Subjects -> PALEONTOLOGY (Total: 43 journals)
Showing 1 - 21 of 21 Journals sorted alphabetically
Alcheringa: An Australasian Journal of Palaeontology     Hybrid Journal   (Followers: 6)
Ameghiniana     Open Access  
Annales de Paléontologie     Full-text available via subscription   (Followers: 4)
Annals of Carnegie Museum     Full-text available via subscription   (Followers: 1)
Boreas: An International Journal of Quaternary Research     Hybrid Journal   (Followers: 13)
Comptes Rendus Palevol     Open Access  
European Journal of Protistology     Hybrid Journal   (Followers: 5)
EvoDevo     Open Access   (Followers: 4)
Facies     Hybrid Journal   (Followers: 9)
Fossil Record     Open Access   (Followers: 5)
Geobios     Full-text available via subscription   (Followers: 4)
Geologica Saxonica     Open Access   (Followers: 2)
Historical Biology: An International Journal of Paleobiology     Hybrid Journal   (Followers: 9)
Ichnos: An International Journal for Plant and Animal Traces     Hybrid Journal  
International Journal of Speleology     Open Access   (Followers: 3)
Journal of Paleolimnology     Hybrid Journal   (Followers: 5)
Journal of Paleontology     Hybrid Journal   (Followers: 8)
Journal of Quaternary Science     Hybrid Journal   (Followers: 31)
Journal of Vertebrate Paleontology     Full-text available via subscription   (Followers: 8)
Marine Micropaleontology     Hybrid Journal   (Followers: 2)
Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen     Full-text available via subscription   (Followers: 3)
Novitates Paleoentomologicae     Open Access   (Followers: 1)
Open Quaternary     Open Access  
Palaeogeography, Palaeoclimatology, Palaeoecology     Hybrid Journal   (Followers: 13)
Palaeontographica A     Full-text available via subscription   (Followers: 3)
Palaeontology     Hybrid Journal   (Followers: 17)
Palaeoworld     Hybrid Journal   (Followers: 3)
Paläontologische Zeitschrift     Hybrid Journal   (Followers: 4)
Paleobiology     Full-text available via subscription   (Followers: 6)
PaleoBios     Open Access   (Followers: 1)
Paleoceanography and Paleoclimatology     Full-text available via subscription   (Followers: 5)
Paleontological Journal     Full-text available via subscription   (Followers: 4)
Palynology     Hybrid Journal   (Followers: 1)
Papers in Palaeontology     Hybrid Journal  
Peer Community Journal     Open Access   (Followers: 4)
Quaternaire     Open Access   (Followers: 3)
Quaternary Research     Full-text available via subscription   (Followers: 19)
Quaternary Science Reviews     Hybrid Journal   (Followers: 26)
Review of Palaeobotany and Palynology     Hybrid Journal   (Followers: 1)
Revue de Micropaleontologie     Full-text available via subscription  
Rivista Italiana di Paleontologia e Stratigrafia (Research In Paleontology and Stratigraphy)     Open Access   (Followers: 1)
Spanish Journal of Palaeontology     Open Access  
Swiss Journal of Palaeontology     Hybrid Journal   (Followers: 4)
Vertebrate Anatomy Morphology Palaeontology     Open Access   (Followers: 1)
Zitteliana     Open Access  
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Journal of Paleolimnology
Journal Prestige (SJR): 1.019
Citation Impact (citeScore): 2
Number of Followers: 5  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1573-0417 - ISSN (Online) 0921-2728
Published by Springer-Verlag Homepage  [2469 journals]
  • Holocene climate evolution: information from the Lacustrine–Fluvial
           sediment in North China

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      Abstract: Abstract We reconstructed the Holocene climate in the study area using data from a BZ section in the Baiyangdian paleo-lake. Samples were analyzed for multiple proxies for climate conditions, including grain size, magnetic susceptibility (MS), and carbonate content, which were combined with accelerator mass spectrometry (AMS) 14C data. The results show that from 10.0 to 6.3 kyr BP, the study area experienced an interval of increasing precipitation and rising water level at Lake Baiyangdian. For a very short period, ~ 8.4 kyr BP, the extent of the lake reached the sampling point. The climate during this stage was relatively humid. The water level dropped abruptly at 6.5 kyr BP as a result of a weak monsoon event. From 6.3 to 2.9 kyr BP the climate became humid once again. The continuous lacustrine sediment of the strata indicated that the water level of Lake Baiyangdian expanded rapidly during this period and reached the sampling point. After 2.9 kyr BP, the climate in the region changed again from humid to dry. The abrupt increase in MS after ~1 kyr BP (993 AD) is consistent with records of human activities in local chronicles, which indicates that the environment in the study area was influenced by human activities. Through a comparison of the BZ section and the East Asian summer monsoon (EASM) records, we found that precipitation in the study area was controlled by the EASM. A series of cold Holocene events were clearly recorded by the sediment in the BZ section, and these events are synchronous with the North Atlantic ice-rafting events (IRD). The connection between the characteristics of the BZ section and the EASM and IRD indicate that climate evolution in the study area was strongly affected by EASM and IRD.
      PubDate: 2022-06-01
       
  • Paleoenvironmental significance of 5α-stigmastanol in surface soil and
           lake sediment from the Nianbaoyeze Mountains, eastern Qinghai-Tibet
           Plateau

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      Abstract: Abstract We identified a suite of steroid biomarkers in sediments and surface soils around Lake Ximencuo, a typical glacial lake in the Nianbaoyeze region, eastern Qinghai-Tibet Plateau (QTP). Various sterols, stanols, sterones, and sterenes appear in the sediments and surface soil samples. Among these steroids, plant-derived β-sitosterol and the 5α-stigmastanol that is derived from it exhibit high relative abundances. Notably, we found that the relative abundance of 5α-stigmastanol and the 5α-stigmastanol/n-alkanol ratio in a core of Lake Ximencuo sediment increased significantly in the last 200–300 year. These biomarker changes are broadly consistent with the growth of human settlement and the rapid development of animal husbandry in this region, which resulted in the former nomadic pastoral lifestyles gradually being transformed into permanent settlements since the early eighteenth century. The environmental and cultural changes led to greater delivery to soils around the lake of β-sitosterol that was transformed into 5α-stigmastanol by microbial communities in soil horizons, which include aerobic and anaerobic bacteria, and eventually surface runoff transport of the increased abundance of 5α-stigmastanol into Lake Ximencuo. We further postulate that the progressively greater human impacts in the Nianbaoyeze region over the past 200–300 year have modified the kinds of microbes that participate in the biogeochemical cycles of local soils.
      PubDate: 2022-06-01
       
  • Human impacts on the cladoceran community of Jili Lake, arid NW China,
           over the past century

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      Abstract: Abstract Deterioration of aquatic ecosystems, as a consequence of human-induced disturbances, is a critical global concern. To fully understand the responses of aquatic systems to anthropogenic impacts, it is crucial to assess long-term changes in lakes. The water quality of Jili Lake, a large water body in northwest China, has deteriorated recently, owing to the growing impacts of regional warming and human activities. Thus, Jili Lake was a prime candidate for evaluation of historical multi-stressor impacts. Meteorological data, historical documents, and assemblages of cladoceran microfossils in the sediments of Jili Lake were employed to investigate changes in the cladoceran community over the past century, and to evaluate the response of that aquatic community to human activities. From the 1920s to the 1950s, species richness of the cladoceran community was high, which reflected conditions of relatively low human impact. From the 1960s to 1970s, a sharp decrease in Bosmina longirostris, a planktonic cladoceran species, suggested a decrease in water level as a result of dam construction and intensified water exploitation. Since the 1980s, the water level in the lake has been restored, but increased fish farming and construction of a water storage facility caused salinisation and eutrophication of Jili Lake. Accordingly, the cladoceran community displayed distinct signs of a regime shift, with a gradual transition to dominance of B. longirostris and a sharp decrease in littoral species (e.g. Leydigia leydigi, L. acanthocercoides, Alona quadrangularis, Alona affinis). Our results suggest that human-induced disturbances were the main factor that drove changes in the cladoceran community since about the mid-20th century.
      PubDate: 2022-06-01
       
  • Holocene-Anthropocene transition in northwestern Yunnan revealed by
           records of soil erosion and trace metal pollution from the sediments of
           Lake Jian, southwestern China

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      Abstract: Abstract Accelerated soil erosion and trace metal pollution in aquatic environments have become a pervasive aspect of global environmental changes during the Anthropocene, threatening food security and ecosystem viability. Long-term records of these processes can promote an improved understanding of their timing, amplitude, and environmental impacts. Here we present a sedimentary record from Lake Jian in Yunnan Province, southwestern China, which shows that land-use changes affected the lake watershed by at least 1200 CE, and that the intensity of soil erosion increased from 1450 CE onwards, as evidenced by increases in magnetic susceptibility and high concentrations of trace metals. The timing of the increase in atmospheric lead (Pb) transport, which was possibly related to the growth of metallurgical activity in the region, occurred ~250 years earlier than the anthropogenic soil erosion. Pb emissions resulting from the mining and smelting industry, coal burning, and the use of leaded gasoline led to enhanced Pb pollution in the area since the 1950s CE. Comparison of the results with geochemical records from lakes in northwestern Yunnan reveals that environmental disturbances were relatively limited during the intervals of the Nanzhao and Dali Kingdoms. However, enhanced human disturbances of lake watersheds in Yunnan occurred from the Yuan dynasty onwards, as a result of population increases caused by immigration to the area, which was followed by the changes in the type and intensity of human activity, with an enhanced anthropogenic impact after the middle twentieth century. Overall, our study provides a case study for understanding the historical background of the Anthropocene.
      PubDate: 2022-06-01
       
  • Holocene vegetation evolution, hydrologic variability and sea-level
           fluctuations on the south coastal plain of Laizhou Bay, Bohai Sea, China:
           new evidence from pollen, freshwater algae and dinoflagellate cysts

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      Abstract: Abstract Holocene palynological evidence from the Bohai Sea coastal areas have not been sufficiently discovered. In this study, we carry out analyses using detailed palynological records of pollen, spores, freshwater algae and marine dinoflagellate cysts from Borehole X1 on the south coastal plain of Laizhou Bay, Bohai Sea, northern China. The results based on radiocarbon chronology show vegetation evolution, hydrologic variability and sea-level fluctuations during the Holocene. Abundant non-arboreal pollen (mainly, Artemisia, Chenopodiaceae and grass-type Poaceae) and small amounts of arboreal pollen (mainly Pinus and Quercus-deciduous) and fern spores were identified in this study, suggesting that coastal steppes and coniferous and broadleaved mixed forests flourished in the study area and its adjacent areas, and a cold and dry climate with less precipitation and lower sea-level than the present during the Early Holocene, ca. 9910–7440 cal. yr BP. After that, the steppe areas began to shrink, and coniferous and broadleaved mixed forest areas began to expand, indicating a relatively warm and humid climatic conditions, with more precipitation and marine transgression processes during the Mid-Holocene, ca. 7440–3650 cal. yr BP. Afterwards, relatively cool and dry climatic conditions predominated, with less precipitation. While sea-level continued to rise slowly during the Late Holocene, ca. 3650 cal. yr BP to the present, and the steppe areas shrank, the coniferous and broadleaved mixed forest areas continued to expand.
      PubDate: 2022-06-01
       
  • Climate change as the dominant driver of recent ecological changes in a
           semi-arid alpine lake from the Chinese Loess Plateau

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      Abstract: Abstract Semi-arid areas of northern China are under increasing pressures from anthropogenic activities and climate change. Although wetland areas in these drylands have experienced dramatic, unidirectional shifts in their ecological status in recent centuries, fundamental driving forces are poorly quantified. Here, we examine changes in sedimentary proxies (diatoms, spectrally-inferred chlorophyll-a, stable isotopes) preserved in a radiometrically-dated core from Tianchi Lake, an alpine lake within the margin of the East Asian Summer Monsoon (EASM) limit in China’s southwestern Loess Plateau. Our algal trends were compared with regional instrumental records, changes in EASM intensity, and with previously published paleolimnological data from this same lake to determine the principal drivers of regional ecological changes. We found no clear evidence that geochemical and biological proxies were strongly affected by deforestation and other human activities. Major environmental changes during the past ~ 200 years were found to be predominantly driven by climatic fluctuations, extreme precipitation events, and changes in EASM intensity. Prior to ~ 1965 CE, diatom assemblages indicate an oligotrophic, clear water state. Shifts in dominance between benthic Staurosirella pinnata and planktonic Lindavia comensis were likely controlled by ice-cover dynamics. Between ~ 1965 and 1980 CE an abrupt shift to a turbid water state during a period of extreme precipitation events was caused by excessive nutrient-laden soil erosion in the already susceptible deforested catchment. This turbid period was evidenced by a rapid increase to dominance of Achnanthidium minutissimum, a sharp decline in oligotrophic Lindavia comensis, increased primary production, and peaks in sediment grain size and SiO2 content. Post- ~ 1980 CE, we provide evidence that a shift towards planktonic diatom dominance can best be explained by changes in climate and EASM intensity, despite substantial nitrogen deposition in the region during the past few decades. Specifically, a drier and warmer climate together with weakened EASM wind strength resulted in decreased erosion and a return to a clear water state, coupled with enhanced thermal stability. Collectively, these observations expand our understanding of how changes in climate, extreme precipitation events, and fluctuations in EASM intensity influence semi-arid alpine lakes in northern China, as well as climate’s leading role in driving ecological change over the past two centuries, despite the intensification of human disturbances during recent decades.
      PubDate: 2022-06-01
       
  • Paleolimnological evidence for lacustrine environmental evolution and
           paleo-typhoon records during the late Holocene in eastern Taiwan

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      Abstract: Abstract The late Holocene lacustrine environmental evolution and paleo-typhoon records are poorly understood around lowland Liyu Lake and mountain Tunlumei Pond in eastern Taiwan. In this study, we use records of diatom populations, magnetic susceptibility, total organic carbon, carbon-to-nitrogen ratio, and δ13C from two lacustrine sediment cores in eastern Taiwan to reconstruct the paleoenvironment and the paleo-typhoon records during the late Holocene. Significant changes in lithology and in multi-proxy data in the record from lowland Liyu Lake (LYL) show that LYL became hydrologically isolated by 2850 cal BP, possibly as a result of landslide-induced alluvial fan formation. Synchronous increases of the diatom-inferred lake level proxy for LYL and regional precipitation proxies reflect a strengthened East Asia summer monsoon since 1600 cal BP. Eutrophication of the water in LYL is also inferred, and this is interpreted to be related to agricultural activities, which provides evidence for changes in land use during the past 200 years. The occurrence of diatom valves in sediment of the mountain Tunlumei Pond (TLM) indicates that the pond area has been stable since 760 cal BP, which reflects an increase in the local precipitation. The decrease of diatom-inferred pH indicates an increase in the input of acid runoff from the watershed during typhoon-triggered heavy rainfall. Both lacustrine records suggest that the typhoon intensity increased during the early Little Ice Age. The sediment records in northeastern Taiwan also suggest an increase in typhoon activity during the late Little Ice Age. The asymmetric pattern of typhoon intensity during the last 1000 years is interpreted to reflect the control exerted by anomalies in both global temperature and the El Niño-Southern Oscillation intensity on typhoon tracks over several centuries.
      PubDate: 2022-06-01
       
  • Lake restoration time of Lake Taibai (China): a case study based on
           paleolimnology and ecosystem modeling

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      Abstract: Abstract Reducing excessive external nutrient loading is in principle the first adaptive management against eutrophication, whereas little is known about the recovery time of such intervention, especially in the context of global warming. Here, we use an ensemble approach of paleolimnological records and modeling PCLake to evaluate the recovery time of Lake Taibai, China under diverse combinations of nutrient reduction and climate change scenarios. The model was calibrated for seven sensitive parameters and further validated using the total phosphorus (TP) concentrations in sediment cores reconstructed using a diatom-TP transfer function. The paleolimnological records show that species indicative of eutrophic conditions and the diatom-inferred TP (DI-TP) were low before the 1980s and slightly increased thereafter. The calibrated model not only captures the dynamics of TP concentrations but also performs well in identifying the regime shift between the 2 alternative stable states of the lake: macrophyte-dominated (clear) and algae-dominated (turbid) states. The scenarios results suggest that lake restoration (from turbid to clear state) would take 10–20 years with an annual nutrient loading (both N and P) reduction rate of 15–25% from 2019. Meanwhile, global warming would impede the effectiveness of nutrient reduction by not only increasing the restoration time but also decreasing the vegetation restoration level (as indicated by vegetation dry weight in lake water) and critical nutrient loading for re-oligotrophication. Our results imply that in the long run, nutrient loading reduction measurement for sustainable lake restoration should be adjusted following temperature changes. The present study highlights the feasibility and relevance of a novel methodology using paleolimnological records for model calibration and projections. The modeling approach presented here may provide a better understanding and critical implications of the long-term dynamics and future restoration of Lake Taibai and other similar shallow lake ecosystems.
      PubDate: 2022-06-01
       
  • Spatial variation of diatom diversity with water depth at Huguang Maar
           Lake, Southern China

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      Abstract: Abstract An investigation of changes in lake diatom assemblages and diversity with water depth can help determine whether the biodiversity of a single sediment core is representative of that of the entire lake, as well as can improve our understanding of the relationship between diatom assemblages and water depth. In this study, Huguang Maar Lake in Southern China was investigated in order to explore the spatial patterns of diatom diversity and diatom assemblages of 95 surface sediment samples from different locations and depth zones within the lake. The results show an essentially constant diatom diversity, dominated by planktonic diatoms, in the open deep water zone (OD), and consistent diatom diversity in the northern gently-sloping shallow water zone (NS). However, there is a much higher diatom diversity in different microhabitats in the southern and western shallow water zone (SWS), where the bathymetry is much steeper. This difference may reflect the influence of the bathymetry on the occurrence of sediment slumping. In the steeply-sloping SWS zone, frequently influenced by wave action and sediment slumping, diatom diversity is less representative of that of the entire lake, possibly due to the presence of diatoms from different sources and of different depositional ages. The results indicate that for relatively strongly mixed lakes with a simple morphometry, water depth has little influence on diatom diversity; however, the possible influence of local lake basin topography should be considered when reconstructing past diatom diversity changes from sediment cores.
      PubDate: 2022-06-01
       
  • A computational method for rapid orthographic photography of lake sediment
           cores

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      Abstract: Abstract Photographs of sediment cores are an important dataset, often containing visual evidence for environmental change via sediment composition and structure. These photographs may be used to stratigraphically correlate adjacent cores or for automated image analysis, and can facilitate collaboration amongst researchers through sharing and annotation of the image files. Here we describe the use of computational photogrammetry (also known as Structure from Motion–Multi-View Stereo) to generate orthographic imagery of sediment cores. Computational photogrammetry is a rapid and economical technique, typically requiring only a few minutes for each metre of core, using consumer-grade digital camera equipment. The photogrammetric methodology corrects for topographic distortion caused by sediment surfaces that are not perfectly flat, and can also record features of the scene surrounding the core, such as notes, colour reference cards and measurement tapes or rulers. As the photogrammetric process also generates a three-dimensional reconstruction of the sediment core, spatial-based analysis can be used to identify damaged or non-representative sections of the core that are to be avoided during image analysis. Using an intermittently laminated sediment core from Lake Surprise, Australia, we tested 22 scenarios using control points in a variety of configurations, as well as calibrated and uncalibrated cameras, to identify techniques that can reconstruct the core accurately and generate orthophotos. Multiple techniques were able to achieve suitable accuracy. In particular, targets placed on the table alongside the core, combined with a calibrated camera, achieved high accuracy and enabled a simple, rapid, and repeatable method for generating high-quality sediment core images.
      PubDate: 2022-04-07
       
  • Linking paleoecology with paleolimnology: evaluating ecological shifts,
           human impacts and monsoon climate from sediment signals in East Asia

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      Abstract: Abstract This special issue, entitled “Paleolimnology and Paleoecology in a Rapidly Changing Asia,” was initiated during the third China Workshop on Lake Paleoecology that was held in Kunming, China, in December, 2019. Here, we summarize some of the key findings from the 10 papers that are included in this issue. The papers present sediment surveys of lakes from different parts of East Asia, and studies that spanned a variety of timescales, through multi-proxy analyses of modern samples, short cores and Holocene records. Overall, this special issue provides an up-to-date research snapshot in the fields of paleolimnology and paleoecology from rapidly changing regions of Asia, with a focus on the sediment signals of lake development, ecological shifts and anthropogenic forcing in the context of continuing climatic and societal changes.
      PubDate: 2022-04-05
       
  • Influence of the Late Quaternary climate on sedimentology of the Jazmurian
           Playa, SE Iran

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      Abstract: Abstract The Jazmurian Playa in southeast Iran is a sediment archive that has preserved a record of climate and environmental changes since the late Pleistocene. The late Pleistocene was dominated by sub-arid to arid climate interspersed with short periods of warm and humid conditions that impacted the vegetation cover and landscape. This study used sedimentological variations in a sediment core, supported by geochemical and mineralogical characteristics, to reconstruct climate change impacts and water-level fluctuations in the playa. These changes were inferred using grain-size data, magnetic susceptibility, total organic matter content, carbonate content, elemental concentrations, and mineralogical composition in a 14C-dated sediment core. Based on the inferred water level fluctuations in the playa, the core was divided into two major units. Unit 2 belonged to the late Pleistocene, characterized by a cold and dry climate. In contrast, Unit 1 was deposited during the Holocene, a time marked by prevailing warm and humid conditions, with short periods of intense dust storms. Since the late Holocene, the IOSM (Indian Ocean Summer Monsoon) has played a dominant role in regional climate. Water-level fluctuations related to humidity significantly influenced the sedimentological variables, including grain-size distribution, sorting, skewness, and roundness. During cold and arid conditions, the water level was low, and coarse sediments were deposited in the playa, with low organic matter content, low concentrations of Cu, Mn, P, and V, and evaporite minerals. In contrast, high organic matter content, presence of illite, and high concentrations of Cu, Mn, P, and V and low values of ICV (Index of Compositional Variability) imply a warm and humid climate during the Holocene. The paleoclimate reconstruction in the playa provides evidence about ongoing changes that are closely related to the paleohydrological conditions in this region.
      PubDate: 2022-04-02
       
  • Acid-volatile sulfide and acid-extractable iron sediment profiles do not
           track changes in lake trophic status and atmospheric sulfur deposition

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      Abstract: Abstract Sulfide formation in anaerobic lake sediments depends on supply rates of organic carbon and sulfate. Improvements to wastewater treatment plant effluent quality (e.g., lower total phosphorus (P)) and sulfur emissions can affect sulfide formation rates, which, in turn, can affect metal chemistry including internal iron loading. To determine if these improvements corresponded with sulfide and iron-related signals in sediments over time, acid-volatile sulfide (AVS) and acid-extractable iron accumulation rates were measured in sediment cores of two lakes with anaerobic hypolimnia, the formerly eutrophic, now mesotrophic central basin of Lake Erie, one of the Laurentian Great Lakes, and a small meso-eutrophic moraine lake in southern Ontario, Lake St. George. AVS accumulation rates declined gradually in both lakes after 1980 by 95% and 57%, respectively. Acid-extractable iron accumulation rate profiles were similar to AVS in both lakes, but acid-extractable iron rates were several orders of magnitude larger than AVS rates, hence most of the iron was not chemically associated with AVS. In contrast to the gradual declines in AVS, total P loading to Lake Erie did not decline much after 1980, total P concentrations in Lake St. George remained relatively constant between 1980 and 2014, and sulfate concentration decreases were too small in both lakes to account for the large AVS declines after 1980. Hence, productivity and sulfur emission signals appear to have been overridden by diagenetic processes, which produced similar profiles. Therefore, AVS and acid-extractable iron do not appear to be useful as paleo-indicators of trophic status and sulfate deposition.
      PubDate: 2022-03-30
       
  • Understanding controls on stanols in lake sediments as proxies for
           palaeopopulations in Mesoamerica

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      Abstract: Abstract Faecal stanols in lake sediments have been used as a proxy for human populations in the past in a variety of contexts, with the assumption that variability in faecal stanol concentration or ratios is a reliable proxy for relative catchment-scale human populations. Despite that, the specific controls on faecal stanol concentrations and ratios in lake sediments remain poorly understood. In this study we analyse faecal stanol concentrations in lake surface sediments across Guatemala and the Yucatán Peninsula of Mexico in order to constrain geographical and biogeochemical variables controlling stanol concentrations and ratios in lake sediments in this region. We propose and test the hypothesis that the stanol ratios coprostanol:(coprostanol + stigmastanol) and coprostanol:(coprostanol + cholestanol) scale according to the proximity to and size of nearby population centres. The key controls on stanol concentrations that we identify are the proximity to human population centres and the human population within 5 km of the sampling point. Based on a transect across Lake Petén Itzá, the ratio coprostanol:(coprostanol + cholestanol) does not appear to be an accurate proxy for proximity to human population centres, nor does it correlate with catchment human population. We suggest that normalising stanol concentrations to TOC is an appropriate way to take into account the effects of mineral dilution as well as the potential effects of organic matter deposition and preservation, and that the ratio coprostanol:(coprostanol + stigmastanol) does not scale with human population but may be an effective approach to determine the relative contribution of coprostanol-producing mammals and herbivores. Further, we discuss the current limitations of the proxy as well as its future directions, including the implications of our results for sediment core siting, the use of stanol ratios in palaeolimnology, as well as the storage, transport, and diagenesis of stanols.
      PubDate: 2022-03-18
       
  • Magnetic properties of core sediments from an alpine lake in Southwest
           China: implications for glacier melting

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      Abstract: Abstract Variations in the extent of glaciated areas are among the most distinct natural responses to climate change. To explore the response mechanism of sediment magnetic properties to glacial-area variation, detailed environmental magnetism investigations were performed on a sediment core from Lake Heihai, an alpine lake located on Haba Snow Mountain in Yunnan Province. We discuss the changes in sediment magnetic properties in the past century and their response mechanism to variations in glacial area caused by climate change, especially air-temperature change, based on the published chronological data. Results of magnetic mineralogy showed that single- and multi-domain magnetite and a small amount of high coercivity magnetic minerals dominated the sediment magnetic properties throughout the core. Magnetic particles within the sediments of Lake Heihai mainly originated from the terrigenous input of the lake basin discharged by glacial meltwater. Significant positive correlations were found among the annual average air temperature in the study area and concentration-dependent magnetic parameters (χlf) while negative correlations occurred among the annual average air temperature and particle size-dependent magnetic parameters (χARM/SIRM), indicating that the sediment magnetic properties of alpine lakes were sensitive to glacial-area variations caused by air-temperature change. Increased input of coarse magnetic particles was a result of glacial-area shrink, while decreased coarse-grain input and occurrence of finer magnetic particles corresponded to glacial-area expand. In addition, we identified three glacial-area shrink and expand cycles based on the variations in sediment magnetic properties in the study area. We propose that the sediment magnetic properties of alpine lakes can be used for monitoring variations in glacial area caused by climate change.
      PubDate: 2022-03-15
       
  • An ostracod-based record of paleoecological conditions during MIS6 and
           MIS5, from Lake Chalco, Basin of Mexico

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      Abstract: Abstract A sediment record from Lake Chalco, Basin of Mexico, revealed the presence of two endemic ostracod species during the latter part of Marine Isotope Stages (MIS) 6 (146–130 ka) and MIS5 (130–72 ka), namely Candona alchichica and Limnocytherina axalapasco. Higher abundance of C. alchichica was found during MIS6, when prevailing conditions were cold, lake waters were fresh, and relatively deep bottom waters were anoxic. The species is typically associated with saline environments today, consistent with its presence in MIS5 sediments. The Chalco record, however, reveals that it coexisted with freshwater diatom species during MIS6. Thus, we suggest that C. alchichica had a wider salinity tolerance, ranging from freshwater to more saline environments. Examination of MIS5 substages provides further insights into ostracod species responses to changing lake conditions. During MIS5e, the lake water level declined and salinity and dissolved oxygen in the water column increased, thereby favouring L. axalapasco productivity, whereas C. alchichica productivity decreased. Enhanced runoff and lower than average evaporation during MIS5d coincided with the increasing abundance of C. alchichica, suggesting a period of relatively high lake level and more dilute waters. These environmental conditions, however, changed during MIS5c when lake stage dropped once again and L. axalapasco abundance increased. Shallow conditions during this substage were optimal for L. axalapasco. Subsequently, as the lake level continued to decline during MIS5b, both ostracod species disappeared from the sediment record. Finally, during MIS5a, runoff increased and both ostracod species reappeared in the record, with L. axalapasco dominating, suggesting another period of lake level recovery. Increased evaporation rates during the last part of this substage (75–72 cal ka BP) may have led to disappearance of ostracods from the sediment record. Overall, during MIS5, we detected higher L. axalapasco, which represent relatively shallow lake conditions.
      PubDate: 2022-03-08
       
  • Variation in the seasonal response to climate change during the past
           

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      Abstract: Abstract Diatoms are universally recognized as good bio-indicators due to their high diversity and rapid response to environmental and climate changes. This paper explores whether the sedimentary diatom record from Sanjiaolongwan Maar Lake (SJML), northeastern China, reveals variations in seasonal pattern over the past 1000 years. The observed succession in diatom assemblages reveals that between 980 and 1310 CE the small-celled planktonic diatom Discostella pseudostelligera was abundant. Its relative abundance peaked during 1020–1060 CE, indicating that the duration of summer conditions over this interval was the longest within the last millennium. By contrast, the interval between 1470 and 1850 CE was marked by an increase in benthic diatoms pointing to a shortened duration of the ice-free season, and generally cold conditions. During the twentieth century warm period, the succession of eutrophic diatoms and changes in diatom cell size also reveal temperature-controlled seasonal variations in limnological conditions. The differences observed between the diatoms assemblages associated with the two warm periods indicate that the summers of the warmest part of the Medieval Climate Anomaly were longer than that of the current warm period. This result is supported by the diatom record from Erlongwan, another maar lake in the region that differs from SJML by its topographic features and in the level of human impact on its catchment.
      PubDate: 2022-02-10
      DOI: 10.1007/s10933-021-00228-3
       
  • Micro-XRF-inferred depositional history of the Orakei maar lake sediment
           sequence, Auckland, New Zealand

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      Abstract: Abstract Lake sediment records offer insights into past climate and environmental changes. There are, however, few continuous lake sediment records from the Southern Hemisphere mid-latitudes that span the last glacial interval (LGI) and have the requisite chronological control and sampling resolution. Orakei maar paleolake in the Auckland Volcanic Field, New Zealand, is an exception, as it contains a high-resolution record of continuous lacustrine sedimentation from its formative phreatomagmatic eruption ~ 130 ka, until post-glacial sea-level rise breached the crater tuff rim and connected the lake to the sea ~ 9 ka. We used micro-XRF core scanning, dry bulk density, loss-on-ignition and visual facies descriptions to investigate the depositional history of Orakei maar lake as a response to regional and global drivers of climate change, and to erosional events in the lake catchment. The climate history of the lake was divided into six depositional phases: (I) Early warming with frequent in-wash events, followed by climate fluctuations coeval with marine isotope stages (MIS) 5e to mid-5c, (II) Warm, quiescent depositional conditions during mid-MIS 5c to 5a, (III) A colder, windier interval during MIS 4, (IV) Warmer conditions with dominantly autochthonous sedimentation during MIS 3, (V) Cold conditions followed by a slow temperature increase and the onset of sea-level rise during late MIS 2, (VI) Warm conditions that culminated in formation of a peat unit at the top of the Orakei lacustrine sediment sequence, which was terminated by an influx of massive marine muds into the basin at 9.75 ka. Comparison of the inferred climate evolution at Orakei with climate inferences from the global marine benthic MIS record during LGI shows general agreement, though inferred climate changes consistently occur earlier at Orakei than in the MIS. There is also general agreement in temperature changes inferred from the Orakei record and from other regional lake sediment records, but more detailed comparison requires additional proxy climate data such as pollen, organic geochemistry and biomarkers, to better understand discrepancies between some records. This study demonstrated the great potential of the Orakei record for paleoclimate inference and the applicability of micro-XRF core scanning data for addressing questions about paleoclimate and paleoenvironment. It also highlighted past intervals that require further study.
      PubDate: 2022-02-07
      DOI: 10.1007/s10933-022-00235-y
       
  • Paleolimnological comparison of algal changes in a clear-versus a
           brown-water lake over the last two centuries in the northeastern U.S.A

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      Abstract: Abstract We reconstructed historical diatom and algal pigment records from a clear-water versus a brown-water lake in the northeastern U.S. to compare ecological responses to reduced acid deposition in recent decades in the context of a 140-year record, during which time multiple external drivers influenced both lakes. In the clear-water lake, diatom community structure changed continually from the beginning of the record, while it was more static in the brown-water lake over time, with the period of greatest change occurring after 1990. Concentrations of algal pigments were low in the clear-water lake until 1940, then increased during the 1940 to 1990 period, after which they slightly declined. The opposite pattern occurred in the brown-water lake—algal pigments were high until 1940, decreased in the period from 1940 to 1990, and increased after 1990. The clear-water lake was more responsive to long-term climate warming beginning at the end of the Little Ice Age. During the period of higher acid deposition, light availability was more important for controlling algal responses in the clear-water lake, while nutrient subsidies from allochthonous DOC were likely the primary control in the brown-water lake. With reductions in atmospheric sulfate deposition, both lakes showed signs of recovery toward pre-acidification conditions, but these changes were dampened in the clear-water lake, suggesting greater sensitivity to acid deposition and other external drivers such as effects of climate change. Our study highlights strong and divergent algal responses in a clear-water vs. a brown-water lake during a period of higher acid deposition, and considers these changes in the context of multiple drivers of environmental change over the past 140 years.
      PubDate: 2022-02-04
      DOI: 10.1007/s10933-022-00233-0
       
  • An illustrated guide of subfossil Chironomidae (Insecta: Diptera) from
           waterbodies of Central America and the Yucatan Peninsula

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      Abstract: Abstract We provide a photographic guide and taxonomic diagnosis of Chironomidae larval remains obtained from surface sediments and short cores of 92 waterbodies situated on the Yucatan Peninsula and in Central America, namely Mexico, Belize, Guatemala, El Salvador and Honduras. A total of 101 morphotypes belonging to 64 genera were identified. Chironominae was the most species-rich subfamily represented by 57 morphotypes of 34 genera. The most widespread and abundant genus was Goeldichironomus followed by Chironomus and Polypedilum. Orthocladiinae were represented by 26 morphotypes and 17 genera, with the most common one being Cricotopus. Remains of this subfamily were recorded in only \({^{1} \!\mathord{\left/ \!{\vphantom {\left(d+4\right)}} \right.} _{5}}\) of the surveyed lakes. Tanypodinae included 17 morphotypes belonging to 12 genera. Labrundinia along with Ablabesmyia and Coelotanypus were the most common genera. Subfamily Podonominae was represented by the genus Parochlus. We believe that our study includes most of the Chironomidae genera of Central America and will have broad applicability for both paleolimnologists and aquatic ecologists.
      PubDate: 2022-01-29
      DOI: 10.1007/s10933-021-00225-6
       
 
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