Oceanographic variations over the last 150,000 yr in the Japan Sea and synchronous Holocene with the Northern Hemisphere     

Itaru Koizumi  Hirofumi Yamamoto 《Journal of Asian Earth Sciences》2011,40(6):32-1213

The paleo-hydrography in the Japan Sea called a “mini-Ocean” was reconstructed based on the high-resolution analysis of diatom assemblages over the period of 150,000 yr. The decrease of diatom fertilization in the Japan Sea, when it was isolated from surrounding seas due to the drop of sea-level during the glacial to stadial phase, resulted in dissolution and/or extremely low diatom production in the northern cores in the subarctic water-masses. The annual Td′-derived paleo-SSTs (°C) were controlled by the fluctuations of 2-kyr and 4-kyr periods at intervals of 20 kyr and 40 kyr over the last 160 kyr BP, respectively. A 23-kyr cycle is recognized during the periods from 140 ka to 100 ka, according to the Wavelet analysis. After temperature and sea-level increased both at 133–128 ka, 60–53 ka and 15–10 ka, oceanic warm-water diatom species predominated at 127–119 ka and after 9 cal ka in the interstadial phase. At 21.3–16.9 ka and 12.9–9.8 ka, sea-level and salinity increased as the transgression developed. At 10.0–7.0 ka, the oceanic association shifted from cold-water species in the stadial period to warm-water ones in the interstadial phase. The fluctuations of Td′ derived-SSTs (°C) on century to millennial time-scales during the Holocene are well correlated with abrupt climatic events that different paleoclimatic proxies record in many regions of the Northern Hemisphere.  相似文献   

Heinrich 3事件的实证:浙江舟山群岛泥裂          下载免费PDF全文

贾楠  孙立广  袁林喜  谢周清 《地学前缘》2009,16(6):146

在浙江舟山朱家尖岛观音湾海滩地区发现了大量发育良好,深达60cm的泥裂构造。年代学结果表明,该泥裂构造形成于31.2～30.4kaBP期间。孢粉学和粘土矿物学研究结果表明,该构造揭示了研究区域曾经发生的一次强烈的冷干事件,事件发生时植被衰落。这极可能是第四纪晚期全球范围内发生的气候快速变冷事件Heinrich3事件的一个直接的景观证据,为第四纪气候快速变化的研究提供了一种新的研究对象。  相似文献   

Scottish early Holocene vegetation dynamics based on pollen and tephra records from Inverlair and Loch Etteridge,Inverness-shire     

《Proceedings of the Geologists' Association. Geologists' Association》2017,128(1):125-135

This paper presents the results of an investigation of early Holocene cryptotephra layers recovered from sediments in two kettle-hole basins at Inverlair (Glen Spean) and Loch Etteridge (Glen Fernisdale). Electron probe micro-analysis (EPMA) of shards from two cryptotephra layers revealed that the uppermost layer in both sequences has a composition similar to the An Druim tephra, first reported from a site in Northern Scotland. We present evidence that distinguishes the An Druim from the chemically very similar early Holocene Ashik tephra. The lowermost layer at Inverlair matches the composition of the Askja-S tephra found in the Faroe Islands, Ireland, Sweden, Germany and Switzerland. This is the first published record of the Askja-S tephra from mainland Scotland. As at other sites, the Askja-S seems to mark a short-lived climatic deterioration, most likely the Pre-Boreal Oscillation: at Inverlair it occurs just above an oscillation represented by a reduction in LOI values and in the abundance of Betula pollen, and by a peak in Juniperus pollen. The lowermost layer at Loch Etteridge has a Katla-type chemistry and extends through the upper part of the Loch Lomond (Younger Dryas/GS-1) Stadial to the Stadial/Holocene transition; it may represent a composite layer which merges the Vedde and Abernethy tephras. One of the key conclusions is that the glacial-melt deposits in the vicinity of Inverlair (kames and kame terraces) were ice-free by c. 10.83 ka (the age of the Askja-S), providing a limiting age on the disappearance of LLR ice in Glen Spean.  相似文献   

Low-latitude “dusty events” vs. high-latitude “icy Heinrich events”     

Elsa Jullien  Francis Grousset  Bruno Malaiz  Josette Duprat  Maria Fernanda Sanchez-Goni  Frdrique Eynaud  Karine Charlier  Ralph Schneider  Aloys Bory  Viviane Bout  Jose Abel Flores 《Quaternary Research》2007,68(3):379-386

It has been proposed that tropical events could have participated in the triggering of the classic, high-latitude, iceberg-discharge Heinrich events (HE). We explore low-latitude Heinrich events equivalents at high resolution, in a piston core recovered from the tropical north-western African margin. They are characterized by an increase of total dust, lacustrine diatoms and fibrous lacustrine clay minerals. Thus, low-latitude events clearly reflect severe aridity events that occurred over Africa at the Saharan latitudes, probably induced by southward shifts of the Inter Tropical Convergence Zone. At a first approximation, it seems that there is more likely synchronicity between the high-latitude Heinrich Events (HEs) and low-latitude events (LLE), rather than asynchronous behaviours.  相似文献   

Reconstructing past glacier dynamics and erosion from glacial geomorphic evidence: Snowdon,North Wales     

Martin Sharp  Julian A. Dowdeswell  J. Campbell Gemmell 《第四纪科学杂志》1989,4(2):115-130

Bedrock surfaces exposed around Llyn Llydaw, North Wales demonstrate contrasting styles of erosion beneath a Late Devensian ice sheet and a Loch Lomond Stadial (LLS) valley glacier. Ice sheet erosion involved lee-side fracturing, surface fracture wear and abrasive wear, while LLS erosion was primarily by abrasive wear. Preservation of ice sheet erosional features indicates limited rates of erosion during the LLS. Analysis of the geometry and distribution of erosional markings suggests that the low erosional capacity of the LLS glacier was due to a low basal sliding velocity. This prevented the formation of lee-side cavities, reduced the debris flux over the bed and minimised particle-bed contact loads. Reconstructions of the mass balance and geometry of the LLS glacier indicate that most of its balance velocity could be achieved by internal deformation alone. A combination of low subglacial water pressures and an unusually rough substrate explain the low sliding velocities. High bed roughness is due to the absence of leeside cavities and a change in flow orientation between ice sheet and LLS times, which meant that the LLS glacier was in contact with roughness elements which were generated in cavities beneath the ice sheet.  相似文献   

Glacier response to climatic change during the Loch Lomond Stadial and early Flandrian: Geomorphological and palynological evidence from the Isle of Skye,Scotland     

Douglas I. Benn  J. John Lowe  Michael J. C. Walker 《第四纪科学杂志》1992,7(2):125-144

The deglaciation of Skye at the close of the Loch Lomond Stadial is assessed on the basis of detailed geomorphological mapping and pollen-stratigraphic correlations. It is concluded that deglaciation proceeded in two distinct stages. The first was marked by numerous glacier stillstands and readvances, while uninterrupted retreat and local glacier stagnation occurred during the second and final stage. The pollen evidence indicates that the first stage was well advanced before the marked thermal improvement at the start of the Flandrian, and it is inferred that initial glacier retreat occurred in response to a decline in precipitation in the later part of the Loch Lomond Stadial. The first stage of glacier retreat continued into the early Flandrian, during which climatic amelioration was interrupted briefly. Final deglaciation appears to have occurred rapidly in response to sustained temperature increases. The collective evidence also indicates spatial variations in the timing of deglaciation, which appear to reflect differences in glacier morphology.  相似文献   

The geomorphological impact of Loch Lomond (Younger Dryas) Stadial plateau icefields in the central Lake District,northwest England     

Derek A. McDougall 《第四纪科学杂志》2001,16(6):531-543

Detailed geomorphological mapping has revealed evidence for the development of plateau icefields in the central fells of the English Lake District during the Loch Lomond (Younger Dryas) Stadial (ca. 12.9–11.5 ka). The largest plateau icefield system, which covered an area of approximately 55 km² (including outlet glaciers), was centred on High Raise. To the west, smaller plateau icefields developed on Grey Knotts/Brandreth and Dale Head, covering areas of 7 km² and 3 km² respectively. The geomorphological impact of these plateau icefields appears to have been minimal on the summits, where the survival of blockfields and other frost‐weathered debris (mostly peat‐covered) implies the existence of at least patches of protective, cold‐based ice. Ice‐moulded bedrock at some plateau edges, however, documents a transition to wet‐based, erosive conditions. Prominent moraine systems were produced by outlet glaciers, which descended into the surrounding valleys where their margins became sediment traps for supraglacial debris and inwash. In some valleys, ice‐marginal moraines record successive positions of outlet glaciers, which actively backwasted towards their plateau source. This interpretation differs from that of previous workers, who assumed an alpine style of glaciation, with reconstructed glaciers emanating from corries and valley heads. It is likely that plateau icefields were more common at this time in upland Britain than hitherto has been appreciated. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

贵州黔西县水西洞石笋记录的末次冰期Heinrich Stadial 4气候突变事件          下载免费PDF全文

冯唐慧  张鑫  何尧启  杨云月  邱万银  姜修洋 《古地理学报》2023,25(1):245-254

末次冰期Heinrich Stadial 4气候突变事件(HS4事件)是发生于约40 ka B.P.(B.P.表示Before Present, Present为公元1950年)最为显著的一次海因里希冰阶事件,对其转型特征和精细结构的刻画有助于深入理解千年尺度气候突变事件的机制。本研究基于贵州黔西县水西洞SXG-3石笋的11个高精度²³⁰Th年龄和277个δ¹⁸O数据,重建了40.77～37.17 ka B.P.时段平均分辨率为13 a的亚洲夏季风强度演变序列。该石笋氧同位素记录清晰地捕捉到了HS4弱季风事件,呈现出三阶段变化的特征,即：第1阶段(39.97～39.13 ka B.P.),石笋δ¹⁸O在840±90 a内偏正1.32‰,夏季风缓慢减弱,对应于热带辐合带(Intertropical Convergence Zone,简称ITCZ)的南移和格陵兰气候快速变冷;第2阶段(39.13～38.35 ka B.P.),石笋δ¹⁸O整体偏正,平均为-8.34‰,夏季风强度达到最弱,而南美季风达到最...  相似文献   

Heinrich Events and Heinrich(-like) Events     

Jingyu Liu  Nianqiao Fang 《地球科学进展》2019,34(6):618-628

Ice-raft debris layers in the North Atlantic sediments of IRD belt characterize abrupt climate variability, corresponding to Heinrich events during the Last Glacial and Heinrich(-like) events beyond the Last Glacial. During Heinrich/(-like) events, the Earth's atmosphere, hydrosphere and cryosphere interacted strongly on the millennial-scale and had a profound impact on the global climate. In more than 30 years of continuous research on Heinrich/(-like) events and their remote response, the results have been more focused on the trigger mechanism and the new distinguished proxies of Heinrich/(-like) events. The first occurrence of Heinrich/(-like) events in IRD belt during MIS 16 was the initiation of a major landmark climate mechanism after MPT. The research on Heinrich/(-like) events may require a new ice sheet dynamics model related to the large ice sheet and the long-term ice age, which is forming a new hot topic.  相似文献   

Nannoplankton successions in the northern Red Sea during the last glaciation (60 to 14.5 ka BP): Reactions to climate change   总被引：1，自引：0，他引：1  

Heiko-Lars Legge  Jrg Mutterlose  Helge W. Arz  Jürgen Ptzold 《Earth and Planetary Science Letters》2008,270(3-4):271-279

Due to its restricted connection with the Indian Ocean, the desert-enclosed Red Sea is extremely sensitive to global sea level changes and thus ideally suited for paleoceanographic studies of what occurred during the last glaciation. The understanding of its glacial history is, however, still limited. A serious obstacle to obtain satisfactory paleoecological information has been the rarity of microfossil proxy species caused by high salinities. Here, we present a continuous and well-dated calcareous nannoplankton record from the northern Red Sea, covering the interval from 60–14.5 ka BP. Our investigation shows that the composition of the calcareous nannoplankton community varied between  32 ka BP and 14.5 ka BP in response to rapid environmental changes which are closely correlated to climatic fluctuations described from the North Atlantic region. Heinrich events H3, H2 and H1 are dominated by Emiliania huxleyi. Gephyrocapsa oceanica and especially Gephyrocapsa ericsonii are abundant between H3–H2 and H2–H1. A less pronounced response of the calcareous nannoplankton to the high latitudinal climatic oscillations is documented prior to  32 ka BP, suggesting that a strong atmospheric coupling between the northern Red Sea and the North Atlantic realm was established in the late Marine Isotope Stage 3. In contrast to the previously held view of a sea level related salinity increase as the major cause for changes of the plankton communities within the glacial Red Sea, we interpret the documented variations as being caused by local hydrographic changes under the atmospheric control from the extratropics. Temperature changes and especially variations of the water stratification appear to be critical selective factors for the calcareous nannoplankton composition.  相似文献