Late Pleistocene and Holocene lake fluctuations in the Sevier Lake basin,Utah, USA

Sevier Lake is the modern lake in the topographically closed Sevier Lake basin, and is fed primarily by the Sevier River. During the last 12 000 years, the Beaver River also was a major tributary to the lake. Lake Bonneville occupied the Sevier Desert until late in its regressive phase when it dropped to the Old River Bed threshold, which is the low point on the drainage divide between the Sevier Lake basin and the Great Salt Lake basin. Lake Gunnison, a shallow freshwater lake at 1390 m in the Sevier Desert, overflowed continuously from about 12 000 to 10 000 yr B.P., into the saline lake in the Great Salt Lake basin, which continued to contract. This contrast in hydrologic histories between the two basins may have been caused by a northward shift of monsoon circulation into the Sevier Lake basin, but not as far north as the Great Salt Lake basin. Increased summer precipitation and cloudiness could have kept the Sevier Lake basin relatively wet.By shortly after 10 000 yr B.P. Lake Gunnison had stopped overflowing and the Sevier and Beaver Rivers had begun depositing fine-grained alluvium across the lake bed. Sevier Lake remained at an altitude below 1381 m during the early and middle Holocene. Between 3000 and 2000 yr B.P. the lake expanded slightly to an altitude of about 1382.3 m. A second expansion, probably in the last 500 years, culminated at about 1379.8 m. In the mid 1800s the lake had a surface altitude of 1379.5 m. Sevier Lake was essentially dry (1376 m) from 1880 until 1982. In 1984–1985 the lake expanded to a 20th-century high of 1378.9 m in response to abnormally high snow-melt runoff in the Sevier River. The late Holocene high stands of Sevier Lake were most likely related to increased precipitation derived from westerly air masses.This is the first of a series of papers to be published by this journal that was presented in the paleolimnology sessions organized by R. B. Davis and H. Löffler for the XIIth Congress of the International Union for Quaternary Research (INQUA), which took place in Ottawa, Canada in August 1987. Drs. Davis and Löffler are serving as guest editors of this series.     

A late Holocene palaeolimnological record from central Mexico, based on faunal and stable-isotope analysis of ostracod shells

A late Holocene palaeolimnological record for central Mexico has been obtained from Lake Pátzcuaro, using recent and fossil ostracods. Lake Pátzcuaro, Michoacán, is a closed-basin lake which responds rapidly to changes in the ratio of precipitation/evaporation in the region. The record from a single lake-sediment core, dated by AMS radiocarbon method, covers the last ~3,530 yrs, and is based on ostracod faunal palaeoecology coupled with analysis of the stable-isotope (¹⁸O/¹⁶O and ¹³C/¹²C) composition of ostracod valves. The faunal distribution is determined by the presence or absence of aquatic vegetation and, to a lesser extent, salinity. The ¹⁸O/¹⁶O and ¹³C/¹²C ratios in ostracod calcite show good agreement with palaeolimnological inferences from the faunal assemblages, principally recording changing precipitation/evaporation and primary-productivity levels, respectively. Wetter conditions existed in central Mexico between approximately ~3,600 and ~2,390 yr BP, between ~1,330 to ~1,120 yr BP, and from ~220 yr BP to present, characterised by fluctuating lake levels. A dilution of the sediment load in the lake reduced turbidity levels allowing for a marked increase in productivity. During these phases, the combination of a deeper lake and increased macrophyte cover reduced the degree of mixing of the waterbody. In the earliest of these phases there was sufficient stratification of the waterbody for methanogenesis to occur in the sediment interstices. The wet phases were separated by prolonged dry periods, during which time the climatic conditions were relatively stable. Good agreement was found between the findings of this study and others from the central Mexican/Caribbean region suggesting that abrupt climate changes occurred at least at a regional scale.     

Response of chironomids to late Pleistocene and Holocene environmental change in the eastern Bolivian Andes

We present the first palaeolimnological investigation of chironomid larval assemblages from the Bolivian Eastern Cordillera. Taxonomic diagnoses are provided for the 10 chironomid taxa (subfamilies: Chironominae, Orthocladiinae and Tanypodinae) identified in the lake sediments. We compared changes in the chironomid assemblage from two Andean sites with previously reported palynological, charcoal and geochemical data, and highlight the potential of chironomid analysis to provide additional insights into environmental change in this region of high biodiversity over the last 18,000?years. At Lake Challacaba (17°33.257??S, 65°34.024??W; 3,400?m asl), the chironomid and geochemical data indicate periodic desiccation and hypersalinty of the basin c. 4,000?C3,460?cal?year BP. Increased abundance of Chironomus sp. at c. 1,000?cal?year BP suggests a change in human activity, supporting inferences from the pollen and spore records, which indicate elevated pastoral agriculture at this time. The greatest assemblage change in the chironomid record from Laguna Khomer Kocha Upper (17°16.514??S, 65°43.945??W; 4,153?m asl) occurred at c. 6,380?cal?year BP, concomitant with an increase in marsh woodland taxa, wetter conditions and a rising lake level at the end of a Holocene dry event. There is no apparent response in the chironomid assemblage to burning, however, at the onset of this dry event (c. 10,000?cal?year BP), which is the major transformative agent of the terrestrial vegetation. This study shows that chironomid assemblages in the tropical Andes responded to regional and local environmental changes, and in particular, that they were sensitive to adjustments in net moisture balance (water level fluctuations and salinity) and anthropogenic impacts (nutrient input). This suggests that within-lake processes are more important as drivers of chironomid assemblage composition than terrestrial vegetation or fire regime. Nevertheless, the full potential of subfossil chironomid analysis will only be realised once more modern autecological data are available.     

Late Pleistocene: Holocene record of environmental changes in Lake Zirahuen,Central Mexico

Geochemical data obtained from X-ray fluorescence, physical properties, total organic and inorganic carbon content (TOC/TIC), and diatom analysis from a 6.61-m-long sedimentary sequence near the modern northern shore of Lake Zirahuen (101° 44′ W, 19° 26′ N, 2000 m asl) provide a reconstruction of lacustrine sedimentation during the last approximately 17 cal kyr BP. A time scale is based on ten AMS ¹⁴C dates and by tephra layers from Jorullo (AD 1759-1764) and Paricutin (AD 1943-1952) volcanoes. The multiproxy analyses presented in this study reveal abrupt changes in environmental and climatic conditions. The results are compared to the paleo-record from nearby Lake Patzcuaro. Dry conditions and low lake level are inferred in the late Pleistocene until ca. 15 cal kyr BP, followed by a slight but sustained increase in lake level, as well as a higher productivity, peaking at ca. 12.1 cal kyr BP. This interpretation is consistent with several regional climatic reconstructions in central Mexico, but it is in opposition to record from Lake Patzcuaro. A sediment hiatus bracketed between 12.1 and 7.2 cal kyr BP suggests a drop in lake level in response to a dry early Holocene. A deeper, more eutrophic and turbid lake is recorded after 7.2 cal kyr BP. Lake level at the coring site during the mid Holocene is considered the highest for the past 17 cal kyr BP. The emplacement of the La Magueyera lava flows (LMLF), dated by thermoluminiscence at 6560 ± 950 year, may have reduced basin volume and contributed to the relative deepening of the lake after 7.2 cal kyr BP. The late Holocene (after 3.9 cal kyr BP) climate is characterized by high instability. Extensive erosion, lower lake levels, dry conditions and pulses of high sediment influx due to high rainfall are inferred for this time. Further decrease in lake level and increased erosion are recorded after ca. AD 1050, at the peak of Purepechas occupation (AD 1300–1521), and until the eighteenth century. Few lacustrine records extend back to the late Pleistocene—early Holocene in central Mexico; this paper contributes to the understanding of late Pleistocene-Holocene paleoclimates in this region.     

A late Pleistocene and Holocene mineral magnetic record from sediments of Lake Aibi,Dzungarian Basin,NW China

We studied mineral magnetic properties of a 6-m-long, late Pleistocene through Holocene sediment sequence from Lake Aibi in Dzungaria (Zunggary, Junggar), northern Xinjiang, China. Results were used to infer environmental changes and are compared with previously studied cores from Lake Manas. Both water bodies occupy the deepest parts of the Dzungarian Basin and are remnants of large Holocene lakes. During the Late Pleistocene, the magnetic mineralogy in both lakes was dominated by detrital, iron oxide minerals. Oxic conditions, which dominated during sedimentation and early diagenesis, persisted over the Pleistocene–Holocene transition. Later, during the middle Holocene, lake bottom conditions enabled authigenic formation of iron sulphide minerals such as pyrite (FeS₂) in Lake Aibi, and pyrite and greigite (Fe₃S₄) in Lake Manas. This iron sulphide mineralogy suggests increased biological activity in stagnant, anoxic bottom waters. Anoxic bottom conditions started about 9.8 cal kyr BP in Lake Manas and at about 7.2 cal kyr BP in Lake Aibi. A short dry event recorded in Lake Manas between 6.8 and 5.2 cal kyr BP is not clearly observed in Lake Aibi. In the late Holocene, i.e. the last 2.8 cal kyr, sediments of both lakes are again characterised by iron oxides, suggesting well-mixed, shallow water bodies. For this recent period, it seems that the detrital material in the two lakes had a common origin. Magnetic properties of sediments in Lakes Aibi and Manas show broadly similar environmental evolution during the late Pleistocene and Holocene. Nevertheless, despite the close proximity of the two lakes (~200 km) in the same basin, they display some different magnetic properties and record environmental changes at different times.     

Mid–late Holocene hydrological changes in the Mahi River, arid western India

This paper attempts to quantify contemporary and palaeo-discharges and changes in the hydrologic regime through the mid–late Holocene in the alluvial reach of the arid Mahi River basin in western India. The occurrence of terraces and pointbars high above active river levels and change in the width/depth ratio can be regarded as geomorphic responses to changes in discharge. Discharge estimates are made based on the channel dimensions and established empirical relations for the three types of channels: mid–late Holocene, historic (the channel that deposited extensive pointbars above the present-day average flow level) and the present ones. The bankfull discharge of the mid–late Holocene channel was  55 000 m³ s^− 1 and that of the historic channel was  9500 m³ s^− 1, some  25 times and  5 times greater than that of the present river (2000 m³ s^− 1), respectively. Since the mid–late Holocene, the channel form has changed from wide, large-amplitude meanders to smaller meanders, and decreases in the width/depth ratio, unit stream power and the bed shear stresses have occurred. It can be inferred that there has been a trend of decreasing precipitation since the mid–late Holocene.     

Diatom-inferred limnological changes in Lake Inawashiro-ko,Japan, over the past 1700 years

Journal of Paleolimnology - We inferred paleoenvironmental conditions in Lake Inawashiro-ko, Japan, over the past 1700 years, using diatom assemblages in the uppermost 2 m of...     

Mud and magnetism: records of late Pleistocene and Holocene environmental change recorded by magnetic measurements

The paper presents a personal summary of the role of magnetic measurements in lake sediment studies. Examples are used to illustrate the main variations in lake sediment magnetic properties and the processes controlling their variations. These are considered in terms of sediment sequences: (1) that are virtually devoid of magnetic minerals; (2) the magnetic properties of which are dominated by input of magnetic minerals from ‘primary’, unweathered catchment sources (3) with magnetic properties indicative of erosion of weathered material, mainly magnetically enhanced topsoil; (4) that have received minimal input of terrigenous ferrimagnetic minerals but are rich in biogenic magnetite (5) parts of which have experienced dissolution diagenesis (6) in which signals from erosion, biogenic magnetite and dissolution can all be detected and (7) that are dominated by the presence of authigenic greigite. Additional issues, including the importance of particle size variations as a control of magnetic properties, the under-representation of haematite and goethite in the magnetic record and the significance of atmospheric deposition are also considered. A concluding section briefly outlines the present status of environmental magnetism and its role in palaeoenvironmental research based on lake sediment studies.     

Bathymetry of Lake Lisan controls late Pleistocene and Holocene stream incision in response to base level fall

This paper examines the millennial-scale evolution of the longitude profile of Nahal (Wadi) Zin in the Dead Sea basin in the northern Arava valley, Israel. Nahal Zin has incised ~ 50 m into relatively soft late Pleistocene Lake Lisan sediments. Incision was forced by the regressive (> 10 km) lake level fall of a total of > 200 m of Lake Lisan from its highest stand at ~ 25 ka and exposure of the lake-floor sediments to fluvial and coastal processes. Alluvial cut terraces of the incising channel are well preserved along the 17.5 km of the lowermost reach of Nahal Zin. At its outlet into the Dead Sea basin, Nahal Zin deposited a Holocene alluvial fan at the base of a 10–80 m high escarpment in unconsolidated sediments. The escarpment is associated with the Amazyahu fault, which forms the southern structural boundary of the present Dead Sea basin. Geomorphic mapping, optically stimulated luminescence (OSL) ages, and soil stratigraphy allowed correlation of terrace remnants and reconstruction of several past longitudinal profiles of Nahal Zin and its incision history. Together with the published lake level chronology, these data provide an opportunity to examine stream incision related to base level lowering at a millennial scale. OSL ages of the terraces fit relatively well with the established lake level chronology and follow its regression and fall. For a few thousands of years the longitudinal profile response to the lake level fall was downstream lengthening onto the exposed former lake bed. Most of the incision (~ 40 m) occurred later, when the lake level reached the top of the Amazyahu fault escarpment and continued to drop. The incision was a relatively short episode at about 17 ka and cut through this escarpment almost to its base. The fast incision, its timing, and the profiles of the incising channels indicate that the escarpment was an underwater feature and was not formed after the lake retreated.This fairly simple scenario of regressive lake level fall and knickpoint exposure and incision is modeled here using a one-dimensional numerical incision model based on a linear diffusion equation. The calculated diffusion coefficient fits earlier results and data obtained from other streams in the area and confirms the upscaling of this simple model to the millennial scale.     

Upper Pleistocene and Holocene paleosalinity and trophic state changes in relation to sea level variation in Rocha Lagoon, southern Uruguay

Paleolimnological data are presented on trophic development in relation to sea level variation in Rocha Lagoon, a 72 km² coastal lagoon in southern Uruguay. Using sediment cores that extended to ∼20,000 yr BP, analyses of grain size, organic matter, carbonate, total carbon, nutrients, and diatoms allowed us to infer changes in trophic state and paleosalinities, which were closely related to Holocene relative sea level variation. Higher trophic states were observed during regressive events, most probably due to increases in runoff and erosion as regressions progressed. Diatom Association Zones (DAZ) were identified in both cores. Those DAZ corresponding to transgressive events were dominated by marine/brackish taxa and relatively low organic matter and nutrient values, while those DAZ corresponding to regressive events showed increases in brackish/freshwater diatoms and both organic matter and nutrients. Although the lagoon formed after the first Holocene marine transgression, our data indicate the existence of a marine/brackish aquatic system during upper Pleistocene (i.e., before 15,000 yr BP), but by ∼20,000 yr BP, the system was still likely to be a semi-arid terrestrial system.     

黄土高原晚更新世的植被与气候环境

通过对黄土高原上陕西洛川、富县省等黄土剖面的地质调查、采样和孢粉分析 ,在曾被人们认为孢粉贫乏的黄土中分析出了大量孢粉 ,作出了黄土地层的孢粉浓度图式。结合其他地区数个剖面上孢粉组合的变化 ,阐明了晚更新世的植被与气候在时间上演变与空间上分布的规律 ,证明了各地植被在时间上的演变韵律十分相似 ,说明它们同受全球气候变化的控制 ;但在同一时期各地植被不尽相同 ,则是局部自然环境差异所致。     

Multi-proxy data from Kaksoislammi Lake in Finland: dramatic changes in the late Holocene cladoceran assemblages

A small lake, Kaksoislammi (60° 3830N, 24° 4550E), in southern Finland was studied for Cladocera, diatoms and pollen from a core which covers the entire Holocene. The diatom remains indicate a steady development from alkaliphilous taxa towards the dominance of acidophilous forms and lowering pH in the late Holocene. About 1800–1700 BP, dramatic changes took place in the microfauna, mainly the planktonic Cladocera. Bosmina longirostris, the dominant species, suddenly disappeared, and Daphnia, Chydorus sphaericus and Chaoborus increased. The change is simultaneous with a decline of the diatom-inferred pH to 4.8. It is probable that there was a sudden, profound change in predator-prey relationships. The acidity of the lake water probably increased to such a low level that it led to the disappearance of even the most acid-tolerant fish. Consequently invertebrate predators increased and quickly altered the species composition in the lake. There is also pollen evidence of the onset of Iron Age cultivation and grazing almost simultaneously with the faunal change. Therefore, it cannot be ruled out that the sudden lowering of pH was indirectly caused by prehistoric human activity; possibly the acidic peatland surrounding the lake was disturbed.     

Natural and human-induced environmental changes in Eastern Europe during the Holocene: a multi-proxy palaeolimnological study of a small Latvian lake in a humid temperate zone

This study uses the Holocene lake sediment of Lake ?ū?i (Latvia, Vidzeme Heights) for environmental reconstruction with multi-proxy records including lithology, computerised axial tomography scan, grain-size analysis, geochemistry, diatoms and macrofossils, supported by AMS radiocarbon dating. Numerical analyses (PCA; CONISS) reveal three main phases in the development of the lake. Response to the Lateglacial–Holocene transition in Lake ?ū?i took place around 11,300 cal. BP. Organogenic sedimentation started with distinctive 5-cm-thick peat layer and was followed by lacustrine sedimentation of carbonaceous gyttja. Several findings of the peat layer with similar dated age and position at different absolute altitudes indicate that lake basin was formed by glaciokarstic processes. In the Early Holocene (until around 8,500 cal. BP), the lake was shallow and holomictic, surrounded by unstable catchment with erosion and inflow events. Predominance of diatom species of Cyclotella and Tabellaria, large numbers of respiratory horns of phantom midge pupae (Chaoboridae), high Fe/Mn ratio, as well as the presence of laminated sediments indicates the transition to a dimictic and oligo-mesotrophic lake conditions with high water level, anoxia in the near-bottom and stable catchment in the Middle Holocene (8,500–2,000 cal. BP). This contrasts with many hydrologically sensitive lakes in Northern and Eastern Europe in which the water level fell several meters during this period. During the Late Holocene (from 2,000 cal. BP to the present), the lithological and biotic variables reveal major changes, such as the increase in erosion (coarser grain-size fraction) and eutrophication [diatoms Aulacoseira ambigua (Grun.) Sim., Stephanodiscus spp., Cyclostephanos dubius (Fricke) Round]. Characteristics of lake-catchment system during the Late Holocene reflect anthropogenic signal superimposed on the natural forcing factors. To date, the Late Quaternary palaeolimnological reconstructions using lake sediment has been limited in the Baltic region. Therefore, findings from Lake ?ū?i provide important information about environmental and climatic changes that took place in this part of Eastern Europe. This study shows that the relative importance of climate and local factors has varied over the time and it is essential to consider the lake basin topography, catchment size and land cover as potential dominant forcing factors for changes in sedimentary signal.     

Palaeomagnetic record in Late Pleistocene and Holocene dry lake deposits at Tlapacoya, Mexico

Summary. A palaeomagnetic investigation of Carbon-14-dated marsh and near-shore lacustrine sediments deposited between about 25000–5000 yr bp at Tlapacoya, Mexico, reveals normal polarity of the geomagnetic field in all samples measured. At one site, anomalous palaeomagnetic directions in a mud unit dated about 14500 yr bp raised the possibility of a geomagnetic excursion, but subsequent work at six additional sites in the unit revealed no abnormal directions. Thus the anomalous directions are most likely not a true reflection of geomagnetic field behaviour, although no specific alternative explanation is entirely convincing. The preliminary Tlapacoya data of anomalous directions have been cited by others as positive evidence for an excursion. We strongly recommend it no longer be considered as such.     

Geological controls on Pleistocene glaciation and cirque form in Greece

Limestone and ophiolite rocks are common across the eastern Mediterranean and many of the highest mountains are formed in these rock types. In northwest Greece, Pleistocene glacial erosion was much more effective on limestone terrain where pronounced glacial incision and subglacial glacio-karst processes produced locally-complex topography. This enabled Pleistocene glaciers to form on a range of slope orientations in contrast to ophiolite terrains, where glaciers were strongly controlled by aspect. On limestone terrains, the largest ice masses formed on south-facing slopes, whereas in neighbouring higher mountains formed in ophiolite, glaciers were much more restricted and predominantly formed on north- and east-facing slopes.     

Baptiste Lake,Alberta — A late Holocene history of changes in a lake and its catchment in the southern Boreal forest

Lead-210 assay and dating are subject to several sources of error, including natural variation, the statistical nature of measuring radioactivity, and estimation of the supported fraction. These measurable errors are considered in calculating confidence intervals for ²¹⁰Pb dates. Several sources of error, including the effect of blunders or misapplication of the mathematical model, are not included in the quantitative analysis. First-order error analysis and Monte Carlo simulation (of cores from Florida PIRLA lakes) are used as independent estimates of dating uncertainty. CRS-model dates average less than 1% older than Monte Carlo median dates, but the difference increases non-linearly with age to a maximum of 11% at 160 years. First-order errors increase exponentially with calculated CRS-model dates, with the largest 95% confidence interval in the bottommost datable section being 155±90 years, and the smallest being 128±8 years. Monte Carlo intervals also increase exponentially with age, but the largest 95% occurrence interval is 152±44 years. Confidence intervals calculated by first-order methods and ranges of Monte Carlo dates agree fairly well until the ²¹⁰Pb date is about 130 years old. Older dates are unreliable because of this divergence. Ninety-five per cent confidence intervals range from about 1–2 years at 10 years of age, 10–20 at 100 years, and 8–90 at 150 years old.This is the third of a series of papers to be published by this journal which is a contribution of the Paleoecological Investigation of Recent Lake Acidification (PIRLA) project. Drs. D.F. Charles and D.R. Whitehead are guest editors for this series.     

Records of environmental and climatic changes during the late Holocene from Svalbard: palaeolimnology of Kongressvatnet

A multi-core, multidisciplinary palaeolimnological study of the partially varved sediment of a deep, meromictic, arctic lake, Kongressvatnet (Svalbard, Western Spitsbergen), provides a record of environmental and climatic changes during last ca. 1800 years. The chronology of sedimentation was established using several dating techniques (¹³⁷Cs, ²¹⁰Pb, varve counts, palaeomagnetic correlation). A multiproxy record of palaeolimnological variability was compiled based on sedimentation rates, magnetic properties, varve thickness, organic matter, geochemistry, pigments from algal and photosynthetic bacteria, mineralogy and biological assemblages (diatoms, Cladocera). The major features recognised in our master core K99-3 include a shift in sediment source and supply (magnetic measurements, geochemistry) probably caused by glaciological changes in the catchment around 38–32 cm core depth (AD 700–820). Additional environmental changes are inferred at 20–18, 8–4.5 and 3–2 cm (AD ca. 1160–1255; 1715–1880; 1940–1963, respectively). During the past ca. 120 years a prominent sedimentological change from brownish-grey, partly laminated silt-clay (varves) to black organic-rich deposits was observed. From AD 1350 to AD1880 the sediment is comprised of a continuous sequence of varves, whereas the earlier sediments are mostly homogeneous with only a few short intercalated laminated sections between AD 860 and 1350. Sedimentation and accumulation rates increased during the last 30 years (modern warming). Pigment concentrations are very low in the lower ca. 32 cm of the core (AD 820) probably because of the high turbidity high energy environment. The high sulphur content in the uppermost 32 cm of sediment has given rise to two horizontally stratified populations of sulphur anaerobic photosynthetic bacteria, as inferred from their specific carotenoids. These bacteria populations are much more abundant during the Little Ice Age (LIA) than during warmer periods (e.g., during the Medieval Warm Period and 20th century). Diatoms are lacking from the core base up to 18 cm (ca. AD 1255); at this level, species indicative of mesotrophic water are present, whereas from 17 cm to the top of the core, oligotrophic taxa such as Staurosira construens/S. pinnata complex dominate, indicating extended ice coverage and more oligotrophic waters during the LIA. The concentration of Cladocera subfossil remains (dominated by Chydorus) are relatively high in the deepest sections (54–32 cm), whereas the upper 32 cm are characterized by a very low concentration of remains, possibly because of the strongly anoxic conditions, and in this upper sediment section rotifer resting eggs become prevalent. We interpret these changes as responses to climate forcing through its impact on glacial melt water, lake ice cover duration and mainly redox conditions in deep water. The observed changes suggest that at least some of our recorded changes may parallel the Greenland Ice core, although our study added more details about the inferred climatic changes. Further aspects are discussed, such as catchment processes, glacial activity, duration of the Medieval Warm Period, the Little Ice Age, local human activity, and limnology.