末次盛冰期以来巴伦支海-喀拉海古海洋环境及海冰研究进展

巴伦支海-喀拉海是北冰洋最大的边缘海,能够对环境变化做出快速的响应和反馈,是全球气候变化最为敏感的区域之一,其古海洋环境演变及海冰变化研究是全球气候变化研究的重要组成部分。末次盛冰期以来,该区域的古海洋环境受到太阳辐射、海流强度、海平面变化、温盐环流和河流输入等因素影响发生了一系列不同尺度的波动。巴伦支海受到北大西洋暖水和极地冷水两大水团相互作用的影响,在水团交界处 （极锋) 由于不同水团性质的差异,导致其海水温度、盐度及海冰发生剧烈变化。而喀拉海则受到叶尼塞河和鄂毕河大量淡水输入影响,海流系统较巴伦支海相对复杂,沉积物主要来源于河流输入的陆源物质,并可以通过磁化率的分析明确区分两条河流的陆源物质。由于受到冷水和暖水的相互作用,巴伦支海-喀拉海海冰变化迅速,并且在全新世中晚期存在 0.4 ka 和 0.95 ka 的变化周期,但海冰变化的影响因素并不是单一的,而是气候系统内部各因子相互作用的结果。目前古海冰重建研究工作主要为定性研究,定量研究相对较少,所选用的重建指标也相对单一,另外存在年代框架差、分辨率低等不足。本文以巴伦支海和喀拉海为中心,总结了其快速气候突变事件、古温度盐度、海平面及海冰的变化,对影响因素进行了探讨,并通过分析末次盛冰期以来古海洋环境研究的不足,提出了相应的展望。     

Morphological characteristics of the paleochannel of the Yihe River in the Last Glacial Maximum,Shandong Province,China

The paleochannel of the Wenhekou–Liudaokou reach of the Yihe River was investigated using electrical soundings along the Zhuyong and Chuanliujie cross sections and drilling at the Chuanliujie cross section. Drilling data from the Liuhang Rubber dam and the Jiefang, Taoran, Yihe, and Luocheng road bridges were also used. Seven stratigraphic cross sections of the Yihe River paleochannel were confirmed based on electrical sounding and drilling, and samples were collected for ¹⁴C and optically stimulated luminescence dating near Zhuyang village, Chuanliujie village, Liuhang Rubber dam, south bank of the Benghe River bridge, and the riverbed near the Yihe Road bridge. The dating results suggest that the channels below 76.0, 70.0, 69.5, 55.1, 52.4, 56.5, and 56.4 m near Zhuyang village, Chuanliujie village, Liuhang Rubber dam, Jiefang Road bridge, Taoran Road bridge, Yihe Road bridge, and Luocheng Road bridge are paleochannels of the Yihe River during the Last Glacial Maximum (LGM). Lithology of the riverbed is complex and characterized by fracture zones. This reach of the river was braided with high width–depth ratios and the deep, incised valley at the Jiefang and Taoran road bridges was formed by a regional deep cut during the LGM.     

末次盛冰期巽他大陆北部草本植被扩张

末次盛冰期(Last Glacial Maximum,LGM)全球低海平面时,巽他陆架大面积暴露,其上的植被类型对于生物多样性演化和全球陆地碳储库有重要影响。但目前植被重建结果仍存在很大争议:一种观点认为LGM时巽他陆架主要分布稀树草原植被,雨林只零星存在于少数区域;而一些数值模拟结果和沉积记录显示巽他陆架上不存在大面积跨赤道的稀树草原,雨林植被仍占主导。LGM时巽他大陆北部可靠的植被记录十分有限。本研究依据靠近巽他陆架北部古河流入海口的沉积物岩芯,利用叶蜡烷烃含量和正构烷烃平均链长指标重建LGM时北巽他大陆的植被信息,结果显示平均链长在22~14.5 kaBP期间出现最大值,推测相对于全新世,冰期时巽他大陆北部草本成分增加。海平面降低使得冰期太平洋沃克环流减弱,呈现类厄尔尼诺状态,导致巽他大陆地区干旱加重,特别是赤道外围区域(南北纬7°以外)降水季节性增强,这种气候状态可能是草本植被成分增多的主要因素。     

Changes of Atmospheric Circulation since the LastInterstadial as Indicated by the Lake-statusRecord in China

The effective precipitation and the frame of atmospheric circulation in the past three key periods, i.e. 30 ka BP, 18 ka BP and 6 ka BP, have been analyzed on the basis of the palaeolake status record produced by the Chinese Lake Status Data Base. The results show that the west-central part of China was characterized by high lake-levels at 30 ka BP, resulting from strengthened southwest monsoons; whereas the high lake stand, occurring in the west-central part of China at 18 ka BP, was caused by the southward shift and the strengthening of westerlies although the high-stand distribution was reduced. Meanwhile, the east-central part of China was under the control of strong winter monsoons at 18 ka BP. The high lake-levels, which occurred in the east-central part of China at 6 ka BP, are related to the enhanced East-Asian summer monsoons; while the lowering of the lake-level in the west-central part of China at 6 ka BP was due to the northward shift and corresponding shrink of the westerlies.A comparison b     

Stratotype for the Mérida Glaciation at Pueblo Llano in the northern Venezuelan Andes

The Mérida Glaciation (cf. Wisconsinan, Weichselian) as proposed by Schubert (1974b) culminated at about 18 ka during the last glacial maximum (LGM) and ended at about 13 ka as indicated by ¹⁴C dating and correlation with the Cordillera Oriental of Colombia. Moraines of an early stade of Mérida Glaciation reached to 2800 m a.s.l. and were largely overrun or eradicated by the maximum Wisconsinan advance (LGM); where they outcrop, the older moraines are characterized by eroded, weathered glacial diamictons and outwash fans.At Pueblo Llano in the central Mérida Andes (Cordillera de Trujillo), older to younger beds of contorted glacitectonized diamict, overlying beds of bouldery till and indurated outwash, all belong to the early Mérida stade. Overlying the early Mérida stade, deposits of rhythmically bedded glaciolacustrine sediments are in turn overlain with contorted sand and silt beds capped with outwash. Above the outwash terrace a loop moraine of LGM age completely encircles the margins of the basin. A stream cut exposed by catastrophic (tectonic or surge?) release of meltwater displays a lithostratigraphic succession that is bereft of organic material for radiocarbon dating. Five optically-stimulated luminescence (OSL) dates place the maximum age of the lowest till at 81 ka.Particle size distributions allow clear distinctions between major lithic units. Heavy mineral analysis of the middle and lower coarse units in the section provide information on sediment sourcing and on major lithostratigraphic divisions. Trace element concentrations provide information on the relative homogeneity of the deposits. The HREE (heavy rare earth element) concentrations allow discrimination of the lower till from the rest of the section; the LREE (light rare earth element) concentrations highlight differences between the lower till, LGM till, and the rest of the section.     

Sediment dynamics in the Eurasian Arctic Ocean during the last deglaciation — The clay mineral group smectite perspective

This study focuses on sedimentological investigations of sediment cores recovered during the international Arctic′91, expeditions with the German research ice breaker RV “Polarstern” to the European sector of the Arctic Ocean. Here, we deduce the last glacial/interglacial changes in transport mechanism and sedimentation from the clay mineral group smectite. We choose the smectites as an example of how sediment mineralogy can be linked with particular source regions (the Kara and Laptev seas), distinct transport mechanism (sea ice and surface currents) and sedimentation processes. Smectite contents in Arctic sediments discussed for two time slices, including the Last Glacial Maximum (LGM), and the last deglaciation (Termination I), reveal the highest variability subsequent to the retreat of the Eurasian ice sheets. Our results show that smectite anomalies in the Eurasian Basin are associated with distinct meltwater pulses and occurred around 13.5–13.0 ¹⁴C ka B.P. Compelling evidence is provided that these anomalies are deduced from sea-ice entrained sediments from the eastern Kara Sea that entered the Arctic Ocean after ice-sheet break-up and eventually flooding of the Kara Sea. We propose that smectite anomalies in sediments of the eastern Arctic Ocean can be utilized to identify deglacial events and to help decipher configurations of the Eurasian ice sheets. The identification of smectite maxima along the modern sea-ice edge in the Eurasian Basin further indicates biologically enhanced sedimentation from melting sea ice allowing the reconstruction of seasonally open water in the region. Hence, considering the poor preservation conditions of primary paleoceanographic proxies in the Arctic Ocean, the clay mineral contents, particularly the smectite group, may be one alternative tool for paleoclimatic reconstruction in the Eurasian Basin.     

本土产业发展视角下的乡村地方性重构——基于阳美玉器产业的文化经济地理分析

以广东揭阳的玉器生产专业村阳美村为例,从文化经济地理学视角解读本土产业发展中地方性的嵌入与重构。研究发现：本土产业在地方性多方要素的驱动与支撑下产生,在多重尺度政治经济过程作用与地方主体的响应下发展。地方性是本土产业产生并建立对外功能联系的初始条件,也是主体响应结构变动所做战略选择和地方营销的依托。在地方性嵌入产业发展的同时,生产、生活和宗教等地方活动被强化了与玉器生产相关的功能和意义,民居、街巷、宗祠等空间形制因传统功能被挤压而出现重塑。地方活动与景观的变化并未弱化地方意义,村民的地方依赖和依恋因本土产业提供了更好的发展机会与荣誉感而增强。     

末次盛冰期长江南京段河槽特征及古流量(英文)

The stratigraphical cross-sections of the Yangtze River incised-valley near the No.1,No.3 and No.4 Nanjing Yangtze River bridges were established with respective bore date and documents.By 14C age analysis of the samples of four drilling cores near the No.4 Bridge(to be built),we can find that the time range of paleo-valley is dated in the LGM at a depth of-60 m to-90 m near Nanjing.It is also indicated that the deep incised-valley channel was narrow and the river flowed swiftly.The ancient Yangtze River deep channel presented partially and deeply incised features near the No.1 Bridge.According to previous publications,much research has been done on the main paleo-channel of the Yangtze River,but few results have been achieved on discharge estimation.In this paper,the incipient velocity and average velocity of the LGM was calculated with Vc = 4.60 d 1/3 h1/6,95 Vc 1.28lg 13.15.h.gd,d = 6 * 90 V 6.5u h≈ d,etc.,in terms of the river shape,sedimentary grain size and sequences near the No.3 and No.1 bridges.Moreover,the discharge in Nanjing reach of the Yangtze River during the LGM has been estimated to be around 12,000-16,000 m3/s according to the relationship of discharge,velocity of flow and cross-section.     

末次盛冰期西太平洋海温差异对亚洲夏季风影响的数值模拟

文章利用Zhao等的模拟结果,进一步研究了在末次盛冰期(LGM)情景下汪品先和CLIMAP两种重建海洋表面温度(SST)资料差异对亚洲夏季风的影响。模拟结果表明:在LGM情景下西太平洋海域SST资料的不同对模拟的亚洲夏季风有着十分重要的作用。夏季,与CLGM方案相比,在WLGM方案中,当热带西太平洋SST较暖时,印度地区的大气热量出现显著增加,大气热量的这种变化,使得南非高压、南印度洋经向Hadley环流加强,伴随着索马里越赤道气流加强,也导致了印度季风区纬向季风环流的加强,从而造成了印度夏季风增强、降水增多;与较暖的热带西太平洋相对应,澳大利亚高压和120°E附近越赤道气流减弱,东亚季风区20°N以南经向季风环流加强、20°N以北经向季风环流减弱,指示着一个强的南海夏季风和较弱东亚副热带大陆夏季风。     

Connectivity analyses of valley patterns indicate preservation of a preglacial fluvial valley system in the Dyfi basin, Wales

Coastal valleys in the west part of Mid-Wales, such as the Mawddach, Dysynni, Tal-y-llyn and Dyfi, acted as corridors for ice which drained the Welsh Ice Cap during the Devensian. Analyses of detailed digital elevation models, and interpretation of satellite images and aerial photographs, show the existence of large variations in the amount of glacial modification between these valleys. Although all the valleys are glacially over-deepened along late Caledonian fault lines, only the Dyfi basin exhibits a dendritic pattern, with V-shaped cross-profiles and valley spurs typical of valleys formed by fluvial processes. Connectivity analysis of the Dyfi basin shows that it exhibits an almost completely dendritic pattern with connectivity α and β values of 0.74 and 1.01, respectively, with little glacial modification of the preglacial fluvial valley pattern in the form of glacial valley breaching. Several examples of glacial meltwater incision into a well-developed pre-existing river valley system, causing river capture across watersheds, have been identified in the Dyfi basin. The degree of preservation of the preglacial fluvial valley system within the Dyfi basin indicates limited modification by glacial processes, despite the area being subjected to glacier activity during the Late Devensian at least. It is possible that major parts of the basin were covered by cold-based or slow-moving ice, close to, or under, a migrating ice-divide, with the major ice drainage occurring along the weaker zone of the Pennal Fault along which teh Dyfi valley is located, causing minor adjustments to the surrounding interfluves and uplands. It is proposed here that the general river valley morphology of the Dyfi basin is of a pre-Late Devensian age.