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1.
In order to show that dolphins use estuary habitats differently depending on the season and tidal state, possibly in response to prey distribution, temperature, risk of stranding and accessibility, Indo-Pacific bottlenose dolphins (Tursiops aduncus) were observed year-round during a 3-year study in the Clarence River estuary (CR) and Richmond River estuary (RR) in northern New South Wales, Australia. Peak dolphin sightings occurred during the spring season and one or 2 h prior to high tide. The spatial distribution of the dolphins in each estuary was analysed using the distance in kilometres that the dolphins travelled upstream with seasons and tidal phase as determinants. A General Linear Model showed that in the CR the dolphin spatial distribution in the estuary was not determined by season (F = 0.434, df = 3, P = 0.729) but was by tidal phase (F = 9.943, df = 3, P < 0.001) and the interaction between season and tidal phase (F = 3.398, df = 9, P < 0.002). However, in the RR the spatial distribution of the dolphin use of the estuary was not determined by either season (F = 1.647, df = 3, P = 0.194) or tidal phase (F = 0.302, df = 3, P = 0.824). In the CR, the spatial distribution of the dolphins was largest on high and flood tides. This pattern of spatial distribution may occur because the CR is a relatively shallow estuary and this increased spatial distribution may reflect a lower stranding risk and an increase in accessibility of shallow areas during periods of higher tide. These areas could also provide access to their preferred prey items of sea mullet (Mugil cephalus) and sand whiting (Sillago ciliata).  相似文献   

2.
Foraging behavior and diet of breeding seabirds may be analysed simultaneously with the combined use of remote sensing devices and stable isotope analysis. Imperial shag, Phalacrocorax atriceps, breeding at Punta León colony, Argentina, were equipped with global positioning system (GPS) loggers to record foraging trips and blood samples were taken after removal of the devices in order to analyse their nitrogen and carbon stable isotope composition in whole blood and plasma. Whole blood was correlated to plasma isotopic composition for each individual (n = 35), linking diet in the short and medium term. Sexes did not differ in isotopic signatures. The maximum distance reached and the total number of dives that individuals made on two consecutive foraging trips were correlated to their plasma nitrogen isotopic signature. Individuals that went further from the colony and dived fewer times presented more positive signatures, indicative of benthic prey consumption (e.g. Raneya brasiliensis). Diet was predominantly benthic with some individuals incorporating pelagic prey (Engraulis anchoita) and even cephalopods (Octopus tehuelchus). Within breeding pairs (n = 9), different combinations of foraging and prey preferences were observed. Estimated trophic levels of these individuals were similar to those of the same species in other colonies further south along the Patagonian coast.  相似文献   

3.
To estimate the influence of mercury emitted from submarine fumaroles, the horizontal and vertical distribution of mercury in sediment of Kagoshima Bay was studied. The fumaroles are located in the northern bay head area, and the sediment samples had been taken from 52 points throughout the bay with a gravity core sampler. The core samples obtained were cut at a thickness of 1–2 cm and used for measurements. The total concentration of mercury in surface sediment in the northern and central areas of the bay was 51–679 μg kg− 1 (average 199 μg kg− 1, n = 22) and 23–100 μg kg− 1 (average 55 μg kg− 1, n = 30), respectively. The highest value was obtained in the vicinity of the fumaroles. The mercury concentration in sediment near the fumaroles varied with depth, which may reflect the variation in fumarolic activity. A successive extraction method was applied to the speciation of mercury in the sediment. The results showed that sediment taken in the vicinity of submarine fumaroles contained a higher percentage of mercury bound with organic matter.  相似文献   

4.
The NW-SE striking Otway Basin in southeastern Australia is part of the continental rift system that formed during the separation of Australia from Antarctica. The development of this sedimentary basin occurred in two phases of Late Jurassic-Early Cretaceous and Late Cretaceous rifting. The evolution of this basin is mainly associated with extensional processes that took place in a pre-existing basement of Archean, Proterozoic to Paleozoic age. In this study, the total amounts of extension and stretching factor (β factor) have been measured for six transects across the entire passive margin of the Otway Basin region. The results show significant variation in extensional stretching along the basin, with the smallest stretching factors in the easternmost (β = 1.73, 1.9) and westernmost part of the basin (β = 2.09), and the largest stretching factors in the central part (β = 2.14 to 2.44). The domain with the lowest β factor is underlain mostly by thicker lithosphere of the Delamerian Orogen and older crustal fragments of the Selwyn Block. In contrast, the region with the largest β factor and amount of extension is related to younger and thinner lithosphere of the Lachlan Orogen. The main basement structures have been mapped throughout eastern South Australia and Victoria to examine the possible relationships between the younger pattern of extensional faults and the older basement fabrics. The pattern of normal faults varies considerably along onshore and offshore components of the Otway Basin from west to east. It appears that the orientation of pre-existing structures in the basement has some control on the geometry of the younger normal faults across the Otway Basin, but only in a limited number of places. In most areas the basement fabric has no control on the younger faulting pattern. Basement structure such as the north-south Coorong Shear Zone seems to affect the geometry of normal faults by changing their strike from E-W to NW-SE and also, in the easternmost part of the basin, the Bambra Fault changes the strike of normal faults from NW-SE to the NE-SW. Our results imply that the properties of the continental lithosphere exert a major influence on the β factor and amount of crustal extension but only a minor influence on the geometry of extensional faults.  相似文献   

5.
Benthic macroalgae form an important part of temperate marine ecosystems, exhibiting a complex three-dimensional character which represents a vital foraging and spawning ground for many juvenile fish species. In this research, image-based techniques for classification of multibeam backscatter are explored for the detection of benthic macroalgae at Cashes Ledge in the Gulf of Maine, USA. Two classifications were performed using QTC-Multiview, differentiated by application of a threshold filter, and macroalgal signatures were independently extracted from the raw sonar datagrams in Matlab. All classifications were validated by comparison with video ground-truth data. The unfiltered classification shows a high degree of complexity in the shallowest areas within the study site; the filtered demonstrates markedly less variation by depth. The unfiltered classification shows a positive agreement with the video ground-truth data; 82.6% of observations recording Laminaria sp., 39.1% of Agarum cribrosum and 100.0% (n = 3) of mixed macroalgae occur within the same acoustically distinct group of classes. These are discrete from the 8.1% recorded agreement with absences and nulls (>40 m) of macrophytes (n = 32) from a total of 86 ground-truth locations. The results of the water column data extraction (WCDE) show similar success, accurately predicting 78.3% of Laminaria sp. and 30.4% of A. cribrosum observations.  相似文献   

6.
The seismic, drilling and logging data reveal that a large-scale igneous intrusion with a width of 14 Km and a maximum thickness of 170 m intruded within the Paleogene Liushagang Formation in the Fushan Depression, Beibuwan Basin, South China Sea (SCS). In this study, we report the geochemistry and Sr-Nd-Pb-Hf isotopic compositions of the igneous rocks, and evaluate the thermal effect induced by this large-scale igneous intrusion on the host rocks. The analyzed igneous samples exhibit strong enrichment in light rare earth elements (LREE) and large-ion lithophile elements (LILE), having characteristics similar to intra-plate oceanic island basalts (OIB). The Sr-Nd-Pb-Hf isotopic data display narrow ranges (e.g. 87Sr/86Sri = 0.7042–0.7044, 143Nd/144Ndi = 0.5128–0.5129, 206Pb/204Pbi = 18.90–18.94, εHf(t) = +7.56∼+9.60). Geochemical and isotopic compositions suggest a mixed mantle source between depleted mid-ocean-ridge-basalt (MORB) mantle (DMM)-like mantle and enriched mantle type II (EMII, possibly the Hainan mantle plume). Vitrinite reflectance values, major mineralogical changes together with a maturity-related biomarker [Ts/(Ts + Tm)] all reveal significant thermal effect induced by the igneous intrusion. Vitrinite reflectance values of the host rock are up to 2.5% in the intrusion region, whereas lower reflectance values (0.62–0.73%) occur in the unaffected area of the same strata. Moreover, our results suggest that the host rocks above the igneous intrusion are characterised by higher maturity than below, which should be attributed to the different behavior of hydrothermal fluids. These observations suggest that the thermal effect of large-scale thick igneous intrusions is much more intense than that of thin igneous intrusions, and the behavior of hydrothermal fluids induced by magmatic intrusive events should be a critical impact factor during heat transfer process.  相似文献   

7.
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   

8.
We examined the bioaccumulation and trophic transfer of mercury in two marine finfish species, striped bass (Morone saxatilis) and tautog (Tautoga onitis), collected from the Narragansett Bay (Rhode Island, USA). For each of these target fish, white muscle tissue was analyzed for total mercury (Hg) and results were evaluated relative to fish age, body size, and Hg content of preferred prey. Dietary and stable isotope analysis was also used to elucidate the effect of trophic processes on Hg concentrations in fish. The Hg content of muscle tissue was positively correlated with fish age and length for both species, although striped bass accumulated Hg faster than tautog. Accelerated Hg bioaccumulation in striped bass is consistent with its high trophic level (trophic level = 4.07) and Hg-enriched prey (forage fish and macrocrustaceans; mean Hg content = 0.03 mg Hg kg wet wt?1). In contrast, tautog maintain a lower trophic status (trophic level = 3.51) and consume prey with lower Hg levels (mussels and crabs; mean Hg content = 0.02 mg Hg kg wet wt?1). Despite differences in Hg bioaccumulation between target fish, the mean Hg concentration of tautog exceeded levels in striped bass (0.24 and 0.16 mg Hg kg wet wt?1, respectively) due to a disparity in age-at-catch between sampled groups (mean age of tautog and bass = 11.3 and 4.3 yr, respectively). Taking into account legal minimum catch lengths further revealed that 75.0% of legal-size striped bass (>70.2 cm TL; n = 4) and 44.8% of tautog (>40.6 cm TL; n = 29) had Hg levels beyond the US EPA regulatory threshold of 0.3 mg Hg kg wet wt?1. Moreover, Hg-length relationships suggest that each target fish meets this threshold near their minimum legal catch length. Our findings reiterate the value of species ecology to improve predictions of fish Hg and permit better management of human contamination by this important dietary source.  相似文献   

9.
It has been shown that salt marshes may function as efficient sinks for contaminants, namely for mercury. At the rhizo-sediment Hg may be associated with Mn and Fe oxyhydroxides, precipitated as sulphides or incorporated into organic matter. However, to our knowledge, in situ studies have not focused on the related processes at a daily or tidal cycle scales. Thus, the present work aims to study the effect of a common salt marsh halophyte in temperate latitudes (Sarcocornia perennis) on dissolved Fe, Mn and Hg concentrations in the water column. The in situ approach was carried out at a mercury-contaminated salt marsh and at the adjacent non-vegetated area (distance ≤ 4 m), covering two consecutive tidal cycles in order to include the photosynthetic active period and the night processes. During high tide no daily or spatial effects were observed on the concentrations of Mn, Fe and Hg in the water column, due to the dilution effect of the incoming seawater. During low tide the concentrations of Mn, Fe and Hg were significantly higher in the overlaying water column of the salt marsh. At S. perennis mats the concentration of dissolved total Hg was significantly related with the concentration of Mn (r = 0.459, p = 0.028, n = 23), but not with that of Fe (r = 0.367, p = 0.085, n = 23) while no significant relations were found at the adjacent non-vegetated sediments.  相似文献   

10.
Seawater samples were collected for microbial analyses between 55 and 235 m depth across the Arctic Ocean during the SCICEX 97 expedition (03 September–02 October 1997) using a nuclear submarine as a research platform. Abundances of prokaryotes (range 0.043–0.47×109 dm−3) and viruses (range 0.68–11×109 dm−3) were correlated (r=0.66, n=150) with an average virus:prokaryote ratio of 26 (range 5–70). Biomass of prokaryotes integrated from 55 to 235 m ranged from 0.27 to 0.85 g C m−2 exceeding that of phytoplankton (0.005–0.2 g C m−2) or viruses (0.02–0.05 g C m−2) over the same depth range by an order of magnitude on average. Using transmission electron microscopy (TEM), we estimated that 0.5% of the prokaryote community on average (range 0–1.4%) was visibly infected with viruses, which suggests that very little of prokaryotic secondary production was lost due to viral lysis. Intracellular viruses ranged from 5 to >200/cell, with an average apparent burst size of 45±38 (mean±s.d.; n=45). TEM also revealed the presence of putative metal-precipitating bacteria in 8 of 13 samples, which averaged 0.3% of the total prokaryote community (range 0–1%). If these prokaryotes are accessible to protistan grazers, the Fe and Mn associated with their capsules might be an important source of trace metals to the planktonic food web. After combining our abundance and mortality data with data from the literature, we conclude that the biomass of prokaryoplankton exceeds that of phytoplankton when averaged over the upper 250 m of the central Arctic Ocean and that the fate of this biomass is poorly understood.  相似文献   

11.
Biodegradation and oil mixing in Silurian sandstone reservoirs of the Tarim Basin, one of the largest composite basins in China, were investigated by analyzing the molecular characteristics and stable carbon isotopic signatures of low-molecular-weight (LMW) saturated hydrocarbons and high-molecular-weight (HMW) asphaltenes. Detection of 25-norhopanes and 17-nortricyclic terpanes in most Silurian tar sands from the Tabei Uplift in the Tarim Basin suggests a much greater degree of biodegradation here than in the Tazhong Uplift. This explains the relatively more abundant tricyclic terpanes, gammacerane, pregnane and diasteranes in tar sands from the Tabei Uplift than in those from the Tazhong Uplift. Hence, care must be taken when assigning oil source correlations using biomarkers in tar sands because of the biodegradation and mixing of oils derived from multiple sources in such an old composite basin. Asphaltenes in the tar sands seem to be part of the oil charge before biodegradation, depending on the relative anti-biodegradation characteristics of asphaltenes, the similarity in carbon isotopic signatures for asphaltenes and their pyrolysates, and the consistent product distribution for flash pyrolysis and for regular steranes in asphaltene pyrolysates, regardless of whether the tar sands were charged with fresh oil. According to the relative distributions of regular steranes and the relatively abundant 1,2,3,4-tetramethylbenzene significantly enriched in 13C, the oil sources for asphaltenes in the tar sands might be related to lower Paleozoic marine source rocks formed in euxinic conditions. Nevertheless, the relatively low abundance of gammacerane and C28 regular steranes observed in asphaltene pyrolysates and residual hydrocarbons, within limited samples investigated in this work, made a direct correlation of oils originally charged into Silurian tar sands with those Cambrian source rocks, reported so far, seem not to be possible. Comparison of carbon isotopic signatures of n-alkanes in asphaltene pyrolysates with those of LMW saturated hydrocarbons is helpful in determining if the abundant n-alkanes in tar sands are derived from fresh oil charges after biodegradation. The limited carbon isotopic data for n-alkanes in LMW saturated hydrocarbons from the tar sands can be used to classify oils charged after biodegradation in the composite basin into four distinct groups.  相似文献   

12.
Moored sediment traps were deployed from January 2004 through December 2007 at depths of 550 and 800 m in San Pedro Basin (SPB), CA (33°33.0′N, 118°26.5′W). Additionally, floating sediment traps were deployed at 100 and 200 m for periods of 12-24 h during spring 2005, fall 2007, and spring 2008. Average annual fluxes of mass, particulate organic carbon (POC), ??13Corg, particulate organic nitrogen (PON), ??15N-PON, biogenic silica (bSiO2), calcium carbonate (CaCO3), and detrital material (non-biogenic) were coupled with climate records and used to examine sedimentation patterns, vertical flux variability, and organic matter sources to this coastal region. Annual average flux values were determined by binning data by month and averaging the monthly averages. The average annual fluxes to 550 m were 516±42 mg/m2 d for mass (sdom of the monthly averages, n=117), 3.18±0.26 mmol C/m2 d for POC (n=111), 0.70±0.05 mmol/m2 d for CaCO3 (n=110), 1.31±0.21 mmol/m2 d for bSiO2 (n=115), and 0.35±0.03 mmol/m2 d for PON (n=111). Fluxes to 800 and to 550 m were similar, within 10%. Annual average values of ??13Corg at 550 m were −21.8±0.2‰ (n=108), and ??15N averages were 8.9±0.2‰ (n=95). The timing of both high and low flux particle collection was synchronous between the two traps. Given the frequency of trap cup rotation (4-11 days), this argues for particle settling rates ≥83 m/d for both high and low flux periods. The moored traps were deployed over one of the wettest (2004-2005, 74.6 cm rainfall) and driest (2006-2007, 6.6 cm) rain years on record. There was poor correlation (Pearson's correlation coefficient, 95% confidence interval) of detrital mass flux with: Corg/N ratio (r=0.10, p=0.16); ??15N (r=−0.19, p=0.02); and rainfall (r=0.5, p=0.43), suggesting that runoff does not immediately cause increases in particle fluxes 15 km offshore. ??13Corg values suggest that most POC falling to the basin floor is marine derived. Coherence between satellite-derived chlorophyll a records from the trap location (±9 km2 resolution) and SST data indicates that productivity and export occurs within a few days of upwelling and both of these parameters are reasonable predictors of POC export, with a time lag of a few days to 2 weeks (with no time lag—SeaWiFS chlorophyll a and POC flux, r=0.25, p=0.0014; chlorophyll a and bSiO2 flux, r=0.28, p=0.0002).  相似文献   

13.
《Marine Chemistry》2007,103(1-2):1-14
We succeeded in determining the Ce isotopic composition (138Ce/142Ce) in seawater with an error of 2σm = 0.3–0.7 of ε unit. In this study, 1000–3000 L of seawater samples were passed through MnO2 fibers to concentrate Ce and Nd for precise measurement of their isotope ratios. Four surface seawater samples of the northwestern Pacific and a coastal sample in Tokyo Bay were analyzed. Most Ce isotope ratios in the surface water showed positive εCe values (+ 0.8 to + 1.4) in the northwestern Pacific Ocean. These values indicate that Ce in the surface water originates from the continental crust preferentially over mantle-derived materials. We examined binary mixing model between the continental crust and mid-ocean ridge basalt. However the model could not explain both isotopic compositions and concentrations, which implies that the atmospheric input was a possible pathway for Ce into the ocean. A negative εCe value was observed in Tokyo Bay, suggesting mantle-derived sources.  相似文献   

14.
In order to test the hypothesis that the ambient iron concentrations could regulate sulfate reducing activity (SRA) in mangrove areas, 10 cm cores were examined from test and reference sites. The test site at Diwar mangrove ecosystem is highly influenced by iron released by the movement of barges carrying iron ore during the non-monsoon seasons and the reference site at Tuvem is relatively pristine. The average iron concentrations were 17.9% (±8.06) at Diwar and 6.3% (±1.5) at Tuvem. Sulfate reducing rates (SRR) ranged from 50.21 to 698.66 nM cm−3 d−1 at Tuvem, and from 23.32 to 294.49 nM cm−3d−1 in Diwar. Pearson’s correlation coefficients between SRR and environmental parameters showed that at Tuvem, the SRR was controlled by SO4−2 (r = 0.498, p < 0.001, n = 60) more than organic carbon (r = 0.316 p < 0.05, n = 60). At Diwar, the SRR was governed by the iron concentrations at an r-value of −0.761 (p < 0.001, n = 60), suggesting that ca.58% of the variation in SRR was influenced negatively by variations in ambient iron concentrations. This influence was more than the positive influence of TOC (r = 0.615, p < 0.001, n = 60). Laboratory experiments to check the influence of iron on SRR also supported our field observations. At an experimental manipulation of 50 ppm Fe3+ there was an increase in SRR but at 100 ppm an inhibitory effect was observed. At 1000 ppm Fe3+ there was a decrease in the SRR up to 93% of the control. Thus, our study showed that ambient iron concentrations influence SRR negatively at Diwar and counters the positive influence of organic carbon. Consequently, the influence could cascade to other biogeochemical processes in these mangrove swamps, especially the mineralization of organic matter to carbon dioxide by sulfate respiration.  相似文献   

15.
Euphotic zone plankton production (P) and respiration (R) were determined from the in vitro flux of dissolved oxygen during six latitudinal transects of the Atlantic Ocean, as part of the Atlantic Meridional Transect (AMT) programme. The transects traversed the North and South Atlantic Subtropical Gyres (N gyre, 18–38°N; S gyre, 11–35°S) in April–June and September–November 2003–2005. The route and timing of the cruises enabled the assessment of the seasonal variability of P, R and P/R in the N and S gyres, and the comparison of the previously unsampled N gyre centre with the more frequently sampled eastern edge of the gyre. Mean euphotic zone integrated rates (±SE) were P=63±23 (n=31), R=69±22 (n=30) mmol O2 m−2 d−1 in the N gyre; and P=58±26 (n=30), R=62±24 (n=30) mmol O2 m−2 d−1 in the S gyre. Overall, the N gyre was heterotrophic (R>P) and it was more heterotrophic than the S gyre, but the metabolic balance of both gyres changed with season. Both gyres were net heterotrophic in autumn, and balanced in spring. This seasonal contrast was most pronounced for the S gyre, because it was more autotrophic than the N gyre during spring. This may have arisen from differences in nitrate availability, because spring sampling in the S gyre coincided with periods of deep mixing to the nitracline, more frequently than spring sampling within the N gyre. Our results indicate that the N gyre is less heterotrophic than previous estimates suggested, and that there is an apparent decrease in R from the eastern edge to the centre of the N gyre, possibly indicative of an allochthonous organic carbon source to the east of the gyre.  相似文献   

16.
《Marine Chemistry》2007,103(1-2):146-162
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17.
Interdecadal Pacific variability (IPV) is commonly observed in both the tropical and mid-latitude Pacific Ocean, and has a widespread influence on surface climate in the Pan-Pacific Basin. This variability is recorded by climate proxies such as geochemical parameters preserved in corals. However, the origins of IPV remain uncertain. To shed light on this, interdecadal variations in two long coral δ18O records from Nauru Island and the South China Sea (SCS), respectively located in the tropical Pacific and the mid-latitude North Pacific Ocean, were investigated. The interdecadal fluctuations in the δ18O series from Nauru Island (tropical Pacific) match those of the NINO3.4 index reasonably well (r=–0.30, n=96, p=0.0015), but are not correlated with those of the Pacific decadal oscillation (PDO) index (r=–0.17, n=96, p=0.05). The δ18O time series from the SCS (northwestern Pacific), by contrast, co-vary with the PDO index (r=–0.30, n=156, p=0.0007), but are out of phase with the NINO3.4 index at the interdecadal timescale (r=0.04, n=156, p=0.31). The impact on the interdecadal variability of processes occurring outside the growth region of corals is generally weak. The results thus do not support a tropical origin of IPV, but demonstrate that the interdecadal variability in the tropical Pacific and the North Pacific originates predominantly from local coupled ocean–atmosphere processes within these regions. The results also suggest that tropical–extratropical interactions played a role in IPV between 1920 and 1940, which indicates that IPV is a complex climatic phenomenon that involves multiple forcing mechanisms.  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.
Structural analysis of the Indian Merge 3D seismic survey identified three populations of normal faults within the Exmouth Sub-basin of the North West Shelf volcanic margin of Australia. They comprise (1) latest-Triassic to Middle Jurassic N-NNE-trending normal faults (Fault Population I); (2) Late Jurassic to Early Cretaceous NE-trending normal faults (Fault Population II); and (3) latest-Triassic to Early Cretaceous N-NNE faults (Fault Population III). Quantitative evaluation of >100 faults demonstrates that fault displacement occurred during two time periods (210–163 and 145–138 Ma) separated by ∼20 Myr of tectonic quiescence. Latest Jurassic to Early Cretaceous (145–138 Ma) evolution comprises magmatic addition and contemporaneous domal uplift ∼70 km wide characterised by ≥ 900 m of denudation. The areally restricted subcircular uplift centred on the southern edge of the extended continental promontory of the southern Exmouth Sub-basin supports latest Jurassic mantle plume upwelling that initiated progradation of the Barrow Delta. This polyphase and bimodal structural evolution impacts current hydrocarbon exploration rationale by defining the nature of latest Jurassic to Early Cretaceous fault nucleation and reactivation within the southern Exmouth Sub-basin.  相似文献   

20.
To describe the larval and juvenile fish fauna and to evaluate the relative contribution of the ocean and the estuary as settlement areas for benthic species, we compared the composition and abundance of larval fish supply to that of recently settled juvenile fishes in both ocean and an adjacent estuary habitats in southern New Jersey. The study was conducted from May to November 1992 in the Great Bay–Little Egg Harbor estuary (<1–8 m sampling depth) and on the adjacent inner continental shelf in the vicinity of Beach Haven Ridge (8–16 m). During the study more larvae nearing settlement (postflexion) were captured in the estuary than in the ocean. Settlement occurred earlier in the estuary than in the ocean perhaps under the influence of earlier, seasonal warming of estuarine waters. There appeared to be two spatial patterns of settlement in the study area based on the dominant species (n = 17) represented by a sufficient number of individuals (n ≥ 25 individuals). There were species that primarily settle in the estuary, as represented by both estuarine residents (n = 3) and transients (n = 4), and those that settle in both the estuary and the ocean (n = 10). However, there were no species whose larvae were present in the estuary yet settle in the ocean. The fact that many of the species settle in both the estuary and the ocean indicates an overlap between these habitats because, at least for some species, these habitats may function in the same way. Further resolution of fish settlement patterns, and its influence on recruitment will need to rely on synoptic comparisons between estuaries and the ocean over multiple years.  相似文献   

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