Subjects -> PALEONTOLOGY (Total: 46 journals)
 Showing 1 - 21 of 21 Journals sorted alphabetically Acta Palaeontologica Polonica       (Followers: 6) Alcheringa: An Australasian Journal of Palaeontology       (Followers: 7) Ameghiniana       (Followers: 1) Annales de Paléontologie       (Followers: 7) Annals of Carnegie Museum       (Followers: 1) Boreas: An International Journal of Quaternary Research       (Followers: 12) Comptes Rendus Palevol European Journal of Protistology       (Followers: 6) EvoDevo       (Followers: 4) Facies       (Followers: 10) Fossil Record       (Followers: 5) Geobios       (Followers: 6) Historical Biology: An International Journal of Paleobiology       (Followers: 9) Ichnos: An International Journal for Plant and Animal Traces International Journal of Speleology       (Followers: 3) Journal of Paleolimnology       (Followers: 6) Journal of Paleontology       (Followers: 11) Journal of Quaternary Science       (Followers: 32) Journal of Vertebrate Paleontology       (Followers: 12) Marine Micropaleontology       (Followers: 2) Micropaleontology Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen       (Followers: 4) Novitates Paleoentomologicae       (Followers: 1) Open Quaternary       (Followers: 1) Palaeogeography, Palaeoclimatology, Palaeoecology       (Followers: 13) Palaeontology       (Followers: 18) Palaeoworld       (Followers: 3) PALAIOS       (Followers: 7) Paläontologische Zeitschrift       (Followers: 4) Paleobiology       (Followers: 6) PaleoBios       (Followers: 1) Paleoceanography and Paleoclimatology       (Followers: 4) Paleontological Journal       (Followers: 5) Paleontological Research       (Followers: 3) Palynology       (Followers: 2) Papers in Palaeontology       (Followers: 1) Quaternaire       (Followers: 3) Quaternary Research       (Followers: 20) Quaternary Science Reviews       (Followers: 25) Review of Palaeobotany and Palynology       (Followers: 2) Revue de Micropaleontologie Rivista Italiana di Paleontologia e Stratigrafia (Research In Paleontology and Stratigraphy)       (Followers: 2) Spanish Journal of Palaeontology Swiss Journal of Palaeontology       (Followers: 4) Vertebrate Anatomy Morphology Palaeontology       (Followers: 2) Zitteliana       (Followers: 4)
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 Journal of PaleolimnologyJournal Prestige (SJR): 1.019 Citation Impact (citeScore): 2Number of Followers: 6      Hybrid journal (It can contain Open Access articles) ISSN (Print) 1573-0417 - ISSN (Online) 0921-2728 Published by Springer-Verlag  [2656 journals]
• Factors that controlled deposition of lacustrine, mixed
siliciclastic-carbonate sediments in the upper fourth member of the Eocene
Shahejie Formation in the Zhanhua Sag, East China
• Abstract: The Zhanhua Sag is located in the east-central Jiyang Depression, southern Bohai Bay, northeast China, and is a half-graben, lacustrine basin. Mixed siliciclastic-carbonate sediments are quite common in Eocene deposits of the Zhanhua Sag. We established characteristics of the lithofacies, facies associations, and depositional environments of the upper fourth member of the Eocene Shahejie Formation in the Zhanhua Sag, using core descriptions, thin sections and well logging data. Mixed grainstones and mixed wackestones are two lithofacies of mixed sediments identified in the study area. Paleogeomorphology, sediment supply and gravity flows jointly controlled development of the mixed sediments in this study. Subaqueous highs, formed by terrigenous clastic sediments, provided substrates for carbonate production. The Ordovician carbonate strata exposed on both sides of the rise provided the material for carbonate production on the north and south sides. The clastic sediment supply, however, developed mainly on the south side. Less siliciclastic influx in the north was probably associated with weakening of tectonic activity and less topographic difference. Massive mixed sediments were the product of gravity flows developed under low-energy hydrodynamic conditions between the carbonate shoals and a deltaic system. Most of the siliciclastic material in the mixed sediments was transported by gravity flows from the fan delta to lows in a shallow lake.
PubDate: 2021-06-01

• Seasonal deposition of authigenic calcite out of isotopic equilibrium with
DIC and water, and implications for paleolimnological studies
• Abstract: We conducted year-round, monthly monitoring of the stable isotope composition of DIC and water in hypereutrophic Lake Kierskie, western Poland, along with isotope measures of calcite collected in sediment traps installed at 16 and 30 m water depth in the lake. Isotope data were supplemented by previously published data on physico-chemical variables in the lake water column. We sought to determine how carbon and oxygen isotopic disequilibria in calcite deposited in the lake’s laminated sediments vary seasonally, and what factors drive this variability. Deposition of calcite out of equilibrium with DIC and water was documented over the entire study period. For δ18O, the disequilibrium difference between successive months far exceeded the amplitude of the seasonal variability in the isotope composition of water. The biggest difference between the measured and calculated δ13Ccalcite and δ18Ocalcite values was observed during late autumn and winter sediment resuspension and redeposition (2.4‰ and 5.4‰, respectively). In the spring, δ13Ccalcite and δ18Ocalcite offsets from equilibria, 0.5‰ and 1.3‰, respectively, resulted from rapid precipitation of large calcite crystals. During summer, intense productivity and processes related to calcifying algae (“vital effects”) caused lower δ13C (0.5–1.8‰) and δ18O (2.8–2.9‰) in calcite. Differences between isotope values of calcite collected from the two water depths were small, and might have resulted from different settling velocities of small and large crystals, and/or preferential dissolution of smaller grains. We suggest that winter laminae should be excluded from isotope studies of varved sediments whenever possible, as they likely contain redeposited carbonate in which the isotope value is not indicative of conditions in the lake at the time of laminae formation. We also recommend supplementing isotope analysis of calcite in varved lake sediments with seasonally resolved analysis of carbonate content. It appears that major shifts in the proportion of carbonate deposited across seasons can cause notable changes in mean annual values of δ18Ocalcite and δ13Ccalcite, even if DIC and water isotopic compositions remain stable.
PubDate: 2021-06-01

• Organic carbon accumulation in oligotrophic coastal lakes in southern
Brazil during the last century
• Abstract: We report organic carbon (OC) accumulation rates in three freshwater ecosystems in southern Brazil, along the largest shallow coastal lagoon ecosystem in the world, the Patos-Mirim-Mangueira. After European colonisation in the seventeenth century, regional wetlands started being replaced by agricultural fields (mostly rice). We used excess 210Pb to develop chronologies for lagoon sediment cores and quantify bulk sediment and OC accumulation rates. In the past 120 years, OC accumulation rates in Mirim and Mangueira Lagoons, which are influenced by rice paddies, averaged 14.9 ± 8.5 and 6.4 ± 3.7 g C m−2 year−1, respectively. Greater accumulation rates were estimated for macrophyte-dominated Nicola Lake (69.9 ± 38.5 g C m−2 year−1) located within the protected Taim Wetland with no direct influence of rice plantations. Starting in the early twentieth century, the construction of dams and drainage canals altered regional hydrology. Despite these anthropogenic changes, only a mild increase in OC accumulation was observed in Mirim Lagoon (15% only in site MIR2) after 1970. Mangueira Lagoon experienced the lowest OC burial rates despite increasing sedimentation rate and OC burial after the mid-1970s. This is probably because these large lakes (> 500 km2) have great nutrient-dilution potential, and their well-mixed water columns prevent nutrients from accumulating in the sediments over time.
PubDate: 2021-06-01

• Effects of recent climate and environmental changes on the ecology of a
boreal forest lake in Manitoba, Canada
• Abstract: Application of paleoenvironmental approaches provides insight into the magnitude and timing of responses to climate warming in aquatic-ecosystems of northern Canada. We examined subfossil biological (Diptera:Chironomidae) and geochemical indicators (organic carbon and elemental nitrogen and stable isotope composition) in a sediment core from Buckland Lake, northern Manitoba, to assess the influence of recent warming (1981–2011) in the central subarctic region of Canada. The earlier part of the paleolimnological record (1830–1980) was characterized by relatively low chironomid diversity (N2 ~ 6), consisting primarily of profundal taxa (Orthocladius consobrinus and Chironomus), low organic matter content of sediments (< 12%), low C:N ratios (< 9), and high δ15N values (> 3‰), indicative of a cold-water environment with low nitrogen demand. Between 1910 and 1980, there was a decline in profundal taxa, with small gradual increases in littoral taxa, such as Cladotanytarsus mancus-group. Post-1980 sediment core intervals had distinct geochemistry, with declines in δ13Corg from − 27.5‰ to almost − 29‰, consistent with warming, increased terrestrial influence, and increased snowfall and runoff. We found substantial inferred warming (+ 1–2 °C), with several chironomid-inferred temperatures nearly 3 °C warmer than typical pre-1980 inferences. Concurrently, several warm-water-adapted littoral chironomid taxa (Cladopelma, Cryptochironomus, Polypedilum) recorded increases. The post-1990 records reflected continued increases in warm-water taxa, changes in the benthic:pelagic trophic structure, and reversal of previous trends in the δ13Corg, %Organic Carbon, and δ15N profiles, suggestive of increased aquatic productivity. The meteorological station at Gillam, Manitoba, also recorded warming (1.5 °C) and a reduction in snowfall during that time period. A reduction in spring recharge may have increased littoral habitat associated with lake-level drawdown. The climate-driven shift observed ~ 1980 is in generally good agreement with other regional analyses, which show regime shifts occurred ~ 1995. The earlier lake response (~ 1980), however, demonstrates the role of increased catchment-mediated influences on northern boreal lake productivity that may only appear in records with sufficiently high resolution and multiple paleolimnological indicators.
PubDate: 2021-06-01

• Correction to: Experimental determination of the temperature dependence of
oxygen-isotope fractionation between water and chitinous head capsules of
chironomid larvae
• Abstract: A correction to this paper has been published: https://doi.org/10.1007/s10933-021-00196-8
PubDate: 2021-05-04

• Structure and dynamics of a Pampa plain, (Argentina) shallow lake over the
last 600 years
• Abstract: A multi-proxy analysis, including pollen, non-pollen palynomorphs and plant macrofossil remains was performed to reconstruct the paleoenvironmental history of the Cabeza de Buey shallow lake (36°17′S, 61°10′W) over the last 600 years. We identified the main forcing factors behind changes in the structure and dynamics of the lake communities. Given the relatively low intensity of human activity during the early period of the lake history (prior to 1880 AD), changes in dominant communities were mainly controlled by climate. Afterwards, changes probably resulted from a combination of climate and human impacts that generated an accelerated eutrophication. Four periods in the lake’s evolution were recognized based on changes in macrophyte and algae communities’ structure. Between ca. 1320 and ca. 1630 AD a shift was evidenced from an oligotrophic brackish with low nutrient content (dominated by Botryococcus braunii) to a mesotrophic fresh water body (dominated by Pediastrum and Scenedesmus), due to an increase in the water level associated with an increase in precipitation. At ca. 1840 AD a transition towards a phase dominated by Myriophyllum spicatum was noted, induced by a low water level as a consequence of low precipitation. Later, at ca. 1880 AD, the current lake conditions were established, and the increase in nutrient and organic matter supply influenced plant community structure towards organic tolerant species of submerged macrophytes (Potamogeton pectinatus). Towards the beginning of the twenty-first century, the lake turned to a more eutrophic state, which is evidenced by the dominance of the phytoplankton community. The last hundred years of the lake history were characterized by the eutrophication process related to the impact of agriculture and cattle breeding implemented in the landscape as well as to the urban settlement. This study made it possible to infer changes in the structure and dynamics of Cabeza de Buey lake and to elucidate the forcing factors that induced these changes on a high-resolution scale.
PubDate: 2021-04-21

• Temporal changes in diatom valve diameter indicate shifts in lake trophic
status
• Abstract: When diatoms undergo vegetative cell division the new siliceous wall components are slightly smaller than those of the parent because they are produced within the confines of the parent wall. Thus, with continued growth the mean size of cells in a population declines. Given this unique feature of diatom cell division, if the growth of a species in a lake increases (decreases) under more (less) favorable conditions, then the mean size of the resulting population will decline (increase). Numerous paleolimnological investigations rely on shifts in the relative abundances of diatom species over time to infer lake conditions. Although relative abundance data yield information about the dominance of species in the community, they do not necessarily provide evidence about growth of a given species. For instance, a species could have increased in growth, but simply to a lesser extent than other taxa, resulting in a decline in relative abundance. In a similar fashion, relative abundance values can be misleading when used to infer environmental change, such as trophic status change in lakes. We propose that including data on mean size of diatom valves can yield greater insight into changes in growth and improve observations and conclusions based on relative abundance data. To test this concept, we examined changes in the mean diameter of Aulacoseira ambigua (Grunow) Simonsen valves relative to known shifts in lake trophic status in a core from Bantam Lake, Connecticut, representing ~ 130 years of sediment accumulation. The mean valve diameter of A. ambigua declined from 9.7 to 7.6 µm, with the largest declines clearly tracking significant increases in trophic status. We conclude that changes in the mean size of diatom frustules over time can provide valuable information for understanding long-term environmental changes.
PubDate: 2021-04-15

• Experimental determination of the temperature dependence of oxygen-isotope
fractionation between water and chitinous head capsules of chironomid
larvae
• Abstract: Oxygen-isotope values of invertebrate cuticle preserved in lake sediments have been used in palaeoenvironmental reconstructions, generally with the assumption that fractionation of oxygen isotopes between cuticle and water ( $$\upalpha_{\text{cuticle}-\text{H}_{2}\text{O}}$$ ) is independent of temperature. We cultured chironomid larvae in the laboratory with labelled oxygen-isotope water and across a range of closely controlled temperatures from 5 to 25 °C in order to test the hypothesis that fractionation of oxygen isotopes between chironomid head capsules and water ( $$\upalpha_{\text{chironomid}-\text{H}_{2}\text{O}}$$ ) is independent of temperature. Results indicate that the hypothesis can be rejected, and that $$\upalpha_{\text{chironomid}-\text{H}_{2}\text{O}}$$ decreases with increasing temperature. The scatter in the data suggests that further experiments are needed to verify the relationship. However, these results indicate that temperature-dependence of $$\upalpha_{\text{chironomid}-\text{H}_{2}\text{O}}$$ should be considered when chironomid δ18O is used as a paleoenvironmental proxy, especially in cases where data from chironomids are combined with oxygen-isotope values from other materials for which fractionation is temperature dependent, such as calcite, in order to derive reconstructions of past water temperature.
PubDate: 2021-04-15

• The ecology of testate amoebae and Cladocera in Hawaiian montane peatlands
and development of a hydrological transfer function
• Abstract: Peatland complexes in the humid highlands of Hawai‘i are vital refuges of biodiversity and freshwater resources. Hawaiian peat deposits are also rare repositories of terrestrial ecosystem archives located in an otherwise vast expanse of ocean. We investigated the potential for researching the paleohydrological history of Hawaiian montane peatlands on Kohala, Hawai‘i Island through analyses of testate amoebae and Cladocera. Surface peat was collected from a variety of ecohydrological habitats (from water pools to hummocks) and analyzed for modern testate amoeba and cladoceran species relative abundance. We identified 54 morphotype taxa from 21 genera of testate amoebae, 4 taxa and genera of littoral Cladocera, and the common peat rotifer Habrotrocha angusticollis. Testate amoeba diversity and morphotype occurrence mirrored observations from many high-latitude peatland studies. Constrained and unconstrained ordinations support the hypothesis that surface moisture, measured as water-table depth, is an important control on the distribution of testate amoebae and Cladocera in Hawaiian peatlands. Transfer functions relying on weighted-averaging and modern analogs were developed to predict water-table depths from species relative abundance data, and these perform well under leave-one-site-out cross-validation: RMSEP = 9.75–10.3 cm, R2 = 0.56–0.62. Including cladoceran abundance data in the calibration dataset produced modest model improvement: RMSEP = 1–8% and R2 = 2–13%. A weighted-average partial-least-squares transfer function was applied to microfossil assemblages from a 0.5 m-long peat core with a 210Pb decay chronology anchored by ten existing measurements of 210Pb activity and a Bayesian statistical framework. Microfossils were well-preserved in the peat core. The water-table depth optima of an abundant down-core taxa, Hyalosphenia subflava, is not precisely constrained in the calibration data set, but estimates match those of other tropical studies. A reconstruction of water-table depth indicates dry early nineteenth-century conditions, wet conditions in the late 19th to early twentieth centuries, followed by progressive drying for much of the twentieth-century. Testate amoeba composition appears to have been sensitive to severe drought in recent decades. The results signal that assemblages of testate amoebae and Cladocera are useful proxies of Hawaiian peatland paleohydrology and should be considered alongside other archives of Hawaiian environmental history.
PubDate: 2021-04-08

• A multi-proxy record of climate variations over the last millennium from
Kulun-nuur Lake sediments, Inner Mongolia, north-central China
• Abstract: Reconstructing climate change over the last millennium is important for understanding natural climate variability and improving global climatic prediction. Precipitation variations from different records in north-central China, especially in the EASM margin area, are controversial. Here, we present a multi-proxy (grain size, pollen, TOC and TOC/TN ratio) record from Kulun-nuur Lake in east-central Inner Mongolia as an archive of moisture variations over the last millennium. Our record reveals that the Kulun-nuur Lake area is characterized by a wet Medieval Warm Period (MWP; 900–1300 AD), a dry Little Ice Age (LIA; 1300–1820 AD) and a relatively wet Current Warm Period (CWP; 1820 AD to present). In addition, within the context of an overall wet climate during the MWP, a short-term relatively dry episode occurred from 1000 to 1070 AD. The climate patterns reconstructed from Kulun-nuur Lake display good consistency with other records and models, suggesting that warm-wet/cold-dry are the main climate patterns in north-central China during the last millennium. These patterns of regional hydrological changes on multi-decadal to centennial scales may be related to solar activity and the Atlantic Multidecadal Oscillation.
PubDate: 2021-04-05

• Human impacts on the cladoceran community of Jili Lake, arid NW China,
over the past century
• 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: 2021-03-23

• 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
DOI: 10.1007/s10933-021-00179-9

• 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
DOI: 10.1007/s10933-020-00171-9

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
DOI: 10.1007/s10933-021-00177-x

• 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
DOI: 10.1007/s10933-021-00174-0

• 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

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