Variations In Mean Grain Size Research Articles

The thermal impacts of beach nourishment across a regionally important loggerhead sea turtle (Caretta caretta) rookery

AbstractBeach nourishment is a common coastal management practice used to protect and maintain infrastructure, tourist revenue, and sandy beach habitats. Coastal erosion and increased development along the coast of North Carolina, USA, have resulted in increased use of beach nourishment as an environmentally friendly alternative to hard structures, such as groins and jetties. Despite its advantages, beach nourishment can alter the thermal properties of a beach, potentially impacting the incubation environment of species that utilize this habitat during reproduction. Importantly, in organisms with temperature‐dependent sex determination, the incubation environment plays a key role in determining offspring sex ratios, hatchling survival, and fitness. Here we investigate how beach nourishment influences thermal properties and sand characteristics of eight beaches in the high‐density loggerhead sea turtle (Caretta caretta) nesting region of North Carolina. We find that, despite considerable spatial and temporal variation, nourishment is a significant predictor of mean monthly sand temperatures in both univariate and multivariable predictive models. Across a season, nourished beach sections are, on average, 0.4°C (range 0.3–0.8°C) warmer than their unnourished counterparts. Nourishment is also a significant predictor of the mean and variance of sand grain size. Furthermore, variation in mean grain size, the relative percent of small, medium and large grain sizes and albedo are mainly responsible for differences in mean monthly sand temperatures. As such, the coarser and darker sand often used in nourishment projects may exacerbate climate driven increases in surface temperature.

Paleolimnological reconstruction of the centennial eutrophication processes in a sub-tropical South American reservoir

Reservoirs hold a detailed record of the changes in the input of sediments and nutrients over decades to centuries. Paleolimnological multi-proxy analysis makes it possible to reconstruct baseline conditions to infer early evidence of environmental change. Our study aims to reconstruct historical human impacts derived from urban development on the San Roque reservoir (Córdoba, Argentina) related to the centennial dynamics of sedimentary and eutrophication processes.A paleolimnological record, dated by 210Pb and 137Cs, made it possible to identify two stages during the environmental evolution of the San Roque reservoir. Physical processes, such as fluvial discharge and water level variation, dominantly ruled stage 1 (Unit C) during the initial infilling of the reservoir. Nutrient load and eutrophication processes controlled stage 2 (Units B and A). Stage 1 (77-55 cm; AD 1921 to 1965) occurred before and after the second dam was built and while the level of water increased by ≈ + 8 m; it displayed a high variation in mean grain size and maximum values of magnetic susceptibility. Stage 2 (AD 1965–2017) records a new reservoir base level and the maintenance of high water levels and comparatively more stable conditions. Regarding the eutrophication process throughout stage 2, three sub-stages were defined: a) Sub-stage I (AD 1965–1985) is a period of incipient eutrophication; b) Sub-stage II (AD 1985–2005) is an interval of increase of eutrophication as shown by the increase in several organic proxies related to the abundance of phytoplankton. Echinenone, zeaxanthin and myxoxanthophyll indicate that cyanobacteria increased concentration by three-to four-fold in comparison with the previous sub-stage. c) Sub-stage III (AD 2005–2017) shows the transition to a hypereutrophic state. Diatomea (fuco and diato), dinophyceae (diadino), chlorophyta (lut) and cryptophyta (allo) groups show a comparatively higher contribution.Our results mostly highlight that during the last century the main drivers of changes in the environmental state of the San Roque reservoir were trophic, fluvial and hydrometeorological. These results might provide tools for anticipating future scenarios for water management plans under increasing anthropic pressure.

What Can We Learn From X‐Ray Fluorescence Core Scanning Data? A Paleomonsoon Case Study

AbstractX‐ray fluorescence (XRF) core scanning of marine and lake sediments has been extensively used to study changes in past environmental and climatic processes over a range of timescales. The interpretation of XRF‐derived element ratios in paleoclimatic and paleoceanographic studies primarily considers differences in the relative abundances of particular elements. Here we present new XRF core scanning data from two long sediment cores in the Andaman Sea in the northern Indian Ocean and show that sea level related processes influence terrigenous inputs based proxies such as Ti/Ca, Fe/Ca, and elemental concentrations of the transition metals (e.g., Mn). Zr/Rb ratios are mainly a function of changes in median grain size of lithogenic particles and often covary with changes in Ca concentrations that reflect changes in biogenic calcium carbonate production. This suggests that a common process (i.e., sea level) influences both records. The interpretation of lighter element data (e.g., Si and Al) based on low XRF counts is complicated as variations in mean grain size and water content result in systematic artifacts and signal intensities not related to the Al or Si content of the sediments. This highlights the need for calibration of XRF core scanning data based on discrete sample analyses and careful examination of sediment properties such as porosity/water content for reliably disentangling environmental signals from other physical properties. In the case of the Andaman Sea, reliable extraction of a monsoon signal requires accounting for the sea level influence on the XRF data.

Size dependence of elastic mechanical properties of nanocrystalline aluminum

The effect of grain size on the elastic mechanical properties of nanocrystalline pure metal Al is quantified by molecular dynamics simulation method. In this work, the largest nanocrystalline Al sample has a mean grain size of 29.6nm and contains over 100 millions atoms in the modeling system. The simulation results show that the elastic properties including elastic modulus and ultimate tensile strength of nanocrystalline Al are relatively insensitive to the variation of mean grain size above 13nm yet they become distinctly grain size dependent below 13nm. Moreover, at a grain size <13nm, the elastic modulus decreases monotonically with decreasing grain size while the ultimate tensile strength of nanocrystalline Al initially decreases with the decrease of the grain size down to 9nm and then increases with further reduction of grain size. The increase of ultimate tensile strength below 9nm is believed to be a result of an extended elasticity in the ultrafine grain size nanocrystalline Al. This study can facilitate the prediction of varied mechanical properties for similar nanocrystalline materials and even guide testing and fabrication schemes of such materials.

Correlation between microstructure and electrical, optical properties of thermal annealed ITO thin films

Indium tin oxide (ITO) thin films with the thickness of 300 nm were deposited on quartz substrates via electron beam evaporation. Five samples were post-annealed in air atmosphere for 10 min at five selected temperature points from 200 to 600 °C, respectively. X-ray diffractometer, Hall measurement system and UV–Vis spectrophotometer were adopted to characterize the ITO thin films. Influence of thermal annealing in air atmosphere on microstructure was investigated. Furthermore, the correlation between microstructure and electrical, optical properties of ITO thin films was discussed in detail. All of the ITO thin films had a polycrystalline structure and a preferred orientation of (222), no matter annealed or not. The intensity ratio of I(222)/I(440) initially increased and then decreased, it reached the maximum of 7.37 after annealed at 400 °C for 10 min. The lattice expansion evidently reduced after annealed at 300 °C or even higher temperature. The variation of mean grain size was minor during thermal annealing process regardless of annealing temperature. The carrier concentration is predominant in electrical conductivity, and it is dependent on the activation of donors and the density of oxygen vacancies. Hall mobility is strongly dependent on the mean grain size, lattice distortion and defect density. The optical transmittance is influenced by the density of oxygen vacancies and the consistency of grain orientations.

Nonlinear modelling of shoreface-connected ridges; Impact of grain sorting and interventions

The evolution of shoreface-connected sand ridges on micro-tidal inner shelves and the variations in the mean grain size over these ridges are investigated with process-based models. A review of previous studies is presented, as well as new results that concern the influence of grain sorting on the finite-amplitude behaviour of the ridges, the application of the model to La Barrosa beach and the role of wave-topography feedbacks. The ridges initially form due to morphodynamic self-organisation, in which the presence of waves and a storm-driven current are crucial. Predicted growth time scales, migration speeds, topography and spatial pattern of the mean grain size agree with field data collected on micro-tidal shelves in the case that both bedload and suspended load sediment transport are accounted for, together with spatially non-uniform wave orbital motion. The model can not successfully explain the presence of large-scale ridges observed on La Barrosa inner shelf, because strong and complex behaving tidal currents occur in that area. Nonlinear model simulations show that on the long term the height of the ridges evolves towards a finite, constant value, whilst their migration speed hardly changes during the evolution. In the saturated stage the ridges have asymmetrical profiles, with steep slopes on the downstream sides. The maximum variation in mean grain size also tends to a constant value and during the evolution the spatial lag between the patterns in the mean grain size and topography decreases. The processes that cause these changes are identified and explained. Model results can be obtained for transverse bottom slopes up to 50% of their observed values on micro-tidal shelves. Extrapolation of results to realistic values of the inner shelf slope yields, in case of Long Island shelf, a final height that agrees with observed ridge heights, but the modelled variation in mean grain size is small compared to field data. Finally, the response of ridges to large-scale interventions is considered. Experiments reveal that extraction of sand on the inner shelf causes a decrease of the sand volume stored in the surf zone.

남서태평양 리코후 드리프트 퇴적층의 쇄설성 실트입자 크기의 수직적 변화를 이용한 플라이스토세 후기 심해서안경계해류의 세기 변화

Hole 1124 of ODP Leg 181 was located in the Rekohu sediment drift off eastern New Zealand in the southwest Pacific Ocean. Mean gain sizes of sortable silt were measured in two drilled cores (1124A and l124B). Chronostratigraphy of core 1124 was correlated with the well-dated nearby core S931, resulting that the age of core 1124 covers the late Pleistocene spanning about MIS (Marine Isotope Stage) 5. Mean grain size of sortable silt seemed to be relatively large during the glacial period, whereas that of the interglacial period was smaller, although several tephra layers contain some coarse-grained pyroclatic particles. The variation in mean grain size of sortable silt in Rekohu sediment drift during the late Pleistocene indicates that the intensity of Deep Western Boundary Current (DWBC) might have been enhanced during the glacial period as a result of increased production of Antarctic Bottom Water (AABW).

Coherence between solar activity and the East Asian winter monsoon variability in the past 8000 years from Yangtze River-derived mud in the East China Sea

AMS 14C dating and grain-size analysis for Core PC-6, located in the middle of a mud area on the inner shelf of the East China Sea (ECS), were used to rebuild the Holocene history of the East Asian winter monsoon (EAWM). The 7.5-m core recorded the history of environmental changes during the postglacial transgression. The core’s mud section (the upper 450 cm) has been formed mainly by suspended sediment delivered from the Yangtze River mouth by the ECS Winter Coastal Current (ECSWCC) since 7.6 kyr BP. Using a mathematical method called “grain size vs. standard deviation”, we can divide the Core PC-6’s grain-size distribution into two populations at about 28 μm. The fine population (< 28 μm) is considered to be transported by the ECSWCC as suspended loads. Content of the fine population changes little and represents a stable sedimentary environment in accord with the present situation. Thus, variation of mean grain-size from the fine population would reflect the strength of ECSWCC, which is mainly controlled by the East Asian winter monsoon. Abrupt increasing mean grain size in the mud section is inferred to be transported by sudden strengthened ECSWCC, which was caused by the strengthened EAWM. Thus, the high resolution mean grain-size variation might serve as a proxy for reconstruction of the EAWM. A good correlation between sunspot change and the mean grain-size of suspended fine population suggests that one of the primary controls on centennial- to decadal-scale changes of the EAWM in the past 8 ka is the variations of sun irradiance, i.e., the EAWM will increase in intensity when the number of sunspots decreases. Spectral analyses of the mean grain-size time series of Core PC-6 show statistically significant periodicities centering on 2463, 1368, 128, 106, 100, 88-91, 76-78, and 70-72 years. The EAWM and the East Asian summer monsoon (EASM) agree with each other well on these cycles, and the East Asian Monsoon (EAM) and the Indian Monsoon also share in concurrent cycles in Holocene, which are in accord with the changes of the sun irradiance.

Effect of annealing on the surface microstructural evolution and the electromigration reliability of electroplated Cu films

This paper presents the effects of annealing, performed over a temperature range from 200°C to 400°C, on the surface microstructural evolution and the electromigration reliability of electroplated Cu films. After annealing, a substantial increase in surface roughness was observed, while variations in mean grain size and nanoindentation hardness were minor. Given the annealing temperature, the surface roughness was larger for the films annealed in forming gas, due to the existence of hydrogen. In particular, the films annealed at 400°C in forming gas demonstrated severe grain-boundary grooving and surface voiding. The defective nature of the annealed surface can be alleviated by chemical-mechanical polishing (CMP), when annealing is conducted prior to the CMP. However, it appears that a sequential thermal excursion at relatively high temperatures re-aggravates the integrity of the Cu surface. This argument may be supported by the electromigration-test results on dual-damascene interconnects fabricated using two different thermal profiles. The electromigration lifetimes were longer by more than a factor of two for the interconnects that skipped a post-passivation anneal at 400°C. The experimental evidence presented in this work suggests that controlling the integrity and quality of the Cu surface is an important step in ensuring good electromigration reliability.

Mobile‐bed effects in oscillatory sheet flow

Field observations often show a considerable variation in mean grain size along the coastal profile. Under high waves in shallow water, bed ripples are washed out, and sheet flow becomes the dominant transport mode: large amounts of sand are transported in a thin layer close to the bed, i.e., the sheet flow layer. This paper focuses on grain size influences on transport processes in oscillatory sheet flow. Experiments were carried out in the Large Oscillating Water Tunnel (LOWT) of Delft Hydraulics, in which near‐bed orbital velocities in combination with a net current can be simulated at full scale. Three uniform sands with different mean grain size were used. It was found that in contradiction to expressions found in literature, both the erosion depth and the sheet flow layer thickness are larger for fine sand (D50 = 0.13 mm) than for coarser sand (D50 ≥ 0.21 mm). Measured time‐averaged velocity and concentration profiles indicate that the presence of a sheet flow layer leads to an increased flow resistance and to damping of turbulence and that these effects are stronger for a thicker sheet flow layer (i.e., for fine sand). These mobile‐bed effects are analyzed further by comparing the measurements with the results of a one‐dimensional vertical advection‐diffusion boundary layer model. Simulating the mobile‐bed effects in the model by introducing an increased roughness height and a reduced turbulent eddy viscosity showed that the roughness height is of the order of the sheet flow layer thickness and that turbulence damping increases for a decreasing grain size.

Size effects in the electrical resistivity of polycrystalline nanowires

Grain-boundary and surface scattering are known to increase the electrical resistivity of thin metallic films and wires. The length scale at which these produce appreciable effects is of the order of the electronic mean free path. For the well-studied case of thin films, both mechanisms can, in principle, be used to explain the observed thickness dependence on resistivity. In order to evaluate which of these mechanisms is more relevant, we have carried out an experimental study of the width dependence of the resistivity of narrow thin-film polycrystalline gold wires (nanowires), and computed the expected behavior on the basis of both surface and grain-boundary scattering mechanisms independently. We find that the resistivity increases as wire width decreases in a manner which is dependent on the mean grain size and cannot be explained adequately by either model alone. We propose a modification to the well-known model of Mayadas and Shatzkes, incorporating the variation of mean grain size on wire dimensions.

INFLO1: A model predicting the behaviour of turbidity currents generated at river mouths

INFLO1 is an ANSI standard FORTRAN-77 predictive sedimentation model that simulates the behaviour of a hyperpycnal inflow. From data on discharge and sediment load at the river mouth as well as the basin geometry, INFLO1 predicts the flow parameters of the resulting turbidity current—flow thickness, velocity, volume and sediment discharge, and interstitial fluid density—and the deposition and erosion of sediment. Sensitivity analyses show that the simulated deposit morphology is most affected by changes in the drag coefficient and that the internal deposit architecture, parameterized by vertical variations in mean grain size, is most sensitive to the form of the flood hydrograph. Model predictions compare favourably with data derived from the 1663 Saguenay event. Given that hyperpycnal inflows are relatively frequent both on recent and geological timescales, INFLO1 allows for the reconstruction of flow parameters for past events yielding valuable paleoclimatic information and the assessment of the potential affects of future hyperpycnal inflows on sedimentation patterns and subaqueous structures.

The influence of grain size and porosity on crack initiation stress and critical flaw length in dolomites

Abstract The influence of rock texture on crack initiation stress ( σ i ) and critical flaw length ( L i ) is studied by a series of triaxial tests performed on monomineralic dolomites. The critical flaw length, as predicted by analytical models, is shown to be larger than the measured mean grain size ( d m ) by two–three orders of magnitude. This discrepancy is explained by rock texture variations, which influence the fracture propagation mode and consequently fracture initiation stress. The quantification of rock texture is accomplished using porosity. Fracture initiation stress is shown to be inversely related to both porosity and mean grain size. When porosity is low, the sensitivity of σ i to mean grain size is high. This effect is reduced with higher porosity values. A model for initial flaw length is developed by a synthesis of Griffith initiation criteria with our empirical model for fracture initiation stress. Initial flaw length is found to be directly proportional to the elastic modulus, mean grain size and porosity of the rock. When porosity and mean grain size decrease simultaneously, the initial flaw length rapidly decreases and approaches the mean grain size value. Therefore, the classical assumption that grain size scales initial flaw size is shown to be valid only in the very restricted case of low porosity-low grain size rocks. In such textures, where void space is minimal, available crystal faces function as truly initial flaws, and variations in mean grain size influence crack initiation stress significantly. In more porous textures, however, the initial flaw length is shown to be up to two orders of magnitude higher than the mean grain size in the rock, depending upon the porosity and mean grain size values. In such textures crack initiation stress is much less sensitive to variations in mean grain size, indicating that the role of individual grains is less significant.

The Influence of Grain Size and Porosity on Crack Initiation Stress and Critical Flaw Length in Dolomites

The influence of rock texture on crack initiation stress (σi) and critical flaw length (Li) is studied by a series of triaxial tests performed on monomineralic dolomites. The critical flaw length, as predicted by analytical models, is shown to be larger than the measured mean grain size (dm) by two–three orders of magnitude. This discrepancy is explained by rock texture variations, which influence the fracture propagation mode and consequently fracture initiation stress. The quantification of rock texture is accomplished using porosity. Fracture initiation stress is shown to be inversely related to both porosity and mean grain size. When porosity is low, the sensitivity of σi to mean grain size is high. This effect is reduced with higher porosity values. A model for initial flaw length is developed by a synthesis of Griffith initiation criteria with our empirical model for fracture initiation stress. Initial flaw length is found to be directly proportional to the elastic modulus, mean grain size and porosity of the rock. When porosity and mean grain size decrease simultaneously, the initial flaw length rapidly decreases and approaches the mean grain size value. Therefore, the classical assumption that grain size scales initial flaw size is shown to be valid only in the very restricted case of low porosity-low grain size rocks. In such textures, where void space is minimal, available crystal faces function as truly initial flaws, and variations in mean grain size influence crack initiation stress significantly. In more porous textures, however, the initial flaw length is shown to be up to two orders of magnitude higher than the mean grain size in the rock, depending upon the porosity and mean grain size values. In such textures crack initiation stress is much less sensitive to variations in mean grain size, indicating that the role of individual grains is less significant.

Milankovitch cyclicity and the Boom Clay Formation: an Oligocene siliciclastic shelf sequence in Belgium

AbstractThe Boom Clay Formation of northeast Belgium consists of a sequence of alternating, laterally persistent beds of silt and clay. Power-spectral analysis of grain-size variations indicates regular sedimentary cycles with wavelengths of about 100 and 46cm that had periods of 124 and 57 thousand years (ka) or less. The lateral continuity ofthe beds, combined with the regularity and estimated periods of the cycles, suggests an indirect link to the 100 and 41 ka orbital (Milankovitch) cycles. The variations in meangrain size were caused by changing bottom-water turbulence as controlled by storms and/or glacio-eustatic water depth fluctuations. This study confirms that certain marinesiliciclastic sequences can provide proxy-records of palaeoclimatic variance.

Palaeochannel reconstructions from point bar deposits: a three‐dimensional perspective

ABSTRACTQuantitative determination of palaeochannel geometry and hydraulics from point bar deposits requires an understanding of the interaction between channel‐bend migration, temporal and spatial variation of point bar geometry and facies, and outcrop orientation. This interaction is modelled with the aid of a computer program which predicts three‐dimensional (3‐D) geometry and grain size variation of point bars. Synthetic deposits are produced for the cases of down‐valley bend migration and/or increase in channel‐bend sinuosity. Two‐dimensional (2‐D) cross‐sections in varying orientations across these simulated deposits display lateral‐accretion bedset surface geometry, and variation in mean bedset grain size and local palaeocurrent orientation.Most cross‐sections show point bar deposits thickening away from the meander‐belt axis due to a lateral progression from thinner bend‐exit deposits to thicker bend‐apex deposits (caused by down‐valley channel translation), and/or due to a progression from thinner low sinuosity deposits to thicker high sinuosity deposits caused by channel bend expansion. In association with this lateral thickening, bedset surfaces become steeper and more convex upwards while the variation in mean grain size up bedsets commonly increases. Down‐valley point bar translation allows preservation only of deposits formed downstream of the band apex, and produces characteristic fining upwards sequences. Marked lateral and vertical variations in palaeocurrent directions due to varying channel orientation relative to a given cross‐section are also predicted. These results indicate a need in palaeochannel reconstructions, for a more detailed examination of 3‐D variations in bedset surface geometry, palaeocurrent orientation and grain size distribution within and between bedsets of laterally accreted sediment.

Critical Appraisal of Fluvial Facies Models: ABSTRACT

Interpretation (and subsequent prediction) of the lithofacies geometry of ancient river-channel deposits requires full understanding of the formative processes. This is ideally gained by linking channel geometry and hydraulics with sediment erosion, transport, and deposition, using generalized (quantitative) physical models. Such models exist for high-stage deposition in single curved channels of simple planform: they are capable of approximating the three-dimensional variation of mean grain size and internal structure of point-bar deposits in channels with differing geometries and flow characteristics. However, such models cannot presently predict processes operating on point bar tops (e.g., sheet floods, chute channel and bar formation, scroll bars, flow separation zone ) or the nature of low-flow deposits. Lateral lithofacies variation due to meander-loop evolution and cutoff is also inadequately understood. Generalized physical models of braided and anastomosed river deposition are particularly poorly developed, and need urgent attention. Single-channel and braided rivers can be distinguished on the basis of their water discharge, slope, width/depth ratio, and sinuosity; quantitative analysis of ancient alluvium is required for reconstruction of these parameters. Although braided river deposits should typically have a high proportion of coarse-grained channel fills relative to lateral accretion deposits, coarse-grained channel fills are also common in sinuous rivers with cutoffs. It appears that presently available qualitative facies models do not adequately represent the range of lithofacies geometries expected from different kinds of rivers, and therefore do not allow thorough and uneq ivocal interpretation of paleochannel geometry, flow characteristics, and evolution. End_of_Article - Last_Page 429------------

Depositional environments of coastal sediments of Calangute, Goa

The grain-size statistics and environmental conditions of deposition of the beach and dune sediments from the Calangute region, Goa, have been studied. The results of Student's t test and bivariate plots reveal that there exist distinct differences in grain-size parameters of the sediments from different environments and that these differences are highly significant. The study shows that the variations in mean grain size (Mz), graphic standard deviation (O1), graphic skewness (Sk1), simple sorting measure (Sos) and simple skewness measure (Os) are significant in identifying the sediments from different environments. Further, the study reveals the usefulness of grain-size parameters not only in differentiating beach and dune sediments, but also in delineating the beach into foreshore and backshore. The differences in grain-size characteristics of the sediments between the environments reflect the transport, erosional and depositional mechanisms (active hydrodynamic processes in the beach foreshore and aerodynamic processes in the backshore and dune environments) prevailing in the area of study.

330. Structural state and mechanical properties of polycrystalline Ni 3Fe alloys : Y Calvayrac and M Fayard, Phys Stat Sol (a), 17 (2), 1973, 407–421 ( in French)

AMS14C dating and grain-size analysis for Core PC-6, located in the middle of a mud area on the inner shelf of the East China Sea (ECS), were used to rebuild the Holocene history of the East Asian winter monsoon (EAWM). The 7.5-m core recorded the history of environmental changes during the postglacial transgression. The core’s mud section (the upper 450 cm) has been formed mainly by suspended sediment delivered from the Yangtze River mouth by the ECS Winter Coastal Current (ECSWCC) since 7.6 kyr BP. Using a mathematical method called “grain size vs. standard deviation”, we can divide the Core PC-6’s grain-size distribution into two populations at about 28 μm. The fine population (< 28 μm) is considered to be transported by the ECSWCC as suspended loads. Content of the fine population changes little and represents a stable sedimentary environment in accord with the present situation. Thus, variation of mean grain-size from the fine population would reflect the strength of ECSWCC, which is mainly controlled by the East Asian winter monsoon.Abrupt increasing mean grain size in the mud section is inferred to be transported by sudden strengthened ECSWCC, which was caused by the strengthened EAWM. Thus, the high resolution mean grain-size variation might serve as a proxy for reconstruction of the EAWM. A good correlation between sunspot change and the mean grain-size of suspended fine population suggests that one of the primary controls on centennial- to decadal-scale changes of the EAWM in the past 8 ka is the variations of sun irradiance, i.e., the EAWM will increase in intensity when the number of sunspots decreases. Spectral analyses of the mean grain-size time series of Core PC-6 show statistically significant periodicities centering on 2463, 1368, 128, 106, 100, 88-91, 76-78, and 70-72 years. The EAWM and the East Asian summer monsoon (EASM) agree with each other well on these cycles, and the East Asian Monsoon (EAM) and the Indian Monsoon also share in concurrent cycles in Holocene, which are in accord with the changes of the sun irradiance.

Relationships between grain size, size-sorting, and foreshore slope on mixed sand - shingle beaches

Abstract The variation of mean grain size (Mzφ), sorting (σI), and beach face slope over mixed-sand shingle beaches at two areas along the east coast, South Island, New Zealand, it analysed in order to determine the nature of the relationships between these three variables. The study is confined to mean grain sizes between 0.25 and 16.0 mm, and the sorting and slope values associated with this range of sizes. Trend analysis of the data has been performed by fitting curves with the aid of a computer. As distinct from the linear average relationship betweeen size and slope distinguished by many workers, it is demonstrated that for given beaches curvilinear trends in size/sorting are reflected in slope/size relationship. Thus, the best sorted sediments are found to be associated with the steepest gradients on the curves, while zones of poor sorting are associated with “plateaus” in the size/slope trend. It is suggested that size is the primary control of sorting trends in the sediments examined whilst hydrau...