Lake Cores Research Articles

Climate driven declines in terrestrial input over the middle and late Holocene of perched boreal lakes in northeast Ontario (Canada) and teleconnections to the North Atlantic

The landscape of northeast Ontario, Canada, is dominated by glacial and postglacial landforms including numerous boreal lakes that formed following the retreat of the Laurentide Ice Sheet (LIS) and Glacial Lake Ojibway. This study uses micro-X-Ray Fluorescence elemental analysis to examine changes in sediment cores from two boreal lakes from northeast Ontario with the goal of inferring changes in terrestrial inputs and redox status of these lakes over the middle to late Holocene. These headwater lakes were selected as they have small watersheds that minimizes the complexity of hydrological responses, and as they are relatively proximal (∼130 km distance between lakes) to allow the detection of regional signals related to changes in climate over the Holocene. Strong correlations between Si, K, Ca, and Ti in Hogback Lake and Green Lake cores suggest that these elements represent proxies of terrestrial input. Standardized composite trends of these elements were very similar between the two lakes and were combined to represent a regional signal, with the highest terrestrial inputs between ∼6000 and ∼4000 cal yr BP, that subsequently declined through the Holocene. These results suggest that regional patterns in terrestrial input are linked to changes in hydroclimate and likely increased terrestrial stability over the middle to late Holocene. These composite trends are compared to similar geochemical composite trends from Iceland suggesting climate teleconnections between northeast North America and the North Atlantic. Cool conditions in the North Atlantic result in increased soil erosion in Iceland and correspond to cool and dry conditions in boreal northeast Ontario with corresponding low inputs of terrestrial material, and vice versa, over multidecadal time scales over the middle to late Holocene.

Drought coincident with aeolian activity in a Great Lakes coastal dune setting during the Algoma Phase (3.1–2.4 ka), southwest Michigan

Aeolian studies of Lake Michigan’s coastal dunes have yet to elucidate what factors control their episodic activity over the past 5000 years. High lake levels exposing sand along with increased storminess is generally accepted for high perched dunes. This hypothesis, however, remains poorly tested for low perched dunes along the southeast Lake Michigan coastline. Here, small lakes in the lee of dune complexes contain aeolian sand and various biological proxies. Age and sedimentation rate models from Gilligan Lake cores guide analysis of aeolian sand, charcoal, pollen, and diatoms at high resolution (1 cm [10.4 yr/cm]) during the high-water Algoma Phase (3.1–2.4 ka) of the upper Great Lakes. The diatoms record a transition from a deep, more acidic lake to a shallower, more alkaline lake with fewer wetlands. This transition is accompanied by a stepped increase in the amount of aeolian sand. There is a weak correlation (R2 0.5, p < 0.01) between increasing abundances of charcoal chunks and sand. Peaks of sand follow peaks in charcoal threads and sheets, suggesting fire played a role in removing vegetation, presaging the landscape for increases in storminess. Arboreal pollen records a transition from a mesic forest Fagus-Acer-Quercus-Abies assemblage suggestive of moister conditions to one richer in mesic hardwoods tolerant of drier conditions. Together, the environmental proxy data record a shallowing lake concomitant with increasing aeolian sand, suggesting that drought-like conditions along the coastline conditioned the landscape for renewed aeolian activity. Once initiated, increased storminess and shoreline erosion maintained dune activity through increased sediment supply.

A global Bayesian temperature calibration for lacustrine brGDGTs

Despite widespread use of branched glycerol dialkyl glycerol tetraethers (brGDGTs) for paleo-temperature reconstruction, no global calibration for their application in lakes has been generated since improved analytical methods have allowed for the separation of the structural isomers. This is a substantial obstacle for the application of this tool as soil calibrations underestimate temperature values when applied to lake sediments. Here, we present a comprehensive dataset (N=272) of lacustrine brGDGT distributions, consisting of both new and previously reported samples, spanning a wide range of geographical locations, air temperatures, and lakewater pH values. Empirical Orthogonal Function (EOF) analysis on the fractional abundance of brGDGTs indicates that temperature exerts a strong control (explaining 58% of the variance) on brGDGT distribution. The influence of water chemistry is weaker, with pH and conductivity explaining 24% of the variance. We use our dataset to generate a new Bayesian calibration to the mean temperature of Months Above Freezing (MAF), which has an R2=0.82 and RMSE = 2.9°C. Application of the new temperature calibration to a previously published lake core record spanning the last 900 years demonstrates that it generates values comparable to instrumental observations of MAF. Our new calibration facilitates the use of lacustrine brGDGTs to reconstruct continental temperatures, a vital piece of information for understanding past climates.

Climatic and tectonic significance of Taboche Lake, Khumbu Region, Nepal

SummaryThe Everest region is characterized by its alpine glacial environment. In an effort to understand environmental change and tectonic activity, our team cored Taboche Lake, situated at 4,712 m along the western margin of the Ngozumpa Glacier. This research catalogs past earthquakes using geological records of the lake core that are important for the assessment of future earthquake hazards in the region and provides information for tectonic risk of glacial lake floods. Core grain size characteristics and internal sedimentary structures from computed tomographic scan were coupled with radiocarbon dating of organic matter preserved in the core to reconstruct the environmental history of the area. The 58-cm-long core consists of laminated silty sands and sandy silts with particle diameters <2 mm. The core records a syn-sedimentary deformational structure, folded sediments, rhythmically alternating dark- and light-colored laminations, and turbidites, which indicate coeval climatic and tectonic variations over the past ∼1,600 years.

Paleomonsoonal shifts during ∼13700 to 3100 yr BP in the central Ganga Basin, India with a severe arid phase at ∼4.2 ka

We present a multiproxy record of grain size and stable carbon isotope from the Lilaur lake, Ganga Basin, India to understand the history of lake formation linked to changes in Indian monsoon precipitation during ~13714 to 3073 calibrated year before Present (cal yr BP). A comparison is made between Lilaur lake proxy record with those from other parts of South Asia as well as North Atlantic to understand extent and causes of monsoon variability and its influence on the fauna and flora of the region. Chronology of lake core was constrained using AMS 14C and optically stimulated luminescence (OSL) dates. This study suggests a transition from river to lake during ~5800 to 5189 cal yr BP which is supported by reduced precipitation with weakening of the Indian summer monsoon (ISM). This river to lake transition culminated in a severe arid phase during 4250 to 4050 cal yr BP (4.2 ka event), corresponding to enhanced El Niño activity, southward shift of the Inter-Tropical Convergence Zone, and aridification of India when the ISM was weak.

Application and problems of &lt;sup&gt;210&lt;/sup&gt;Pb and &lt;sup&gt;137&lt;/sup&gt;Cs dating techniques in lake sediments

湖泊沉积记录研究对了解流域侵蚀、揭示区域气候环境变化及人类活动影响、建立外生地球化学循环模式等均具有重要意义.放射性同位素²¹⁰Pb和¹³⁷Cs组合定年法是百年尺度湖泊沉积记录研究的首选方法，在过去几十年中得到了广泛应用，大力推动了湖泊沉积记录的高分辨率气候环境变化研究的开展.然而，如何理解和选择适用的计算模式来尽可能地提高定年准确度目前仍存在争议，这在一定程度上限制了该方法的应用.鉴于上述问题，本文基于本实验室近年来从青藏高原获取的若干支代表性湖芯的定年结果，从样品前处理、仪器及测试、数据分析及计算等全过程对²¹⁰Pb、¹³⁷Cs定年原理和方法进行了较为系统的阐述；在此基础上，提出了²¹⁰Pb定年样品封装原则，探讨了高纯锗γ谱仪在放射性活度测量中的影响因素，并建立了准确有效的比活度校正方法；明确指出了恒定初始浓度模式（constant initial concentration，CIC）可用于计算沉积物每层的年龄，而不是部分研究中认为的平均沉积速率，这对于深刻理解该定年模式并提供准确的定年结果具有重要的参考意义.同时，通过对比两种放射性核素的分布特征发现，相对于²¹⁰Pb而言，¹³⁷Cs更容易发生垂向迁移进而影响其时标准确性，这需引起研究者的充分重视，因此，当二者定年结果出现明显差异时，建议以²¹⁰Pb定年结果为准.;The study of lacustrine sedimentary records is of great significance for understanding basin erosion, revealing regional climatic and environmental changes and the influence of human activities, and establishing exogenous geochemical cycle patterns. The combined dating method of ²¹⁰Pb and ¹³⁷Cs is the preferred method for the study of centennial-scale lake sedimentary records. It has been widely used in the past decades, which greatly promotes the study of high-resolution climate and environmental changes in lake sedimentary records. However, it is still controversial how to understand and select the applicable calculation model to improve the accuracy of the dating as much as possible, which limits the application of this method to a certain extent. Because of the above problems, based on the dating results of several representative lake cores obtained from the Tibetan Plateau by our laboratory in recent years, the principles and methods of dating with ²¹⁰Pb and ¹³⁷Cs were systematically expounded from the whole process of sample pretreatment, instrument and sample measurement, data analysis and calculation. On this basis, the packing principle of ²¹⁰Pb dating samples was proposed, the influencing factors of High-purity germanium Gamma-Ray Spectrometer in radioactive activity measurement were discussed, and an accurate and effective specific activity correction method was established. It was pointed out that constant initial concentration (CIC) model could be used to calculate the age of each layer of sediments, rather than the average deposition rate in some studies, which is of great significance for understanding the model and providing accurate dating results. Meanwhile, by comparing the distribution characteristics of the two radioisotopes, it was found that ¹³⁷Cs was more likely to have vertical migration compared with ²¹⁰Pb, and thus affected the dating accuracy, which should be paid more attention to by researchers. Therefore, in case of the obvious difference between the two results, it was suggested that ²¹⁰Pb results should prevail.

Influence of glacial turbidity and climate on diatom communities in two Fjord Lakes (British Columbia, Canada)

Inputs of glacial meltwater and changes in climate can profoundly influence lake ecosystems. Anderson and Seton lakes, two morphologically and chemically similar fjord lakes within the Fraser River Basin, British Columbia, experience a common biogeoclimatic setting, yet contrasting turbid-water influences from a hydroelectric development which diverts glacially-turbid water into Seton Lake, but not Anderson Lake. We conducted a comparative paleolimnological study of these two lakes to infer climatic and hydro-system influences affecting the freshwater algal community over the past ~ 200 years. Paleolimnological analysis of multiple cores for sedimentary diatom assemblages from Seton Lake revealed substantial diversion-related reductions in diatom concentrations and fluxes following the completion of the Bridge River Diversion (ca. 1950). Diatom compositional changes in Seton Lake were consistent with decreased light penetration due to increased turbidity. These changes did not occur in Anderson Lake, indicating the changes in the Seton Lake cores were likely driven by inflow of the glacially-turbid waters. Both lakes exhibited diatom compositional changes ca. 1980, with a rise in Lindavia comensis coincident with significant increases in local mean annual air temperatures and presumably associated limnological changes. Modern phytoplankton data, collected as part of this study, provides support for the occurrence of different L. comensis morphs throughout the sampling period (May–October) in Anderson Lake and in the fall in Seton Lake. The rise of L. comensis in both Anderson and Seton lakes is conceivably linked to the recent ice-free conditions enabling this taxon to persist throughout the year.

Climatic and Tectonic Significance of Taboche Lake, Khumbu Region, Nepal

The Mount Everest region is characterized by its alpine glacial environment. In an effort to understand environmental change in the area, our team cored Taboche Lake, situated at 4,712 m along the western margin of the lateral moraine of the Ngozumpa Glacier. This research catalogues past earthquakes using geological records of the lake core that are important for the assessment of future earthquake hazards in the region. To achieve the aims of the study, core grain size characteristics and internal sedimentary structures from CT scan tomography, were coupled with radiocarbon dating of organic matter preserved in the core to reconstruct the environmental history of Loboche Lake. The 58 cm-long core consists of laminated silty sands and sandy silts with particle diameters less than 2 mm, covering ∼ 2,000 years of sedimentation history. Syn-sedimentary deformational structure, folding of sediments, rhythmically alternating dark- and light-coloured laminations, and turbidites are discussed in terms of their origins as past climatic and tectonic indicators.

Enhanced middle Holocene organic carbon burial in tropical floodplain lakes of the Pantanal (South America)

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 Caceres (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 Caceres 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.

Biogeochemical proxy evidence of gradual and muted geolimnological response of Lake Nkunga, Mt. Kenya to climate changes and human influence during the past millennium

Lake Nkunga is a crater Lake on the north eastern slopes of Mount Kenya that provides a record of catchment changes covering the last millennium. A multi proxy study was carried out on 89 cm of sediment core retrieved from 20 m near the lake shoreline. The mineralogy, magnetic mineralogy, organic and elemental geochemical proxies indicate a rejuvenating lake during the Medieval Climatic Anomaly with limited sediment supply and sustained by ground water. A progressive response to wetter conditions commences ca. 810 cal yr. BP with an increase in sediment influx that peaked at 500 cal yr. BP, a period that encompasses the start of the Little Ice Age (LIA). The establishment of the present-day maar conditions may have occurred during this period of the LIA. The lake has been relatively stable with declining terrestrial input from 290 cal yr. BP to present. The inferred changes in Lake Nkunga levels from deep to shallow phases are characterized by slow and muted response to both abrupt (e.g. Medieval Climate Anomaly) and sustained and prolonged climate shifts (e.g. Little Ice Age), reflecting the resilience of geolimnological and catchment processes in this lake and its watershed to climatic changes and human influence. This study provides new insights into the utility of biogeochemical proxies from nearshore lake cores in the equatorial east Africa highlands whose responses to extreme weather events are not well understood over the last 1000 years.

A 50,000-year record of lake-level variations and overflow from Owens Lake, eastern California, USA

A continuous lake-level curve was constructed for Owens Lake, eastern California by integrating lake-core data and shoreline geomorphology with new wind-wave and sediment entrainment modeling of lake-core sedimentology. This effort enabled refinement of the overflow history and development of a better understanding of the effects of regional and global climate variability on lake levels of the paleo-Owens River system during the last 50,000 years. The elevations of stratigraphic sites, plus lake bottom and spillway positions were corrected for vertical tectonic deformation using a differential fault-block model to estimate the absolute hydrologic change of the watershed-lake system. New results include 14C dating of mollusk shells in shoreline deposits, plus post-IR-IRSL dating of a suite of five beach ridges and OSL dating of spillway alluvial and deltaic deposits in deep boreholes. Geotechnical data show the overflow area is an entrenched channel that had erodible sills composed of unconsolidated fluvial-deltaic and alluvial sediment at elevations of ∼1113–1165 m above mean sea level. Owens Lake spilled most of the time at or near minimum sill levels, controlled by a bedrock sill at ∼1113 m. Nine major transgressions at ∼40.0, 38.7, 23.3, 19.3, 15.6, 13.8, 12.8, 11.6, and 10.6 ka reached levels ∼10–45 m above the bedrock sill. Several major regressions at or below the bedrock sill from 36.9 to 28.5 ka, and at ∼17.8, 12.9, and 10.4–8.8 ka indicate little to no overflow during these times. The latest period of overflow occurred ∼10–20 m above the bedrock sill from ∼8.4 to 6.4 ka that was followed by closed basin conditions after ∼6.4 ka. Previous lake core age-depth models were revised by accounting for sediment compaction and using no reservoir correction for open basin conditions, thereby reducing discrepancies between Owens Lake shoreline and lake-core proxy records. The integrated analysis provides a continuous 50 ka lake-level record of hydroclimate variability along the south-central Sierra Nevada that is consistent with other shoreline and speleothem records in the southwestern U.S.

Comparison of Diatom Paleo-Assemblages with Adjacent Limno-Terrestrial Communities on Vega Island, Antarctic Peninsula

Diatoms are useful ecological and paleolimnological indicators routinely used to reconstruct past conditions and monitor environmental change. Despite this, diatom assemblages from lake sediment cores are often difficult to interpret due to a limited knowledge of the ecology of some species, some of which may originate from the adjacent limno-terrestrial landscape. Here, we compare diatom assemblages from two recently published Antarctic lake sediment cores collected from the northeast and southwest sides of Vega Island, Antarctic Peninsula. We further compare the sediment core assemblages with adjacent modern communities inhabiting four different limno-terrestrial habitat types to gauge the importance of landscape connectivity in determining paleo-assemblage structure. We found that diatom assemblage composition was significantly different between the two cores, and our survey of modern habitats further revealed habitat type to be an important factor determining the composition of limno-terrestrial samples. Differences in modern habitats were driven primarily by Chamaepinnularia krookiformis in mosses, Nitzschia paleacea in ponds, and Fistulifera pelliculosa in streams. When modern communities were compared with paleo-assemblages through ordination, the cored lake from the northeast side, which exhibited greater hydrological connectivity with its surroundings, clustered more closely with the adjacent modern samples. Meanwhile, the cored lake from the southwest side, which was more hydrologically isolated, formed a distinct cluster separate from the others. Overall, species richness and diversity were greater on the southwest side of the island than the northeast, and the known distributions of diatom taxa supported the notion that Vega Island was a transitional zone between the Maritime and Continental Antarctic bioregions. These results collectively suggested that while environmental and spatial controls may be influential in determining diatom community composition, the unique hydrogeological setting of individual waterbodies was an important consideration for determining the assemblage structure of lake cores. This paper furthermore expanded ongoing research of diatom diversity and distributions on maritime Antarctic islands, which will improve diatom-based interpretations for regional ecological monitoring and paleolimnology in the future.

Discrepancy in the responses of diatom diversity to indirect and direct human activities in lakes of the southeastern Tibetan Plateau, China

Abstract Both global warming and human impacts are inimical to the maintenance of biodiversity across the planet. Although there is some consensus regarding the probable responses of biodiversity changes under different global change scenarios, the factors controlling biodiversity on regional scales are unclear. Using surveys of lake-bed surface sediments and an analysis of diatoms from six lake cores across 116 lakes in the southeastern Tibetan Plateau of China, we investigated (i) changes in diatom richness and (ii) β diversity and its components at various spatial and temporal scales. β diversity partitioning revealed that the most important factor affecting changes in diatom communities was species turnover across both spatial and temporal scales. This finding indicates that conservation planning requires a regional approach that focuses on multiple lake systems. Temporal changes in the trend of β diversity were shown to result from changes in nestedness components. The results showed that climate warming and indirect human impacts caused the decline of species nestedness, thereby increasing biodiversity, while the intensification of direct human activities caused species nestedness to rise, resulting in concomitant loss of biodiversity. Since nestedness is often related to ordered species gain/loss dynamics, the results suggest that species gain slows down in lakes affected indirectly by human activities, while species loss accelerates in lakes subjected to direct human impacts. Thus, we predict that species richness will continue to decline across this vast region in the future.

Human settlement of East Polynesia earlier, incremental, and coincident with prolonged South Pacific drought

The timing of human colonization of East Polynesia, a vast area lying between Hawai'i, Rapa Nui, and New Zealand, is much debated and the underlying causes of this great migration have been enigmatic. Our study generates evidence for human dispersal into eastern Polynesia from islands to the west from around AD 900 and contemporaneous paleoclimate data from the likely source region. Lake cores from Atiu, Southern Cook Islands (SCIs) register evidence of pig and/or human occupation on a virgin landscape at this time, followed by changes in lake carbon around AD 1000 and significant anthropogenic disturbance from c. AD 1100. The broader paleoclimate context of these early voyages of exploration are derived from the Atiu lake core and complemented by additional lake cores from Samoa (directly west) and Vanuatu (southwest) and published hydroclimate proxies from the Society Islands (northeast) and Kiribati (north). Algal lipid and leaf wax biomarkers allow for comparisons of changing hydroclimate conditions across the region before, during, and after human arrival in the SCIs. The evidence indicates a prolonged drought in the likely western source region for these colonists, lasting c. 200 to 400 y, contemporaneous with the phasing of human dispersal into the Pacific. We propose that drying climate, coupled with documented social pressures and societal developments, instigated initial eastward exploration, resulting in SCI landfall(s) and return voyaging, with colonization a century or two later. This incremental settlement process likely involved the accumulation of critical maritime knowledge over several generations.

Biodiversity patterns of Arctic diatom assemblages in lakes and streams: Current reference conditions and historical context for biomonitoring

Abstract Comprehensive assessments of contemporary diatom distributions across the Arctic remain scarce. Furthermore, studies tracking species compositional differences across space and time, as well as diatom responses to climate warming, are mainly limited to paleolimnological studies due to a lack of routine monitoring in lakes and streams across vast areas of the Arctic. The study aims to provide a spatial assessment of contemporary species distributions across the circum‐Arctic, establish contemporary biodiversity patterns of diatom assemblages to use as reference conditions for future biomonitoring assessments, and determine pre‐industrial baseline conditions to provide historical context for modern diatom distributions. Diatom assemblages were assessed using information from ongoing regulatory monitoring programmes, individual research projects, and from surface sediment layers obtained from lake cores. Pre‐industrial baseline conditions as well as the nature, direction and magnitude of changes in diatom assemblages over the past c.200 years were determined by comparing surface sediment samples (i.e. containing modern assemblages) with a sediment interval deposited prior to the onset of significant anthropogenic activities (i.e. containing pre‐1850 assemblages), together with an examination of diatoms preserved in contiguous samples from dated sediment cores. We identified several biotypes with distinct diatom assemblages using contemporary diatom data from both lakes and streams, including a biotype typical for High Arctic regions. Differences in diatom assemblage composition across circum‐Arctic regions were gradual rather than abrupt. Species richness was lowest in High Arctic regions compared to Low Arctic and sub‐Arctic regions, and higher in lakes than in streams. Dominant diatom taxa were not endemic to the Arctic. Species richness in both lakes and streams reached maximum values between 60°N and 75°N but was highly variable, probably reflecting differences in local and regional environmental factors and possibly sampling effort. We found clear taxon‐specific differences between contemporary and pre‐industrial samples that were often specific to both ecozone and lake depth. Regional patterns of species turnover (β‐diversity) in the past c.200 years revealed that regions of the Canadian High Arctic and the Hudson Bay Lowlands to the south showed most compositional change, whereas the easternmost regions of the Canadian Arctic changed least. As shown in previous Arctic diatom studies, global warming has already affected these remote high latitude ecosystems. Our results provide reference conditions for future environmental monitoring programmes in the Arctic. Furthermore, diatom taxa identification and harmonisation require improvement, starting with circum‐Arctic intercalibrations. Despite the challenges posed by the remoteness of the Arctic, our study shows the need for routine monitoring programmes that have a wide geographical coverage for both streams and lakes.

Reliability of the Artemisia/Chenopodiaceae pollen ratio in differentiating vegetation and reflecting moisture in arid and semi-arid China

The reliability of the ratio between Artemisia and Chenopodiaceae pollen percentage (i.e. A/ C) in differentiating vegetation and reflecting moisture conditions in arid and semi-arid regions has been disputed and this hindered its potential application in palaeoclimate reconstructions. In this paper, we investigated the A/ C ratios of lake-centre surface sediment from 45 lakes in the Inner Mongolia Plateau and the Qaidam Basin in arid and semi-arid China, and numerically studied the relationships of A/ C ratios with vegetation and moisture. We found that the A/ C ratio of lake-centre surface sediments can be used as an effective index to differentiate desert and steppe and also can be used as a valid indicator to infer mean annual precipitation (MAP) in the Inner Mongolia Plateau and the Qaidam Basin in arid and semi-arid China. Moreover, the A/ C ratio from lake-centre surface sediments is more reliable and robust than that of soil-surface samples in differentiating vegetation and reflecting moisture conditions, and this might be attributed to its larger pollen source area and regional representation. In addition, the ( A − C)/( A + C) index helps to overcome the inherent weakness of non-linearity of the A/ C ratio and may be useful in paleo-vegetation reconstruction. These findings provide useful references for pollen-based vegetation and climate reconstructions of lake cores in arid and semi-arid China.

Correlation of the annual temperature reconstructed with _XRF-SR method and pollen data from varved sediments of Lake Kucherla, the Altai Mountains, for the last 500 years

This paper presents an attempt to correlate the temperature curve built by the transfer function method based on data from elemental analysis _XRF-SR and the results of pollen analysis of the core of the Kucherla Lake bottom sediments in the 1500 - 2016 CE. A comparison of geochemical reconstruction with pollen data was carried out by calculation of pair correlation coefficients. For this, temperatures were averaged to intervals corresponding to the interval of the pollen sample metric size (10 mm). Depending on the age-depth model the time interval of the pollen sample varied from 4 to 12 years. After that, a pairwise comparison of one-year data of temperature reconstruction and palynological analysis was performed. The paired correlations of mean annual temperatures obtained based on geochemical studies of the Kucherla Lake core by the _XRF-SR method and pollen data showed a significant negative correlation between the content of terrestrial herbs, grasses, and wormwood and mean annual temperatures. This can be explained by the expansion of the steppe area during cold periods, probably accompanied by a decrease in precipitation.

Sediment Cores from White Pond, South Carolina, contain a Platinum Anomaly, Pyrogenic Carbon Peak, and Coprophilous Spore Decline at 12.8 ka

A widespread platinum (Pt) anomaly was recently documented in Greenland ice and 11 North American sedimentary sequences at the onset of the Younger Dryas (YD) event (~12,800 cal yr BP), consistent with the YD Impact Hypothesis. We report high-resolution analyses of a 1-meter section of a lake core from White Pond, South Carolina, USA. After developing a Bayesian age-depth model that brackets the late Pleistocene through early Holocene, we analyzed and quantified the following: (1) Pt and palladium (Pd) abundance, (2) geochemistry of 58 elements, (3) coprophilous spores, (4) sedimentary organic matter (OC and sedaDNA), (5) stable isotopes of C (δ13C) and N (δ15N), (6) soot, (7) aciniform carbon, (8) cryptotephra, (9) mercury (Hg), and (10) magnetic susceptibility. We identified large Pt and Pt/Pd anomalies within a 2-cm section dated to the YD onset (12,785 ± 58 cal yr BP). These anomalies precede a decline in coprophilous spores and correlate with an abrupt peak in soot and C/OC ratios, indicative of large-scale regional biomass burning. We also observed a relatively large excursion in δ15N values, indicating rapid climatic and environmental/hydrological changes at the YD onset. Our results are consistent with the YD Impact Hypothesis and impact-related environmental and ecological changes.

A new varve sequence from Windermere, UK, records rapid ice retreat prior to the Lateglacial Interstadial (GI-1)

Annually laminated sediments (varves) provide excellent temporal resolution to study rapid environmental change, but are rare in the early part of the Last Termination (∼19–∼11.7 ka BP). We present a new >400 varve year (vyr) varve sequence in two floating parts from Windermere, a lake at the southern margin of the mountains of northwest England. This sequence records the final retreat of the Windermere glacier at the southern edge of the Lake District Ice Cap during the transition from Heinrich Stadial 1 (∼18–∼14.7 ka BP) into the Lateglacial Interstadial (∼14.7–∼12.9 ka BP).Laminated sediments from four lake cores from Windermere's northern and southern basins were investigated and shown to be varved. These sequences are integrated with seismic reflection evidence to reconstruct south-to-north deglaciation. Seismic and sedimentological evidence is consistent with gradual stepped ice retreat along the entire southern basin and into the northern basin between 255 and 700 vyr prior to the appearance of significant biota in the sediment that heralded the Lateglacial Interstadial, and had retreated past a recessional moraine (RM8) in the northern basin by 121 vyr prior to the interstadial. The Lateglacial Interstadial age of this biota-bearing unit was confirmed by 14C-dating, including one date from the northernmost core of ∼13.5 cal ka BP. A change in mineralogy in all four cores as the glacier retreated north of the Dent Group (the northernmost source of calcareous bedrock) and a decrease in coarse grains in the varves shows that the ice had retreated along the entire North Basin at ∼70 vyr prior to the Lateglacial Interstadial. The estimated retreat rate is 70–114 m yr−1 although buried De Geer moraines, if annual, may indicate retreat of 120 m yr−1 with a ≥3 year stillstand at a recessional moraine halfway along the basin. The glacier then retreated north of the lake basin, becoming land-terminating and retreating at 92.5–49 m yr−1.The northernmost core has a varve sequence ending at least 111 vyr after the other core chronologies, due to the increased proximity to remnant ice in the catchment uplands into the early Lateglacial Interstadial. We show that almost all of the glacier retreat in the Windermere catchment occurred before the abrupt warming at the onset of the Lateglacial Interstadial, in keeping with similar findings from around the Irish Sea Basin, and suggesting a similar retreat timescale for other radial valley glaciers of the Lake District Ice Cap. The seismic and core evidence also show the potential for a much longer varve chronology extending at least 400 and potentially over 1000 vyr further back into Heinrich Stadial 1 (18–14.7 ka BP), suggesting that glacier retreat in the Windermere valley initiated at least before 15.5 ka BP and perhaps 16 ka BP.

Spatial-temporal assessment of pollutions in Ekbatan lake using qualitative indices and statistical methods.

The purpose of this study was to use water quality indices and statistical methods based on physicochemical parameters for spatial-temporal assessment of Ekbatan lake pollution. Sampling stations were selected based on systematic, non-random approach, and it was performed in 7 stations, with intervals of 30 days in 2010-2011. At first, indices model of IRWQI, NSFWQI, and TLI was prepared in GIS environment based on qualitative parameters by interpolation functions (deterministic and geostatistical methods). Results demonstrated that qualitative parameters of FC, NO3-, BOD5, DOSat%, pH, PO43- and Turb respectively with annual average quality of 13.5 very bad, 27.4 bad, 46.8, 47.2 and 48.6 moderate, 70 goodish, and 71 good using statistical and geostatistical methods-accounted for highest pollution level and created greatest impact on lake pollution status. This amount was considered as bad and eutrophication quality on the southern and east margins of the lake because of the effluent load of the rivers under high land use activities (especially residential and then agricultural) in comparison with the lake core and north (showing baddish and moderate quality status) has more pollution level than that. Also, all parameters showed a high positive correlation and significance with increased of water temperature owing to increase in pollutant land use activities and condensation of pollutants and decreased of floodrains in warm seasons, and two parameters of TDS and Turb show high significance rather than beginning floodrains in spring and autumn. Also, lake was in qualitative status of baddish 43.7, moderate 58.2, and mild eutrophication 57.2 based on IRWQI, NSFWQI, and TLIChl.a respectively. Further, according to IRWQI index, the quality of lake in summer was in baddish status of 35, in half of initial winter in goodish condition of 56 and spring and autumn in moderate qualitative status of 46.