Quantitative models for reconstructing catchment ice-extent using physical-chemical characteristics of lake sediments     

P.E. Noon  H.J.B. Birks  V.J. Jones  J.C. Ellis-Evans 《Journal of Paleolimnology》2001,25(3):375-392

The physical characteristics of surface sediments from a suite of pristine lakes on Signy Island, maritime Antarctic, were used to develop a quantitative link between catchment ice-extent and lake-sediment response. Percentage dry weight, median particle size, percentage loss-on-ignition and wet density of the lakes' surface sediments were the most significant variables explaining contemporary catchment ice-extent. Two independent reconstruction models – Partial Least Squares (PLS) and a Modern Analog Technique (MAT) – were applied to dated sediment cores at two sites on Signy Island. The validity of the reconstructions was tested against historical information on catchment ice-extent. With sufficiently high sedimentation rates and sampling resolution, the models can predict sub-decadal changes in ice-extent. The model results are best regarded as indicators of erosion resulting from meltwater activity in the catchment. Comparison of results with Twentieth Century climate records affirms the hypothesis that climatic warming is the most likely cause for the ice retreat observed on Signy Island during the last 40 yrs. Similar reconstruction models using these simple sedimentary measures could be developed for analogous locations in the Antarctic and in Arctic and Alpine regions.  相似文献   

Quaternary vertical offset and average slip rate of the Nojima Fault on Awaji Island, Japan   总被引：5，自引：0，他引：5  

Akihiro Murata  Keiji Takemura  Takao Miyata  Aiming Lin 《Island Arc》2001,10(3-4):360-367

Abstract Drilling was carried out to penetrate the Nojima Fault where the surface rupture occurred associated with the 1995 Hyogo-ken Nanbu earthquake. Two 500 m boreholes were successfully drilled through the fault zone at a depth of 389.4 m. The drilling data show that the relative uplift of the south-east side of the Nojima Fault (south-west segment) was approximately 230 m. The Nojima branch fault, which branches from the Nojima Fault, is inferred to extend to the Asano Fault. From the structural contour map of basal unconformity of the Kobe Group, the vertical component of displacement of the Nojima branch–Asano Fault is estimated to be 260–310 m. Because the vertical component of displacement on the Nojima Fault of the north-east segment is a total of those of the Nojima Fault of the south-west segment and of the Nojima branch–Asano Fault, it is estimated to total to 490–540 m. From this, the average vertical component of the slip rate on the Nojima Fault is estimated to be 0.4–0.45 m/10³ years for the past 1.2 million years.  相似文献   

Recent sedimentation in a high arctic lake, northern Ellesmere Island, Canada     

Bern Zolitschka 《Journal of Paleolimnology》1996,16(2):169-186

A multiple core study was conducted on laminated minerogenic sediments from Lake C2, Northern Ellesmere Island, Canadian High Arctic. Lateral persistence, distal thinning, variation in grain size of these laminations as well as present-day processes of highly seasonal sediment transfer into the lake basin suggest that clastic varves have been formed. Sedimentation rates based on ²¹⁰Pb dating agree well with sedimentation rates based on lamination counts giving further evidence that laminations are annual. Errors in varve counting were reduced from 12% to < 2% using the multi-core approach of cross-correlating all records. Varved sediments are occasionally interrupted by thick coarse-grained layers, which are interpreted as deposits of turbidity currents and may be related to extremely high discharge events and slope failures of the delta front. Micro-laminated sediments spanning the last two centuries were studied in detail. Suspension settling is the dominant process of deposition depending upon stream discharge which is controlled by nival melt and summer temperatures. Application of varve chronology thus allows to use lamination thickness measurements as source of high resolution proxy data for palaeoclimatic reconstruction.This is the fifth in a series of papers published in this issue on the Taconite Inlet Lakes Project. These papers were collected by Dr R. S. Bradley.  相似文献   

The late Quaternary development of three ancient tarns on southwestern Cumberland Peninsula, Baffin Island, Arctic Canada: paleolimnological evidence from diatoms and sediment chemistry     

Alexander P. Wolfe  Joachim W. Härtling 《Journal of Paleolimnology》1996,15(1):1-18

Sediment diatom and chemical analyses of cores from three poorly buffered extra-glacial lakes on the northeastern margin of the Canadian Shield (Cumberland Peninsula, Baffin Island) record interactions between aquatic and terrestrial spheres that were influenced by late Quaternary climatic conditions. Although differences exist between each of the lakes, notably with regards to the intensity of pre-Holocene catchment erosion and the timing of the onset of organic sedimentation, an underlying pattern of lake ontogeny, common to all three lakes, is identified. Although intensified watershed erosion characterized the Late Wisconsinan and Neoglacial cold periods, the lakes nonetheless remained viable ecosystems at these times. Sudden catchment stabilization during the late-glacial to earliest Holocene is associated with incipient organic sedimentation. Lake-water pH increased at this time, likely in response both longer base cation residence times as lake flushing rates decreased, and enhanced alkalinity production from sediment biogeochemical reactions. Subsequently, as the catchments remained stable during the productive early Holocene (c.9–7 ka BP), then gradually received a renewed increase of minerogenic sedimentation, the breakdown of sources of lake alkalinity resulted in natural acidification. Burial of cation-rich mineral sediments and the loss of permanent sedimentary sinks for the products of microbial reduction likely impeded within-lake alkalinity production, and catchment-derived base cations appeared ineffective in curtailing pH declines. The general nature of the Holocene development of these lakes is similar to that observed elsewhere on crystalline terrains, following deglaciation. Our data therefore suggest that catchment glaciation is not a necessary precursor for models of lake development characterized by initial base cation enrichment and subsequent gradual acidification.  相似文献   

Suspended sediment transport and deposition in a high arctic meromictic lake     

Michael J. Retelle  Jonathan K. Child 《Journal of Paleolimnology》1996,16(2):151-167

A study of sedimentary processes and sediment yields in a high arctic meromictic lake (Lake C2, Taconite Inlet, Northern Ellesemere Island, Canada) was undertaken from May 1990 through August 1992 to understand the links between climatic controls, hydrology, and the laminated sediment record preserved in the lake. Understanding the relationships between processes and the sediment record is critical for interpreting the climatic significance of the laminated sediments in a region where high resolution climate proxy records are quite limited.Sediment transport to Lake C2 is dominated by fluvial processes. During the early part of the melt season slushflows transport sediment to the lake surface. Subsequently, suspended sediment is delivered to the lake by the main inlet stream and distributed lakeward by a plume emanating the main inlet channel. Due to the strong density stratification of the water column the plume distributes sediment downlake by overflows and interflows in the epilimnion. In general, overflows are generated by lower discharge events whereas interflows penetrate to the halocline during high discharge with increased suspended sediment concentration.Sediment trap analysis demonstrates that suspended sediment transport and deposition responds to diurnal through annual changes in stream discharge. Seasonal and annual sediment trap yields agree with average accumulation rates determined from varve thickness measurements and cumulative suspended sediment discharge from the main inlet stream indicating a close link between climatological, hydrological, and sedimentological controls and varve deposition.This is the fourth in a series of papers published in this issue on the Taconite Inlet Lakes Project. These papers were collected by Dr R. S. Bradley.  相似文献   

海南岛前寒武纪地层的确定其大地构造演化     

侯威  陈惠芳  梁新权  王可伏 《吉林大学学报(地球科学版)》1992,(2)

通过钐—钕同位素测定,抱板群中的斜长角闪片岩、混合花岗片麻岩及其中的暗色包体等时线年龄分别为1.7Ga、1.4Ga和2.9Ga.用单矿物铅同位素测斜长角闪片岩、混合花岗片麻岩年龄分别为1.1～1.2Ga和940Ma.铷—锶全岩等时线法测得抱板群斜长角闪片岩和石碌群、抱板群中的云母片岩为1.3Ga和1.2Ga。因此,海南岛存在着前寒武纪地层,其中,具有花岗—绿岩且含有玄武质科马提岩组合的抱板群是前寒武纪结晶基底或前地槽构造层.石碌群是地槽早期发展阶段形成的构造亚层。海南岛大地构造演化经历了前地槽(X)、地槽(Ⅰ)、地台(Ⅱ)、地洼(Ⅲ)等多个发展阶段。  相似文献   

台湾岛地形对台风移动路径的作用   总被引：27，自引：3，他引：27       下载免费PDF全文

罗哲贤  陈联寿 《大气科学》1995,19(6):701-706

本文用一个β平面准地转正压模式实施了九组试验，研究台湾岛地形对台风移动路径的作用。初始场系根据SPECTRUM和TCM-90期间加强观测资料确定。结果表明:台湾岛地形的引进会使台风路径向右偏移；地形使台风环流的最大风速区向台风中心方向推移，造成台风环流空间尺度减小，这个结构的变化是路径右偏的一个可能原因。  相似文献   

海南岛中生代地洼期构造与金银多金属成矿特征   总被引：3，自引：0，他引：3  

龙文国 《大地构造与成矿学》1999,23(4):308-314

海南岛地洼活动始于二叠纪末,白垩世达到剧烈期。经历了基性一中性,中一酸性岩浆喷发及侵人和基性岩浆活动三个阶段。时空分布由南向北迁移。区内发育四种金、银、多金属矿床：（1）多因复成型;（2）隐爆角砾岩型;（3）热液型;（4）矽卡岩型。矿体产于断裂构造内,与酸偏碱性侵人岩相伴生。  相似文献   

厦门旧城建设步行街区的初步研究   总被引：1，自引：0，他引：1  

陈玉慧 《地域研究与开发》2003,22(1):44-49

以厦门旧城区西南部为例,对商业街土地利用和商服业现状作了详尽的调查和分析,在阐述旧城区商业街存在总体地位下降,以服装店为主的零售商业功能过于突出,购物环境容量不足等现实问题的基础上,提出以“步行街区”作为厦门旧城商业街更新发展的对策,并据此对步行街区建设涉及到的部分问题进行了探讨。  相似文献   

Toxic contaminants and their biological effects in coastal waters of Xiamen,China. II. Biomarkers and embryo malformation rates as indicators of pollution stress in fish   总被引：3，自引：0，他引：3  

Klumpp DW  Humphrey C  Huasheng H  Tao F 《Marine pollution bulletin》2002,44(8):761-769

Baseline information is presented on embryo malformation rate and biomarkers in fish as indicators of sub-lethal stress caused by pollution in coastal waters of Xiamen, PR China. Fish and eggs were sampled from several areas in Xiamen coastal waters (Xiamen Harbour, Maluan and Tongan Bays and East Channel), where varying levels of pollutant input have been documented. Comparative sampling was done at a "cleaner" reference site at Dongshan Island. Embryonic malformation rates, which indicate general water quality, varied with location and species of fish, and exceeded background levels for unpolluted waters (assumed approximately 5%) by up to eightfold at some sites. Generally, sites around Xiamen Harbour show signs of poor water quality having highest mean levels of embryo deformity (20-30%) and these decreased towards open waters (Tongan Bay, Eastern Channel) where abnormalities approached background levels. An indication that toxic contaminants may be having a localised effect in the region, particularly in the harbour was reinforced by the biomarker assays. However, activities of the biomarkers ethoxyresorufin O-deethylase (EROD) and glutathione S-transferase in fish livers indicate no clear pattern, and there is no evidence that fish from the four sampling areas have been more or less exposed to PAHs and other compounds that induce these biomarkers. Antioxidant biomarkers (glutathione peroxidase, catalase, superoxide dismutase, and reduced glutathione) suggest that exposure to xenobiotics appears to be lowest in Dongshan and Maluan and highest in the harbour and Tongan. Inhibition of acetylcholinesterase in fish muscle indicated possible effects by organophosphate and carbamate pesticides in Xiamen waters and these effects may be greatest in the area of the harbour.  相似文献