Northwestern Hellenic Arc: Concurrent sedimentation and deformation in a compressive setting

Seismic (air-gun) and 3.5-kHz systems and coring in the northwestern sector of the Hellenic Arc, Ionian Sea, serve to define the regional configuration, attitude and geometry of the unconsolidated sedimentary cover in a compressive tectonic setting. The Pliocene and Quaternary deposits are deformed to varying degrees throughout the region southwest of the island of Zakinthos. Depositional trends, overall structural configuration of the cover, and assemblages of deformation structures, including tilted, folded and faulted strata associated with a very complex topography, clearly reflect syndepositional modification in a tectonically mobile area. The structural attitude of the unconsolidated strata can be distinguished from that in tectonically active regions of the Mediterranean where extension prevails. The youthful physiography, sediment dispersal patterns and depositional distribution reveal prevailing NW—SE and NE—SW trends. Sediment deformation structures, whose axes strike primarily NW—SE, reveal a general NE—SW compressive stress trend. The geologically recent nature and orientation of the deformation are compatible with present theories concerning the evolution of the Hellenic Arc.     

Mathematical modeling of the terrigenous sedimentation in the Sea of Azov

Based on balance calculations with the use of a spatially detailed mathematical model for transport and sedimentation of the particulate matter adjusted to the conditions of the Sea of Azov, particular spatiotemporal features of the terrigenous sedimentation in the second half of the 20th century are recognized. The general tendency for the deceleration of the accumulation of terrigenous sediments and for the decrease in the areas with a negative balance of the terrigenous matter is related to the 2.5-fold fall in the volumes of the matter supplied from land. During the period considered, the intensity of the sedimentation decreased from 1000 to 400 g/m²/year. The accumulation of terrigenous sediments proceeds in the regions where the sources of the matter supply are concentrated and where features of the bottom morphology and hydrodynamical activity are favorable for the sedimentation: in Taganrog and Temryuk bays. In the central part of the sea, the intensity of the sedimentation comprises a value of about 300 g/m²/year. In Taganrog Bay and in the sea proper, areas with a negative balance of terrigenous sedimentary matter increased up to 30%.     

Reviewing the far-reaching ecological impacts of human-induced terrigenous sedimentation on shallow marine ecosystems in a northern-New Zealand embayment

ABSTRACT

Human settlement in Bay of Islands, New Zealand, beginning ～1300 AD, wrought immense, conspicuous and enduring change to local shallow-water marine ecologies, this review addressing those transformations attributable to increased rates of anthropogenically induced, land-derived sedimentation. Elevated silt inflow, particularly after the late-1800s, in course led to ～130% expansion in mangrove (Avicennia marina) cover, with concomitant loss of saltmarsh, uppershore coarse-shell beaches/cheniers, and (probably) intertidal seagrass (Zostera muelleri). Sedimentation also led to widespread loss of estuarine shellfish habitat, and, although not necessarily categorically causal, seems, at the same time to have contributed to such degradation among cockle (Austrovenus stutchburyi) populations that few individuals attain their potential size. Most changes, many seemingly irreversible, can be described as ecologically catastrophic, with ecosystems altered and destroyed, and uncommon habitats threatened. Sedimentation appears the single-most important and enduring contributor to ecological degradation in shallow waters of this northern harbour, with time lags between stressor-onset and realisation of impact (decades to centuries) that only now are becoming clear. Outstanding issues concern establishing the extent of relationship between levels of terrigenous sedimentation and cockles seldom attaining their previous maximum sizes, and origins of the possibly new, widespread phenomenon of living cockles accumulating and dying atop beach surfaces.     

Deep-sea terrigenous organic carbon transfer and accumulation: Impact of sea-level variations and sedimentation processes off the Ogooue River (Gabon)

Sedimentary, isotopic and bulk geochemical proxies measured in sediment samples of five gravity cores collected in the distal part of the Ogooue turbidite system (around 4000 m-depth) were used to develop a conceptual model to describe the accumulation of terrigenous organic matter (OM) during the last 200,000 yrs BP in the eastern part of the Gulf of Guinea. This model takes into account the influence of the different depositional processes (turbiditic vs hemipelagic sedimentation), geomorphological features and sea-level variations.Total organic carbon (TOC) and the stable organic carbon isotopes of the OM (δ¹³C) variability follow the highstand/lowstand (interglacial/glacial) cyclicity with a very low accumulation rate of terrigenous OM during periods of high sea-level and higher accumulation rate during period of low sea-level. A sea-level of 80–120 m below present day seems to favor the transfer of terrigenous sediments to the deep offshore environment through the turbidite system and thanks to the connection of the canyons heads with the river system presently located at the shelf edge at −120 m water depth.In this system, terrigenous OM matter delivered by the river accumulate in the sediments via two main processes. Indeed, a part of the terrigenous OM settles in combination with the finest particles forming hemipelagites, while another part, formed of very well preserved land plant debris, is transported and deposited far offshore with turbidity currents. The proportion of terrigenous OM accumulated due to turbidity currents is important as it can represent more than 70% of the carbon accumulated during sea-level lowstand. Moreover, terrigenous OM seems to preferentially accumulate in the levees and the lobes of the system notably due to the higher frequency of organic-rich turbidites.This study demonstrates that gravity flows, influenced by the sea-level variations, can significantly affect the terrigenous OM budget of the deep offshore Atlantic margins and that channel-levee complexes as well as turbidite lobes can be regarded as good sink for terrestrial organic carbon. These processes should be taken into consideration in the context of source rocks exploration but also for the estimation of the general carbon accumulation in ocean sediment.     

Sources and distributions of terrigenous organic matter in a mangrove fringed small tropical estuary in South China

The sources and distributions of terrigenous organic matter (OM) were investigated in a small tropical estuary in the Hainan Island, South China. Plants, suspended particulate matter (SPM), and surface sediments samples in the estuary and coast were collected. Bulk properties [organic carbon (OC%), total nitrogen (TN%), stable carbon isotope (δ13C) and grain size] and lignin phenol concentrations were measured. OC% of mangrove plants was (43.4 ± 2.1)%, which is similar to the values reported for mangrove plants in other regions. OC% of sediment samples ranged from 0.07% to 1.42%, and they were related to the sediment texture. Lignin phenols in the sediment ranged from 5.16 mg/100 mg OC in the uppermost station to 0.51mg/100mg OC in the coast. The molar ratio of organic carbon to total nitrogen (C/N) (～7) and δ 13 C (～-31.1×10-3 ) of riverine SPM revealed that the major OM sources of riverine SPM were aquatic OM (phytoplankton and/or bacteria). Moreover, the lower lignin concentration (Λ8) and higher (Ad/Al)v of lignin phenols suggest that terrestrial OM in riverine SPM were mainly from soil. Furthermore, C/N ratio, δ13C and lignin phenols reveal that mangrove plants were the predominant OM sources of mangrove surface sediment. Based on the δ13C and lignin phenols, it can be concluded that the major OM sources in estuarine and coastal surface sediments were marine phytoplankton, riverine SPM and mangrove surface sediment. In addition, the higher (Ad/Al)v of lignin phenols in those coastal sediments indicate that seagrass might be a potential OM source in coastal sediments, however, the lower (Ad/Al)v in the estuarine sediments in turn suggests that seagrass could not be transported to the mangrove fringed region. A three-end-member model which is based on lignin concentrations and δ13C was applied to evaluate the contribution of mangroves to the organic matter preserved in the surface sediments. Around the mangrove fringed region, mangrove could contribute more than 50% to the sedimentary OM, and this value is much higher than riverine OM. Nevertheless, mangrove OM could not be efficiently transported to the coastal region. Our study suggests that mangrove forest is an important OM source in this small estuary.     

Tectonic control over topography and channel sedimentation across the forearc slope of the southern Kurile Trench

A high-resolution seismic survey covering more than 2,000 km² has revealed the processes responsible for the slope morphology and channel sedimentation across the forearc slope-basin of the Kurile Arc–NE Japan Arc collision zone, offshore from Tokachi (Hokkaido, Japan). The dominant slope contours parallel the trench but, in the middle and lower reaches of the southern slope, contours are convex-shaped with an offshore trend. This sector of the slope is traversed diagonally by the Hiroo submarine channel. The offshore-trending convex contours and the channel course have developed through the interplay of tectonic and sedimentary processes, including the development of anticlines, anticline-induced lobe sedimentation and channel avulsion. In its upper reaches, the channel is restricted by a topographic low associated with NNW–SSE-trending anticlines which developed within the upper and middle slope sectors during late Miocene uplift. The uplift timing and trend of these anticlines indicate that they resulted from collision, the channel sedimentology and slope morphology of the middle and lower slopes having been influenced by Pliocene uplift of NE–SW-trending anticlines. The trends of these anticlines parallel those of the Kurile Trench. The Pliocene and early Pleistocene strata of the middle and lower slopes consist of ponded lobe sediments deposited along the palaeo-Hiroo submarine channel on the landward side of the anticlines. As a lobe pile accumulated, the channel thalweg shifted to the north of the stack, allowing the channel to bypass the topographic high formed by the growing stack. Thick levee deposits built up along the channel course during the late Pleistocene and Holocene. These levees, along with the Pliocene and early Pleistocene lobes, are reflected in the present-day sigmoid-shaped, convex offshore-trending contours. Thus, the interplay of subduction- and collision-related anticlines, tectonic-related channel ponding, and avulsion has contributed to the slope morphology of the southern Kurile Trench.     

The contribution of near-bed currents to modern sedimentation processes in the deep waters of the Hellenic Arc-Trench system, eastern Mediterranean

The effects of near-bed current activity on modern sedimentation were examined in various deepwater environments (>500 m) of the Hellenic Arc-Trench system. Near-bed currents were able to resuspend essentially flat beds covered by very fine sediments (>8.5 J) only when current speeds exceeded 11 cm s^-1. At lower speeds, the initiation of resuspension of the muddy sediments was related to increased hydraulic bed roughness resulting from biogenic benthic activity. As such, observed near-bed currents make different contributions to the regional sedimentation processes, i.e., at levels which are low in the Gulf of Corinth, moderate in the NW Aegean Sea and Zakynthos Channel, and high in the NE Ionian Sea.     

An overview of sedimentation on the amazon continental shelf

Sedimentological, geochemical, and physical-oceanographic studies of the Brazilian continental shelf near the Amazon River help provide a broad understanding of this major sediment dispersal system. Amazon River sediment accumulates as a subaqueous delta, with the most rapid accumulation (10 cm/yr) occurring near the seaward edge of the topset beds and in the foreset beds. Amazon River sediment is dispersed northwestward along the shelf and is transported beyond the Brazilian border. Radiographic studies of sediment cores delineate three sedimentary environments: interbedded mud and sand, faintly laminated mud, and bioturbated mud. The distribution of these environments is a function of proximity to the river mouth and of sediment accumulation rate.     

微尺度滑动平均方法计算海浪谱奇阶矩的公式

Glazman提出了一种计算海浪谱高阶谱矩的微尺度平均方法,但是,他利用随机过程理论导出的计算偶阶矩的公式和参照偶阶矩结论定义的奇阶矩计算公式之间存在着内在的不一致性.本文在Glazman工作的基础上根据随机过程理论推导了“微尺度平均方法”计算奇阶谱矩的公式,纠正了他的错误.上述结论随即应用于讨论破碎对波面水质点水平速度分布的影响.通过破碎的加速度判据考虑了破碎对速度分布的限制,给出了未破碎波面上水质点水平速度的的统计分布的初步结果.该分布取决于谱宽度参数及白浪覆盖率的大小,当白浪覆盖率较大时明显偏离正态分布.     

Quantitative links between fluvial sediment discharge,trapped terrigenous flux and sediment accumulation,and implications for temporal and spatial distributions of sediment fluxes

The southwestern-most Okinawa Trough (SOT), characterized by high sedimentation rates (>0.1 cm/yr), has the potential for recording high-resolution episodic events, such as storm floods and seismic activities, at least on a regional scale. To retrieve data on past climate change from nearby sediment cores and quantitatively reconstruct it, particularly with respect to precipitation (or typhoon-induced flood events), a linkage between fluvial sediment discharge and terrigenous sediment flux is warranted. Apparent sediment fluxes, observed with four arrays of sediment traps deployed in the SOT, were found to vary with fluvial sediment discharges. Empirical equations for individual arrays of sediment traps are site-dependent and related to the scenario of initial supply, transport and final deposition of terrigenous sediments (i.e. land–sea interaction). Using these equations and hydrological data from 1950 to 2000, the long-term temporal and spatial variations of settling sediment fluxes were simulated. Simulation results agree well with sediment mass accumulation rates derived from literature data on ²¹⁰Pb and ¹³⁷Cs chronology. The simulated spatial patterns of sediment fluxes along a slope–trough section illustrate that sediment plumes can disperse concurrently in two manners, namely near-bottom and mid-depth plumes, and the flood-driven plumes can travel very long distances, approaching 125°E or beyond. The sediment burial budget in the SOT was estimated to be approximately 5.2 Mt/yr, representing about 80% of riverine exports from the Lanyang Hsi, Taiwan. This is the first study dealing qualitatively and quantitatively with two parameters, namely terrigenous sediment flux and fluvial sediment discharge.     

An inverse design approach for minimising wake at propeller plane using CFD

Knowledge of wake characteristics in the stern region is important for ensuring good propeller design and performance. This work examines the utility of CFD in the analysis of flow in the case of full aft beam vessels having characteristic cut stern shape to facilitate propeller aperture. The underwater stern shape may be more complex due to the occurrence of stern appendages such as bossings, strut supports and local shape variations. To this extent, CFD offers an effective tool for both qualitative as well as quantitative assessment of the local geometry. Wake estimate is required for choice of the most favorable propeller geometry. In the present method, the analysis quantifies the effects of small changes in stern rake angles and offers an inverse design approach towards finalising the stern shape. The method consists of solving the standard k-ε turbulent model of RANS equations in cell centered finite volume multi zone grid in the flow domain. This approach has been used in estimating the velocity at the propeller plane. The results have been compared with experimentally obtained values of nominal wake. The approach suggests that CFD can provide a cost effective and quick assessment of flow. It is also an attractive means of pre-empting heterogeneous flow related problems such as vibration and noise due to unfavorable wake in the stern region.     

Generating extreme ship responses using non-uniform phase distributions

Modified Gaussian phase distributions are used to generate short time series containing a specific extreme value of a ship response. The corresponding incident wave train is calculated via linear systems theory. Sample response and wave time series are compared to the expected time series as calculated by probabilistic analysis. The average of the sample response time series compares favorably to the expected time series, but the average of the sample wave trains does not, in general, match the expected wave train. These comparisons show the danger in estimating extreme ship responses considering only extreme waves. A sample analysis for a Great Lakes bulk carrier is included for illustration.     

The effect of glucose on the productivity of seawater: An experimental approach using controlled aquatic ecosystems

Small quantities (1 to 5 mg litre) of glucose were added to 60-ton enclosed water columns together with inorganic nutrients. Heterotrophic production by bacteria in the glucose-enriched water columns depressed photosynthetic production by algae. This effect was believed to have been caused by heterotrophic growth out-competing the autotrophic organisms for a limited supply of nitrate. Secondary and tertiary production in the glucose-enriched water columns was higher than under conditions of predominantly autotrophic production.     

An offshore eddy in the California current system Part IV: Plankton distributions

The distribution of plankton across a warm-core eddy system in the California Current 400 km off Point Conception, California was studied in January 1981. The eddy system, about 150 km in diameter at the 7°C isotherm, was made up of a 75 m thick surface layer, a cold-core region extending from 75 m to about 200 m, and a warm-core eddy below 200 m extending to at least 1450 m. Casts for the vertical distribution of chlorophyll/phaeophytin and integrating zooplankton net tows were taken at 37 stations located about 20 km apart on two orthogonal transects across the eddy system. Vertical distributions of microplankton were determined on one section from the eddy center to beyond the eastern edge. Integrated chlorophyll/phaeophytin values were highest to the north and east of the eddy system; across the system itself, there was only a small increase of values near the center. Asymmetrical distributions of maximum concen Current water was being entrained into the center of the eddy system from the northeast. Dinoflagellates were numerically the most important member of the microplankton, especially in the deep chlorophyll maximum. Zooplankton distributions indicated the intermingling of warm and cool water species throughout at least the upper 200 m of the eddy system. Some cold water species were as abundant inside the system as outside to the north and east; their numbers were much reduced in a band surrounding the system where warm water species were most abundant. The presence of species characteristic of different water types throughout the region of the eddy system provides an indication of the mixing that had occurred since the system originally formed. The biological data, together with the physical and chemical results, indicate the importance of frontal boundary processes and lateral entrainment of surrounding water into the eddy system in determining the character and productivity of such systems.     

Measuring fishery profitability: An index number approach

Tracking the financial well-being of vessels that depend on a marine fishery resource is an important function of regulators. This research demonstrates how simple indices can be constructed and utilized to track the economic well-being of vessels operating in the Northeast (USA) Multispecies (Groundfish) Fishery. The indices, which use both public and private data, can separately track trends in inputs, outputs, and prices. For the Northeast Multispecies Fishery, the indices reveal that the economic well-being of the groundfish fleet has improved under catch share management through gains in productivity.     

Estimating wave crest distributions using the method of L-moments

The design of fixed or floating offshore structures requires accurate information of the met-ocean data at the intended offshore site. In the design process it is recognized that this environmental data is modified in the near-field by the interaction with the particular geometrical configuration of the offshore structure. This transformation of the incident wave field around and beneath an offshore structure presents a challenge for ocean engineers when specifying the wave gap elevation to avoid impact loads on the underside of the deck and inundation of the topsides. Thus, the accurate estimation of the wave crest distributions from measurements at various locations near and under the offshore structure during model test studies is essential. A semi-empirical approach is presented herein that builds upon the findings of previous studies and introduces the Method of L-moments. A three parameter model for a wave crest probability distribution function is presented and explicit relationships between the parameters of the distribution and its’ first three L-Moments are established. Furthermore, three narrow-band models from earlier research studies are reviewed and compared with the new model. Wave measurements from a mini-TLP model test program are used as the basis for comparison of the four distributions. The root-mean-square error is used as a metric to quantify the overall fit of the data and its accuracy in the high end tail of the data. The L-Moment model is shown to be more robust in representing the data in both the far-field and beneath the deck of the mini-TLP where the wave field demonstrates increased non-linear behavior.     

Tracing terrigenous dissolved organic matter and its photochemical decay in the ocean by using liquid chromatography/mass spectrometry

Reversed-phase liquid chromatography/mass spectrometry (LC/MS) is introduced as a new molecular fingerprinting technique for tracing terrigenous dissolved organic matter (DOM) and its photochemical decay in the ocean. DOM along a transect from the mangrove-fringed coast in Northern Brazil to the shelf edge was compared with mangrove-derived porewater DOM exposed to natural sunlight for 2–10 days in a photodegradation experiment. DOM was isolated from all samples via solid-phase extraction (C18) for LC/MS analysis. DOM in the estuary and ocean showed a bimodal mass distribution with two distinct maxima in the lower m/z range from 400 to 1000 Da (intensity-weighted average of 895 Da). Terrigenous porewater DOM from the mangroves was characterized by a broad molecular mass distribution over the detected range from 150 to 2000 Da (intensity-weighted average of 1130 Da). Polar compounds, i.e., those that eluted early in the reversed-phase chromatography, absorbed more UV light and had on average smaller molecular masses than the more apolar compounds.     

Bathymetry of the Tonga Trench and Forearc: a map series

Four new bathymetric maps of the Tonga Trench and forearc between 14 °S and 27 °S display the important morphologic and structural features of this dynamic convergent margin. The maps document a number of important geologic features of the margin. Major normal faults and fault lineaments on the Tonga platform can be traced along and across the upper trench slope. Numerous submarine canyons incised in the landward slope of the trench mark the pathways of sediment transport from the platform to mid- and lower-slope basins. Discontinuities in the trench axis and changes in the morphology of the landward slope can be clearly documented and may be associated with the passage and subduction of the Louisville Ridge and other structures on the subducting Pacific Plate. Changes in the morphology of the forearc as convergence changes from normal in the south to highly-oblique in the north are clearly documented. The bathymetric compilations, gridded at 500- and 200-m resolutions and extending along 500 km of the landward trench slope and axis, provide complete coverage of the outer forearc from the latitude of the Louisville Ridge-Tonga Trench collision to the northern terminus of the Tonga Ridge. These maps should serve as a valuable reference for other sea-going programs in the region, particularly the Ocean Drilling Program (ODP) and the National Science Foundation MARGINS initiative.     

Pigeonite-bearing basalts dredged from the Puerto Rico Trench: A microprobe study

A microprobe study was carried out on zoned clinopyroxene, composed of a pigeonite core mantled by augite, and plagioclase in six tholeiitic basalts dredged from the Puerto Rico Trench (20° 06.8′N, 65° 06.5′W). The pigeonite cores are characterized by high magnesium contents [Fe/Fe + Mg = 0.19 on the average]; their crystallization temperatures based on the three-pyroxene geothermometer are thus estimated to be higher than those of the well-studied tholeiitic pyroxene assemblages (Hakone, Weiselberg, Mull, Skaergaard, and Bushveld). It is suggested from textural and chemical relationships that pyroxene crystallization started first with precipitation of pigeonite followed by simultaneous precipitation of pigeonite and augite and finally by crystallization of augite alone in the groundmass.