A 2000 year varve-based climate record from the central Brooks Range,Alaska     

Broxton W. Bird  Mark B. Abbott  Bruce P. Finney  Barbara Kutchko 《Journal of Paleolimnology》2009,41(1):25-41

Varved minerogenic sediments from glacial-fed Blue Lake, northern Alaska, are used to investigate late Holocene climate variability. Varve-thickness measurements track summer temperature recorded at Atigun Pass, located 41 km east at a similar elevation (r ² = 0.31, P = 0.08). Results indicate that climate in the Brooks Range from 10 to 730 AD (varve year) was warm with precipitation inferred to be higher than during the twentieth century. The varve-temperature relationship for this period was likely compromised and not used in our temperature reconstruction because the glacier was greatly reduced, or absent, exposing sub-glacial sediments to erosion from enhanced precipitation. Varve-inferred summer temperatures and precipitation decreased after 730 AD, averaging 0.4°C above the last millennial average (LMA = 4.2°C) from 730 to 850 AD, and 0.1°C above the LMA from 850 to 980 AD. Cooling culminated between 980 and 1030 AD with temperatures 0.7°C below the LMA. Varve-inferred summer temperatures increased between 1030 and 1620 AD to the LMA, though the period between 1260 and 1350 AD was 0.2°C below the LMA. Although there is no equivalent to the European Medieval Warm Period in the Blue Lake record, two warm intervals occurred from 1350 to 1450 AD and 1500 to 1620 AD (0.4 and 0.3°C above the LMA, respectively). During the Little Ice Age (LIA; 1620 to 1880 AD), inferred summer temperature averaged 0.2°C below the LMA. After 1880 AD, inferred summer temperature increased to 0.8°C above the LMA, glaciers retreated, but aridity persisted based on a number of regional paleoclimate records. Despite warming and glacial retreat, varve thicknesses have not achieved pre-730 AD levels. This reflects limited sediment availability and transport due to a less extensive retreat compared to the first millennium, and continued relative aridity. Overall, the Blue Lake record is similar to varve records from the eastern Canadian Arctic that document a cool LIA and twentieth century warming. However, the occurrence and timing of events, such as the LIA and Medieval Warm Period, varies considerably among records, suggesting heterogeneous climatic patterns across the North American Arctic.

Broxton W. BirdEmail:

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A soil chronosequence in Late Glacial and Neoglacial moraines, Humboldt Glacier, northwestern Venezuelan Andes     

W.C. Mahaney  V. Kalm  B. Kapran  M.W. Milner  R.G.V. Hancock   《Geomorphology》2009,109(3-4):236-245

Late Glacial and Neoglacial (Little Ice Age) deposits on the Humboldt Massif were analyzed for relative-age dating parameters, including geomorphic and weathering characteristics, geochemical and soil properties. The soil chronosequence, formed in chemically uniform parent materials, provides an important database to study soil evolution in a tropical alpine environment. Extractable and total Fe and Al concentrations, examined to assess their use in relative-age determination, and as paleoenvironmental indicators, provide an important measure of the accumulation and downward profile movement over time of organically-bound Al, ferrihydrite and other crystalline forms (hematite and goethite) of extractable Fe. Ferrihydrite is particularly useful in determining former perched water levels in soils with relation to paleoclimate. The ratios of most Fe extracts are time dependent. The Fe_d/Fe_t ratio, within statistical limits, shows a slow increase from LIA (Little Ice Age) to Late Glacial soils, which closely correlates with other alpine soil studies in the middle latitudes and other tropical alpine locales. Values of Al_d (dithionite) and Al_o (oxalate extractable) generally do not correlate with time; however, Al_p (pyrophosphate extractable) measured against Al_t (total) provides insight on the downward translocation over time of organically-bound Al. Low leaching rates in this chronosequence are further supported by clay mineralogy trends and the geochemical data.  相似文献   

巢湖流域新石器至汉代古聚落变更与环境变迁   总被引：7，自引：1，他引：6  

吴立  王心源  周昆叔  莫多闻  高超  刘丽  韩伟光 《地理学报》2009,64(1)

以GIS为手段,在对巢湖流域新石器中晚期至汉代聚落遗址时空分布特征进行分析的基础上,探讨流域内古聚落变更对环境变迁的响应关系.研究表明,巢湖流域新石器中晚期至汉代古聚落变更的规律主要表现为,随着时代推进聚落遗址从高海拔逐渐向低海拔地区转移并向湖泊靠近,这种变更响应于中全新世以来流域气候由温暖湿润向温和干燥的发展,以及由此导致的巢湖湖泊收缩、水位持续下降和生活范围扩展,反映了在气候变化的大背景下,地貌演化和水文条件的改变对古聚落变更的影响;而各时期聚落遗址西多东少的分布格局,则与流域东部极易受河道摆动和洪涝灾害影响的地貌条件有关.因此,气候变化成为巢湖流域古聚落变更的重要激发因子,对古聚落的分布、扩展、演变都产生了重要影响,古聚落变更对环境变迁的响应明显.  相似文献   

全球小冰期的气候变化   总被引：1，自引：0，他引：1  

王立国  钟巍  李偲 《冰川冻土》2002,24(6):750-758

根据全球小冰期气候信息的不同代用指标的结果分析,全球小冰期冷、暖气候变化趋势具有一致性.其中,太阳活动是影响全球小冰期气候变化的主要因素,强火山爆发及厄尔尼诺事件则是其强化因素,这些因素通过海-气作用这一复杂机制对全球气候产生深远影响.  相似文献   

新疆阿勒泰地区小冰期特征的树轮δ13C记录   总被引：9，自引：6，他引：3  

陈拓  秦大河  刘晓宏  李江风  任贾文  孙维贞 《冰川冻土》2002,24(1):83-86

建立了新疆阿勒泰地区一个长约450a的落叶松树轮碳同位素年表.该年表一个最为明显的特点是1850年后年轮δ¹³C显著降低,这是化石燃料燃烧和土地利用方式改变的缘故.在1550—1850年期间,该年表经历了明显的距平“正负”(即暖冷)变化:17世纪年轮δ¹³C值相对偏负,气温较低,18世纪年轮δ¹³C值相对偏正,温度较高.根据已有的树轮δ¹³C温度系数,17世纪的温度相对偏低约0.67～2.46℃.广泛的区域性对比表明,该年表所揭示的小冰期温度变化具有较高的可信度。  相似文献   

祁连山西段小冰期以来的冰川变化研究   总被引：66，自引：30，他引：36  

刘时银  沈永平  孙文新  李刚 《冰川冻土》2002,24(3):227-233

根据航空摄影相片、地形图、遥感影像数据,分析了祁连山西段自小冰期至1990年的冰川变化,得出该地区在小冰期至1956年间冰川面积减小幅度为16.9%,冰川储量减少了14.1%;1956-1990年间冰川仍以退缩为主,此时段冰川面积和储量减小量占1956年时相应量的10.3%和9.3%.分析认为冰川退缩主要与1956-1966年时段气温偏高、降水偏少有关,而且该流域区对应于1956-1966年间强负物质平衡的冰川退缩可能出现于1960年代中期至1970年代中期.  相似文献   

广东韶关南华寺水松的年代及生境初步研究     

李平日  谭惠忠  刘禹  宋丽莉 《热带地理》2004,24(4):321-325

通过树轮钻取样及查考历史资料,论证南华寺水松栽种年代分别为明代正德十四年、清代康熙初年及清代同治末年.取水样作化学分析及收集近数十年环境观测资料,分析水松荣枯的原因.认为环境污染及不恰当人为活动是多株水松枯萎的主要原因.  相似文献   

红原泥炭6000a以来元素异常及其可能反映甘青地区人类活动信息的初步研究   总被引：4，自引：3，他引：1  

于学峰  周卫健 《第四纪研究》2006,26(4):597-603

通过对红原泥炭沉积剖面Pb,Zn,Fe,Mn,Cu,Co,Ni,Ti,V,Al等10种元素和灰分的测试,发现多数元素在该剖面的变化与灰分变化较为一致,但Cu,Pb和Zn元素的变化在剖面300cm以上出现较大异常:这3种元素的变化与其他元素变化呈相反的规律,而且Pb和Zn两种元素的含量较之剖面下部出现数量级的增大。通过对比,发现元素含量的异常与位于剖面上风区的甘青地区新石器时代晚期-青铜时代文化在发生时间上较为吻合,认为这可能是人类活动环境效应的记录。用600~300cm段的元素变化作为背景值,用与Pb,Zn元素相关较好的4种元素分别计算出二者变化的自然背景值,从而分离出了人类活动强度信息与自然环境背景值,分离结果与著名的青海柳湾墓地出土人口规模对比较好。  相似文献   

借助同位素方法研究地下水     

李云峰 《地球科学与环境学报》1993,(Z2)

本文归纳介绍了现代地质年代学中可直接用于地下水研究的多种同位素方法:~(14)C、~3H、~2H、~(18)O、~(85)Kr、~(39)Ar等方法。  相似文献   

宁蒗铜厂河铜矿床成矿条件研究   总被引：3，自引：0，他引：3  

胡受权  郭文平  杨凤根  徐旃章  张寿庭 《云南地质》2001,20(1):46-58

宁蒗铜厂河铜矿床系喜马拉雅期隐伏斑岩体外接触带玄武岩系热液型铜矿床，其主要含矿层位为上二叠统玄武岩组三段（P2β^3）与黑泥哨组（P2h)，主干控矿构造为南北向断裂体系，铜矿化均产于NW向F1断裂的下盘（南盘）。矿区具显著的成矿多期，多阶段性和矿化体水平，垂直分带性规律，通过对碳，氧，硫等稳定同位素和包裹体分析及成矿热液演化特征探讨，建立了铜矿热液成矿模式。  相似文献