near Sfax (Tunisia). The contribution of these salinity niches to egg formation of two typically piscivorous bird species breeding in the area and feeding within saltworks, Little Tern (Sternula albifrons) and Little Egret (Egretta garzetta), was inferred trough a triple-isotope (δ13C, δ15N and δD) Bayesian mixing model. Isotopic trends for fish δ15N and δD across the salinity gradient followed the equations: δ15N = e(1.1 + 47.68/Salinity) and δD = −175.74 + Salinity + Salinity2; whereas fish δ13C increased as salinity rose (δ13C = −10.83 + 0.02·Salinity), after a sudden drop in fish isotopic values for salinities >60 (Practical Salinity Scale) (average fish δ13C for salinities <60 = −5.92‰). Both bird species fed largely on low hypersalinity ponds (salinity = 43; average contribution = 37% and 22% for Little Egrets and Little Terns, respectively), although the use of intermediate hypersalinities (salinities 63 and 70) by Little Terns also occurred (16% and 21%, respectively). Isotopic patterns across salinity gradients allow the use of isotopic measurements to inform studies of habitat occupancy within evaporative systems and provide further insights into how wildlife communities interact with them.  相似文献   

19.
利用稳定同位素技术;分析了2015年5月在红海湾海域采集的远海梭子蟹Portunus pelagicus及其潜在食物的碳（δ13C）和氮（δ15N）稳定同位素比值;通过稳定同位素混合模型（SIAR）;估算不同食物对远海梭子蟹食性的相对贡献。结果表明:远海梭子蟹的δ13C值在-18.1‰~-14.1‰之间;δ15N值的范围为9.8‰~13.8‰;平均值分别为-16.9‰±1.3‰和12.1‰±2.3‰。δ13C和δ15N值的变化范围均较大;表明远海梭子蟹食物来源广泛、多样。远海梭子蟹的食物主要由双壳贝类、螺类、鱼类、头足类、虾类、蟹类和藻类组成。SIAR模型计算结果显示:藻类为远海梭子蟹的主要食物;其平均贡献为32.5%;双壳贝类的相对食性贡献为21.9%;虾类、螺类、鱼类和蟹类的平均贡献差异较小;分别为9.7%、9.7%、9.6%和9.3%;头足类的贡献最低;仅为7.3%。此外;根据δ15N值及营养位置的计算公式得出:远海梭子蟹在红海湾海域位于2.91±0.68营养级。远海梭子蟹的7类潜在食物中;藻类的营养位置最低;为1.21±0.58;其次为双壳贝类;为2.00±0.25;蟹类、螺类、虾类和鱼类的营养位置分别为2.85±0.33、2.87±0.26、3.01±0.16和3.08±0.18;头足类的最高;为3.41±0.17。  相似文献   

20.
This study performed a detailed geochemical analyses of the components, stable carbon isotopes of alkane gas and CO2, stable hydrogen isotopes of alkane gas and helium isotopes of reproducing gas from the largest tight gas field (Sulige) and shale gas (Fuling) field in China. The comparative study shows that tight gas from the Sulige gas field in the Ordos Basin is of coal-derived origin, which is characterized by a positive carbon and hydrogen isotopic distribution pattern (δ13C1 > δ13C2 > δ13C3 > δ13C4; δ2H1 > δ2H2 > δ2H3), i.e., the carbon and hydrogen isotopes increase with increasing carbon numbers. Carbon dioxide from this field are of biogenic origin and the helium is crust-derived. Shale gas from the Fuling shale gas field belongs to oil-derived gas which has complete carbon and hydrogen isotopic reversal of secondary alteration origin (δ13C1 < δ13C2 < δ13C3; δ2H1 < δ2H2 < δ2H3), i.e., the carbon and hydrogen isotopes decrease with increasing carbon numbers. Such complete isotopic reversal distribution pattern is due to the secondary alteration like oil or gas cracking, diffusion and so on under high temperature. In that case, positive carbon or hydrogen isotopic distribution pattern will change into complete isotopic reversal as the temperature increases. Carbon dioxide is of abiogenic origin resulting from the thermal metamorphism of carbonates and helium is crust-derived.  相似文献   

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