Impact of environmental forcing on the acoustic backscattering strength in the equatorial Pacific: Diurnal,lunar, intraseasonal,and interannual variability

We analyzed several records of mean volume backscattering strength (S_v) derived from 150 kHz acoustic doppler current profilers (ADCPs) moored along the equator in upwelling mesotrophic conditions and in the warm pool oligotrophic ecosystem of the Pacific Ocean. The ADCPs allow for gathering long time-series of non-intrusive information about zooplankton and micronekton at the same spatial and temporal scales as physical observations. High S_v are found from the surface to the middle of the thermocline between dusk and dawn in the mesotrophic regime. Biological and physical influences modified this classical diel cycle. In oligotrophic conditions observed at 170°W and 140°W during El Niño years, a subsurface S_v maximum characterized nighttime S_v profiles. Variations of the thermocline depth correlated with variations of the base of the high S_v layer and the subsurface maximum closely tracked the thermocline depth from intraseasonal to interannual time-scales. A recurring deepening (20–60 m) of the high S_v layer was observed at a frequency close to the lunar cycle frequency. At 165°E, high day-to-day variations prevailed and our results suggest the influence of moderately mesotrophic waters that would be advected from the western warm pool during westerly wind events. A review of the literature suggests that S_v variations may result from changes in biomass and species assemblages among which myctophids and euphausiids would be the most likely scatterers.     

In-situ stress state in the Linxing region,eastern Ordos Basin,China: Implications for unconventional gas exploration and production

The Carboniferous and Permian sedimentary rocks (mainly the Shanxi and Taiyuan formations) in the Linxing region, eastern Ordos Basin, China, host a significant volume of unconventional gas resources (coalbed methane, shale gas and tight sandstone gas). Currently, the in-situ stress state is poorly understood but knowledge of this is extremely important for a range of applications, such as gas exploration and production, fracture stimulation and wellbore stability. The maximum horizontal stress (S_Hmax), minimum horizontal stress (S_hmin) and vertical stress (S_v) magnitudes, and the S_Hmax orientation in the Linxing region were systematically analyzed for the first time in the present study, which can provide a reference for subsequent numerical simulation and hydraulic fracturing design. Based on borehole breakouts and drilling-induced tensile fractures interpreted from borehole imaging logs, the S_Hmax orientation rotates from ∼NEE-SWW-trending in the southern part to ∼ NWW-SEE-trending in the northern part of the Linxing region. Both conventional logs and extended leak-off tests were used for stress magnitude determination. The results revealed three types of in-situ stress fields (S_v > S_Hmax > S_hmin, S_Hmax > S_v > S_hmin and S_Hmax > S_v ≈ S_hmin), and a dominant strike-slip stress regime (S_Hmax > S_v ≥ S_hmin) was found for the entire well section in the target Shanxi Formation and Taiyuan Formation in the Linxing region. In addition, differential stress increased with depth in the Linxing region, which indicates that wellbore instability might be a potentially significant problem when drilling wells that are vertical or ∼ N-S-trending.     

Late Cretaceous (Late Turonian,Coniacian and Santonian) petroleum source rocks as part of an OAE,Tarfaya Basin,Morocco

Late Turonian, Coniacian and Santonian source rock samples from a recently drilled well (Tafaya Sondage No. 2; 2010) in the Tarfaya Basin were analyzed for quantity, quality, maturity and depositional environment of the organic matter (OM). To our knowledge such a thick sequence of organic matter-rich Turonian to Santonian source rocks was investigated in that great detail for the first time. Organic geochemical and organic petrological investigations were carried out on a large sample set from the 200 m thick sequence. In total 195 core samples were analyzed for total organic carbon (C_org), total inorganic carbon contents and total sulfur (TS) contents. Rock-Eval pyrolysis and vitrinite reflectance measurements were performed on 28 samples chosen on the basis of their C_org content. Non-aromatic hydrocarbons were analyzed on selected samples by way of gas chromatography–flame ionization detection (GC–FID) and GC–mass spectrometry (GC–MS). The organic matter-rich carbonates revealed a high source rock potential, representing type I kerogen and a good preservation of the organic matter, which is mainly of marine (phytoplankton) origin. HI values are high (400–900 mg/g C_org) and in a similar range as those described for more recent upwelling sediments along the continental slope of North Africa. TS/C_org ratios as well as pristane over phytane ratios indicate variable oxygen content during sediment deposition. All samples are clearly immature with respect to petroleum generation which is supported by maturity parameters such as vitrinite reflectance (0.3–0.4%), T_max values (401–423 °C), production indices (S₁/(S₁ + S₂) > 0.1) as well as maturity parameters based on ratios of specific steranes and hopanes.     

Sediment retention at the Changjiang sub-aqueous delta over a 57 year period,in response to catchment changes

The growth of a river delta system is controlled mainly by fluvial sediment discharge and sediment retention in the deltaic areas. In the present study, we attempt to define a sediment retention index, R, and its relation to the deposition rate of the delta. Based upon two assumptions that the amount of the sediment that escapes from the deltaic areas, Q_E, is stationary with minor fluctuations, and that there is a linear relationship between the deposition rate averaged over the sub-aqueous delta (D_av) and the deposition rate at accretion sites within the delta (D_R), the changes in the accretion/erosion patterns of the Changjiang sub-aqueous delta during the period of 1951–2007, in response to river sediment discharge changes, are analyzed. The results show that the sediment retention index can be related to the deposition rate of the sub-aqueous delta; the spatial-temporal distribution pattern of the deposition rate reveals the behaviour of sediment retention of a delta system. For the Changjiang sub-aqueous delta, fluvial sediment discharge data, together with Pb-210 based deposition rates, provide useful information on sediment retention. Changes in the sediment retention index and the accretion/erosion patterns of the sub-aqueous delta have taken place in response to river input changes. In order to improve our understanding of the processes associated with estuarine sediment retention, sediment cores with sufficient spatial coverage may be collected and analyzed to establish accurate Q_E–R and D_av–D_R relationships. In combination with numerical modeling of sediment transport, these relationships form a basis for the analysis of sediment retention mechanisms.     

Oxygen consumption in the shrimp,Palaemonetes pugio,exposed to fluctuating temperatures and food contaminated with the diaromatic petroleum hydrocarbon,dimethylnaphthalene

Oxygen consumption rates (V?o₂) in the grass shrimp Palaemonetes pugio were determined after a 32 day exposure to fluctuating temperatures (FT) (18–22°C) and/or dimethylnaphthalene (DMN)-contaminated food (0·24 μg DMN g wet wt^?1) and again after a 16 day recovery period of stable temperatures (20°C) and uncontaminated food. Ingestion of DMN-contaminated food for 32 days resulted in elevated V?>o₂ in shrimp exposed to declining oxygen concentrations. After the 32 day exposure period, FT had no significant effect on V?o₂ at 15, 20 and 25°C, tissue V?o₂ and V?o₂ in declining oxygen. Hemolymph copper concentrations were significantly depressed in shrimp exposed to DMN-contaminated food. After the 16 day recovery period, shrimp from the FT regime exhibited depressed V?o₂ when exposed to 25°C but not to 15°C. These depressed respiratory rates were offset by the stimulatory effect of DMN-contaminated food.These respiration studies were generally unproductive in explaining the previously reported effects of FT and DMN-contaminated food on the survival of P. pugio under hypoxic conditions.     

Simulation of tides,residual flow and energy budget in the Gulf of California

With the application of a two-dimensional nonlinear hydrodynamical-numerical semi-implicit model, the principal tides M₂, S₂, K₂, N₂, K₁, P₁ and O₁ were studied. Energy budgets of the semi-diurnal M₂ and S₂ were calculated separately. The linear sum of these budgets was compared with the tidal energy budget obtained when these two tidal constituents interact. Since a quadratic form for the bottom friction was used, remarkable differences were found. The results show that in the area of the Colorado River delta, the dissipation of tidal energy is very strong. Intense tidal currents were observed in the same region and over the Salsipuedes Sill. Energy budgets calculated for forcing waves of different periods, but of the same amplitude, were used to estimate the principal periods of resonance. Although the topography of the Gulf is very complex, the model reproduced observed sea-surface elevation and current patterns. To study spring tide conditions, the above seven tidal constituents were simulated. Estimates of residual currents reveal the presence of several intense cyclonic and anticyclonic gyres. Over the Salsipuedes Sill, residual currents of the M₂ tide reach values of more than 15 cm s⁻¹. Horizontal distributions of dissipation rates of tidal energy and of kinetic energy were also obtained.     

Variations in the boundary-drag coefficient in the tidal entrance to Chesapeake Bay,Virginia

Use of the quadratic shear-stress law for estimating boundary drag requires specific knowledge of the magnitude of a drag coefficient, C_D, and sectional mean velocity, $\text{u}\text{?}$. In previous attempts to adapt the relationship for use in studies of marine-sediment transport, the flow measurement has been standardized at a level 100 cm above the bed. The particularized value of the drag coefficient has been designated as C₁₀₀.In the entrance area to Chesapeake Bay, Virginia, C₁₀₀ has been found to range through unacceptably wide limits. Two-thirds of the values obtained are between 3.5 · 10^?3 and 5.4 · 10^?2. Mean C₁₀₀ for the area is 1.3 · 10^?2 as compared to 3 · 10^?3 for tidal channels within Puget Sound, Washington.Present data suggest that, given a moveable bed, a size hierarchy of mobile bed forms, time-varying flow, and a lack of equilibrium between flow and bed, C₁₀₀ changes continuously with boundary shear stress.Accurate evaluation of boundary shear stress in tidal entrances with high flow rates and mobile beds presently requires measurement of velocity profiles.     

Models for dynamic evaluation of mudstone/shale cap rocks and their applications in the Lower Paleozoic sequences,Sichuan Basin,SW China

The estimation of the sealing capability of cap rocks dynamically is one of the fundamental geological problems that must be resolved in petroleum exploration. In this paper, a porosity–capillary pressure (ϕ–P_c) method was used to estimate the sealing capacity during cap rock burial and a permeability–capillary pressure (K–P_c) plus over-consolidation ratio (OCR) method to estimate the sealing capacity during uplift. Based on 120 capillary pressure–porosity measurements, a ϕ–P_c mathematical model has been established for the burial phase. By analyzing the permeability data measured from 12 mudstone/shale samples from different stratigraphic intervals under step loading conditions, a permeability–confining pressure (K–P) mathematical model has been constructed. Moreover, capillary pressure–permeability data measured from 141 mudstone or shale cap rocks have been used to establish a K–P_c mathematical model for seal capacity evaluation during uplift. Additionally, the OCR of mudstone or shale was calculated from the results of reconstructed burial and uplift histories. These mathematical models were used in case studies in the Sichuan Basin, South China. The results indicate that capillary pressure (P_c) is inadequate in evaluating sealing capacity of cap rocks but the combination of parameters P_c and OCR works well. The agreement between calculated and measured values shows the effectiveness and reliability of the models for dynamic estimation of the sealing capacity of mudstone/shale cap rocks established in this study.     

Thickness of the mixed bottom layer in the Northern Atlantic

The thickness of the mixed bottom boundary layer (BBL) has been analyzed based on the CTD data at transoceanic sections in abyssal waters of the Northern Atlantic. The measurements were carried out at two transoceanic sections approximately along 48° N (ASV-99) and 5° N (AI-2000) in 1999 and 2000. These data, and the WOCE data obtained at four zonal sections (AR7E and AR12 along 57° N, AR01 along 24.5° S, and A06 along 7.5° N), were used for the calculation of the statistical characteristics of the BBL??s thickness H _B . The probability distribution function F(H _B ) was close to lognormal. The mean value ??H _B ?? at different latitudes was in the range from 30 to 60 m. The averaged BBL thickness = 46.1 m. The BBL??s thickness was about 1% of the ocean??s depth D; the ratio H _B /D was the minimum (0.8%) near the equator and increased up to 1.6% in the polar latitudes.     

Phytoplankton community adaptation to changing light levels in the southern Beaufort Sea,Canadian Arctic

The chlorophyll a specific absorption coefficient of phytoplankton, a_φ^∗(λ) is an important parameter to determine for primary production models and for the estimation of phytoplankton physiological condition. Knowledge of this parameter at high latitudes where nutrient rich cold water submitted to low incident light is a common environment is almost nonexistent. To address this issue, we investigated the light absorption properties of phytoplankton as a function of irradiance, temperature, and nutrients using a large data set in the southern Beaufort Sea during the open water to ice cover transition period. The a_φ^∗(λ) tended to increase from autumn when open water still existed to early winter when sea ice cover was formed, resulting from a biological selection of smaller-size phytoplankton more efficient to absorb light. There was no significant correlation between a_φ^∗(λ) and irradiance or temperature for both seasons. However, a_φ^∗(λ) showed a significant positive correlation with NO₃ + NO₂. Implications of the results for phytoplankton community adaptation to changing light levels are discussed.     

Empirical ocean-color algorithms to retrieve chlorophyll-a, total suspended matter, and colored dissolved organic matter absorption coefficient in the Yellow and East China Seas

A bio-optical dataset collected during the 1998?C2007 period in the Yellow and East China Seas (YECS) was used to provide alternative empirical ocean-color algorithms in the retrieval of chlorophyll-a (Chl-a), total suspended matter (TSM), and colored dissolved organic matter (CDOM) absorption coefficients at 440 nm (ag₄₄₀). Assuming that remote-sensing reflectance (Rrs) could be retrieved accurately, empirical algorithms for T_Chl (regionally tuned Tassan??s Chl-a algorithm) in case-1 waters (T_Chl2i in case-2 waters), T_TSM (regionally tuned Tassan??s TSM algorithm), and T_ag440 or C_ag440 (regionally tuned Tassan??s or Carder??s ag₄₄₀ algorithm) were able to retrieve Chl-a, TSM, and ag₄₄₀ with uncertainties as high as 35, 46, and 35%, respectively. Applying the standard SeaWiFS Rrs, T_Chl was not viable in the eastern part of the YECS, which was associated with an inaccurate SeaWiFS Rrs retrieval because of improper atmospheric correction. T_Chl behaved better than other algorithms in the turbid case-2 waters, although overestimation was still observed. To retrieve more reliable Chl-a estimates with standard SeaWiFS Rrs in turbid water (a proxy for case-2 waters), we modified T_Chl for data with SeaWiFS normalized water-leaving radiance at 555 nm (nLw₅₅₅) > 2 mW cm^?2 ??m^?1 sr^?1 (T_Chl2s). Finally, with standard SeaWiFS Rrs, we recommend switching algorithms from T_Chl2s (for case-2 waters) to MOC_Chl (SeaWiFS-modified NASA OC4v4 standard algorithm for case-1 waters) for retrieving Chl-a, which resulted in uncertainties as high as 49%. To retrieve TSM and ag₄₄₀ using SeaWiFS Rrs, we recommend empirical algorithms for T_TSM (pre-SeaWiFS-modified form) and MT_ag440 or MC_ag440 (SeaWiFS Rrs-modified forms of T_ag440 or C_ag440). These could retrieve with uncertainties as high as 82 and 52%, respectively.     

On the CO2O2 system in the Northeastern Pacific

The TCO₂, O₂, TA and δ¹³C data of the 1969 Geosecs Intercalibration Cruise was analyzed and found to be consistent with a vertical mixing model which assumes that each point along a vertical profile is a mixture of the upper and lower boundaries. Calculated regression coefficients are in agreement with the model of Redfield et al. (1963) and with the assumption that TA variation is due to carbonate reaction. Oxygen consumption and TCO₂ production decrease exponentially with depth and approximately 80% of ΔCO₂ can be accounted for, on average, by O₂ consumption. The remaining 20% are probably due to carbonate solution which seems to take place at depths below 2,500 m. The present study suggests that the isotopic composition (δ¹³C) of the carbon source, required to account for most of the oxygen consumed, may be heavier than the value of −23%. assigned to dissolved organic carbon and particulate organic carbon.     

Environmental influences on the trawl catches in a bay-estuarine system of Goa,west coast of India

The degree of relationship between trawl catch and environmental variables was assessed in a bay-estuarine system of Goa, west coast of India using multivariate techniques. The demersal fish assemblage was dominated by the families, Leiognathidae, Sciaenidae, Clupeidae, Cynoglossidae and Stromateidae and were considered to be typical for the Indo-Pacific. Patterns in community-structure were analyzed by principal component analysis (PCA) which identified five major species-groups that explained 66% of the variation in absolute fish biomass. PCA was also performed using 13 environmental variables to reduce data set variability to four components which accounted for 75% of environmental variation. The model that best explained variation in absolute biomass based on maximum R² (adjusted) and minimum Mallows' C_p statistic was 71% and included six variables such as dissolved oxygen, macrobenthic density, sediment pH, photosynthetic pigment (Chl a), particulate organic carbon (POC) and seston. The regression coefficients were significant (P<0.05) and small values of C_p indicated the preciseness of the developed model. Path analysis was used to construct a hypothetical causal path diagram to depict the interaction between fish biomass and environmental variables. The study demonstrated the most important variables with regard to environmental–biotic interactions, although the measured variables did not account for all the variation in trawl catches. Further studies elucidating ecologically meaningful relationships should be helpful in bay-estuarine fisheries management.     

Simulating the Propagation of Infrasonic Waves and Estimating the Energy of the Chelyabinsk Meteoroid Explosion Observed on February 15, 2013

Results obtained from simulating the propagation of infrasonic waves from the Chelyabinsk meteoroid explosion observed on February 15, 2013, are given. The pseudodifferential parabolic equation (PDPE) method has been used for calculations. Data on infrasonic waves recorded at the IS31 station (Aktyubinsk, Kazakhstan), located 542.7 km from the likely location of the explosion, have been analyzed. Six infrasonic arrivals (isolated clearly defined pulse signals) were recorded. It is shown that the first “fast” arrival (F) corresponds to the propagation of infrasound in a surface acoustic waveguide. The rest of the arrivals (T1–T5) are thermospheric. The agreement between the results of calculations based on the PDPE method and experimental data is satisfactory. The energy E of the explosion has been estimated using two methods. One of these methods is based on the law of conservation of the acoustic pulse I, which is a product of the wave profile area S/2 of the signal under analysis and the distance to its source E _I [kt] = 1.38 × 10^–10 (I [kg/s])^1.482. The other method is based on the relation between the energy of explosion and the dominant period T of recorded signal E _T [kt] = 1.02 × (T [s]²/σ)^3/2, where σ is the dimensionless distance determining the degree of nonlinear effects during the propagation of sound along ray trajectories. According to the data, the explosion energy E _I,T ranges from 1.87 to 32 kt TNT.     

Petroleum pollution in surface sediments of Daya Bay,South China,revealed by chemical fingerprinting of aliphatic and alicyclic hydrocarbons

Nine surface sediments collected from Daya Bay have been Soxhlet-extracted with 2:1 (v/v) dichloromethane-methanol. The non-aromatic hydrocarbon (NAH) fraction of solvent extractable organic matter (EOM) and some bulk geochemical parameters have been analyzed to determine petroleum pollution of the bay. The NAH content varies from 32 to 276 μg g⁻¹ (average 104 μg g⁻¹) dry sediment and accounts for 5.8–64.1% (average 41.6%) of the EOM. n-Alkanes with carbon number ranging from 15 to 35 are identified to be derived from both biogenic and petrogenic sources in varying proportions. The contribution of marine authigenic input to the sedimentary n-alkanes is lower than the allochthonous input based on the average n-C₃₁/n-C₁₉ alkane ratio. 25.6–46.5% of the n-alkanes, with a mean of 35.6%, are contributed by vascular plant wax. Results of unresolved complex mixture, isoprenoid hydrocarbons, hopanes and steranes also suggest possible petroleum contamination. There is strong evidence of a common petroleum contamination source in the bay.     

Shell form,growth, and production of Astarte borealis (Schumacher, 1817) (Astartidae,Bivalvia) in the southeastern Baltic Sea

The relationships between the linear dimensions and body weight and the ratio between the masses, growth, and production were studied for the bivalve Astarte borealis inhabiting the southeastern Baltic Sea. The maximal shell length was 21.09 mm, while the maximum age was 8+. The linear growth was described by the Bertalanffy equation L _τ = (1 - e ^{-0.0894(τ-(-0.7354))}). The annual production was 7.60 kJ/m² at a P _s/B coefficient of 0.41. It was found that the A. borealis inhabiting the southeastern Baltic Sea was characterized by a lower linear growth rate compared to the mollusks of other parts of the geographical range due to the low salinity of the Baltic Sea.     

Evaluation of two WAM white capping parameterizations using parallel unstructured SWAN with application to the Northern Gulf of Mexico, USA

The performance of two well accepted formulations for white capping and wind input of third generation wave models, viz., WAM-3 and WAM-4, were investigated using parallel unstructured SWAN (PunSWAN). Several alternative formulations were also considered to evaluate the effects of higher order steepness and wave number terms in white capping formulations. Distinct model configurations were calibrated and validated against available in situ measurements from the Gulf of Mexico. The results showed that some of the in situ calibrated models outperform the saturation level calibrated models in reproducing the idealized wave growth curves. The simulation results also revealed that increasing the power of the steepness term can enhance the accuracy of significant wave height (H_s), at the expense of a higher bias for large waves. It also has negative effects on mean wave period (T_a) and peak wave period (T_p). It is also demonstrated that the use of the quadratic wave number term in the WAM-3 formulation, instead of the existing linear term, ameliorates the T_a underestimation; however, it results in the model being unable to reach any saturation level. In addition, unlike H_s and T_p, it has been shown that T_a is sensitive to the use of the higher order WAM-4 formulation, and the bias is decreased over a wide range of wave periods. However, it also increases the scatter index (SI) of simulated T_a. It is concluded that the use of the WAM-4 wind input formulation in conjunction with the WAM-3 dissipation form, is the most successful case in reproducing idealized wave growth curves while avoiding T_a underestimation of WAM-3 and a potential spurious bimodal spectrum of WAM-4; consequently, this designates another perspective to improve the overall performance of third generation wave models.     

Probability distributions of peaks,troughs and heights of wind waves measured in the black sea coastal zone

The present paper examines the adequacy of different probability density functions to describe the peaks, troughs and peak-to-trough excursions of wind waves measured in the coastal zone of the Bulgarian part of the Black sea. For that purpose various theories for non-Gaussian random process are applied. Some theories depend on the mean, variance and coefficient of skewness γ₃ of the process. Others also take the coefficient of kurtosis γ₄ into consideration. The analyzed field data are gathered in the coastal zone of the Bulgarian part of the Black sea with depth decreasing from 18 to 1.3 m. The measurements are carried out simultaneously for 11 points with time series of 20 min duration. The coefficients of skewness and kurtosis in those time series are expressed as functions of depth and spectral peak frequency. Analogous dependencies on depth of other parameters are also found. As a result of the investigation it is concluded that the probabilities of occurrence of large wave crests and heights are underpredicted by all of the theories considered.     

Geochemistry and charge history of oils from the Yuqi area of Tarim Basin,NW China

The geochemistry, origin and charge history of oils from the Yuqi area of Tarim Basin have been investigated, through GC, GC-MS and fluid inclusion microthermometry analysis. The Yuqi oils accumulated mainly in three intervals: (1) in the Lower-Middle Ordovician Yingshan Formation (O_1-2y) carbonate reservoirs; (2) in the overlying Upper Triassic Halahatang Formation (T₃h); and (3) in the Lower Cretaceous Yageliemu Formation (K₁y) sandstones. Oils from different reservoirs have distinct physical properties, varying from extra-heavy (O_1-2y), heavy (T₃h), to light oils (T₃h and K₁y). However, their geochemical compositions show a high degree of similarity, which indicates that they derive from the same source rock. Abundant tricyclic terpanes, gammacerane, dibenzothiophene and C₂₁C₂₂steranes, together with a low level of diasteranes, indicate an anoxic marine source rock for oils in the Yuqi area. Oil-oil correlation shows that Yuqi oils derive from the same source bed as Tahe oils. The co-occurrence of intact n-alkanes and 25-norhopanes in all the samples supports the proposition that there is a mixture of an early filled severely biodegraded oil and a late filled fresh oil.In this study, charge history is examined on the basis of integration of fluid inclusion homogenization temperature data with 1D burial-thermal history models. Two episodes of oil charging are identified in the O_1-2y reservoir (well YQX1-1) at around 436-420 Ma (Middle-Late Silurian) and 10-3 Ma (Miocene to Pliocene), respectively. For the samples from the T₃h and K₁y intervals, only one episode of oil charge is indicated by the homogenization temperatures of coexisting aqueous inclusions with an inferred timing around 10-3 Ma. The T₃h heavy oil reservoir is assumed to be a secondary hydrocarbon pool, which accumulated by re-migration and re-distribution of hydrocarbons from O_1-2y hydrocarbon pools. The few early biodegraded oils in the K₁y light oils were probably picked up along the migration pathway during the late fresh oil charging.