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1.
通过对北大西洋IODP U1313站深海沉积序列高密度取样和粒度分析,利用粒级-标准偏差变化算法和EMD方法提取了对环境敏感粒度组分并探讨了气候变化的周期.本文粒度组分可分为细组分(＜1.73μm,组分Ⅰ)和粗组分(＞1.73μm,组分Ⅱ),其中粗组分又分为组分Ⅱa(1.73 ～ 34.26μm)和组分Ⅱb(＞34.26μm).综合分析认为:组分Ⅰ为西风环流搬运堆积形成,组分Ⅱ为洋流搬运下沉积形成,组分Ⅱb虽然含量较低,但能指示冰漂砾事件的发生.比值曲线组分Ⅰ/组分Ⅱ和组分Ⅰ/组分Ⅱa波动幅度较大,可作为反映古气候冷暖波动的敏感指标.对组分Ⅱ、组分Ⅰ/组分Ⅱ进行EMD分解,结果表明:在本研究时段内,两指标对地球轨道三要素的周期体现均不明显,而2ka(2.12ka和2.15ka)的亚轨道千年周期是主要的周期之一.依据上述多个指标的波动情况,把研究剖面69.93 ～ 115.18mcd(1471.53～2415.60ka)分为9个古气候变化阶段:A阶段(1471.53～1640.09ka),对应深海氧同位素阶段(MIS)49～ 57,冰期和间冰期迅速转换,发生多次IRD事件;B阶段(1640.09～ 1865.57ka),对应MIS 58 ～ 69,间冰期显著而冰期不明显;C阶段(1865.57～1914.70ka),对应MIS 70～72,冰期显著而间冰期不明显;D阶段(1914.70～2021.13ka),对应MIS 73～76,冰期不显著;E阶段(2021.13～2092.21ka),对应MIS 77～78,冰期显著,发生多次IRD事件;F阶段(2092.21 ～ 2226.43ka),对应MIS 79～85,间冰期显著;G阶段(2226.43 ～2261.53ka),对应MIS 86期,发生多次IRD事件;H阶段(2261.53～ 2384.61ka),对应MIS 87～93,冰期不显著而间冰期显著;Ⅰ阶段(2384.61 ～2415.60ka),对应MIS 94 ～ 95,发生多次IRD事件. 相似文献
2.
《地质科技情报》2021,40(1)
黄土作为典型的多物源沉积物,粒度分布常呈现多峰分布。端元分析可以从复杂的沉积物粒度中分离出代表不同沉积物源和沉积动力的端元组分,在黄土研究中得到了广泛应用。利用Paterson参数化端元模型对处于毛乌素沙漠东南缘的靖边三道沟剖面粒度进行端元分离与解释,并讨论其代表的环境意义。靖边三道沟黄土可分为4个端元:EM1(众数粒径8.93μm)为背景粉尘;EM2(众数粒径25.18μm)为与季风环流有关的组分;EM3(众数粒径39.91μm)和EM4(众数粒径56.37μm)都是与冬季风有关的组分,其中EM3为黄土高原黄土主要组分,EM4与现代沙尘暴的粒级大致相同。通过对各端元组分随年龄变化的曲线进行分析,得到以下结论:该剖面记录了靖边地区自MIS 3以来经历了MIS 3(32.8～29.8 ka BP)、LGM(29.8～22.8 ka BP)、冰消期(22.8～11.3 ka BP)和全新世(8.7～1.7 ka BP)共4个气候时期。端元组分还记录了冰消期H 1事件(16.2～13.8 ka BP)、B/A事件(13.8～12.8 ka BP)、YD事件(12.8～11.3 ka BP)共3次气候快速变化事件和D-O旋回。该剖面还记录了毛乌素沙漠末次冰期经历的3次主要的扩张-收缩旋回以及全新世8.7～8.2,6.0～5.0,3.5～2.5 ka共3次干旱沙进事件。 相似文献
3.
沉积物环境敏感粒度是进行古环境研究的重要方法之一, 然而华北平原地区很少进行完整的第四纪全取心深孔沉积物环境敏感粒度组分的提取及分析.对天津渤海湾G1和G2孔第四纪沉积物样品进行粒度分析, 采用粒级-标准偏差和主成分分析两种方法进行了沉积物环境敏感粒度组分提取.对比提取结果发现, 两种方法存在差异性的同时还存在一定的兼容性, 沉积层理厚度越薄, 兼容性越明显; 主成分分析方法对沉积物环境敏感粒度组分刻画得更为细致, 粒级-标准偏差方法不适合深孔沉积物整体敏感粒度组分的提取.G1孔环境敏感粒度组分的粒度峰值为6.700μm、15.650μm、36.240μm、176.900μm、282.100μm、716.800μm; G2孔环境敏感粒度组分的粒度峰值为0.578μm、176.000μm, 分别对应6个和3个粒度分布区间, 指示两孔整体上的沉积物来源及沉积环境空间存在差别.G2孔相对于G1孔整体上的沉积强度大且沉积环境较为稳定, 适合于开展高分辨率的古环境重建工作. 相似文献
4.
南黄海北部晚更新世以来常量元素记录的化学风化作用 总被引：1，自引：0，他引：1
以南黄海北部高沉积速率柱状样DLC70-3孔作为研究对象,对沉积物的黏土矿物和常量元素地球化学组成进行了综合分析。结果显示,DLC70-3孔沉积物中黏土矿物组合以伊利石为主,其次为蒙皂石,绿泥石和高岭石含量较低;绝大部分样品中伊利石与蒙皂石含量的比值<6,表明沉积物主要来源于黄河物质的输送。研究认为DLC70-3孔沉积物的化学风化指标CIA值受到海平面变化和源区气候变化共同控制,其中源区的气候变化为主要控制因素,而海平面变化造成的机械沉积分异作用主要影响27.80~38.00 m（MIS 4）层位沉积物的CIA值。CIA值显示在MIS 5和MIS 3期大陆化学风化作用较强,与内陆黄土高原地区夏季风和化学风化指标的变化趋势一致,尤其是在MIS 3早期（40~60 ka）记录的化学风化作用非常强,反映了黄河流域地区出现强夏季风降雨过程。 相似文献
5.
济州岛西南泥质区粒度组分变化的古环境应用 总被引：14，自引：1，他引：13
利用激光粒度仪对位于东海陆架济州岛西南泥质区的B2孔进行了沉积物粒度分析,根据标准偏差变化检出了B2孔含有4个粒度组分：〉65．6、65．6～10．5、10．5～1．3和〈1．3μm,其中〉65．6μm粗组分含量很低,主要是以底栖有孔虫为主的生源沉积．各组分平均粒径和粒度含量随孔深的变化显示了65．6～10．5μm组分在B2孔含量较高（21％～30％）,变化最明显,是该孔对环境变化最敏感的粒度组分．研究表明该敏感组分的粒度含量和平均粒径变化主要受东亚冬季风的强弱变化制约,其变化恢复的近2ka来东亚冬季风变化和中国东部气候变化序列具有很好的一致性,证明65．6～10．5μm粒度组分可以作为东亚冬季风的替代指标． 相似文献
6.
对南海神狐海域水合物钻探区SH1B和SH5C等2个钻孔顶部0~39.41 m和0~23.85 m的连续沉积物开展高分辨率碳酸盐旋回研究,结合浮游有孔虫氧同位素地层学、AMS14C年代学和生物地层学进行地层划分。结果表明：SH1B孔MIS12期以来CaCO3曲线总体上具有明显的冰期和间冰期旋回,表现为较典型的冰期低、间冰期高的“大西洋型”旋回特征,具有良好的地层意义;SH5C孔除MIS1-MIS2期外,MIS3-MIS8期的CaCO3含量较SH1B孔的要低,冰期和间冰期旋回性较差,MIS3-MIS 4和MIS7期出现明显的低钙事件;同时,SH5C孔MIS3-MIS5期浮游有孔虫G.ruber的δ13C值明显负偏,平均值为-0.11‰;两孔MIS1期的沉积速率是MIS2期的近2倍,与前人的研究结果相反,为MIS2期部分地层缺失所致。SH1B孔受水合物分解影响不大,而SH5C孔受水合物分解影响明显。SH5C孔MIS2期的地层缺失事件和MIS3-MIS4、MIS7期的低钙事件以及MIS3-MIS5期δ13C值负偏事件主要发生在末次冰期,推测与下伏水合物分解产生的海底滑塌、海水酸化等环境效应有关。 相似文献
7.
从沉积速率和沉积物粒度看冰后期海侵以来珠江三角洲西江大鳌沙的形成 总被引：2，自引：2，他引：2
大鳌沙处于珠江三角洲西江河口的近口段，洪季西江河口的潮区界西线在其顶端附近。冰后期海侵以来，大鳌沙顶端的PRD05和中部的PRD04两个钻孔的沉积速率和沉积物粒度有着极大的差别。7 630 a BP以前，PRD04孔的沉积速率小于PRD05孔的沉积速率；但7 630 a BP以来，PRD04孔的沉积速率大于PRD05孔的沉积速率。从粒度分析看，埋深12.28 m以下，PRD04孔沉积物比PRD05孔的粗，分选性比PRD05孔的差；埋深12.28 m以上，PRD04孔的沉积物比PRD05孔的细，分选性相对比PRD05孔的好。分析表明，9 000～4 200a BP， 沉积物由南（中部）向北（顶部）输运，涨潮流冲蚀老沉积物，在喷出磨刀门通道后，流速迅速降低，粗颗粒泥沙先沉积，而细颗粒泥沙被涨潮流搬运至更北的区域沉积。近3500年以来，河流动力占优势，沉积物由北（顶部）向南（中部）输运。大鳌沙的形成与涨潮射流密切相关。涨潮射流口的位置在蛇地山和右岸纵向山地之间，宽约2200 m。 相似文献
8.
滦河三角洲南部MT04孔磁性地层研究及其构造与气候耦合关系的探讨 总被引：1，自引：0，他引：1
对滦河三角洲南部孔深383m的MT04孔进行了详细的岩石磁学和古地磁研究,结果显示:1)孔深0~90m和244~383m沉积物携磁矿物主要为磁铁矿,90~244m沉积物携磁矿物主要为赤铁矿;2)基于208个样品(28个交变样品,180个热退样品)分离出的特征剩磁,建立了钻孔的磁性地层,并与标准极性年表相对比。结果显示,MT04孔记录了Mammoth负极性亚时(C2An.2r)至Brunhes正极性时(Cln)之间的沉积,钻孔M/B界限埋深122.4m,G/M界限埋深为327.2m,钻孔底部年龄约为3.2Ma,而钻孔上更新统底界埋深为83m。MT04孔包括3个沉积阶段:Ⅰ阶段为1.0~3.2Ma,沉积速率平均为92m/Ma,湖相地层为主,为构造稳定期,气候控制了MT04孔的沉积环境和速率;Ⅱ阶段为0.8~1.0Ma,为构造活动期,沉积物以细砂为主,且多为入湖河流和富有机质的粉砂;Ⅲ阶段为0~0.8Ma,构造和气候变化双重作用控制沉积过程,MIS 5阶段T3阶地形成之后河流下切,研究区沉积约30m厚连续砂层,且部分层位受海侵影响形成潮控河流;MIS 3阶段滦河东流并入青龙河入海,在此沉积约15m厚连续砂层;MIS 1阶段滦河摆动至此入海形成典型的两期沙坝-澙湖海岸。 相似文献
9.
基于新疆伊犁盆地肖尔布拉克黄土剖面粒度数据,以贝叶斯粒度端元模型法为主,粒级标准偏差法为辅探寻对气候变化响应敏感的粒级组分及其对粉尘来源示踪和古气候重建的意义。研究结果表明粒度端元组分EM1（众数粒径:21.22 μm）代表大气粉尘中较为稳定的背景值,其含量的变化与高空西风环流强度有关。EM2（75.29 μm）主要代表了近源河流沉积物的悬移搬运组分,可视为较敏感的古气候指标。EM3（47.5 μm）也代表了近距离的悬移搬运组分,可能主要由较粗颗粒对地表的碰撞磨蚀作用而产生。EM2记录了深海氧同位素2阶段（MIS2）以来的北大西洋气候波动事件,如Heinrich事件、YD事件等。贝叶斯粒度端元模型能够区分不同的沉积动力过程,在新疆黄土古气候研究中具有广泛的应用前景。 相似文献
10.
YQ0902孔位于浙江南部瓯江三角洲南侧温瑞平原上。沉积相、粒度分析以及AMS 14C测年数据表明,硬土层之下为海洋氧同位素3阶段(MIS 3）形成的潟湖相沉积,据此推测MIS 3高海平面至少达到现今海平面之下30m左右(未经构造升降和沉积物压实作用等影响的校正,下同）。硬土层的成土过程发生于MIS 2,其母质部分为MIS 3的潟湖沉积,部分为河漫滩沉积。硬土层之上是一套形成于全新世的海侵—海退旋回,与长江三角洲南翼前缘的沉积相组合类似。研究钻孔初始海泛面约形成于9 cal ka BP,推算当时的海平面约低于现今海平面25 m。中全新世最大海侵前后,东亚季风较强,通过径流或沿岸流输入本区的沉积物较充足,沉积速率较大。随着海平面相对稳定或略有下降,东亚季风减弱,可容空间减小,中晚全新世(5～2 cal ka BP）沉积速率较低。高分辨率的XRF岩心扫描获得的元素相对含量是古环境与古气候研究的重要指标,其中Cl/Ti、Fe/Ti值可分别作为海相性(与海洋联通程度）与东亚季风强弱的替代指标。 相似文献
11.
JOCHEN KNIES JENS MATTHIESSEN CHRISTOPH VOGT RUEDIGER STEIN 《Boreas: An International Journal of Quaternary Research》2002,31(1):82-93
A multiproxy analysis of Hole 911A (Ocean Drilling Program (ODP) Leg 151) drilled on the Yermak Plateau (eastern Arctic Ocean) is used to investigate the behaviour of the Svalbard/Barents Sea ice sheet (SBIS) during late Pliocene and early Pleistocene (~3.0-1.7 Ma) climate changes. Contemporary with the 'Mid-Pliocene (~3 Ma) global warmth' (MPGW), a warmer period lasting ~300 kyr with seasonally ice-free conditions in the marginal eastern Arctic Ocean is assumed to be an important regional moisture source, and possibly one decisive trigger for intensification of the Northern Hemisphere glaciation in the Svalbard/Barents Sea area at ~2.7 Ma. An abrupt pulse of ice-rafted debris (IRD) to the Yermak Plateau at ~2.7 Ma reflects distinct melting of sediment-laden icebergs derived from the SBIS and may indicate the protruding advance of the ice sheet onto the outer shelf. Spectral analysis of the total organic carbon (TOC) record being predominantly of terrigenous/fossil-reworked origin indicates SBIS and possibly Scandinavian Ice Sheet response to incoming solar radiation at obliquity and precession periodicities. The strong variance in frequencies near the 41 kyr obliquity cycle between 2.7 and 1.7 Ma indicates, for the first time in the Arctic Ocean, a close relationship of SBIS growth and decay patterns to the Earth's orbital obliquity amplitudes, which dominated global ice volume variations during late Pliocene/early Pleistocene climate changes. 相似文献
12.
Based on literature and our data, analysis of sedimentation rates during the last glacial/interglacial cycle (during the last 130 ka) is given for the Norwegian-Greenland Basin, the Arctic Ocean, Bering and Okhotsk seas, as well as a number of seas in the Southern Ocean. Sedimentation rates in the studied zone are controlled by the development of continental ice sheets, sea ice covers, and biogenic sedimentation, which, in turn, depends on climate variations. 相似文献
13.
Stanislaus G. Fabian Stephen J. Gallagher David De Vleeschouwer 《Boreas: An International Journal of Quaternary Research》2023,52(4):476-497
Deep Sea Drilling Program (DSDP) Site 548 was cored in 1984 at a water depth of 1256 m on the Goban Spur, offshore southwest Ireland. Coring retrieved a ~100-m-thick Pleistocene contourite sequence. This study uses planktonic foraminiferal assemblage and benthic foraminiferal oxygen isotope analyses to establish an age model for the upper 40 m of this core. This site's multidisciplinary analyses of planktonic foraminiferal assemblages, lithic grains, facies and calcium carbonate concentration reveal a 250 000-year record of the North Atlantic polar front variability and British–Irish Ice Sheet (BIIS) history. The sequence is characterized by alternations of ice rafted debris (IRD) laden pelagic mud facies with calcium carbonate-rich silty sand contourite facies that track glacial/interglacial cycles. The polar front migrated southward across the area several times during glacial maxima and stadial periods, while warmer Mediterranean Outflow Water (MOW) flowed northward across the region during interglacial and interstadial periods depositing contourites. Lithic analyses reveal a complex history of IRD deposition associated with iceberg calving from the Laurentide Ice Sheet and northwest European ice sheets, mainly the BIIS. Comparison between the Goban Spur (DSDP Site 548) and the Celtic Margin (MD03-2692) and central North Atlantic Integrated Ocean Drilling Program (IODP) Site U1308 suggests differences between the ‘non-Laurentide Ice Sheet’ Heinrich Events (HE) 6 and 3 at the Goban Spur, with IRD from the BIIS being prominent during HE 6 and IRD from other European ice sheets north of the BIIS likely being more dominant during HE 3. The nature of lithics in IRD-rich horizons during Terminations 3, 3A, 2 and 1 suggests significant iceberg calving episodes preceding BIIS retreat during the onset of interstadial intervals. 相似文献
14.
北冰洋西部晚第四纪浮游有孔虫氧碳同位素记录的海冰形成速率 总被引：2，自引：0，他引：2
北冰洋西部晚第四纪浮游有孔虫Neogloboquadrina pachyderma(sin.)(Nps)壳体的δ18O和δ13C与浮游有孔虫丰度和筏冰碎屑含量的综合研究表明,MIS 7晚期以来,Nps的δ18O和δ13C值出现7次明显的偏轻,可能与海冰形成速率的提高造成轻同位素卤水的生产和下沉相关.偏轻的Nps δ18O和δ13C值对应于极低的浮游有孔虫丰度和筏冰碎屑含量,因此这些轻值与温暖的大西洋水和淡水的输入无关,应当指示进入北冰洋的大西洋水减弱和楚科奇海陆架水的大量减少.相反,Nps δ18O的重值则反映输入北冰洋的淡水和太平洋水的减少;Nps δ13C的重值指示来自陆架流通性更好的表层和盐跃层水向北冰洋的输送. 相似文献
15.
John Walden Emilie Wadsworth William E. N. Austin Clare Peters James D. Scourse Ian R. Hall 《第四纪科学杂志》2007,22(2):163-172
The composition of ice‐rafted debris (IRD) within a sediment core from the European continental slope (core OMEX‐2K; 49° 5′ N, 13° 26′ W) has been examined using environmental magnetic analyses. The data demonstrate compositional variability of the IRD within Heinrich layers 2 (H2) and 1 (H1) and these differences are most readily explained by changes in the contribution of different IRD sources to the core site. Some IRD within the main Heinrich layers show magnetic signatures that are similar to IRD derived from the Laurentide ice sheet found in cores from within the main North Atlantic IRD‐belt. In contrast, other IRD‐rich layers, both prior to and within the main Heinrich layers, demonstrate different magnetic behaviour, suggesting a contribution from a non‐Laurentide sourced IRD, most likely derived from ice streams discharging from northeast Atlantic ice sheets such as the British and Fennoscandian ice sheets. These data are consistent with published compositional data from the same core and, given the rapid, highly sensitive and non‐destructive nature of the method, suggest that environmental magnetic analysis has considerable potential for characterising IRD materials within Heinrich layers for the purposes of defining provenance. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
16.
Anne E. Jennings John T. Andrews Brett Oliver Maureen Walczak Alan Mix 《Boreas: An International Journal of Quaternary Research》2019,48(4):825-840
Nares Strait, a major connection between the Arctic Ocean and Baffin Bay, was blocked by coalescent Innuitian and Greenland ice sheets during the last glaciation. This paper focuses on the events and processes leading to the opening of the strait and the environmental response to establishment of the Arctic‐Atlantic throughflow. The study is based on sedimentological, mineralogical and foraminiferal analyses of radiocarbon‐dated cores 2001LSSL‐0014PC and TC from northern Baffin Bay. Radiocarbon dates on benthic foraminifera were calibrated with ΔR = 220±20 years. Basal compact pebbly mud is interpreted as a subglacial deposit formed by glacial overriding of unconsolidated marine sediments. It is overlain by ice‐proximal (red/grey laminated, ice‐proximal glaciomarine unit barren of foraminifera and containing >2 mm clasts interpreted as ice‐rafted debris) to ice‐distal (calcareous, grey pebbly mud with foraminifera indicative of a stratified water column with chilled Atlantic Water fauna and species associated with perennial and then seasonal sea ice cover) glacial marine sediment units. The age model indicates ice retreat into Smith Sound as early as c. 11.7 and as late as c. 11.2 cal. ka BP followed by progressively more distal glaciomarine conditions as the ice margin retreated toward the Kennedy Channel. We hypothesize that a distinct IRD layer deposited between 9.3 and 9 (9.4–8.9 1σ) cal. ka BP marks the break‐up of ice in Kennedy Channel resulting in the opening of Nares Strait as an Arctic‐Atlantic throughflow. Overlying foraminiferal assemblages indicate enhanced marine productivity consistent with entry of nutrient‐rich Arctic Surface Water. A pronounced rise in agglutinated foraminifers and sand‐sized diatoms, and loss of detrital calcite characterize the uppermost bioturbated mud, which was deposited after 4.8 (3.67–5.55 1σ) cal. ka BP. The timing of the transition is poorly resolved as it coincides with the slow sedimentation rates that ensued after the ice margins retreated onto land. 相似文献
17.
The Antarctic and the Arctic regions play a key role in global sea level change and carbon cycle, and reserve key information of the Cenozoic transition from a green-house to an ice-house Earth. They have become hot spots in earth science studies. The geological drilling projects in both polar regions (e.g., DSDP/ODP/IODP/ICDP) have achieved remarkable successes, which have freshened the knowledge of global environmental and climatic evolution. Along with the Cenozoic global cooling, the timing of glaciation was almost synchronous on both the Antarctic and the Arctic. Accompanied with the Antarctic ice sheet build-up and increased terrestrial weathering, the enhanced formation of Antarctic Bottom Water exerts significant impact on global ocean circulation. The volume of unstable West Antarctic Ice Sheet fluctuates during glacial-interglacial periods showing 40 ka obliquity cycles, its volume significantly reduced or collapsed during several peak interglacials or long warm intervals. The Southern Ocean plays a significant role modulating atmospheric CO2 concentration, global deep water circulation and nutrient distribution, productivity at different time scales. Sea level responses to the waxing and waning of polar ice sheets at different time intervals were tested, which provide valuable clue for predicting future sea level changes. The upcoming IODP drilling projects on polar regions will keep focusing on the high latitude ice sheet development, Southern Ocean paleoceanographic evolution, land-ocean linkages in the Arctic, and the impacts on the global climate, which will provide important boundary conditions for predicting global future climate evolution. 相似文献
18.
格陵兰海海冰外缘线变化特征分析 总被引：2，自引：0，他引：2
格陵兰海作为北冰洋的边缘海之一,容纳了北极输出的海冰,其海冰外缘线的变化既受北极海冰输出量的影响,也受局地海冰融化和冻结过程的影响。利用2003年1月到2011年6月AMSR-E卫星亮温数据反演的海冰密集度产品,对格陵兰海海冰外缘线的变化特征进行了分析。结果表明,格陵兰海海冰外缘线不仅存在一年的变化周期,还存在比较显著的半年变化周期,与海冰在春秋两季向岸收缩有关。格陵兰海冬季的海冰外缘线极大值呈逐年下降的趋势,体现了北极增暖导致的冬季海冰范围减小;而夏季海冰外缘线离岸距离的极小值呈上升趋势,表明夏季来自北冰洋的海冰输出量增大。2003—2004年是格陵兰海夏季海冰融化最严重的2年。2007年北冰洋夏季海冰覆盖范围达到历史最小;而格陵兰海夏季的最小海冰范围最大,表明2007年北冰洋海冰的输出量大于其他年份。此外,夏季格陵兰岛冰雪融化形成的地表径流对海冰外缘线有一定的影响。对海冰外缘线影响最大的不是格陵兰海的局地风场,而是弗拉姆海峡(Fram Strait)区域的经向风,它直接驱动了北冰洋海冰向格陵兰海的输运,进而对格陵兰海海冰外缘线的分布产生滞后的影响。 相似文献
19.
Late Quaternary changes in sediment composition on the NE Greenland margin (~73° N) with a focus on the fjords and shelf 
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下载免费PDF全文 John T. Andrews Rüdiger Stein Matthias Moros Kerstin Perner 《Boreas: An International Journal of Quaternary Research》2016,45(3):381-397
In order to document changes in Holocene glacier extent and activity in NE Greenland (~73° N) we study marine sediment records that extend from the fjords (PS2631 and PS2640), across the shelf (PS2623 and PS2641), to the Greenland Sea (JM07‐174GC). The primary bedrock geology of the source areas is the Caledonian sediment outcrop, including Devonian red beds, plus early Neoproterozoic gneisses and early Tertiary volcanics. We examine the variations in colour (CIE*), grain size, and bulk mineralogy (from X‐ray diffraction of the <2 mm sediment fraction). Fjord core PS2640 in Sofia Sund, with a marked red hue, is distinct in grain size, colour and mineralogy from the other fjord and shelf cores. Five distinct grain‐size modes are distinguished of which only one is associated with a coarse ice‐rafting signal – this mode is rare in the mid‐ and late Holocene. A sediment unmixing program (SedUnMixMC) is used to characterize down‐core changes in sediment composition based on the upper late Holocene sediments from cores PS2640 (Sofia Sund), PS2631 (Kaiser Franz Joseph Fjord) and PS2623 (south of Shannon Is), and surface samples from the Kara Sea (as an indicator of transport from the Russian Arctic shelves). Major changes in mineral composition are noted in all cores with possible coeval shifts centred c. 2.5, 4.5 and 7.5 cal. ka BP (±0.5 ka) but are rarely linked with changes in the grain‐size spectra. Coarse IRD (>2 mm) and IRD‐grain‐size spectra are rare in the last 9–10 cal. ka BP and, in contrast with areas farther south (~68° N), there is no distinct IRD signal at the onset of neoglaciation. Our paper demonstrates the importance of the quantitative analysis of sediment properties in clarifying source to sink changes in glacial marine environments. 相似文献
20.
The evidence for the extent and timing of Weichselian glaciation in Arctic regions shows that: (1) there were no major marine ice domes in the Arctic at 18,000 B.P. but that glaciers were relatively limited in extent; (2) there were no extensive ice shelves at 18,000 B.P. as envisaged by Hughes, Denton & Grosswald(1977); (3) the major periods of glacier expansion were between 125,000 and 80,000 B.P., just prior to 45,000 B.P., and between 11,000 and 8,000 B.P., and thus that glacier fluctuations at the southern margins of the Laurentide and Fennoscandian ice sheets were out of phase with those in the Arctic which advanced during southern interstadials. Phases of glacier advance in the Atlantic sector of the Arctic can be identified in deep sea cores by the peaks in concentration of iceberg-dropped detritus and an increase in sedimentation rates, which are highest when sub-polar water penetrates to the north. The key to the temporal pattern of Arctic glaciation and its association with oceanic changes is given by the intimate association of present-day Arctic glacierisation with the two major low pressure troughs which penetrate the Arctic in the Atlantic sector and in Baffin Bay. The chronology of glaciation in the Atlantic sector is associated with the activity of these troughs and the related oceanic circulation. Cooling of the Arctic due to reduction in solar radiation at the end of the last interglacial, when the pack ice lay north of 75d?N in the Atlantic, produced ideal conditions for Arctic glacier growth, with moisture transported by a strong cyclonic flux into a cooling Arctic from a strong North Atlantic Drift current. A positive feedback loop involving ocean and atmospheric circulation and pack ice, caused movement of the polar front to the south, thus slowly cutting off the supply of moisture to the Arctic. Further cooling at 75,000 B.P. caused a rapid extension of the polar front south of 45d?N, effectively cut off the northward movement of surface currents on the North Atlantic, and produced a strong zonal oceanic and atmospheric circulation which starved Arctic glaciers of nourishment and caused their retreat, and initiated rapid build up of the Fennoscandian and Laurentide ice sheets. Subsequent extensions of Arctic glaciers were associated with limited northward movement of sub-polar water and associated Atlantic depressions. The expansion of glaciers within the Arctic between 11,000 and 8,000 B.P. was associated with the first and diachronous penetration of moisture into a still cool Arctic during decay of the two great ice sheets. 相似文献