Subjects -> PALEONTOLOGY (Total: 46 journals)
Showing 1 - 21 of 21 Journals sorted alphabetically
Acta Palaeontologica Polonica     Open Access   (Followers: 6)
Alcheringa: An Australasian Journal of Palaeontology     Hybrid Journal   (Followers: 7)
Ameghiniana     Open Access   (Followers: 1)
Annales de Paléontologie     Full-text available via subscription   (Followers: 7)
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     Full-text available via subscription  
European Journal of Protistology     Hybrid Journal   (Followers: 6)
EvoDevo     Open Access   (Followers: 4)
Facies     Hybrid Journal   (Followers: 10)
Fossil Record     Open Access   (Followers: 5)
Geobios     Full-text available via subscription   (Followers: 6)
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: 6)
Journal of Paleontology     Hybrid Journal   (Followers: 11)
Journal of Quaternary Science     Hybrid Journal   (Followers: 32)
Journal of Vertebrate Paleontology     Full-text available via subscription   (Followers: 12)
Marine Micropaleontology     Hybrid Journal   (Followers: 2)
Micropaleontology     Full-text available via subscription  
Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen     Full-text available via subscription   (Followers: 4)
Novitates Paleoentomologicae     Open Access   (Followers: 1)
Open Quaternary     Open Access   (Followers: 1)
Palaeogeography, Palaeoclimatology, Palaeoecology     Hybrid Journal   (Followers: 13)
Palaeontology     Hybrid Journal   (Followers: 18)
Palaeoworld     Hybrid Journal   (Followers: 3)
PALAIOS     Hybrid Journal   (Followers: 7)
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: 4)
Paleontological Journal     Full-text available via subscription   (Followers: 5)
Paleontological Research     Full-text available via subscription   (Followers: 3)
Palynology     Hybrid Journal   (Followers: 2)
Papers in Palaeontology     Hybrid Journal   (Followers: 1)
Quaternaire     Open Access   (Followers: 3)
Quaternary Research     Full-text available via subscription   (Followers: 20)
Quaternary Science Reviews     Hybrid Journal   (Followers: 25)
Review of Palaeobotany and Palynology     Hybrid Journal   (Followers: 2)
Revue de Micropaleontologie     Full-text available via subscription  
Rivista Italiana di Paleontologia e Stratigrafia (Research In Paleontology and Stratigraphy)     Open Access   (Followers: 2)
Spanish Journal of Palaeontology     Open Access  
Swiss Journal of Palaeontology     Hybrid Journal   (Followers: 4)
Vertebrate Anatomy Morphology Palaeontology     Open Access   (Followers: 2)
Zitteliana     Open Access   (Followers: 4)
Similar Journals
Journal Cover
Journal of Paleolimnology
Journal Prestige (SJR): 1.019
Citation Impact (citeScore): 2
Number of Followers: 6  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1573-0417 - ISSN (Online) 0921-2728
Published by Springer-Verlag Homepage  [2653 journals]
  • Ecological distribution of Stephanodiscus niagarae Ehrenberg in central
           Mexico and niche modeling for its last glacial maximum habitat suitability
           in the Nearctic realm
    • Abstract: Stephanodiscus niagarae Ehrenberg is currently restricted to specific regions of central Mexico, however, during the late Pleistocene, it had a wider distribution in the country. This change in distribution is similar to those observed for several organisms that migrated southwards during cold, glacial climates, supporting the hypothesis that central Mexico acted as glacial refugia for these species. This study aims to support this hypothesis for S. niagarae as well as to analyze its ecological distribution in modern environments in central Mexico. For this purpose we studied 18 samples from 16 lakes located around Mexico City, selected among 46 lakes along the Trans-Mexican Volcanic Belt. Diatom assemblages in superficial sediments, and climatic, hydrochemistry, and nutrient parameters of each lake were analyzed by means of canonical correspondence analyses. Additionally, we created an ecological niche model (ENM) with modern occurrence data (n = 47) and environmental variables (WorldClim) to produce potential distribution maps of S. niagarae during the present time and under the LGM conditions in the Nearctic realm. S. niagarae was recorded only in 4 sites in central Mexico (abundances < 10%) associated with temperate, subhumid conditions in freshwater lakes with [Mg2+] − [Ca2+] − [HCO3−] ionic dominance and high turbidity, mesotrophic to hypertrophic systems (based on chlorophyll a values), but with a tendency to P-limitation. In our study sites S. niagarae showed low abundances in diatom assemblages dominated by Aulacoseira spp. Temperature (annual mean, coldest and warmest quarters means) was identified by ENM as the main environmental variable controlling its distribution, with its highest modern support in the USA, southern Canada, and a restricted distribution in the highlands of western and central Mexico. Whereas, the LGM scenario (− 5.5 °C) identified the western and central highlands in Mexico and southern USA as the highest probability distribution areas supporting the approach that the Sierra Madre Occidental could have acted as a migration corridor offering suitable habitats for a southward migration into central Mexico during colder (glacial) periods. In conclusion, S. niagarae distribution in the central and western mountains of Mexico is controlled by temperature changes and its presence may be associated with colder (glacial) periods.
      PubDate: 2021-03-12
       
  • A ~ 40-year paleoenvironmental record from the Swan Oxbow, Yangtze
           River, China, inferred from testate amoebae and sedimentary pigments
    • Abstract: We present a ~ 40–year record of environmental change in the Swan Oxbow, Yangtze River, China, inferred from testate amoeba and sedimentary pigment data, combined with remote sensing and analysis of local socio–economic growth. These data indicate there were several distinct phases of aquatic conditions linked to human activities in the region: (1) Between ca. AD 1970 and 1984, there may have been some exchange of water and organic matter between the Swan Oxbow and the main river channel, following initial hydrologic disconnection in 1972. The lake area was relatively large in the early phase after the oxbow first formed, and the trophic state generally increased during that time frame, (2) From ca. AD 1984 to 1992, the lake area was about a third smaller in size, while the human population and GDP increased about 10% and 10x, respectively, compared to values in 1975. The nutrient status (inferred from testate amoeba and pigment data) increased, owing to the greater discharge of nutrients and separation of the Swan Oxbow from the main Yangtze River, which reduced water supply and increased sedimentation in the oxbow, (3) From ca. AD 1992 to 2003, the lake continued to diminish in size, to an area < 20 km2, except in 1998, when a major flood occurred. The testate amoeba and pigment data suggest that water quality had improved by that time, which probably reflects efforts to control agricultural and industrial activities, including establishment of two national reserves in 1992 and 1993, created to protect the rare Père David’s deer (Elaphurus davidianus) and the freshwater Baiji dolphin (Neophocaena phocaenoides asiaeorientalis), (4) From ca. AD 2003 to 2005, the water area remained relatively unchanged, owing to construction of a dam following the 1998 flood. Occurrence of testate amoeba species Difflugia biwae and D. tuberspinifera, however, indicates that water pollution and eutrophication had been controlled in Swan Oxbow. The Swan Oxbow yielded important information about the effects of environmental protection and restoration in the middle reaches of the Yangtze River.
      PubDate: 2021-03-07
       
  • A new diatom training set for the reconstruction of past water pH in the
           Tatra Mountain lakes
    • Abstract: Lakes located in the Polish and Slovak parts of the Tatra Mountains were included in the Tatra diatom database (POL_SLOV training set). The relationship between the diatoms and the water chemistry in the surface sediments of 33 lakes was the basis for the statistical and numerical techniques for quantitative pH reconstruction. The reconstruction of the past water pH was performed using the alpine (AL:PE) and POL_SLOV training sets to compare the reliability of the databases for the Tatra lakes. The results showed that the POL_SLOV training set had better statistical parameters (R2 higher by 0.16, RMSE and max. bias lower by 0.2 and 0.36, respectively) compared to the AL:PE training set. The better performance of the POL_SLOV training set is particularly visible in the case of Przedni Staw Polski where the curve of the inferred water pH shows an opposite trend for the period from the 1960s to 1990 compared to that based on the AL:PE dataset. The reliability of the inferred pH was confirmed by the comparison with current instrumental measurements.
      PubDate: 2021-03-05
       
  • Chironomid assemblage changes and chitin degradation in response
           to ~ 1700-years of seabird population fluctuations at the world’s
           largest colony of Leach’s Storm-Petrels (Atlantic Canada)
    • Abstract: Seabirds are prominent biovectors whose guano and other wastes are an important source of nutrients that can eutrophy terrestrial and aquatic environments surrounding their breeding and nesting habitats. When these ornithogenically derived nutrients are introduced to waterbodies, they alter aquatic conditions, resulting in shifts in benthic invertebrate communities. In this paleolimnological study, we examined subfossil Chironomidae (non-biting midge) assemblages to assess the impacts of changes in the colony size of the Leach’s Storm-Petrel in three ponds on Baccalieu Island (Newfoundland and Labrador, Canada) over the past ~ 1700 years. Our results indicate that chironomids tracked the growth of the storm-petrel colony (determined by five additional paleolimnological proxies) starting in the early-1800s, and the decline of the colony in the 1980s. Given the shallow nature of the study ponds, assemblage changes likely occurred due to a combination of fluctuations in pH, metal concentrations, and bottom-water oxygen. In the ponds influenced by storm-petrels, we observed a poorly described form of degradation in subfossil chironomids that we attribute to chitinolytic processes mediated by bacteria and/or fungi that thrive on organic matter in productive aquatic systems. This study provides complementary proxy data regarding bottom-water habitats for use alongside other established paleolimnological methods to determine the long-term population dynamics of seabirds.
      PubDate: 2021-02-26
       
  • Development of large‐scale sand bodies in a fault‐bounded lake basin:
           Pleistocene-Holocene Poyang Lake, Southern China
    • Abstract: In fault-bounded lacustrine basins, the lake basement may be exposed due to tilting of crustal blocks, forming islands of varying size. Such islands are commonly associated with sandy facies that may serve as important reservoirs for oil and gas accumulation. The present study investigated large sand bodies of Pleistocene-Holocene age on Songmenshan Island in the center of Poyang Lake, Jiangxi Province, southern China. The relationship of sedimentation on Songmenshan Island to its formation history was analyzed by means of Google satellite observations and field studies combined with scanning electron microscope, grain size, and 14 C dating analyses. The area of Songmenshan Island (39 km2) represents 8% of the total lake area (500 km2), and its height (81 m) is several times greater than that of the depth of the surrounding lake (13 m). The island has been uplifted since ~ 5 Ma at a rate of ~ 16 m Myr− 1 as a consequence of intrabasinal block faulting. The surficial deposits of the island consist of wave-controlled beach-bars in the lower part (< 36 m elevation) and wind-controlled eolian dunes in the upper part. Sedimentary characteristics were different between beach bars and sand dunes in terms of bedding, sedimentary structures, and grain size and texture. The beach bars are characterized by low-angle cross-bedding, fan-shaped conchoidal, and disciform fractures, and small V-shaped impact craters on quartz grain surfaces. The eolian dunes are characterized by large-scale high-angle cross-bedding, dish-, crescent-, and V-shaped impact craters on quartz grain surfaces. Whereas sand movement in the beach-bar facies was dominantly through traction, saltation was the major process in the eolian dune environment. The depositional history of Songmenshan Island can be divided into 3 stages: (1) deltaic sedimentation from the Ganjiang and Xiushui rivers, which are connected to the Yangtze River via a channel; (2) wave reworking of deltaic sediments in shoreline beach-bar facies after initial uplift; and (3) wind reworking of sands in eolian dune facies following further uplift. Later in its history, Songmenshan Island was reduced through wind and wave erosion into two subequal parts (19.6 km2 and 19.8 km2), producing its present configuration. The large sand bodies comprising this island may eventually be buried in a cocoon of organic-rich lacustrine muds, yielding an exploration target. Songmenshan Island may thus serve as a model for development of sand-rich reservoir facies in fault-bounded lacustrine basins.
      PubDate: 2021-02-16
       
  • Cyclostratigraphy and paleoenvironmental inference from downhole logging
           of sediments in tropical Lake Towuti, Indonesia
    • Abstract: Lake Towuti is located on central Sulawesi/Indonesia, within the Indo Pacific Warm Pool, a globally important region for atmospheric heat and moisture budgets. In 2015 the Towuti Drilling Project recovered more than 1000 m of drill core from the lake, along with downhole geophysical logging data from two drilling sites. The cores constitute the longest continuous lacustrine sediment succession from the Indo Pacific Warm Pool. We combined lithological descriptions with borehole logging data and used multivariate statistics to better understand the cyclic sequence, paleoenvironments, and geochronology of these sediments. Accurate chronologies are crucial to analyze and interpret paleoclimate records. Astronomical tuning can help build age-depth models and fill gaps between age control points. Cyclostratigraphic investigations were conducted on a downhole magnetic susceptibility log from the lacustrine facies (10–98 m below lake floor) from a continuous record of sediments in Lake Towuti. This study provides insights into the sedimentary history of the basin between radiometric ages derived from dating a tephra layer (~ 797 ka) and C14-ages (~ 45 ka) in the cores. We derived an age model that spans from late marine isotope stage (MIS) 23 to late MIS 6 (903 ± 11 to 131 ± 67 ka). Although uncertainties caused by the relatively short record and the small differences in the physical properties of sediments limited the efficacy of our approach, we suggest that eccentricity cycles and/or global glacial-interglacial climate variability were the main drivers of local variations in hydroclimate in central Indonesia. We generated the first nearly complete age-depth model for the lacustrine facies of Lake Towuti and examined the potential of geophysical downhole logging for time estimation and lithological description. Future lake drilling projects will benefit from this approach, since logging data are available just after the drilling campaign, whereas core descriptions, though more resolved, only become available months to years later.
      PubDate: 2021-02-12
       
  • Long-term ecosystem change in two highly degraded Lake Ontario (Canada)
           coastal wetlands
    • Abstract: Coastal wetlands are essential to the ecosystem health of the Laurentian Great Lakes (North America) watershed. Multiple anthropogenic stressors have been impacting coastal wetlands since European settlement ca. 1850, and remain a concern for wetland health as watershed development intensifies. We used paleolimnological techniques to explore temporal ecosystem dynamics over the last ~ 100 years in two highly degraded Lake Ontario coastal wetlands located in southern Ontario, Canada, using Cladocera (Branchiopoda, Crustacea) subfossil remains as paleoecological indicators. In Cootes Paradise Marsh (Hamilton, Ontario), cladoceran assemblage changes exhibited a shift in dominance from Chydorus to Bosmina, at the turn of the twentieth century. That shift likely reflected the loss of aquatic macrophytes, and corresponds to the postulated timing of the arrival of invasive carp. Despite recent remediation efforts, including attempts to exclude carp from the wetland, little ecological recovery is evident from the subfossil Cladocera assemblage. No Daphnia remains were observed in our sediment core from Cootes Paradise, in contrast to previous studies on extant zooplankton communities, which reported a large Daphnia population in the west end of the marsh in the 1940s. This could indicate that our sediment core recorded ecological changes solely in the east end of Cootes Paradise Marsh. In Jordan Harbour (Lincoln, Ontario), Bosmina were dominant throughout the sediment record, and increases in littoral cladocerans were observed in the most recent sediments, in particular the appearance of periphytic Pleuroxus taxa after ~ 2008. This suggests that some recovery of aquatic macrophyte communities occurred in response to shoreline remediation efforts. Bosmina size structure exhibited only minimal changes in both wetlands, despite known large changes in historic fish community structure. Overall, our study provides perspectives on the benefits and limitations of paleolimnology for documenting ecological change in the Laurentian Great Lakes coastal wetlands.
      PubDate: 2021-02-09
       
  • A method for reconstructing past lake water phosphorus concentrations
           using sediment geochemical records
    • Abstract: An existing steady state model of lake phosphorus (P) budgets has been adapted to allow reconstruction of long-term average historic lake water total phosphorus (TP) concentrations using lake sediment records of P burial. This model can be applied without site-specific parameterisation, thus potentially having universal application. In principle, it is applicable at any site where there is both a sediment P burial record and knowledge of the current water budget, although we advise caution applying it to problematic sediment records. Tested at six published case study sites, modelled lake water TP concentrations agree well with water-quality monitoring data, and limited testing finds good agreement with wholly independent diatom inferred lake water TP. Our findings, together with a review of the literature, suggest that well preserved lake sediments can usefully record a long-term average P burial rate from which the long-term mean lake water TP can be reliably estimated. These lake water TP reconstructions can provide meaningful site-specific reference values to support decision making in lake eutrophication management, including establishing targets for lake restoration.
      PubDate: 2021-02-05
       
  • Enhanced middle Holocene organic carbon burial in tropical floodplain
           lakes of the Pantanal (South America)
    • Abstract: Wetland carbon storage is an important and environmentally sensitive ecosystem service. Carbon burial in the floodplain lakes of the Pantanal (tropical South America) appears to have varied during the late Quaternary, but several paleolimnological studies have recorded unusually high sediment organic carbon content from ~ 7.3 to 6.0 cal kyr BP in lakes connected to the Upper Paraguay River. We conducted a multi-indicator (phytoliths, sponge spicules, and geochemistry) study of a sediment core from Lake Cáceres (Bolivia), and found evidence for enhanced organic carbon burial during the middle Holocene that provides insights into the flooding history of the Upper Paraguay River. δ13Corg and C/N data suggest that organic matter deposited at that time in Lake Cáceres was from macrophytes. Similar datasets from three other floodplain lakes are consistent with this finding. We suggest that enhanced carbon burial occurred when lake levels declined under relatively dry climate conditions, which increased the littoral area at the expense of open water and captured floating macrophyte islands. This study sheds new light on hydroclimate controls on carbon cycling in the Pantanal wetlands, and improves interpretations of geochemical measures on bulk organic matter in floodplain lake cores.
      PubDate: 2021-02-01
      DOI: 10.1007/s10933-020-00159-5
       
  • Recent climate-driven ecological changes in tropical montane lakes of
           Rwenzori Mountains National Park, central Africa
    • Abstract: Rwenzori Mountains National Park, which straddles the border between the Democratic Republic of Congo and Uganda, has experienced rapid glacier loss since the beginning of the twentieth century, yet there has been little investigation of aquatic biodiversity change in the park. This study presents a paleolimnological analysis from Lake Mahoma (2990 m asl), which is situated in the bamboo-forest transition zone. Diatom and organic geochemistry data from a 39-cm-long sediment core with a basal age of c. 1715 CE were compared with new analyses of previously published data from Lakes Bujuku (3891 m asl) and Lower Kitandara (3989 m asl), in the alpine zone. Comparisons were made to determine if aquatic ecosystem changes exhibited similar inter-lake patterns over the past ~ 150 years of climate warming and glacial recession, or if only local change was apparent. The diatom flora of Lake Mahoma is acidophilous, dominated by Aulacoseira ikapoënsis since at least the mid eighteenth century. In recent decades, the obligate nitrogen-heterotroph Nitzschia palea increased in importance, concurrent with declining δ15Norg values. We suggest that these late twentieth century changes were linked to regional warming and increased thermal stratification of Lake Mahoma. Regional comparisons of the Rwenzori lakes were done using existing organic geochemistry records (total organic carbon, C/N and δ13Corg) and through diatom compositional turnover analyses, and categorisation of species into one of four diatom growth morphology traits, or guilds: tychoplanktonic, high-profile, low-profile and motile. Over the past 150 years, all three lakes showed unidirectional, compositional diatom turnover, indicating that deterministic processes had affected diatom communities. Declining turnover at each site is broadly mirrored by an increase in tychoplanktonic taxa, along with concomitant declines in high-profile diatoms at Lake Mahoma, and low-profile diatoms at Lake Bujuku, and at least for the past 60 years, at Lower Kitandara. The interplay between diatom guilds at all sites is mainly a consequence of competition for available resources. Sediment organic carbon at all sites comes from both autochthonous and allochthonous sources, the relative abundances of which are influenced by the time elapsed since lakes had glaciers in their catchment.
      PubDate: 2021-02-01
      DOI: 10.1007/s10933-020-00161-x
       
  • Reconstructing Holocene landscape and environmental changes at Lago
           Rogaguado, Bolivian Amazon
    • Abstract: We performed geochemical analyses of two lake sediment cores (1.25 and 1.5 m long) from Lago Rogaguado, which is a large (315 km2) and shallow lake in the Llanos de Moxos, Bolivian Amazon, to investigate Holocene environmental changes based on a multi-proxy dataset (XRF, density, grain size, C:N, and macrocharcoal). One of the two cores provides a history of environmental changes in the Llanos de Moxos from 8100 cal BP until present, which supplements previously published pollen and microscopic charcoal records. Our analyses indicate lake expansion at 5800 cal BP, which may relate to tectonic activity. This was followed by further increasing lake levels, peaking at approximately 1050–400 cal BP, which supports increasingly wetter conditions in the Llanos de Moxos after the mid-Holocene. A fourfold increase in macroscopic charcoal accumulation rate and a more than fivefold increase in sedimentation rates supports anthropogenic fire activity at around 1450 cal BP (500 CE), suggesting that pre-Columbian populations used fire to actively manage the landscape during a period of maximum lake levels around Lago Rogaguado. From 400–100 cal BP, higher C:N, larger grain sizes and peaks in macroscopic charcoal accumulation rates suggest increased watershed erosion associated with increased biomass burning, possibly related to intensified land use.
      PubDate: 2021-02-01
      DOI: 10.1007/s10933-020-00164-8
       
  • Building upon open-barrel corer and sectioning systems to foster the
           continuing legacy of John Glew
    • Abstract: The late John Glew contributed valuable equipment to the paleolimnology community for successful collection and processing of cores of sediment from aquatic ecosystems. Unfortunately, tubes that fit his hammer-gravity corer design are no longer conveniently available for purchase and, with his sudden passing, Glew gravity and coring equipment is difficult or impossible to access. In some field-sampling situations, other commercially available equipment present limitations. Here, we provide an updated design of the Glew gravity corer which accommodates a hammer-percussion instrument and overcomes limitations we have encountered when coring lakes in remote locations from floats of a helicopter or small, inflatable watercraft. Our approach integrates the ‘best of both worlds’ provided by the Glew and commercially available Uwitec designs, using readily available components. We updated the Glew corer tube collar to be compatible with standard, commercially available 90-mm external diameter (86-mm internal diameter) PVC tubing that fits Uwitec components (e.g., Uwitec rubber ‘piston’ and ‘stoppers’; using terminology of the Uwitec catalogue), and designed a spring-loaded gasket-style plunger that achieves greater suction than the standard Glew designs. We also updated the Glew vertical sectioner to be compatible with 90-mm-diameter core tubes typically ranging from 60–120 cm long. An outcome is consolidation of the Uwitec and Glew gravity coring systems, which has allowed for interchangeability and choice among use of original and hammer-driven Glew, Uwitec, and the new hybrid ‘Uwi-Glew-ee’ gravity corer and sectioner configurations, depending on logistical constraints of fieldwork and anticipated lake sediment composition. The parts and systems are available from University of Waterloo’s Science Technical Services (https://uwaterloo.ca/science-technical-services/).
      PubDate: 2021-02-01
      DOI: 10.1007/s10933-020-00162-w
       
  • A 450-year record of environmental change from Castle Lake, California
           (USA), inferred from diatoms and organic geochemistry
    • Abstract: A 39-cm sediment core from Castle Lake, California (USA) spans the last ~ 450 years and was analyzed for diatoms and organic geochemistry (δ15N, δ13C, and C:N), with the goal of determining sensitivity to natural climate variation and twentieth century anthropogenic effects. Castle Lake is a subalpine, nitrogen-limited lake with ~ 5 months of annual ice cover. Human impacts include light recreational use, past fish stocking, and experimental use by the Castle Lake Research Station. The base of the core (below 32 cm; pre mid-1700s) represents the period of maximum ice cover. In contrast, the end of the Little Ice Age (mid 1700s–early 1800s) is dominated by cyclotelloids (mostly Discostella stelligera), indicating significant open-water periods, a condition that persisted into the early 1900s. Cyclotelloids began to decline in the 1960s and were replaced by the Fragilaria tenera grp. (peak in 1970s), succeeded by Asterionella formosa (peak ~ 2010), and accompanied by a reduction in δ15N values and a decrease in C:N that may represent increased atmospheric nitrogen deposition. Another anthropogenic signal was discerned in the core and was interpreted to be the result of an ammonium nitrate fertilization experiment of the epilimnion that was conducted in 1980 and 1981. This signal was manifested in the core largely by a negative excursion in δ15N, possibly caused by fractionation during denitrification in surface sediment. A phytoplankton monitoring dataset collected by the Castle Lake Research Station from 1967 to 1984 corroborates the timing of increased araphid euplanktonic species in the 1970s, and increases in two benthic diatoms (Staurosirella pinnata and Tabellaria fenestrata), entrained in the phytoplankton tows during the experimentation years. Both ice cover and nitrogen addition appear to be strong drivers that affected the lake diatoms, although additional drivers, such as fish stocking and associated cascade effects need further exploration. These data will be helpful for interpreting longer core records from Castle Lake, should the opportunity arise, as well as cores from similar systems in the region.
      PubDate: 2021-02-01
      DOI: 10.1007/s10933-020-00160-y
       
  • Palaeohydrological changes recorded from a small Moroccan Middle Atlas
           pond during the last 6000 cal. yr BP: a multi-proxy study
    • Abstract: The perennial and seasonal wetland diversity of the Moroccan Middle Atlas region provides a valuable “test-bed” for understanding the response of different hydrosystems to climatic variations. A multiproxy study, based on sedimentological descriptions, together with mineralogy, carbonate content, XRF core scanning and biological proxies supported by AMS 14C dates, were applied to the 3-m-long core extracted from “Flowers Marsh”, a small Middle Atlas pond. This approach provides evidence for a continuous paleohydrological and paleoenvironmental record during the Mid- to Late Holocene. The investigated aquatic system evolved from a dry or very shallow waterbody towards a system with a progressively rising water level. The dominance of the detrital fraction with poor preservation of bioindicators and eroded pollen, indicate the existence of an ephemeral waterbody from 6000 cal. yr BP until a transitional phase characterized by new sedimentological facies and the appearance of ostracods around 2300 cal. yr BP. This transition, ending at 2000 cal. yr BP, is interpreted as a flooding phase leading to an ephemeral lake. It is certainly fed by the excess water from the nearby Aguelmam Azigza Lake during its high level period. Afterwards, enhanced organic matter deposition and the appearance of well-preserved diatoms until 1400 cal. yr BP corroborate a high water-level trend. Endogenic carbonate to detrital fraction ratios indicate fluctuating, but generally shallow, water levels from 1400 cal. yr BP until 650 cal. yr BP when a relatively rapid rise in water level occurred. Flowers Marsh data are, generally, consistent with most of the existing regional records. The highstand period recorded between 2000 and 1400 cal. yr is a common feature extending to more distant sites from the northern Mediterranean. It corresponds to the wetter Iberian-Roman period. Fluctuating shallow water levels recorded since 1400 cal. yr BP to now could be linked to drier/wetter phases associated with the Medieval Climate Anomaly and the Little Ice Age (650– 150 cal. yr BP) respectively, in the western Mediterranean realm. The present study demonstrates the ability of Flowers Marsh to record valuable palaeohydrological changes since the Mid-Holocene and confirms the high sensitivity of Middle Atlas hydrosystems to climatic changes.
      PubDate: 2021-01-28
      DOI: 10.1007/s10933-020-00166-6
       
  • Reframing Lake Geneva ecological trajectory in a context of multiple but
           asynchronous pressures
    • Abstract: Regime shifts are major reorganization of ecological processes, creating new sets of mechanisms that drive the new ecological regime. Such rearrangements can affect how and how much the system responds to pressures other than those that created the shift (interactive carryover). Lake Geneva still exhibits high levels of productivity despite reductions in phosphorus to its reference baseline; the continued high productivity is likely due to the synergistic effects of climate change. We tested whether the contemporary Lake Geneva plankton community response to air temperature, one symptom of climate change, differed from the responses to past changes in air temperature. We used paleoecology to quantify the changes in plankton communities, as a proxy of general ecological changes, over the past 1500 years. Our results show that from 563 AD (beginning of the record) to the twentieth century, the cladoceran assemblage remained stable, despite climate variability of 3 °C in air temperature. The plankton community of Lake Geneva appeared to shift for the first time in the 1500 year record in 1946, and dynamic linear models suggested that 1958–1961 was a critical transition period when the ecosystem changed state. Littoral species were lost, and the assemblage became dominated by pelagic species. The shift took place around the beginning of the current long-term monitoring program, when local perturbations (eutrophication) were escalating. Our results suggest that eutrophication acted as a switch towards a lake more vulnerable to climate change.
      PubDate: 2021-01-27
      DOI: 10.1007/s10933-021-00176-y
       
  • Effects of climate change and industrialization on Lake Bolshoe Toko,
           eastern Siberia
    • Abstract: Industrialization in the Northern Hemisphere has led to warming and pollution of natural ecosystems. We used paleolimnological methods to explore whether recent climate change and/or pollution had affected a very remote lake ecosystem, i.e. one without nearby direct human influence. We compared sediment samples that date from before and after the onset of industrialization in the mid-nineteenth century, from four short cores taken at water depths between 12.1 and 68.3 m in Lake Bolshoe Toko, eastern Siberia. We analyzed diatom assemblage changes, including diversity estimates, in all four cores and geochemical changes (mercury, nitrogen, organic carbon) from one core taken at an intermediate water depth. Chronologies for two cores were established using 210Pb and 137Cs. Sedimentation rates were 0.018 and 0.033 cm year−1 at the shallow- and deep-water sites, respectively. We discovered an increase in light planktonic diatoms (Cyclotella) and a decrease in heavily silicified euplanktonic Aulacoseira through time at deep-water sites, related to more recent warmer air temperatures and shorter periods of lake-ice cover, which led to pronounced thermal stratification. Diatom beta diversity in shallow-water communities changed significantly because of the development of new habitats associated with macrophyte growth. Mercury concentrations increased by a factor of 1.6 since the mid-nineteenth century as a result of atmospheric fallout. Recent increases in the chrysophyte Mallomonas in all cores suggested an acidification trend. We conclude that even remote boreal lakes are susceptible to the effects of climate change and human-induced pollution.
      PubDate: 2021-01-23
      DOI: 10.1007/s10933-021-00175-z
       
  • Middle Pleistocene to recent diatoms and stratigraphy of the Magadi Basin,
           south Kenya Rift
    • Abstract: Two cores were recovered from the Lake Magadi and Nasikie Engida Basins in the south Kenya Rift. Core MAG14-2A (194 m) contains a middle Pleistocene to Holocene record, whereas core NAS15/19 (4.36 m) covers only the late Holocene. Surficial sediments from springs and shallow-water sites were sampled in both basins. MAG14-2A rests on trachyte dated at 1.08 Ma. Diatoms are rare in the oldest sediments, but well preserved after about 545 ka, documenting a trend from less to more saline water. Core MAG14-2A contains fifteen facies, five of which are diatomaceous. In contrast, NAS15/19 is dominated by two facies, each containing well-preserved diatoms. Both sequences are distinct from others of similar age in the Kenya Rift in lacking pedogenic horizons, reflecting the location of Lake Magadi and Nasikie Engida in a tectonic sump where aquatic environments were maintained by geothermal and meteoric springs. Canonical Correspondence Analysis distinguishes three assemblages in the modern surface muds of Lake Magadi and Nasikie Engida, but with no pre-Holocene counterparts. Eleven diatom zones are recognised in MAG14-2A: Zones D2 to D10 contain rare to common diatoms dominated by Aulacoseira granulata and its varieties, Aulacoseira agassizii, Thalassiosira faurii, Thalassiosira rudolfi and Cyclotella meneghiniana. Individual samples commonly include a mixture of benthic and planktonic taxa and saline and freshwater species. These assemblages indicate waters that ranged between pH 7.4 and 11.5 with conductivities of ~ 300 to > 25,000 μS cm−1. Correlations with the neighbouring Olorgesailie and Koora Basins indicate four major environmental phases that affected the south Kenya Rift during the last million years with fresh to moderately saline water, or land surfaces, developing during Phase I (1000 to 750 ka). These environments gave way to generally wetter conditions and freshwater lakes in all basins during Phase II (~ 750 to 500 ka). Phase III (~ 500 to 325 ka) was characterised by drier conditions with paleoenvironments becoming more variable and dry during Phase IV (325 ka to present).
      PubDate: 2021-01-18
      DOI: 10.1007/s10933-020-00173-7
       
  • Paleolimnological studies on the East European Plain and nearby regions:
           the PaleoLake Database
    • Abstract: The PaleoLake Database contains available information on the lithostratigraphy, biostratigraphy and chronostratigraphy of bottom sediments from numerous lakes located on the East European Plain and nearby regions. The database includes results from more than 70 years of paleolimnological investigations, with information on deposits from 287 water bodies. The compiled data were published mainly in Russian and come from more than 145 monographs, journal articles, dissertations, abstracts, reports and other sources that were difficult to access by the broader science community.
      PubDate: 2021-01-09
      DOI: 10.1007/s10933-020-00172-8
       
  • Long-term primary production trends in the Laurentian Great Lakes: a
           comparison of geochemical methods
    • Abstract: Sediment cores from 12 locations throughout the Laurentian Great Lakes basin were analyzed for geochemical indicators of primary production. Sediment analytes included organic and inorganic contents, carbonates, sediment accumulation rates, total organic carbon and nitrogen concentrations, carbon and nitrogen isotope composition, and trends in spectroscopically inferred chlorophyll a (and its main diagenetic products). When multiple indicators were considered, production records related to recent cultural eutrophication and catchment activities were clear in the paleorecords. Indicators derived from loss-on-ignition (organic and inorganic content) were strongly associated with periods of human settlement in the catchments that increased overall sediment loads to the lakes. The ratio of carbon to nitrogen tracked catchment inputs of carbon, especially during periods of watershed development in western Lake Superior. Sediment records such as chlorophyll a and δ13Corg appear to be reliable indicators of trends in past algal abundance, particularly in Lake Erie, which has a well-known history of higher production and cultural eutrophication. These analytes also correlated well with past measured water quality surrogates for lake primary productivity and stressor data such as human populations in adjacent watersheds. A comparison among indicators revealed that several show redundancy as good proxies of production or productivity, though context was important. For instance, heavier isotopes of carbon and nitrogen are often prescribed as sedimentary indicators of lake productivity, but these two analytes were negatively correlated in Lake Superior, possibly due to long-term increases in cyanobacteria or changes in the nitrogen source. An increase in sediment carbonates can indicate summer blooms of cyanobacteria (a phenomenon that was clearly apparent in Lake Ontario) or catchment erosion. To make convincing geochemical inferences of primary production in the Great Lakes, it is recommended that a weight of evidence be built through the use of multiple indicators.
      PubDate: 2021-01-04
      DOI: 10.1007/s10933-020-00170-w
       
  • Impacts of Norse settlement on terrestrial and aquatic ecosystems in
           Southwest Iceland
    • Abstract: Norse colonization of North Atlantic islands in the 1st millennium of the Common Era led to drastic prehistoric environmental changes in these previously “pristine” landscapes. In Iceland, Norse settlement is associated with a rapid decline in birch trees and heightened soil erosion, yet the timing of Norse exploration in the North Atlantic coincided with large climate changes that also influenced Icelandic environments. To date, there are few records that disentangle climatic and human impacts on terrestrial ecosystems, and there has been very little work on the impacts of Norse arrival on Iceland’s aquatic ecosystems. Here we use a high-resolution lake-sediment record from Vestra Gíslholtsvatn (VGHV), southwest Iceland to investigate these processes during the last 2,000 years. Norse arrival (c. 870 CE) in Iceland is followed by a rapid increase in sedimentation rate and a transition in leaf wax n-alkanes indicating a decrease in trees and expansion of grasses. This transition coincides with limnological changes, including increased primary productivity (i.e. C17 n-alkane and biogenic opal fluxes) and shifts in the haptophyte algal community. Many of these changes are still apparent today. Comparisons with a new winter-spring alkenone temperature reconstruction from VGHV and marine sea surface temperature records show little to no correlation between terrestrial and aquatic ecological changes and climate at this time. Similarly, volcanic eruptions recorded in VGHV are not associated with any long-term environmental changes. Rather, the VGHV record suggests that human settlement had a lasting impact on the catchment area of VGHV and changes within the lake ecosystem.
      PubDate: 2021-01-04
      DOI: 10.1007/s10933-020-00169-3
       
 
JournalTOCs
School of Mathematical and Computer Sciences
Heriot-Watt University
Edinburgh, EH14 4AS, UK
Email: journaltocs@hw.ac.uk
Tel: +00 44 (0)131 4513762
 


Your IP address: 3.230.173.249
 
Home (Search)
API
About JournalTOCs
News (blog, publications)
JournalTOCs on Twitter   JournalTOCs on Facebook

JournalTOCs © 2009-