Limnological Sediment Characteristic And Its Respond To Climate Change In Tumenjiang River Estuary

Drainage area of Tumenjiang River covers China, North Korea and Russia. Theriver originates from east root of Baitou Shan peak, Changbai Mountain. It flowsfrom southwest to northeast, reach Tumen City of China, then head to southeast,reach the mere stone in Fangchuan, Hunchun of China, and then flow in to JapanSea. Drainage area of Tumenjiang River is from 128°17′E to 131°12′E and41°14′N to 44°01′N. Research area of this article is located in north ofdownstream Tumenjiang River, around Fangchuan in Hunchun basin, from130°31′E to 130°33′E and 42°25′N to 42°38′N, 12km from estuary ofTumenjiang River, and 15km from Japan Sea, reaching North Korea and Russiaboundary.Objective of this article is to study the structure of limnological sedimentbetween dunes and the fragmental texture, analyze the sediment series anddistribution characteristic of limnological sediment in estuary of Tumen JiangRiver, and discuss the origin of sediments, deposit environment and sedimentseries respond to global climate changes.During research, scientific methods and techniques have being conducted,include: field investigation and recording, GPS positioning, digital photographing,thermoluminescent dating, granularity analyzing, geochemistry elementsanalyzing, organic chemistry analyzing and dry-density analyzing.By GPS positioning, digital photographing and describe the conformation of dunes,confirming the macro distribution characteristic and conformation characteristic of dunes,revealing the forming origin of dunes. Dunes are located around Fangchuan and estuary ofTumenjiang River, wirelike distributed along the bank. Swamp lakes and wetlands betweendunes are appeared in dunes. Influenced by south wind and southeast wind in summer, theorigins of sands are complicated due to Tumen Jiang River and Japan Sea's affect. Variousconformation of dunes are influenced by shoreward wind from east sea of NorthKorea(Southeast 330°)and monsoon of Tumenjiang drainage area(Northwest 140°). There aremainly types of plant-covered quaquversal ancient dunes, crescent-shaped compounddunes, and large scale pyramidal dunes in North Korea side of Tumenjiang River.By analyzing the granularity distribution characters of research area, thisarticle discuss the source and cause of formation of sediments, and study thetemperature and humidity changes of deposit environment and ancient climate inresearch area. Granularity analyzing result shows that sediments in this area areclayey silt. The sediments' grading is bad;it ranges between extremery positive toextremery negative in skew, the negative skew is main;the frequency curvesshow wide peaks, the double peaks are major. Average particle diameter'schanging character indicate that there are three deposit gyration of "rough→fine",which means these sediments went through three "wet→dry" gyral changes.According to origin distinguishing results and discrete plot, conclude that thedeposit environment of research area is compound of windborne and alluvialdeposition. With studying the sample locations, the above granularitycharacteristics indicate that the limnological sediments are mainly originatedfrom the deposits in riverbed and floodplain of Tumenjiang River, these depositscame out of the river in dry seasons, carried to swamps along the river by windand deposit again, hence the sediments have both characters of modern riversediments and windborne deposits. Other silts powders carried by wind aredeposited along the bank of Tumenjiang River, forming the dunes. Stream flowduring rain seasons also carried some fine-grain down from nearby hills toswamps and deposited. That made the sediments have the characters of bothalluvial and windborne deposits.By testing the proportion of ordinary geochemistry elements, trace elementsand organic carbon of the sediments, calculate the background values andcoefficients of elements in research area, analyze the accumulation/migrationorderliness of elements indifferent period, combining with the values ofthermoluminescent dating,point out the orderliness of climate change since latePleistocene: dry cold→wet cool→dry cold→wet warm→warm of half-wet'sgyration of climate changes. During 17.10±1.46 kaB.P.~ 15.15±1.29 kaB.P., theclimate turned to be warm, supposed to be the warming event in late last ice age;during 15.15±1.29 kaB.P.~14.09±1.19 kaB.P., the climate turned "dry warm→wetcold" changing, the cool and wet's climate is main;during 14.09±1.19 kaB.P.~12.92±1.09 kaB.P. ,the climate got into the phase of relatively dry and cool;during 12.92±1.09 kaB.P.~11.24±0.96 kaB.P., the climate-environmentexperienced a transition of "dry cool→wet warm" slowly;from 11.24 kaB.P. tillnow, the climate were in the period of half-wet's warm, in this phase, theelements curves showed an apparent gyration, supposed to be influenced byYounger Dryas Event.By measuring the dry-density, and integrating with above climate indexcharacters, conclude the ancient climate changing situations. Characteristics ofdry-density changes are related and inosculate to the parameters in granularityanalyzes and indexes of geochemistry elements analyzes, this new technicalmethod of dry-density can be used on discussing the ancient climate change ofsediments in research area. And it shows the orderliness of climate are: during17.10±1.46 kaB.P.~ 15.15±1.29 kaB.P., the climate turned a gyral event of "drycold→wet warm→dry cold", supposed to be the warming event in late last iceage;during 15.15±1.29 kaB.P.~ 14.09±1.19 kaB.P, the climate experienced "drycold-wet warm-dry cold" changing again;from 14.09± 1.19 kaB.P. till now, theclimate is in related stable warm period of half-dry-cold and half-wet-warm.Thermoluminescent dating's data shows the oldest sediments is about17.10kaB.P.. According to the result of thermoluminescent dating, calculate thevelocity of deposition, which are: "small→big→small", indicate that the changeof climate is "dry→wet→dry".Based on above research and intergrating Greenland ice-core O-isotopecurve changing orderliness, this article proved that from 17.10±1.46kaB.P., that isfrom late Pleistocene, the climate change characteristic is from cold to warm,then change back to cool in Holocene period. The humidity is changing from dryto wet then in Holocene period change to relative dry. Noticeably, the data indexchanging timeline of sediments during 17.10±1.46kaB.P. and 11.24±0.96kaB.P.are correspond to last ice-age and Younger Dryas Event, which are recorded inhistory references documents respectively.