Evidence of the final drainage of the Baltic Ice Lake and the brackish phase of the Yoldia Sea in glacial varves from the Baltic Sea

A clay-varve chronology based on 14 cross-correlated varve graphs from the Baltic Sea and a mean varve thickness curve has been constructed. This chronology is correlated with the Swedish Time Scale and covers the time span 11530 to 10250 varve years BP. Two cores have been analysed for grain size, chemistry, content of diatoms and changes in colour by digital colour analysis. The final drainage of the Baltic Ice Lake is dated to c . 10800 varve years BP and registered in the cores analysed as a decrease in the content of clay. This event can be correlated with atmospheric Δ14 C content and might have resulted in an increase in these values recorded between 11565 and 11545 years BP. The results of the correlation between the varve chronology from the Baltic Sea, the Greenland GRIP ice core and the atmospheric Δ14 C record indicate that c . 760 years are missing in the Swedish Time Scale in the part younger than c. 10250 varve years BP. A change in colour from a brownish to grey varved glacial clay recorded c . 10770 varve years BP is found to be the result of oxygen deficiency due to an increase in the rate of sedimentation in the early Preboreal. The first brackish influence is recorded c . 10540 varve years BP in the northwestern Baltic Sea and some 90 years later in the eastern Gotland Basin.     

Lake Mullsjön - a key site for understanding the final stage of the Baltic Ice Lake east of Mt. Billingen

The deglaciation pattern at Mt. Billingen, within the Middle Swedish end moraine zone, and its relationship with dramatic water level changes in the Baltic Ice Lake is a classic topic of Swedish Quaternary Geology. Based on data west of Mt. Billingen, the authors (in two earlier papers) presented a stratigraphic model associated with this subject. This study is an attempt to test the model east of Mt. Billingen, i.e. inside the Baltic Ice Lake itself. Lake Mullsjon is situated 30 km southeast of the drainage area of the Baltic Ice Lake and within the final drainage zone. About 8 m of Late Weichselian sediments (mostly varved clay) were recovered from the lake and analysed from different stratigraphic viewpoints, including lithology, grainsize, varve chronology, and pollen. These analyses show that the site was deglaciated in the later part of the Allerød Chronozone. Shortly thereafter the first drainage of the Baltice Ice Lake took place but without isolating Lake Mullsjon. After a short period of disturbed sedimentation varved clay continued to form as the glacier receded for another 120 varve years until the onset of the Younger Dryas cooling, as registered both in the pollen and in the varve stratigraphies. After c. another 120 varve years our analyses suggest that the Baltic Ice Lake was dammed once again. About 230 varve years of further ice readvance followed west of Mt. Billingen, while the ice margin in the east was more or less stationary. Rapid melting set in, at first producing coarse varves, but soon the clay was thin-varved and fine. This continued for 140 varve years until suddenly the lake became isolated. At this isolation thick beds of silty-sandy deposits were deposited on the lake floor. The isolation is dated to 10,400–10,500 ¹⁴C years B.P., which corresponds to the assumed age of the final drainage of the Baltic Ice Lake. It was also isolated at the same time as lakes (on the same isobase) situated 20 m lower, but west of Mt. Billingen, were raised above sea level. This strongly suggests that Lake Mullsjön was isolated as an effect of the drainage of the Baltic Ice Lake. Significant differences between the clay-varve and the ¹⁴C chronologies are also presented.     

Mechanism of Varve Formation and Paleoenvironmental Research at Lake Bolterskardet, Svalbard, the Arctic

On the basis of observation of thin sections and 137Cs data, laminations in sediment are interpreted to be varves in Bolterskardet Lake (78°06' N, 16°01' E), Svalbard, the Arctic. Varves appear under a petrologic microscope as couplets of dark-silt and light-clay layers. The mechanism of varve formation is surmized as follows: each silt layer is the production of sediment inflow interpreted as mainly derived from snowmelt during summer; each clay layer was deposited in a stillwater environment during an ice-cover period. A light -clay layer provides an important index bed to identify the annual interface. The high accumulation rates, long period of ice cover, and topographically closed basin are probably all critical factors in forming and preserving varves. Varve thickness is known to be controlled mainly by summer temperature. The variation of varve thickness in Lake Bolterskardet can then be used to reconstruct summer temperature. The varve series show that there has been distinct decade-scale variability of summer temperature over the past 150 years. Warm periods occurred in the 1860s, around 1900, the 1930s, 1950s, and 1970s, and in the last 20 years. The varved sediments of Lake Bolterskarde preserve an ideal record for high-resolution paleoclimatic and paleoenvironmental research in this data-sparse area.     

Timing of the first drainage of the Baltic Ice Lake synchronous with the onset of Greenland Stadial 1

Glacial varves can give significant insights into recession and melting rates of decaying ice sheets. Moreover, varve chronologies can provide an independent means of comparison to other annually resolved climatic archives, which ultimately help to assess the timing and response of an ice sheet to changes across rapid climate transitions. Here we report a composite 1257‐year‐long varve chronology from southeastern Sweden spanning the regional late Allerød–late Younger Dryas pollen zone. The chronology was correlated to the Greenland Ice‐Core Chronology 2005 using the time‐synchronous Vedde Ash volcanic marker, which can be found in both successions. For the first time, this enables secure placement of the Lateglacial Swedish varve chronology in absolute time. Geochemical analysis from new varve successions indicate a marked change in sedimentation regime accompanied by an interruption of ice‐rafted debris deposition synchronous with the onset of Greenland Stadial 1 (GS‐1; 12 846 years before AD 1950). With the support of a simple ice‐flow/calving model, we suggest that slowdown of sediment transfer can be explained by ice‐sheet margin stabilization/advance in response to a significant drop of the Baltic Ice Lake level. A reassessment of chronological evidence from central‐western and southern Sweden further supports the hypothesis of synchronicity between the first (penultimate) catastrophic drainage of the Baltic Ice Lake and the start of GS‐1 in Greenland ice‐cores. Our results may therefore provide the first chronologically robust evidence linking continental meltwater forcing to rapid atmosphere–ocean circulation changes in the North Atlantic.     

Varve chronology of the glacial sediments in Blekinge and northeastern Skåne, southeastern Sweden

In sections and cores from an area of the Baltic Ice Lake in Blekinge complete varve series of fine-grained glacial sediments have been found. It is possible to divide the series, from bottom to top, into four varve types. A core from Karlshamn in Blekinge shows most varves of the investigated localities, in all 355 varves. Antevs' (1915) local chronology has been used, as the most recent revision of the Swedish time scale has not yet been completed. The chronology in this investigation ranges from - 325 to + 315, or 640 years. The varve chronology and the velocity of the ice recession, c. 90 m/year in northeastern Skåne, shows good agreement with the work of Antevs, whose unpublished diagrams have been re-worked and used in this investigation.     

An 800-year long, radiocarbon-dated varve chronology from south-eastern Sweden

More than 50 varve-thickness diagrams, which were established from glacial varved clays in south-eastern Sweden were correlated with each other to form an 800-year long floating varve chronology. AMS |214|0C measurements on terrestrial macrofossils from the varved clays enabled synchronization of the record with other high-resolution archives. The synchronization indicates that the chronology spans between c. 13 150 and c. 12 350 calendar years BP and covers the later part of the Allerørd and the early part of the Younger Dryas. Calibrated radiocarbon dates, which were obtained on varved clays south of the floating chronology, indicate that the ice recession in south-eastern Sweden may have started during late Bølling. Our results indicate a longer time-span in varve years for the deglaciation than has been previously estimated     

Palaeomagnetic records from two varved clay sequences in the Middle Swedish ice marginal zone

Two varved clay sequences, at Rystad and Tottnäs, situated in the Middle Swedish ice marginal zone were analysed palaeomagnetically. Two parallel profiles were sampled and analysed at each site. The varved clay at Rystad was dated by floating varve chronology. The varves at Tottnäs can be linked to Swedish time scale, expressed in calendar years B.P. Due to the distance between the sites they cannot be correlated by means of varve diagrams. Palaemagnetic methods were used as an alternative. Based an AF demanetization of pilot samples, the palaeomanetic to be too low, in the order of15, compared to the site latitude. At Tottnäs the inclination records are very close to the expected inclination with respect to the site latitude. Because of a systematic inclination error in the Rystad profiles the correlation was based on the declination records. Statistical comparisons of these records between the two sites indicate that the sediment successions are partly synchronous. It is concluded that the deglaciation at Tottnäs started c. 130 years earlier than at Rystad. This mean that the Swedish ice marginal zone east of Rystad will have a more northeasterly extension than previously thought.     

The use of varved clay chronology for dating paleoseismic events: the Erstavik record in the Stockholm area, south Sweden

Geological structures suggest that the Fennoscandian Shield was subjected to a higher seismicity at the end of the last glaciation than today. This article demonstrates the use of varved clay chronology for dating paleoseismic events. It is argued that the deposited annually layered glacial varves were sensitive to past ground movements. In the Stockholm area, the Erstavik varved clay chronology suggests four paleoseismic events: a first (I) dating from varve year 10,473 to 10,468 BP; a second (II) 10,451 to 10,445 BP; a third (III) 10,429 to 10,425 BP; and a fourth (IV) 10,409 to 10,404 BP. In De Geer's ‘old' (1940) chronology the first (I) dating corresponds with −1117 to −1112, the second (II) with −1095 to −1089, the third (III) with −1073 to −1069, and the fourth (IV) with −1053 to −1048. The most pronounced event was the one at around varve year 10,429 BP (varve −1073 in De Geer's ‘old' chronology). The recurrence time of about 20 years suggests a totally different seismic regime at the time of deglaciation than what exists today. It coincided with the period of maximum isostatic uplift. The complexity of the varved clay response to seismic events is also discussed.     

Climate variability and glacial processes in eastern Iceland during the past 700 years based on varved lake sediments

Striberger, J., Björck, S., Ingólfsson, Ó., Kjær, K. H., Snowball, I. & Uvo, C. B. 2010: Climate variability and glacial processes in eastern Iceland during the past 700 years based on varved lake sediments. Boreas, 10.1111/j.1502‐3885.2010.00153.x. ISSN 0300‐9483. Properties of varved sediments from Lake Lögurinn in eastern Iceland and their link to climate and glacial processes of Eyjabakkajökull, an outlet glacier of the Vatnajökull icecap, were examined. A varve chronology, which covers the period AD 1262–2005, was constructed from visual observations, high‐resolution images, X‐ray density and geochemical properties determined from X‐radiography and X‐ray fluorescence scanning. Independent dating provided by ¹³⁷Cs analysis and eight historical tephras verify the varve chronology. The thickness of dark‐coloured seasonal laminae, formed mainly of coarser suspended matter from the non‐glacial river Grímsá, is positively correlated (r=0.70) with winter precipitation, and our 743‐year‐long varve series indicates that precipitation was higher and more varied during the later part of the Little Ice Age. Light‐coloured laminae thickness, controlled mainly by the amount of finer suspended matter from the glacial river Jökulsáí Fljótsdal, increased significantly during the AD 1972 surge of Eyjabakkajökull. As a consequence of the surge, the ice‐dammed Lake Háöldulón formed and recurrently drained and delivered significant amounts of rock flour to Lake Lögurinn. Based on these observations, and the recurring cyclic pattern of periods of thicker light‐coloured laminae in the sediment record, we suggest that Eyjabakkajökull has surged repeatedly during the past 743 years, but with an increased frequency during the later part of the Little Ice Age.     

Late Weichselian pollen stratigraphy, clay varve chronology and palaeomagnetic secular variations in Lake Bolmen, Småland, south Sweden

Pollen analysis, glacial varve chronology and palaeomagnetic measurements were carried out on Late Weichselian lake sediments from southwestern Smaland, south Sweden. The sequence is correlated to the GRIP event stratigraphy, expressed in calendar years BP, and covers the period from the deglaciation at c. 14 400 to 11 300 calendar years BP. The series encompasses c. 930 varves and has been connected to the local varve chronology. Varve thickness increases markedly after the Older Dryas stadial, which indicates an accelerated deglaciation and melting of dead ice. The pollen diagram displays the vegetation development from the deglaciation at c. 14 400 calendar years BP to the transition to the Holocene. The vegetation succession starts with an arctic pioneer vegetation at the deglaciation, changes to a more stable tundra environment and displays a development which concurs with the traditional lateglacial pollen stratigraphy for southern Sweden. A palaeo-magnetic secular variation curve is presented displaying two westerly declination swings at 14200-13800 and 12 800-11 600 calendar years BP, respectively. The upper one can be recognized from other palaeomagnetic stratigraphies from southern Sweden and Estonia.     

Correlation of stadial and interstadial events in the south Swedish glacial varves with the GRIP oxygen isotope record

A number of correlated varve sequences from the local varve chronology in southeastern Sweden have been selected to make a 1040 varve years long mean varve thickness curve. Pollen analyses were carried out over an interval of 373 varve years in the northern part of the study area. The pollen stratigraphical data have been divided into local pollen assemblage zones which have been correlated with the radiocarbon-dated regional pollen assemblage zones. Based on variations in herb and tree pollen content of the analysed varve sequences, it has been possible to identify well-documented lateglacial pollen zones for southern Sweden, i.e. the Bölling interstadial (GI-1e), the Older Dryas cold event (GI-1d) and the early part of the Alleröd interstadial (GI-1c). The event stratigraphy in this study, based on varying varve thicknesses and the composition of the pollen flora in the varves, has been correlated with the oxygen isotope stratigraphy of the GRIP ice-core on Greenland between 13600 and 14400 GRIP ice-core years BP. It is concluded that five decadal warm events and one centennial warm event (15–60 and 100 varve years long, respectively) occur in the clay varve record along with one centennial cold event (150 varve years long), the Older Dryas (GI-1d).     

The deglaciation of southern Sweden 13,500-10,000 B.P.

Because of its well-developed ice-marginal zones, SW Sweden is an important reference area for the study of deglaciation, chronology and palaeoclimate 13,500-10,000 B.P. The ice-marginal zones are described and defined. Earlier research and opinions concerning the deglaciation are summarized. Based on radiocarbon dates from shells, vertebrate bones and limnic sediments, a revised deglaciation chronology is presented. This chronology is supported by biostratigraphic transects of time-space diagrams. The radiocarbon and varve chronologies are compared. Some ice-marginal zones are supposed to be 400 to 900 years older than expected from the varve chronology. The deglaciation chronology is correlated within the southern margin of the Scandinavian inland ice. Various consequences for the interpretation of glacial dynamics, shoreline displacement, and the biological environment are mentioned.     

高分辨率古环境指示器--湖泊纹泥研究综述

作为高分辨率古环境指示器,湖泊纹泥在重建晚第四纪特别是近代全球环境变化中具有特殊的地位和意义。纹泥携带的各种季节信息反映了区域生物学、地球化学、沉积学对季节性驱动力的响应,而且纹泥本身可以提供反映沉积环境和气候变化的精确计年,近３０年来湖泊纹发展历史表明,纹泥的应用主要集中于以下三个方面：纹波计年、纹泥厚度变化和纹泥沉积物分析,其中纹 精确测年是一切应用的基础。可以看出,在古环境研究中,纹泥作为一     

湖泊沉积物年纹层的研究方法及其意义

文章总结了前人对湖泊沉积物年纹层类型的划分,并根据年纹层的形成过程和组分特征分为3个大类,即碎屑年纹层、生物成因年纹层(如硅藻年纹层等)和化学成因年纹层(如方解石年纹层、菱铁矿年纹层、黄铁矿年纹层、蒸发盐年纹层等)。介绍了目前应用于湖泊沉积物年纹层研究的主要方法和技术包括:1)新鲜沉积物表面照相、X射线照相技术;2)光学显微镜观察;3)数字化图像分析;4)扫描电子显微镜技术等。而岩相学大薄片是目前年纹层研究工作中应用非常广泛的材料,对目前制作大薄片比较普遍采用的快速冷冻-冷冻干燥和水-丙酮-环氧树脂交换这两种方法进行了介绍并比较了各自的优劣。湖泊沉积物年纹层研究的古环境意义主要体现在两个方面,一是提供了高精度的纹层年代学时间标尺,在诸如气候突变事件的时限、大气¹⁴C浓度变化、火山灰层定年、古地磁场长期变化主曲线重建等方面有重要意义;二是年纹层性质研究如年纹层厚度和年纹层微相变化本身所蕴藏的高分辨率古气候环境变化信息,在太阳活动周期、ENSO等气候事件的研究中也有重要意义。最后,文章简单介绍了我国东北龙岗火山区四海龙湾玛珥湖沉积物中年纹层的特征并展望了其研究潜力。     

衡阳盆地始新世含鱼地层的成因分析

衡阳市郊五马归槽始新世鱼化石保存在黑色湖相纹层中。根据纹层序列的对比,发现该地的鱼化石均为同一层位;根据鱼化石在纹层序列中的具体位置及鱼化石的保存状况,笔者推测鱼群的死亡并非由于季节更替,而是由气候干旱引起的湖水盐度升高所控制;黑白纹层的变化是由大气降雨所致。     

Long varve series in Finland

Thinly varved 'postglacial' organic sediments are quite common in Finnish lakes, and attempts have been made to locate a site where they could be connected with the varved 'lateglacial' clays in order to he able to count the entire time since the ice retreat within one varved sequence. One promising site is Lake Valkiajärvi near Ruovesi in the Lake Region. The known sedimentary record covers nearly 9,500 years, which means that it starts very close to the time of the deglaciation of the Valkiajärvi area, around 9,600 B.P., or + 600 according to the original Finnish varve chronology (of Sauramo).     

The multiple chronological techniques applied to the Lake Suigetsu SG06 sediment core,central Japan

The varved sediment of Lake Suigetsu (central Japan) provides a valuable opportunity to obtain high‐resolution, multi‐proxy palaeoenvironmental data across the last glacial/interglacial cycle. In order to maximize the potential of this archive, a well‐constrained chronology is required. This paper outlines the multiple geochronological techniques being applied – namely varve counting, radiocarbon dating, tephrochronology (including argon–argon dating) and optically stimulated luminescence (OSL) – and the approaches by which these techniques are being integrated to form a single, coherent, robust chronology. Importantly, we also describe here the linkage of the floating Lake Suigetsu (SG06) varve chronology and the absolute (IntCal09 tree‐ring) time scale, as derived using radiocarbon data from the uppermost (non‐varved) portion of the core. This tie‐point, defined as a distinct (flood) marker horizon in SG06 (event layer B‐07–08 at 1397.4 cm composite depth), is thus derived to be 11 255 to 11 222 IntCal09 cal. years BP (68.2% probability range).     

The timing of regional Lateglacial events and post-glacial sedimentation rates from Lake Superior

We analyze both new and previously published paleomagnetic records of secular variation (PSV) from Lake Superior sediment cores and compare these records to correlated rhythmite (varve) thickness records to determine post-glacial sedimentation rates and to reassess the termination of glaciolacustrine varves in the basin. The results suggest that offshore sedimentation rates have exhibited considerable spatial variation over the past 8000 years, particularly during the mid-Holocene. We attribute offshore, mid-Holocene sedimentation changes to alterations in whole basin circulation, perhaps precipitated by a greater dominance of the Gulf of Mexico air mass during the summer season. Nearshore bays are characterized by high sedimentation rates for at least 1000 years after varve cessation and during a period between around 4500 and 2000 cal. BP. After 2000 cal. BP, sedimentation rates subsided to earlier rates. The increases between 4500 and 2000 cal. BP are probably due to lake level fall after the Nipissing II highstand.The older glaciolacustrine varve thickness records suggest that the influx of glacially derived sediment ended abruptly everywhere in the lake, except near the Lake Nipigon inlets. Multiple sediment cores reveal 36 anomalously thick varves, previously ascribed to the formation of the Nakina moraine, which were deposited just prior to varve cessation in the open lake. The PSV records support the observation that the cessation of these thick varves is a temporally correlative event, occurring at 9035±170 cal. BP (calibrated years before 1950, ca 7950–8250 ¹⁴C BP). This date would correlate to the eastern diversion of Lake Agassiz and glacial meltwater into Lake Ojibway.     

湖泊沉积物年纹层研究的古地磁学意义综述

年纹层发育的湖泊沉积物可以提供独立的、绝对定年的时间标尺,为重建高分辨率的区域古地磁场长期变化主曲线提供了难得的条件;基于长而连续的湖泊沉积物年纹层时间标尺建立的区域磁偏角和磁倾角长期变化参考曲线大大增强了岩芯对比和古地磁定年结果的精确性。此外,满足特定条件的湖泊沉积物还可以提供古地磁场强度长期变化的记录并有助于反映宇宙成因核素(如^14C、^10Be等)产生速率的变化、太阳活动等信息;目前,湖泊沉积物纹层年代学时间标尺及古地磁研究程度较高的主要是瑞典、芬兰和北美一些地区,区域古地磁场长期变化主曲线的地理分布并不均匀,因此在全球范围内寻找长序列的、连续的年纹层发育的湖泊进行古地磁研究可以更好地理解仪器观测记录以前的地磁场行为。     

Periodic jökulhlaups from Pleistocene glacial Lake Missoula—New evidence from varved sediment in northern Idaho and Washington

Newly examined exposures in northern Idaho and Washington show that catastrophic floods from glacial Lake Missoula during late Wisconsin time were repeated, brief jökulhlaups separated by decades of quiet glaciolacustrine and subaerial conditions. Glacial Priest Lake, dammed in the Priest River valley by a tongue of the Purcell trench lobe of the Cordilleran ice sheet, generally accumulated varved mud; the varved mud is sharply interrupted by 14 sand beds deposited by upvalley-running currents. The sand beds are texturally and structurally similar to slackwater sediment in valleys in southern Washington that were backflooded by outbursts from glacial Lake Missoula. Beds of varved mud also accumulated in glacial Lake Spokane (or Columbia?) in Latah Creek valley and elsewhere in northeastern Washington; the mud beds were disrupted, in places violently, during emplacement of each of 16 or more thick flood-gravel beds. This history corroborates evidence from southern Washington that only one graded bed is deposited per flood, refuting a conventional idea that many beds accumulated per flood. The total number of such floodlaid beds in stratigraphic succession near Spokane is at least 28. The mud beds between most of the floodlaid beds in these valleys each consist of between 20 and 55 silt-to-clay varves. Lacustrine environments in northern Idaho and Washington therefore persisted for two to six decades between regularly recurring, colossal floods from glacial Lake Missoula.