Grain Size Component Research Articles

Bottom water hydrodynamic provinces and transport patterns of the northern South China Sea: Evidence from grain size of the terrigenous sediments

Sediment transport in the source-to-sink systems of the northern South China Sea (SCS) has been of increasing interest during the past few decades. However, the mechanisms for sediment redistribution remain unclear. Sources and transport patterns in the northern SCS were investigated in this study based on grain size analyses of 205 surface sediment samples. Detailed characterizations of hydrodynamic conditions and sediment transport have been made using the log-ratio method to partition grain size components of surface sediments in the northern SCS. Results reveal that sediment dispersal patterns in the region generally contain traction, saltation, graded and uniform suspension modes. Based on the spatial distribution characteristics, the study area can be classified into three hydrodynamic provinces. Province A contains high traction concentrations that are exposed to the longshore current and topographic features, which are distributed in the Taiwan Shoal, Dongsha Islands and extends from the Pearl River estuary to the southeast of Hainan Island. Province B is characterized by higher values of saltation and graded suspension, which are widespread along the northern slope of the SCS, and its formation is interpreted as the result of interactions between down- and along-slope processes. Province C reaches its greatest concentration in the abyssal areas, particularly in the vicinity of Luzon Island, which settles only under calm conditions. Combined with previous data concerning magnetic susceptibility distributions of surface sediments from the northern SCS, the sediment transport route near the mainland is traced. Furthermore, based on distribution pattern of sortable silts and hydrodynamic provenance of the terrigenous sediments, the sediment transport route in the deep water region of the northern SCS is outlined. It flows along marginal channels which cut across the continental slope along isobaths. Taken together, the combination of grain-size components and sortable silts of surface sediment used here is a promising tool to better assess the modern variability of hydrodynamic conditions and transport processes in marine environments.

Variations in late Quaternary wind intensity from grain-size partitioning of loess deposits in the Nenana River Valley, Alaska

AbstractA high-resolution column of 57 loess samples was collected from the Dry Creek archaeological site in the Nenana River Valley in central Alaska. Numerical grain-size partitioning using a mixed Weibull function was performed on grain-size distributions to obtain a reconstructed record of wind intensity over the last ~15,000 yr. Two grain-size components were identified, one with a mode in the coarse silt range (C1) and the other ranging from medium to very coarse sand (C2). C1 dominates most samples and records regional northerly winds carrying sediment from the Nenana River. These winds were strong during cold intervals, namely, the Carlo Creek glacial readvance (14.2–14 ka), a late Holocene Neoglacial period (4.2–2.7 ka), and recent glacier expansion; weak during the Allerød (14–13.3 ka) and Younger Dryas (12.9–11.7 ka); and variable during the Holocene thermal maximum (11.4–9.4 ka). Deposition of C2 was episodic and represents locally derived sand deposited by southerly katabatic winds from the Alaska Range. These katabatic winds occurred mainly prior to 12 ka and after 4 ka. This study shows that numerical grain-size partitioning is a powerful tool for reconstructing paleoclimate and that it can be successfully applied to Alaskan loess.

Effect of mariculture on sediment grain size and its potential environmental significance in Sishili Bay, Yellow Sea, China

The grain-size distribution of sediment is associated with series of environment problems in mariculture area; however, there is still disparity in the effect of marine culture on grain size partly because it is hard to exclude the contribution of other factors such as sources, hydrodynamic. Sediment grain size of two cores (C3 in culture area and A5 in control area) was compared. The results show that the particle sizes of the two cores have the same compositions and variation laws at the bottom sections (during non-culture period), while sand grain-size contents increases from several to 25 % in C3 core than that in A5 core at the surface section (during the culture period), with an average of 15 %. It suggests the grain sizes are coarsened due to marine culture. Moreover, the deviation values of sand grain-size contents, calculated by subtracting grain-size contents of A5 core from those of C3 core at the surface section, were used to quantificationally estimate the variation of grain-size components. It is found that the deviation values of grain size increase with the intensifying of marine culture outputs. Marine culture outputs result in the coarsening of grain sizes; thus, the variation of grain size should be considered when the environmental problems in culture areas are explained, such as heavy metal pollutants, nutrient elements and benthic community structure and so on.

Partitioning of Grain-size Component Populations in Bimodal Sediments

ABSTRACT Choi, T.J.; Park, J.Y., and Choi, J.Y., 2016. Partitioning of Grain-size Component Populations in Bimodal Sediments, Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 1322 - 1326. Coconut Creek (Florida), ISSN 0749-0208. Most continental shelf sediments show bi- and/or poly-modal patterns consisting of overlapping components in the grain-size distribution (GSD), which generally reflect various environmental conditions as well as multiple sources of sediment. Because the laser-diffraction method is accurate and requires only a few grams, it is useful for analyzing cores with complex sedimentary structures of alternating coarse and fine lamina. In this study mathematical method of the partitioning of component (PCP) is applied to high-resolution GSD analysis for a sediment core collected from the central Yellow Sea (14YS-PC-3, 261 cm). Coarser and finer components within the GSDs of the core sediments with a typical ...

Sediment record of abrupt environmental changes in Lake Chenpu, upper reaches of Yellow River Basin, north China

Lake Chenpu is located in the western part of Hetao Basin approaching the Ulan Buh Desert in the upper reaches of the Yellow River in northern China. An 84 cm sediment core was collected from the center of the lake. Geochronology radiometric method using 210Pb was subsequently used to date the short sediment core in the hope that it would reflect environmental changes over the past 150 years. Principal component analysis and the variation of the grain-size standard deviation were used to identify latent factors and extract environmentally sensitive grain-size components in sediment. Then a combination of sensitive grain-size parameters, magnetic susceptibility, total organic matter (TOC), and total nitrogen (TN) was used to reconstruct the recent lake environmental sequence. The result showed that the lake has seen increasing salinization and swampiness over the past 150 years. Further, sensitive grain-size parameters displayed several abrupt environment changes, i.e. 1850 AD, 1920 AD, and 1980 AD, which are supported by written records. In the 1850s, the yellow clay content increased dramatically, and that of silt declined. Magnetic susceptibility and C/N values increased significantly, as indicated by flood action. In the 1920s and the 1980s, dust-sand activity was recorded twice in the lake sediments with a markedly higher value of 16–32 μm and average grain size (C2). Grain size and other environmental proxies showed the period after the mid-1990s to be mainly dominated by wind-sand activity and anthropogenic impacts, which marked by obviously increasing grain-size coarse, carbonate content, TOC, and TN values. The results show that the lake sediments provide a dependable archive for studying the environmental history of the lake.

A Holocene East Asian winter monsoon record at the southern edge of the Gobi Desert and its comparison with a transient simulation

The East Asian winter monsoon (EAWM) exhibits significant variability on intraseasonal, interannual, and interdecadal time scales and the variability can be extended to Holocene centennial and millennial scales. Previous Holocene EAWM proxy data records, which were mostly located in Central, Eastern and Southern China, did not show a consistent Holocene EAWM history. Therefore, it is difficult to provide insights into mechanisms of the long-term winter monsoon variability on the basis of the records. Eolian sediments at the southern edge of the Gobi Desert, Western China, are sensitive to the EAWM changes and less affected by the East Asian summer monsoon due to an obstruction of the Qinghai–Tibet Plateau. This paper presents a comparison between a well-dated Holocene EAWM record and coupled climate model simulations, so as to explore physical processes and influencing factors of the Holocene EAWM. Sediment samples from two Holocene eolian sedimentary sections [Huangyanghe (a) and Huangyanghe (b)] were acquired at the southern edge of the Gobi Desert. Chronologies were established based on twenty bulk organic matter AMS 14C ages and five pollen concentrates AMS 14C ages. Proxy data, including grain-size, total organic carbon, magnetic susceptibility and carbonate content were obtained from the two eolian sections. The grain-size standard deviation model was applied to determine components sensitive to variability of the Holocene EAWM. After a comparison of environmentally-sensitive grain-size components and proxy data, the 20–200 μm component at the Huangyanghe (a) and the 20–159 μm component at the Huangyanghe (b) section were selected as indicators of the Holocene EAWM, which show a strong early Holocene winter monsoon and a decline of the winter monsoon since the mid-Holocene. We also present equilibrium and transient simulations of the climate evolution for the Holocene using a state-of-art coupled climate model: the Community Climate System Model version 3 (CCSM3). Indices for the Holocene EAWM were calculated and are consistent with the reconstructed Holocene EAWM intensity. The simulations indicate that orbital forcing effects on the land-sea temperature and sea level pressure contrast can account for the observed EAWM trends. Other forcings that were present in the early Holocene, including the remnant Laurentide ice sheet and meltwater forcing in the North Atlantic, were not responsible for the Holocene trends.

Numerical partitioning of components for four-modal sedimentary grain-size distribution based on gradient descent method

The gradient descent (GD) method is used to fit the measured data (i.e., the laser grain-size distribution of the sediments) with a sum of four weighted lognormal functions. The method is calibrated by a series of ideal numerical experiments. The numerical results indicate that the GD method not only is easy to operate but also could effectively optimize the parameters of the fitting function with the error decreasing steadily. The method is applied to numerical partitioning of laser grain-size components of a series of Garze loess samples and three bottom sedimentary samples of submarine turbidity currents modeled in an open channel laboratory flume. The overall fitting results are satisfactory. As a new approach of data fitting, the GD method could also be adapted to solve other optimization problems.

The grain-size depositional process in wetlands of the Sanjiang Plain and its links with the East Asian monsoon variations during the Holocene

Compared to the well-studied the grain-size depositional process in hydraulic and aeolian sediments, the process in wetlands is still poorly understood. In this study, the grain-size components of a well-dated mud/peat profile (SJ2) in the Sanjiang Plain were partitioned using a lognormal distribution function. The results suggest that the lacustrine deposits contain four distinct unimodal grain-size distributions, C-1 through C-4, with their modal sizes ranging 0.7–1.6, 2.4–8.7, 15.7–27.8, and 380.2–529.6 μm respectively. Only the C-1 and C-3 were identified in the peat layers. A grain-size depositional modal was introduced to explain the environmental meanings of the four components. C-3, as a nearshore suspension component, was the most sensitive component to the variation of local hydraulic conditions. Based on the variation of C-3 percentages of the profile SJ2, the local hydraulic conditions were tentatively reconstructed, and the results showed a close relation with the monsoon variations during the Holocene. Accordingly, we suggest the relative coarse component of the polymodal peat deposits in monsoonal regions can be used as a sensitive indicator for the hydraulic conditions and the monsoon circulations in the geological past.

Grain-Size Components As Markers of Origin and Depositional Processes In the Coastal Zone of the Golfe Du Lion (Mediterranean Sea, France)

Abstract A study of beach and nearshore sands between the mouth of the River Aude and Cap d'Agde (northwestern Mediterranean Sea) shows the existence of four sediment types (ST): ST1 to ST4, with ST2 seemingly deriving from ST1, revealed by grain-size modal analysis and confirmed by a deconvolution program (LogNormal Deconvolution of Grain Size). Grain-size skewness is related to a much more persistent multimodality than graphic evidence can show. Multimodality results from mixtures of generally three STs and/or variants (the latter defining monotype grain-size distributions). Monotype mixtures are unequally distributed in morphodynamic zones, very abundant on the lower shoreface, significantly present on the berm and inner bar, but rare in the most dynamic zones (i.e., the collision zone and outer bar). On the berm and lower shoreface, modal values of the three sedimentary variants retain a close grain-size relationship. On the berm, where only bedload is present in the swash, monotype grain-size distribution trends towards a lognormal model. This trend can also be observed on the lower shoreface, where there are numerous monotype grain-size distributions (GSDs), possibly indicating a dominant process. When compared with ST1-dominated grain-size distributions of the outer bar zone, the distribution of the derived ST2 on the lower shoreface has an added fine tail derived from the coarse-skewed outer-bar sands. In addition, positive skewness of the lower-shoreface sands could indicate input of fine particles from deeper zones under the influence of shoaling waves and upwelling. Morphodynamic zones are approximately characterized by the distribution of grain-size indices. A change in the direction of the skewness sign can be observed between the shoaling zone and more energetic zones, from the breaker zone up to the berm. Finally, a more detailed description of the spatial properties of grain-size distributions could, first, help explore possible mechanisms underlying sediment sorting in the coastal zone and, second, provide a set of indices that would be of use in paleogeographic reconstructions and organization of basin borders, while improving discrimination and classification of environments.

Testing the model for linking grain-size component to lake level status of modern clastic lakes

A model was proposed recently for linking grain-size component to lake level status based on investigations of Daihai Lake in Inner Mongolia. To test this model, grain-size components of the surface sediments of Dali Lake, 500 km northeast of Daihai Lake, were partitioned and their relationships with the lake level status were examined in this study. The data show that modern clastic sediments of Dali Lake contain five distinct grain-size components representing specific depositional processes and sedimentary environments within the lake in common with Daihai Lake. These components are specified as long-term suspension clay, offshore-suspension fine silt, offshore-suspension medium-to-coarse silt, nearshore-suspension fine sand and nearshore-saltation medium sand. In Dali Lake, by contrast, the offshore-suspension components are lacking in more samples from the nearshore zone; the nearshore-suspension and saltation components occur in more samples from the offshore and transitional zone, respectively; and two adjacent components are well separated. These differences would result from higher-energy hydraulics of Dali Lake generated by stronger and more frequent winds occurring in the lake region. Under this hydraulic condition, clastic materials entering the lake and the resultant components would be reworked more seriously during transportation within the lake, leading to further basin-ward transportations of the major components and better separations of two adjacent components. Percentage of the nearshore components is negatively related to water depth, suggesting the grain-size component–lake level status model for the lake. This model was applied to a sediment core from the lake, showing that high percentages of the nearshore components in the core coincide with low precipitations reconstructed on the pollen profile of the same core. The coincidence of two independent proxies demonstrates the wide applicability of the grain-size component–lake level status model to lake's paleohydrological reconstruction.

Partitioning of grain-size components of estuarine sediments and implications for sediment transport in southwestern Laizhou Bay, China

Sediment transport in estuarine systems has been of increasing interest for scientists during the past few decades. However, the mechanisms for sediment redistribution remain unclear. We characterized in detail sediment transport in the Xiaoqing River estuary using the mathematical Weibull function to partitiongrain-size components of surface sediments in the southwestern Laizhou Bay, Northeast China. Four partitioned components: finer than 4, 4.6–12.5, 23.4–63.3, and 67.1–132.6 μm were interpreted in terms of hydrodynamic conditions. During sediment transport, silt grains were suspended and moved seaward from three depositional centers, whereas fine-grained sands moved generally landward. Overall, sediments are transported clockwise in a generally NNE direction near shore and then turn eastward offshore. The mathematical partitioning method showed a great potential for future estuarine environmental studies.

A model for linking grain-size component to lake level status of a modern clastic lake

Grain-size distributions of fluvial, eolian and marine sediments were explicated decades ago. For lake sediments, however, there is still great uncertainty in explaining the genesis of grain-size components due to the inherent complexity of their polymodal distributions. In this study, the grain-size components of the surface sediments of Daihai Lake, Inner Mongolia, were partitioned using a lognormal distribution function and the relationship between the identity of each component and the specific sedimentary environment was investigated. The data indicate that the modern clastic sediments of Daihai Lake contain five distinct unimodal grain-size distributions representing five grain-size components. Each of the components retains its identity including modal size, manner of transportation and environment of deposition although the relative percentage varies with the hydraulic condition throughout the lake. These components are specified from fine to coarse modes as long-term suspension clay, offshore-suspension fine silt and medium-to-coarse silt, and nearshore-suspension fine sand and saltation medium sand. The percentage of the components interpreted as an indication of nearshore environments displays a negative correlation with water depth across the modern lakebed, suggesting a model for linking the nearshore components in sediment cores to the lake level status in the geological past. The model was applied to a sediment core from the lake where high percentages of the nearshore components in the core sediments were correlated with low regional precipitations reconstructed on the pollen profile of the same core. The coincidences between two independent proxies do not only demonstrate the validity of lognormal distribution function in partitioning polymodal sediments but also reveals the potential of the grain-size component–lake level status model for lake’s paleohydrological reconstruction.

An end-member algorithm for deciphering modern detrital processes from lake sediments of Lake Donggi Cona, NE Tibetan Plateau, China

Deciphering significant sedimentological processes from a set of sediment samples is an important step in reconstructing environmental changes. One approach going beyond classical methods is the unmixing of grain-size distributions. This paper presents a flexible end-member modelling algorithm that is based on eigenspace analysis and considers inherent uncertainties. It has been applied to the detrital grain-size components of lacustrine surface sediment samples of Lake Donggi Cona, Qinghai Province, China. It allows up to five grain-size end-members to be characterised and quantified in an optimal model. An end-member with a major mode in the clay domain accounts for 34% of variance within the grain-size data set. It may represent sedimentation of suspension load from linear and laminar runoff during heavy precipitation events in summer. Three end-members in the fine sand to medium silt domains make up 60% of lacustrine sedimentation. They may represent local to remote aeolian processes that peak in wintertime. A multimodal end-member explaining the remaining 6% of variance may represent further fluvial and littoral dynamics or random fluctuations and measurement errors. Several model runs of different scaling and numbers of end-members provided a suitable way to determine uncertainties inherent to the model. A comparison of 12 different model runs and their respective uncertainties yielded a distinct model of robust end-members. The clay and medium silt end-members are robust features of detrital sedimentation within Lake Donggi Cona. They alone explain 54.4% of total variance in the data. However, no spatial pattern or relation to water depth is found for any of the grain-size end-members. Thus, when past detrital sedimentation at Lake Donggi Cona is reconstructed, a special focus should be on the robust features attributed to aeolian and suspension-related sedimentation processes as well as on effective sediment mixing processes impeding a distinct correlation between grain size and spatial attributes. Further applications of the end-member modelling algorithm to other depositional environments are encouraged to demonstrate its universal applicability.

Grain-size characteristics of sediment in Daniugou peatland in Changbai Mountains, Northeast China: Implications for atmospheric dust deposition

The grain-size distribution characteristics and grain-size parameters of sediment in two vertical sections of Daniugou peatland in the Changbai Mountains were systematically investigated. A comparative analysis of the sediment granularity using a discriminative function with Hongyuan peat, red clay, loess-paleosol, fluvial deposit as well as lacustrine deposit was also conducted. It turns out that the vertical section of Daniugou peat ash is primarily constituted by clay and silt particles, and the content of sand is relatively small. Grain-size frequency curves generally show a single-peak modality while a bimodal pattern is detected in the upper layer. The grain-size component and peak pattern of grain-size frequency curves also illustrate that peat ash materials were transported to the peatland by long-range aeolian dust during the deposition process, while there existed short-distance dust influence in peat deposition of the upper layer. Comparisons of grain-size parameters and the discriminative Y-value of Daniugou peat ash with those of typical aeolian sediments show close similarities, suggesting the possibility that atmospheric dust transport processes were involved in the accumulation of peat again. Moreover, the variations of grain-size distribution suggest the local environmental deterioration which is just the driving force of local dust elevation. Grain-size analysis of peatland sediment is demonstrated to be one effective method to extract information about regional and global environmental evolution, and more attention should be paid to current local ecological environment and to seeking a balance between economic development and environmental protection in Northeast China.

Records of late-Holocene East Asian winter monsoon in the East China Sea: Key grain-size component of quartz versus bulk sediments

Quartz isolated from bulk sediments taken from a core obtained from the distal mud area in the outer shelf of the East China Sea was used as a proxy in order to determine the strength of the East Asian Winter Monsoon (EAWM). This data was compared with the grain-size of bulk sediment from the same core. It was found that the content of the key quartz-based indicator fraction (15.2–65.6 μm) correlated well with the EAWM strength. With reference to current conditions, high content of quartz in the selected fraction reflected strong EAWM and vice-versa. The core record spanned 2100 years, and three periods of change in EAWM strength were identified. A period of increased EAWM strength prior to 1520 cal. BP was followed by a period of weakened EAWM strength from 1520 to 720 cal. BP, which is consistent with the Sui-Tang Warm Period and the Medieval Warm Period. This is followed by a period of slightly increased EAWM between 720 and 220 cal. BP, which corresponds to what is called the Little Ice Age. The history of EAWM revealed by the quartz-based proxy is in striking agreement with results from a previous study on bulk sediment-based proxy. However, the quartz-based proxy showed much higher sensitivity and resolution to the EAWM strength, and displayed much more distinct and sharper boundaries of transition across the three intervals of EAWM change compared to the bulk sediment records. Eleven short EAWM strengthening periods were found, compared with four by the bulk sediment-based proxy. Therefore, this suggests that the quartz grain-size proxy is a superior indicator of the winter monsoon strength in the study area.

Partitioning of the grain-size components of Dali Lake core sediments: evidence for lake-level changes during the Holocene

We recovered a sediment core (DL04) from the depocenter of Dali Lake in central-eastern Inner Mongolia. The upper 8.5 m were analyzed at 1-cm intervals for grain-size distribution to partition the grain-size components and provide a high-resolution proxy record of Holocene lake level changes. Partitioning of three to six components, C1, C2, C3 through C6 from fine to coarse modes within the individual polymodal distributions, into overlapping lognormal distributions, was accomplished utilizing the method of lognormal distribution function fitting. Genetic analyses of the grain-size components suggest that two major components, C2 and C3, interpreted as offshore-suspension fine and medium-to-coarse silt, can serve as sediment proxies for past changes in the level of Dali Lake. Lower modal sizes of both C2 and C3 and greater C3 and lower C2 percentages reflect higher lake stands. The proxy data from DL04 core sediments span the last 12,000 years and indicate that Dali Lake experienced five stages during the Holocene. During the interval ca. 11,500–9,800 cal year BP, lake level was unstable, with drastic rises and falls. Following that interval, the lake level was marked by high stands between ca. 9,800 and 7,100 cal year BP. During the period from ca. 7,100 to 3,650 cal year BP, lake level maintained generally low stands, but displayed a slight tendency to rise. Subsequently, the lake level continued rising, but exhibited high-frequency, high-amplitude fluctuations until ca. 1,800 cal years ago. Since ca. 1,800 cal year BP, the lake has displayed a gradual lowering trend with frequent fluctuations.

East Asia Winter Monsoon changes inferred from environmentally sensitive grain-size component records during the last 2300 years in mud area southwest off Cheju Island, ECS

Environmentally sensitive grain-size component (ESGSC) extracted from grain-size data of a sediment core B2, which were retrieved from mud area southwest off Cheju Island (MACI), East China Sea (ECS), can be used to indicate the variations of East Asia Winter Monsoon (EAWM), with high (low) content/mean-size of ESGCS denote to strong (weak) EAWM. Combined with AMS(14)C datings core B2 provides a continuous high-resolution record of EAWM changes over the past 2300 years, with an average resolution of 13 years. The results show that the variations of EAWM are consistent with temperature changes inferred from historical documents in eastern China over the past 2300 years, from which four climate stages may be identified. In stages before 1900 aBP (50 AD) and 1450-780 aBP (50-1170 AD) the EAWM were comparatively weak, corresponding to warm climate periods in eastern China, respectively. And in stages of 1900-1450 aB P (50 - 500 AD) and 780 - 219 aB P (1170 - 1731 AD) the EAWM we re strongly developed, which correspond well to climate changes of two cold periods in eastern China. It is also shown from this study that the stage at 780-219 aBP (1170-1731 AD) was the coldest climate period during the last 2300 years and could be, therefore, related to the Little Ice Age (LIA). Climatic fluctuations appeared obviously in all the four stages, and two climate events of abrupt changes from warm to cold occurred at around 1900 aBP (50 AD) and 780 aBP (1170 AD), of which the latter is probably related to globe-scale changes of atmospheric circulation at that time.

Grain-size distribution function of polymodal sediments in hydraulic and aeolian environments, and numerical partitioning of the sedimentary components

Most continental sediments are polymodal, composed of overlapping components of which the grain size generally obeys some type of natural distribution. The grain-size components and their function types can be determined from frequency and cumulative curve plots in order to define the function formula of the grain-size distribution. The function parameters can be estimated by fitting a defined function formula to the measured grain-size data of the sample, which simultaneously achieves numerical partitioning of the sedimentary components. Genetic analysis of grain-size components of hydraulic and aeolian sediments demonstrates the following environmental implications: Fluvial sediment is composed of isolated saltation and suspension components. The sediments in closed lake basins are dominated by a suspension silt–clay component with a small proportion of saltation sand. The fine sand component makes up the majority of desert sand, overlapping with a small proportion of fine dust. Aeolian loess is composed of two overlapping components: a short suspension-time silt component and a long suspension-time fine component. Aeolian material in the North Pacific deep-sea sediments is dominated by long suspension-time fine dust. The fine component in aeolian sediments shows a consistent grain-size distribution and genetic connection from the desert sand, loess of northern China to the North Pacific Ocean, which is mainly transported by westerly winds and is dispersed in the atmosphere, forming a background dust.