Quaternary features beneath Lake Simcoe,Ontario, Canada: drumlins,tunnel channels,and records of proglacial to postglacial closed and overflowing lakes

Lake Simcoe is a large lake 45 km across and in places over 30 m deep, located between Lake Huron and Lake Ontario, in the glaciated terrain of southern Ontario, Canada. Seismostratigraphic analysis of high-resolution seismic reflection profiles, together with lakebed sediment sampling and pollen study, revealed distinctive sequences in the sediments beneath Lake Simcoe, Ontario. A surface unit (Blue Sequence) of soft Holocene mud (low-amplitude surface reflection, discontinuous parallel internal reflections) lies in the deeper basins of the lake. The underlying unit (Green Sequence) is characterized by high-amplitude parallel internal reflections; basal sediments of this sequence consist of clay rhythmites with dropstones. The Green Sequence was deposited by lacustrine sedimentation in proglacial Lake Algonquin; sedimentation persisted until the basin was isolated from other glacial lakes at about 10 ¹⁴C ka at the Penetang post-Algonquin phase. Subsequent erosion of the uppermost portion of the Green Sequence is attributed to wave action in a low-level early Holocene lake, possibly closed hydrologically and coeval with closed lowstands in the Huron and Georgian Bay basins. Two sequences with high-amplitude surface reflections and chaotic internal reflections (Purple and Red Sequences) lie below the Green Sequence. Northeast-southwest trending ridges, tens of metres in height, on the Red Sequence (the lowermost of these two units) are interpreted to be drumlins. An erosion surface descends into narrow valleys 50–80 m deep beneath the lake in bays to the west and south of the main lake basin. These depressions are interpreted as subglacial tunnel channels cut by rapid flows of meltwater. The sediments of Purple Sequence are interpreted as channel-fill sediments rapidly deposited during waning stages of the meltwater drainage. The Red Sequence is correlated with the Newmarket Till of the last glacial maximum identified beneath the Oak Ridges Moraine to the south.     

Late Weichselian fluvial evolution on the southern Kara Sea Shelf, North Siberia

Glaciations had a profound impact on the global sea-level and particularly on the Arctic environments. One of the key questions related to this topic is, how did the discharge of the Siberian Ob and Yenisei rivers interact with a proximal ice sheet? In order to answer this question high-resolution (1–12 kHz), shallow-penetration seismic profiles were collected on the passive continental margin of the Kara Sea Shelf to study the paleo-drainage pattern of the Ob and Yenisei rivers. Both rivers incised into the recent shelf, leaving filled and unfilled river channels and river canyons/valleys connecting to a complex paleo-drainage network.These channels have been subaerially formed during a regressive phase of the global sea-level during the Last Glacial Maximum. Beyond recent shelf depths of 120 m particle transport is manifested in submarine channel–levee complexes acting as conveyor for fluvial-derived fines. In the NE area, uniform draping sediments are observed. Major morphology determining factors are (1) sea-level fluctuations and (2) LGM ice sheet influence. Most individual channels show geometries typical for meandering rivers and appear to be an order of magnitude larger than recent channel profiles of gauge stations on land.The Yenisei paleo-channels have larger dimensions than the Ob examples and could be originated by additional water release during the melt of LGM Putoran ice masses.Asymmetrical submarine channel–levee complexes with channel depths of 60 m and more developed, in some places bordered by glacially dominated morphology, implying deflection by the LGM ice masses. A total of more than 12,000 km of acoustic profiles reveal no evidence for an ice-dammed lake of greater areal extent postulated by several workers. Furthermore, the existence of the channel–levee complexes is indicative of unhindered sediment flow to the north. Channels situated on the shelf above 120-m water depth exhibit no phases of ponding and or infill during sea-level lowstand. These findings denote the non-existence of an ice sheet on large areas of the Kara Sea shelf.     

晚冰期以来河西走廊花海古湖泊演化过程及其对气候变化的响应

通过分析河西走廊花海古湖泊沉积物中的盐类矿物组成,结合年代序列,重建了花海晚冰期以来湖泊演化过程及其对气候变化的响应。结果表明：晚冰期及新仙女木时期,花海湖泊以芒硝沉积为主,属硫酸盐型湖泊,湖水的盐度较高且周期性波动频繁;全新世早期（10.47 cal ka BP以前）,湖泊以洪泛堆积和风成沉积为主,揭示了湖泊萎缩、甚至干涸;全新世早期至全新世中期（10.47～8.87 cal ka BP）盐类矿物以碳酸盐沉积为主,为碳酸盐型湖泊,湖水淡化,湖泊水位开始逐渐回升;全新世中期（8.87～5.50 cal ka BP）盐类矿物呈现一定的波动变化,其中,8.8 cal ka BP 时期盐类矿物以硫酸盐沉积为主,湖泊由碳酸盐型转化为硫酸盐型,湖水咸化,盐度升高;随后盐类矿物以碳酸盐沉积为主,湖泊由硫酸盐型转化为碳酸盐型,湖水盐度降低、湖泊扩张;全新世中晚期（5.50 cal ka BP以来）出现沉积间断,表明中晚全新世时期湖泊逐渐萎缩。在全新世期间,花海湖泊千年尺度演化过程揭示了该区域气候干湿状况受亚洲季风和西风共同控制的影响。     

柳夼剖面末次冰期层段Rb/Sr的不稳定变化及其揭示的气候特征

位于山东半岛北部成山头附近的末次冰期地层,被称为“柳夼红层”。在野外调查的基础上,选择柳夼剖面进行工作,其末次冰期地层主要由沙丘砂与古土壤或湖积层叠覆堆积组成,地质时代为13.1―78.9 ka BP。根据铷、锶、Rb/Sr和矿物组成的分析结果,得出结论如下：1）不稳定矿物尤其是钾长石和斜长石等分解释放出铷、锶,释放量随着风化作用加强而增加。地球化学行为的差异使铷在风化过程中被吸附而锶淋失,导致铷的质量分数在沉积相中表现为沙丘砂＜砂质古土壤＜湖积层＜粉砂质古土壤,锶则表现为沙丘砂＞湖积层＞砂质古土壤＞粉砂质古土壤。2）铷、锶和Rb/Sr在层段上呈现出明显的峰谷变化,将末次冰期的气候波动特征呈现为LKS4、LKS2的寒冷期和LKS3的温暖期,LKS3又可划分为LKS3b的寒冷期和LKS3c、LKS3a的温暖期,体现了万年尺度的气候波动特征。这些暖阶段同步于中国季风区葫芦洞石笋记录的夏季风强盛期和65°N 7月份天文辐射总量的高峰,冷阶段对应于夏季风减弱期和天文辐射总量低谷,表明柳夼剖面末次冰期的气候变化是太阳辐射量和东亚夏季风格局共同影响下的结果。     

The Parallel Roads of Glen Roy,Scotland: geoconservation history and challenges

Glen Roy is a classic geosite for ice-dammed lake shorelines, the Parallel Roads, and associated features formed during the Loch Lomond (Younger Dryas) Stade (12.9–11.7 ka). The area played a key part in the development of the glacial theory in the early 19th century and continues today to have outstanding scientific value for understanding the processes and timing of events at the end of the last glaciation. Glen Roy has also been long-appreciated as an awe-inspiring visitor attraction, and is now a flagship site for geotourism within Lochaber Geopark. Statutory geoconservation in Glen Roy, beginning in the second half of the 20th century, was founded on the exceptional scientific value of the area. The history and practice of geoconservation in Glen Roy illustrate the contested values of geoheritage and the evolving approaches adopted. Important lessons include the need for open dialogue and partnership working among the local community, land owners and managers, the statutory conservation agency (Scottish Natural Heritage), Lochaber Geopark and the scientific community.     

Tidal observations on the West Coast,South Island,New Zealand

Harmonic tidal constants, calculated from sea surface elevation observations at Jackson Bay on the West Coast of the South Island, are consistent with available semi‐diurnal and diurnal tidal phase distributions. Current observations taken over a 111 day period at mid‐depth in 1505 m of water on the southern flank of the Challenger Plateau and over a 240 day period in 1430 m of water on the South Island western coast continental slope, are subject to tidal analysis. At both sites there is a component of energy flux directed across the isobaths and only at the northern site for the M2 tide is the phase consistent with a dominant progressive barotropic tide. The successive 30 day harmonic constants at the southern continental slope site exhibit a trend in the M2 tidal ellipse speed and ellipticity suggesting the presence of a regular internal tide. Superposition of ‘internal tidal’ and barotropic tidal flows, as prescribed from progressive‐ and standing‐wave elevations, to fit the observations indicates that the ‘internal tide’ is probably associated with the first baroclinic mode. At the current‐meter depths the speeds of the ‘internal tide’ for the M2 tide are about the same as the barotropic speeds, whereas, the S2 ‘internal tide’ speeds are larger than those of the barotropic tide. The consistency of the trend in ellipse parameters lends support to the theoretical progressive trapped barotropic tidal flows being a good approximation to the actual barotropic tide. Some support for the hypothesis that the S2 tide on the West Coast of New Zealand has a substantial standing wave contribution is given by the northern observations, where the ratio of the S2: M2 internal tidal ellipse current amplitudes are substantially larger than the ratio of the elevations, the internal tide being generated by across‐isobath flows.     

Spatial and temporal variations in the thermodynamics since the Last Glacial Maximum at Jutulstraumen drainage basin,East Antarctica

A flow-line model is coupled to a 2D temperature model to simulate the thermodynamic changes of Jutulstraumen drainage basin due to grounding line retreat and increased surface temperature since the Last Glacial Maximum (LGM). The basin consists of a plateau drained by an outlet glacier, and the simulated ice volume reductions are 1% and 2% respectively of the current grounded volume. The mountain ranges H.U. Sverdrupfjella and Neumayerskarvet fringing the plateau were not overridden by ice at the LGM, while the Nashornet nunataks closer to the grounding line were. Today the glacier is almost in balance with the current climate, with the highest thinning rate?<?5.0×10^?3 ma^?1 at the plateau. The simulated present-day thermal regime of the outlet glacier shows a basal layer at the pressure melting point and negative temperature gradients with depth due to horizontal advection of cold ice from the plateau. Sensitivity studies show that strain heating and horizontal advection are important for the basal temperatures in the fast flowing outlet glacier and for about half of the wide basin at the polar plateau. Increased strain heating and horizontal advection since the LGM control the response time required to readjust to the new conditions, and it controls the present-day volume.     

长江江苏段末次盛冰期古河槽特征

选择长江江苏段作为研究河段,根据南京长江三桥、长江大桥、长江四桥、润扬长江大桥、扬中长江大桥、江阴长江大桥、苏通长江大桥7个断面的285个地质勘探钻孔资料及参考文献中的8个钻孔资料,建立了7个长江古河谷地质剖面图。在拟建南京长江四桥附近、扬中长江大桥附近的7个钻孔进行了采样分析,获得了8个14C年代、1个ESR年代数据。通过分析发现,末次盛冰期长江古河槽镇江以上切割到基岩,镇江以下嵌在老河床相沉积层上,河槽在南京下关-栖霞山段形成局部深切;南京段约-63 m以下的河槽为末次盛冰期的古河槽,相对狭窄陡峭,宽深比较小,向下游宽深比逐渐变大,扬中以下形成分叉河道体系;古河槽中自下而上充填了从粗到细的沉积旋回,河床相沉积物向下游逐渐变细。     

LGM时期气候背景下中国区域植被变化对东亚夏季降水影响的模拟

利用CCM3/NCAR全球气候模式在21kaB.P.(2.1万年前)的末次盛冰期(LGM)气候背景下,对中国区域植被变化对夏季(6～7月)东亚季风降水的影响进行了模拟,结果表明： 在LGM时期气候背景下,植被退化会使得中国东南部夏季降水减少,其中东南沿海减少超过20mm,而在 100°E 以东的中国北方大部分地区降水增加,其中心值大于50mm,从而导致降水南少北多的现象,植被的这种影响可以从物理上得到解释。在LGM气候背景下,植被退化在暖季起着增温的作用,即通过影响地表热状况使夏季大陆增温,增强了夏季东亚大陆与其周边海域的热力差异,从而使夏季东亚地区的西南风增强,35°～45°N的北方地区对流层低层的空气辐合和对流层上升运动加强,伴随着在 30°N 以南的中国南方地区出现异常下沉运动; 同时,西南季风的加强也导致夏季在 30°～40°N 之间的华北地区低层水汽输送加大。在这些因子的共同作用下,中国北方夏季降水增多,而东南部降水减少。这些结果说明使用LGM时期中国区域不同的重建植被资料可以对东亚季风气候模拟产生一定的不确定性。因此,重建可信度高的东亚植被对于降低对气候模拟的不确定性是十分重要的。     

中国东部末次冰期雪线高程重建与成冰气候分析

在蒙山第四纪冰川遗迹与光释光测年研究的基础上,结合以往我国东部猛犸象化石出土位置、孢粉数据库、以及雪线高程的研究成果,首次对我国东部末次冰期时的雪线高程进行了恢复重建,并绘制了我国东部及东亚地区雪线高程图,在此基础上对我国东部蒙山冰期时的气候特征进行了探讨,认为我国东部冰期时的北路寒潮形成的"东亚冷槽",是我国东部第四纪山谷冰川的表现形式及形成原因。