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: 12)
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)
Historical Biology: An International Journal of Paleobiology     Hybrid Journal   (Followers: 8)
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: 29)
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: 11)
Palaeontographica A     Full-text available via subscription   (Followers: 7)
Palaeontology     Hybrid Journal   (Followers: 17)
Palaeoworld     Hybrid Journal   (Followers: 3)
Paläontologische Zeitschrift     Hybrid Journal   (Followers: 4)
Paleobiology     Full-text available via subscription   (Followers: 5)
PaleoBios     Open Access   (Followers: 1)
Paleoceanography and Paleoclimatology     Full-text available via subscription   (Followers: 4)
Paleontological Journal     Full-text available via subscription   (Followers: 4)
Palynology     Hybrid Journal   (Followers: 1)
Papers in Palaeontology     Hybrid Journal  
Quaternaire     Open Access   (Followers: 3)
Quaternary Research     Full-text available via subscription   (Followers: 19)
Quaternary Science Reviews     Hybrid Journal   (Followers: 24)
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]
  • Stability of midge assemblages in productive shallow lakes exposed to
           point and diffuse nutrient inputs

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      Abstract: Human activities in the headwaters of the Carleton River Watershed (southwest Nova Scotia, Canada) are suspected to have led to nutrient enrichment of freshwaters, resulting in downstream effects. However, the presence of multiple nutrient sources in the headwaters, including mink fur farming and land-based aquaculture, have made it difficult to distinguish the dominant stressor(s). We used sedimentary chironomid and chaoborid remains and visible reflectance spectroscopy of sedimentary chlorophyll-a (VRS chl-a) to assess the timing and nature of limnological changes in two shallow eutrophic-hypereutrophic lakes that have been directly monitored for water quality since 2008. The catchment of eutrophic Hourglass Lake contains one mink farm and an aquaculture operation, and the outlet of Hourglass Lake flows into hypereutrophic Placides Lake through a watershed with several mink fur farms. Midge assemblages at Hourglass Lake showed a compositional shift (ANOSIM: 0.65, P < 0.001) coincident with the start of aquaculture in ~ 1990. However, the Chaoborus:chironomid (chaob:chir) ratio and midge-inferred volume-weighted hypolimnetic oxygen (VWHO) did not reflect decreased concentrations of dissolved oxygen. Midge assemblages at hypereutrophic Placides Lake showed no significant compositional shift and the chaob:chir ratio and inferred of dissolved oxygen were stable over the ~ 80-year record. It is likely that hypolimnetic oxygen concentrations have not decreased markedly in these productive lakes. Trends in VRS chl-a were also relatively stable at Placides Lake despite decades of nutrient inputs from the upstream watershed. High water colouration of these eutrophic-hypereutrophic shallow lakes may have increased their resilience to nutrient inputs from the catchment. Moreover, our study confirms that midge assemblage composition does not respond directly to phosphorus inputs in these shallow, stratified lakes. We highlight the stability of midge assemblages to decades of nutrient inputs from a land-based aquaculture operation and mink fur farms.
      PubDate: 2022-01-18
       
  • A multi-proxy lake-sediment record of middle through late Holocene
           hydroclimate change in southern British Columbia, Canada

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      Abstract: Analysis of the oxygen isotopic composition (δ18O) of sedimentary carbonates in Turquoise Lake (N50.83°, W121.69°, 807 m), southwestern British Columbia, provides information on middle through late Holocene hydroclimate variability at decadal-scale temporal resolution. Turquoise Lake water balance is strongly influenced by cold season precipitation and to a lesser extent by warm season evaporation. The lake water isotopic signature falls along the local evaporation line and is slightly enriched relative to local meteoric water, indicating that water losses from the lake occur principally through overflow and groundwater outseepage. An age model was developed using 210Pb, 137Cs, twelve 14C measurements, and one tephra layer. 375 samples of authigenic carbonate (< 63 µm-fraction), collected at 2–10 mm intervals over a 3 m long sediment sequence, were analyzed to produce the δ18O record. Multiple turbidite sequences that complicate the δ18O signal were identified via X-ray fluorescence, magnetic susceptibility, scanning electron microscopy, and powder x-ray diffraction analysis and were removed from the record. The Turquoise Lake δ18O record exhibits anomalously high values at ~ 7.6–6.5 ka, implying a dry middle Holocene and a transition to a wetter climate in the late-middle through late Holocene, with substantial variability on decadal and longer timescales. This result is consistent with other records from the Pacific Northwest, but the magnitude and timing of the transition from dry to wet conditions exhibited by the Turquoise δ18O record is unusual, with only the Castor Lake δ18O record exhibiting a somewhat similar pattern. Differences in hydroclimate signals from δ18O and other records in the Pacific Northwest point to complex intra-regional responses to Pacific ocean–atmosphere dynamics likely related to disparity in the orographic settings of the paleoclimate archives.
      PubDate: 2022-01-11
       
  • 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: 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: 2022-01-06
       
  • Paleoecological analysis of Holocene sediment cores from the southern
           basin of Lake Tanganyika: implications for the future of the fishery in
           one of Africa’s largest lakes

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      Abstract: Extensive research has been conducted at Lake Tanganyika to understand its vulnerability to a warming climate and fishing pressure. However, much of this work has been restricted to the more accessible northern basin. Studies from a limited geographic region of the lake are insufficient to explain whole-lake dynamics of the world’s longest lake (~ 670 km N-S). While strong evidence suggests that lake warming has played a critical role in decreasing fish abundance, limnological changes associated with warming have not been investigated lake wide. This study used paleolimnological data from two deep-water sediment cores from southern Lake Tanganyika to determine whether changes observed in the northern and central basins are, in fact, representative of lake-wide phenomena. We infer a decrease in diatom concentration after  ~ 3000 cal yrs BP to reflect a decrease in net primary productivity associated with decreasing convective mixing. In contrast, the episodic presence of benthic invertebrates (ostracodes and molluscs) at these deep sites between  ~ 1800–500 cal yrs BP, along with high Mn, indicates episodic pulses of much deeper ventilation of the southern basin than has been recognized previously. The presence of periphytic diatom species and benthic invertebrates during periods of strong stratification suggests that the lake bottom was periodically ventilated by descending denser (cooler or more sediment-rich) influent waters along the steep slopes of the coastline. Fish fossil abundance also is correlated with the dominance of heavily silicified diatom taxa, which itself requires stronger wave activity and upwelling of deep, nutrient-rich water. Fossil diatom assemblages show P and Si gradients between the two sites. LT17-TANG17-6A shows a shift in dominance towards lightly silicified taxa (Nitzschia spp.) after ~ 200 cal yrs BP. LT17-TANG17-2A shows a reduction in concentration of mostly the lightly silicified taxa, with few periods having heavily silicified taxa. These results are indicative of a relative reduction in convective lake mixing but are not always coincident with temperature trends, suggesting local windiness may also be important for stratification history. Thus, changes in lake productivity in the southern basin appear to be climate mediated, but in ways not previously documented in the northern and central parts of the lake.
      PubDate: 2022-01-01
       
  • An 1800-year record of lake level and climate change from alkaline lakes
           in southern Inner Mongolia, China

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      Abstract: Paleoclimatic records from the East Asian summer monsoon (EASM) margin are regarded as a direct reflection of the intensity and northern extent of the EASM. Here, we focus on reconstructing climatic evolution over the past 1800 years from two alkaline lakes, Chagan Nuur and Sangin Dalai Nuur, in southern Inner Mongolia. With age control provided by 13 Accelerator Mass Spectrometry radiocarbon ages and 210Pb/137Cs dating, analyses of grain size, X-ray diffraction, magnetic susceptibility, carbonate content, total nitrogen, total organic carbon and the stable isotopic composition of carbon (δ13C) and nitrogen (δ15N) in sedimentary organic matter and calculation of organic carbon to nitrogen atomic ratios have been performed to investigate hydrodynamic processes, ecological conditions and corresponding lake-level fluctuations, in response to climate change. Our results show that the lake level of Changan Nuur frequently fluctuated since 546 CE, with four centennial-scale intervals of lake expansion at around 755, 1178, 1350 CE, and after 1950 CE, and one interval of lake recession from 1593 to 1782 CE. Sangin Dalai Nuur experienced mainly low-amplitude lake-level fluctuations since 212 CE, except for severe lake shrinkage from 1417 to 1872 CE. A regional comparison shows that three warm and humid intervals (640–800 CE, 1088–1288 CE, and after 1950 CE) and one cold and dry interval (1417–1872 CE) recognized from our records could correspond to the Sui-Tang Warm Period, the Medieval Climate Anomaly, the Current Warm Period and the Little Ice Age, respectively. Moreover, our results are roughly synchronous with moisture conditions revealed by proxy records from monsoonal northern China, demonstrating that the highly variable lake levels and climatic conditions in southern Inner Mongolia were controlled by centennial-scale variations in EASM over the past 1800 years.
      PubDate: 2022-01-01
       
  • Late Holocene environmental change in Celestun Lagoon, Yucatan, Mexico

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      Abstract: Epikarst estuary response to hydroclimate change remains poorly understood, despite the well-studied link between climate and karst groundwater aquifers. The influence of sea-level rise and coastal geomorphic change on these estuaries obscures climate signals, thus requiring careful development of paleoenvironmental histories to interpret the paleoclimate archives. We used foraminifera assemblages, carbon stable isotope ratios (δ13C) and carbon:nitrogen (C:N) mass ratios of organic matter in sediment cores to infer environmental changes over the past 5300 years in Celestun Lagoon, Yucatan, Mexico. Specimens (> 125 µm) from modern core top sediments revealed three assemblages: (1) a brackish mangrove assemblage of agglutinated Miliammina and Ammotium taxa and hyaline Haynesina (2) an inner-shelf marine assemblage of Bolivina, Hanzawaia, and Rosalina, and (3) a brackish assemblage dominated by Ammonia and Elphidium. Assemblages changed along the lagoon channel in response to changes in salinity and vegetation, i.e. seagrass and mangrove. In addition to these three foraminifera assemblages, lagoon sediments deposited since 5300 cal yr BP are comprised of two more assemblages, defined by Archaias and Laevipeneroplis, which indicate marine Thalassia seagrasses, and Trichohyalus, which indicates restricted inland mangrove ponds. Our data suggest that Celestun Lagoon displayed four phases of development: (1) an inland mangrove pond (5300 BP) (2) a shallow unprotected coastline with marine seagrass and barrier island initiation (4900 BP) (3) a protected brackish lagoon (3000 BP), and (4) a protected lagoon surrounded by mangroves (1700 BP). Stratigraphic (temporal) changes in core assemblages resemble spatial differences in communities across the modern lagoon, from the southern marine sector to the northern brackish region. Similar temporal patterns have been reported from other Yucatan Peninsula lagoons and from cenotes (Nichupte, Aktun Ha), suggesting a regional coastal response to sea level rise and climate change, including geomorphic controls (longshore drift) on lagoon salinity, as observed today. Holocene barrier island development progressively protected the northwest Yucatan Peninsula coastline, reducing mixing between seawater and rain-fed submarine groundwater discharge. Superimposed on this geomorphic signal, assemblage changes that are observed reflect the most severe regional wet and dry climate episodes, which coincide with paleoclimate records from lowland lake archives (Chichancanab, Salpeten). Our results emphasize the need to consider coastal geomorphic evolution when using epikarst estuary and lagoon sediment archives for paleoclimate reconstruction and provide evidence of hydroclimate changes on the Yucatan Peninsula.
      PubDate: 2021-12-18
       
  • Tracking deepwater oxygen recovery using sedimentary chironomid
           assemblages: Peninsula Lake revisited

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      Abstract: Peninsula Lake, Ontario, Canada, is a Precambrian Shield lake that has experienced many environmental stressors since European settlement of the watershed in the mid-1800s, including forest clearance, water-level management, sewage inputs, and land-use changes. The deterioration of water quality by the 1970s prompted mitigation efforts intended to reduce inputs of nutrients and untreated sewage to the lake. Paleolimnological analysis of a sediment core from Peninsula Lake, collected in 1995, revealed that efforts to address eutrophication had been somewhat successful, in that the lake had returned to oligotrophic status by the early 1990s. Nevertheless, there had been little to no improvement in inferred deepwater oxygen conditions. We used similar paleolimnological techniques on a core collected in 2014 to examine ecological responses to environmental stressors and remediation efforts in the intervening years, with a particular focus on changes in the amount of oxygenated habitat available to lake trout. Specifically, we inferred trends in volume-weighted hypolimnetic oxygen (VWHO), through analysis of sedimentary chironomid assemblages, to assess long-term changes in coldwater fisheries habitat. Potential drivers of VWHO were also investigated, and included diatom-inferred total phosphorus, spectrally derived trends in sedimentary chlorophyll a and its main diagenetic products, and lake-water dissolved organic carbon. The sedimentary chironomid assemblages indicate a long period of VWHO depletion, concurrent with known anthropogenic activities from the early twentieth century to the 1990s, followed by recent recovery to near pre-impact levels. The sedimentary diatom assemblages indicate nutrient enrichment throughout most of the twentieth century, which was also followed by a return to pre-impact conditions, albeit with recent indications of renewed nutrient enrichment. In contrast, strikingly different trajectories were observed in two other regional waterbodies that support lake trout, but experienced relatively little nutrient enrichment over the past ~ 150 years. Peninsula Lake appears to be recovering from nutrient enrichment and hypolimnetic oxygen depletion, but water quality improvements have nevertheless been accompanied by increased primary production, perhaps because climate warming has extended the ice-free season and stratification period. Therefore, instead of returning to pre-impact conditions, Peninsula Lake appears to be developing a novel ecological state. Any future improvements in lake trout habitat that result from nutrient abatement may be offset by rising temperatures.
      PubDate: 2021-12-01
       
  • Post-glacial diatom and geochemical records of ecological status and water
           level changes of Lake Vorota, Western Beringia

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      Abstract: In this study, radiocarbon-dated geochemical and diatom records from Lake Vorota located within the informal meteorological ‘pole of cold’ of the northern hemisphere (Yakutia, Russia) were used to asses responses of the lake’s ecosystem to climate dynamics at the Late Pleistocene–Holocene boundary and over the Holocene. Geophysical research revealed relatively great depths (40–65 m) and a 4-m undisturbed thin-layered sedimentary structure in the central part of the lake where the short sediment core (V3-2014, 85 cm, spanning the last 13.2 kyr) was taken. One-hundred diatom species and intraspecific taxa were identified in the core. The most abundant were planktonic diatom species with predominance of centric Lindavia minuta and Aulacoseira subarctica. The most diverse were benthic diatoms—widespread, indifferent toward salinity, preferring mildly alkaline conditions—xeno-oligosaprobic and oligosaprobic species. We identified four diatom zones indicating the main periods in lake level change (in cal. kyr BP): ~ 13.2–9.0 (relatively deep lake), ~ 9.0–8.3 (decrease of lake level with minimum depths at ~ 8.7–8.6 cal. kyr BP), ~ 8.3–5.5 (maximum level of the lake) and ~ 5.3–0.4 (moderate decrease of lake level). The highest abundance of A. subarctica and the planktonic to benthic biotope diatom taxa ratio (P/B) mark the maximum depth of the lake at ~ 8.3–5.5 cal. kyr BP. Geochemical components are grouped into three types of proxies: terrigenous, biogenic and rather diagenetic, which have essentially different distributions along the core depth. The first ones probably indicate the changes during permafrost thawing and varying inputs from several sources of terrigenous matter. It was found that the lake had a high productivity during the Younger Dryas and the 8.2 cal. kyr BP cooling. The duration of maximal biogenic silica productivity was 11.0–10.1 and 9.7–9.0 cal. kyr BP. Our data suggest that the onset of the Holocene thermal maximum at the study site could have taken place 1.3 kyr earlier than at the same latitudes (~ 62°N) of the Central Yakutia and may correspond to the maximal lake level (~ 8.3–5.5 cal. kyr BP).
      PubDate: 2021-12-01
       
  • Global acceleration of lake sediment accumulation rates associated with
           recent human population growth and land-use changes

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      Abstract: Sediment Accumulation Rate (SAR; measured as mm yr−1) and Mass Accumulation Rate (MAR; measured as g cm−2 yr−1) data were collected from published lake core records that spanned the past ~  150 years, from approximately 500 sites worldwide. For each lake, key watershed characteristics including watershed size, slope, land use and climate were extracted, with the goal of quantifying the relative importance of these variables as drivers of SAR and MAR. General additive models provided evidence of accelerated global lake sediment infilling rates after AD 1950. Whereas the onset of sedimentation acceleration varied across ecoregions, global lake MAR values were found to have increased ~  threefold on average, since baseline conditions pre-1900 (i.e. μbaseline = 0.040 ± 0.044 g cm−2 yr−1 and μmodern = 0.13 ± 0.22 g cm−2 yr−1). The significant drivers, identified through Linear Mixed Effect modeling of MAR time series, were watershed population density (log-transformed) and watershed cropland density (log-transformed). Our results highlight important spatial heterogeneity in SAR and MAR among lakes, precluding the use of simple modeling approaches. SAR and MAR were found to be moderately correlated to one another, despite the potential for post-depositional disparities between segments of the sediment cores. We identified organic matter content (loss-on-ignition, LOI) as a significant co-variate that could be used to correct inflated very recent SAR rates. Our empirical analyses suggest that, despite a wide range of natural variability among lakes, both SAR and MAR increased globally and the increases appear to be mainly the result of enhanced watershed activities associated with agriculture and urbanization.
      PubDate: 2021-12-01
       
  • A record of late Holocene precipitation on the Central Tibetan Plateau
           inferred from varved lake sediments

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      Abstract: Lake sediments on the Tibetan Plateau are important natural archives for studying past climate and environment changes. A precise sediment core chronology is a fundamental prerequisite for reconstructing past climate and environment changes. However, radiocarbon dates on bulk carbon in lake sediment cores are subject to “old carbon” reservoir effects, which can cause problems when trying to establish depth-age relations for sediment cores, especially those from the Tibetan Plateau (TP). Here we present a varve chronology that spans the last ~ 2000 years, from Jiang Co, on the central TP. Clastic-biogenic varves in Jiang Co sediments are comprised of two laminae, a coarse-grain and a fine-grain layer, observed by petrographic microscope and Electron Probe Micro Analyzer. The varve chronology is supported by 210Pb and 137Cs dating and was used to estimate the radiocarbon reservoir ages for the past ~ 2000 years. The thickness percentage of the coarse-grain layer within a single varve was used as a proxy for summer precipitation amount, as coarse grains are transported mainly by runoff. During the past 2000 years, the precipitation record inferred from Jiang Co sediments shows centennial-scale fluctuations that are consistent with other records from the region. The varve chronology from Jiang Co provided a valuable opportunity to estimate the “old carbon” reservoir effect in Jiang Co and reconstruct past precipitation on the Tibetan Plateau.
      PubDate: 2021-12-01
       
  • Early presence of Bythotrephes cederströmii (Cladocera: Cercopagidae) in
           lake sediments in North America: evidence or artifact'

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      Abstract: The spiny water flea (Bythotrephes cederströmii), a freshwater crustacean considered to be the world’s best-studied invasive zooplankter, was first recorded in North America in the Laurentian Great Lakes during the 1980s. Its arrival is widely considered to be the result of ocean-going cargo ships that translocated contaminated ballast water from Eurasia to the Great Lakes during the 1970–1980s. The subsequent first discovery of the species in inland lakes is consistent with the hypothesis that propagules dispersed initially from established Great Lakes populations. Here we present evidence of exoskeletal remains, including mandibles, tail spines, and resting eggs, in 210Pb-dated lake sediment cores, which suggests that B. cederströmii was already resident in four inland North American lakes (two in Minnesota, USA; two in Ontario, Canada) by at least the early 1900s. Densities of exoskeletal remains were low and relatively steady from first appearance until about 1990, after which time they increased in all cores. The earliest evidence that we found was a mandible at 33-cm depth (pre-1650) in the sediments of Three Mile Lake, Ontario, Canada. These unexpected findings challenge the current paradigm of B. cederströmii invasion, renew uncertainty about the timing and sequence of its colonization of North American lakes, and potentially question our ability to detect invasive species with traditional sampling methods. We attempted to eliminate errors in the dated stratigraphies of the exoskeletal remains that might have been introduced either methodologically (e.g., core-wall smearing) or naturally (e.g., bioturbation). Nonetheless, given the very low numbers of subfossils encountered, questions remain about the possible artifactual nature of our observations and therefore we regard our results as ‘preliminary findings’ at this time.
      PubDate: 2021-12-01
       
  • Responses of testate amoebae assemblages (Amoebozoa: Arcellinida) to
           recent volcanic eruptions, inferred from the sediment record in Laguna
           Verde, southern Patagonia, Argentina

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      Abstract: There is little knowledge about testate amoebae in lakes and their responses to volcanic eruptions. To address this knowledge gap, we studied the paleoecology of these protists in a sediment record from Laguna Verde, a lake located east of the southern Patagonian Ice Field, in Santa Cruz Province, Argentina. The lake is under the influence of volcanic eruptions from Lautaro Volcano, Chile, ~ 42 km WNW of Laguna Verde. We evaluated the response of 11 testate amoeba morphospecies in the lake to the last four Lautaro eruptions, using a 61-cm sediment core. Calcium (Ca), a major element of volcanic ash, was the most important variable explaining testate amoeba variability in the three zones determined by detretended correspondence analysis. We identified four declines in testate amoeba abundance and diversity associated with tephra deposition. Poisson regression analysis revealed that Difflugia immanata, D. bidens, and D. glans strain “glans” decrease after deposition of tephra layers. In contrast, Centropyxis constricta strain “constricta,” C. aculeata strain “aculeata” and Zivkovicia compressa respond positively to ash deposition. Our findings suggest a high resilience of testate amoebae to stochastic events such as volcanism because the same assemblage (D. immanata, D. bidens, and D. glans strain “glans”) inhabited the lake before and after the ashfalls. Nevertheless, several volcanic eruptions during the last ~ 300 years may have weakened this resilience and had a long-term effect on community diversity. Multivariate analysis showed that potassium (K) plays a significant role in shaping assemblage composition. Because of the low K content of the Lautaro tephra, we infer that higher potassium concentrations in sediments are not related with volcanic events, but rather, are associated with terrestrial input. Future studies, however, will be needed to identify the source of K in the sediment record and its relationship with testate amoebae assemblages. Our study demonstrates the potential for using lacustrine testate amoebae as environmental proxies, and illustrates the direct effects of volcanic ash deposition on their assemblage composition, diversity and distribution in southern Patagonia.
      PubDate: 2021-11-23
       
  • Stratigraphic relationship between Rimrock Lake and Hay Lake playa
           sediments, Harney Basin, eastern Oregon, USA

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      Abstract: Seven sediment cores from Rimrock Lake (n = 4) and Hay Lake (n = 3) playas (Harney Basin, northwest Great Basin, Oregon, USA) were used to characterize their stratigraphic relationships through time. End-member mixing analysis, conducted on grain-size distributions, identified five end-members (EM), which explain 97.23% of total variance across all samples and represent two major environments of deposition, lacustro-eolian and fluvio-lacustrine. Normalized differences between finest and coarsest EMs were calculated to serve as a visual proxy for comparison of changes in energy within the playas. Playa and watershed morphometric analysis, using GIS, indicates both playas are relatively large (~ 54 ha) compared to other wetlands within Harney Basin. Both playas were established as marshy environments during the late Pleistocene, ca. 19,500–18,500 cal yr BP, and experienced increased fluvial activity during the early Holocene, between ca. 9000 and 8000 cal yr BP. Rimrock Lake playa continued to experience a lacustrine environment with alternating lake levels well into the middle Holocene, even during times of increased regional aridity, whereas Hay Lake playa did not seem to have experienced an expanded lacustrine environment into the middle Holocene. Digital elevation models, aerial imagery, and documented late Quaternary tectonic activity, suggest that tectonics may have played a role in diverting ephemeral channels toward Rimrock Lake and away from Hay Lake.
      PubDate: 2021-10-27
       
  • Ecology and climate sensitivity of a groundwater-fed lake on subtropical
           North Stradbroke Island (Minjerribah), Queensland, Australia over the last
           7500 years

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      Abstract: Lake sediments are important archives of past climate variability and lake responses to climate. In order to accurately infer past climates, it is necessary to understand, and account for, the ecological processes that affect the record of indicators preserved in lake sediment. This is particularly the case with respect to the concentration of carbon and nitrogen (TOC, TN, and calculated C:N), and the stable isotope composition of organic matter preserved in lake sediments. These are common, yet ambiguous, tracers of environmental change. Ideally, palaeoenvironmental reconstructions using the concentration and isotope composition of organic matter should be grounded in a detailed understanding of the sources of the organic material. This study documents the history and evolution of Blue Lake, an environmentally and culturally important oligotrophic, groundwater window lake on North Stradbroke Island, Queensland, Australia. We utilise organic matter δ13C, TOC, TN, and C:N from a 2.4 m sediment core with a basal age of 7.5 cal kyr BP, to investigate changing organic matter sources as a measure of the climate sensitivity of Blue Lake. This interpretation is supported by data from contemporary algae, aquatic and terrestrial plants, and catchment soils. We show that lake nutrient dynamics drove an increase in algal biomass at 4.2 cal kyr BP. This change coincides with a widely documented intensification of the El Niño-Southern Oscillation, which we infer to have influenced lake nutrient concentrations by reducing groundwater throughflow. Climatic changes resulted in marked changes in lake primary productivity, despite relatively little turnover of the lake diatom flora and catchment vegetation. This suggests that south-east Queensland dune lakes are sensitive to climate changes and helps to refine past and future palaeoclimate research using sediments from these lakes. It also indicates that increased nutrient concentrations in Blue Lake may result from projected changes in 21st Century climate.
      PubDate: 2021-10-22
       
  • Spatial variation of diatom diversity with water depth at Huguang Maar
           Lake, Southern China

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      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: 2021-10-21
       
  • Disproportion among Cladocera (Crustacea) skeletal components in lake
           sediment taphocoenoses and significance with respect to two methods of
           sub-fossil enumeration

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      Abstract: Analysis of Cladocera (Crustacea: Branchiopoda) subfossil remains in lake sediments features prominently in paleolimnological studies. It is well known, however, that species composition in a taphocoenosis (assemblage of subfossil remains in sediments) does not represent perfectly that of the original living community (biocoenosis) from which it came. We analyzed the representation of different Cladocera skeletal components in sediments of 27 Russian water bodies to compare two methods of enumerating relative abundances of cladoceran remains: (1) recording the number of most abundant fragments of each taxon to represent the number of individuals, and (2) recording each fragment of a taxon as belonging to an individual specimen. Overall, for all cladoceran taxa and all water bodies sampled, proportions of different skeletal components differed from what would be expected based on those in live individuals. Carapaces were the most abundant component in 23 of 27 water bodies. Head shields were common, but predominated in only four samples, whereas postabdomens were rare, accounting for < 10% of the whole sample set. Several hypotheses are proposed to explain the different proportions of cladoceran skeletal remains in sediment samples. Both methods for counting remains yielded similar relative abundance estimates for different taxa, which can be regarded as evidence that both methods are adequate, with some exceptions. For example, Alona affinis was represented by a relatively high portion of postabdomens, a component that for other taxa was usually poorly represented. In general, recording of the total number of skeletal components, as compared to using the most abundant fragment method (MAF), slightly overestimates the significance of some taxa in the community. Disproportionate preservation of different skeletal components among cladoceran taxa does not compromise the results of cladoceran-based paleoecological analyses using either counting method, but should be considered when interpreting results.
      PubDate: 2021-10-18
       
  • A new ~ 900-year varved record in Lake Walker, Québec North Shore,
           eastern Canada: insight on late Holocene climate mode of variability

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      Abstract: This paper presents a new annually laminated record (varves) from Lake Walker, Québec North Shore (eastern Canada) spanning the period from ~ 3230 to 2320 ± 20 cal BP. A ~ 3.5-m-long composite sequence was established with the best regular and continuous laminated intervals using computed tomography and high-resolution photographs. The varve chronology was built based on two methods: manual multi-parameter counting using the PeakCounter software, and manual counting on thin-section images obtained by scanning electron microscopy (SEM). The latter correlates more closely with the ages derived from AMS radiocarbon dating, suggesting that thin-section analysis is here a more reliable counting technique. Varves are clastic, composed of a silt layer deposited in spring and summer, and a clay layer deposited in winter. Annually resolved grain size obtained using image analysis technique on SEM images of thin sections and elemental composition from X-ray microfluorescence analyses performed on the floating varve chronology suggests that the record is sensitive to the North Atlantic Oscillation (NAO), as revealed by the strong co-variability with another lower resolution record from Greenland. This suggests that periods of negative winter NAO promoted a thicker snow cover that resulted in higher river discharges and stronger clastic component in the varves. In modern times, cooling of the North Atlantic in the mid 1970s to the late 1980s was also characterized by concurrent negative phase of NAO, which condition translated into increase snow precipitation over the region. Overall, these results highlight that the new Lake Walker varve record presents remarkable prospects of developing a longer and high-resolution paleoclimatological reconstruction of the NAO in a region where similar records are scarce.
      PubDate: 2021-10-15
       
  • Loss on ignition vs. thermogravimetric analysis: a comparative study to
           determine organic matter and carbonate content in sediments

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      Abstract: Mass loss at specified temperatures has been used widely to determine amounts of organic matter and carbonate in sediment samples. The loss on ignition (LOI) method is cheap and simple, but is time-consuming and provides information only for specific, pre-determined temperatures. It also requires relatively large sample sizes and is destructive. Thermogravimetric analysis (TGA) is an alternative method for determination of organic and carbonate content in sediment samples, and provides accurate and precise data in a time-efficient manner. We compared results from these two thermal analysis techniques, which were applied to sediment samples from a submerged landscape (Doggerland). An organic-rich peat sample and a silty fine-sand sample were used. An unpaired t-test was used to test agreement and repeatability of the two analytical techniques. One advantage of being able to monitor mass loss throughout the analytical operation is that free and bound moisture losses can be distinguished. TGA is less time-consuming, involves automated sample handling (minimising operator error), and can yield reliable data from sample masses (typically 30–50 mg), which are much smaller than those needed for LOI (typically 3–5 g). The unpaired t-test, along with precision and repeatability analyses led us to conclude that TGA can be used instead of LOI to provide reliable measures of organic matter and carbonate content in sediments, and has several advantages over LOI.
      PubDate: 2021-10-08
       
  • Evaluating sedimentary DNA for tracing changes in cyanobacteria dynamics
           from sediments spanning the last 350 years of Lake Tiefer See, NE Germany
           

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      Abstract: Since the beginning of the Anthropocene, lacustrine biodiversity has been influenced by climate change and human activities. These factors advance the spread of harmful cyanobacteria in lakes around the world, which affects water quality and impairs the aquatic food chain. In this study, we assessed changes in cyanobacterial community dynamics via sedimentary DNA (sedaDNA) from well-dated lake sediments of Lake Tiefer See, which is part of the Klocksin Lake Chain spanning the last 350 years. Our diversity and community analysis revealed that cyanobacterial communities form clusters according to the presence or absence of varves. Based on distance-based redundancy and variation partitioning analyses (dbRDA and VPA) we identified that intensified lake circulation inferred from vegetation openness reconstructions, δ13C data (a proxy for varve preservation) and total nitrogen content were abiotic factors that significantly explained the variation in the reconstructed cyanobacterial community from Lake Tiefer See sediments. Operational taxonomic units (OTUs) assigned to Microcystis sp. and Aphanizomenon sp. were identified as potential eutrophication-driven taxa of growing importance since circa common era (ca. CE) 1920 till present. This result is corroborated by a cyanobacteria lipid biomarker analysis. Furthermore, we suggest that stronger lake circulation as indicated by non-varved sediments favoured the deposition of the non-photosynthetic cyanobacteria sister clade Sericytochromatia, whereas lake bottom anoxia as indicated by subrecent- and recent varves favoured the Melainabacteria in sediments. Our findings highlight the potential of high-resolution amplicon sequencing in investigating the dynamics of past cyanobacterial communities in lake sediments and show that lake circulation, anoxic conditions, and human-induced eutrophication are main factors explaining variations in the cyanobacteria community in Lake Tiefer See during the last 350 years.
      PubDate: 2021-10-01
       
  • Structure-from-motion, multi-view stereo photogrammetry applied to
           line-scan sediment core images

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      Abstract: Images of sediment cores are often acquired to preserve primary color information, before such profiles are altered by subsequent sampling and destructive analyses. In many cases, however, no post-processing of these images is undertaken to extract information, despite the fact that image processing can be used to describe and measure structures within the sample. Improvements of RGB (Red/Green/Blue) cameras and image processing algorithms now enable acquisition of high-resolution, metrically calibrated pictures called ortho-images, which have great potential. The way to obtain such ortho-images is by processing several raw images. We propose a semi-automated method that uses metrically calibrated targets to create the ortho-image, using Agisoft Photoscan software and a Python script. The method was tested on sediment cores up to 1.5 m long. It was compared to an approach without markers, one that uses only image matching. The proposed method showed better resolution and less distortion (GSD: 59 µm, RMSE: 7–18 µm). Images acquired without calibrated targets can still be used, by manually positioning points that can then be metrically calibrated. This approach is very useful for smartphone images taken in the field. There are many potential applications for such images of sediment cores, for instance as metric stratigraphic logs to facilitate description of the profile by unit, to study and measure structures (e.g. laminae, instantaneous deposits), or use of image registration or data fusion to create spatial landmarks for non-destructive sensors or destructive laboratory analyses. High-resolution metrically calibrated RGB images of sediment cores are simple to acquire and can play an important role in paleoclimate and paleoenvironmental studies.
      PubDate: 2021-10-01
       
 
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