Varve Counting Research Articles

Semi-automated counting of complex varves through image autocorrelation

AbstractAnnual resolution sediment layers, known as varves, can provide continuous and high-resolution chronologies of sedimentary sequences. In addition, varve counting is not burdened with the high laboratory costs of geochronological analyses. Despite a more than 100-year history of use, many existing varve counting techniques are time consuming and difficult to reproduce. We present countMYvarves, a varve counting toolbox which uses sliding-window autocorrelation to count the number of repeated patterns in core scans or outcrop photos. The toolbox is used to build an annually-resolved record of sedimentation rates, which are depth-integrated to provide ages. We validate the model with repeated manual counts of a high sedimentation rate lake with biogenic varves (Herd Lake, USA) and a low sedimentation rate glacial lake (Lago Argentino, Argentina). In both cases, countMYvarves is consistent with manual counts and provides additional sedimentation rate data. The toolbox performs multiple simultaneous varve counts, enabling uncertainty to be quantified and propagated into the resulting age-depth model. The toolbox also includes modules to automatically exclude non-varved portions of sediment and interpolate over missing or disrupted sediment. CountMYvarves is open source, runs through a graphical user interface, and is available online for download for use on Windows, macOS or Linux at https://doi.org/10.5281/zenodo.4031811.

Sediment profile dating and reconstructing nuclear events from annually laminated lake sediments in northern Finland

The sediments deposited in Lake Kevojärvi (69°45N, 27°00′E) in northernmost Finland were investigated for radioactivity. Freeze cores recovered from the 35-m deep basin has preserved a distinct succession of annual laminations deposited between 1909 and 2015. The basic varve structure is composed of a detrital snowmelt layer and an organic-rich post-snowmelt layer lying on top of the snowmelt layer. The past nuclear events have been preserved in the lake sediment. In order to study these, sediment freeze with annual sediment laminations were recovered from the lake bottom and measured for gamma emitting radionuclides. A total of 53 sediment subsamples, each incorporating sediment from one to two varves i.e. sediment deposited during one to two years, were taken for gamma spectroscopy measurements using low-background HPGe detector system. The measurements showed large variations in 137Cs and 241Am concentrations between different laminae marking different nuclear events in history. This highly resolved profile revealed a detailed record of anthropogenic radioactive fallout from atmospheric nuclear weapons testing during 1950s and 1960s and the Chernobyl accident in 1986. The measured 137Cs concentrations varied between 0.6 and 229 Bq/kg dry weight (dw) while the measured 241Am concentrations varied between 0.6 and 6.4 Bq/kg dw. The 137Cs showed downward migration in the sediment column since 137Cs was also found in varves dating before 1945. The first clear increase in 137Cs concentration was observed in 1956 varve and the 137Cs concentrations were found to peak in the 1964, 1970 and 1986 varves. The 241Am was first observed in 1957 varve and the concentrations peaked in 1960–1962, 1964 and 1970 varves. This demonstrated that 241Am can be a complementary chronostratigraphic marker to 137Cs in sediment. A time delay of one to two years was observed between the years of intensive atmospheric nuclear weapons testing and the increased 137Cs and 241Am concentrations in the sediment varves. In the 210Pb concentrations long-time periods of low (~1930–1950 and ~1990–2000) and high concentrations (~1950–1980) were observed. The reason for large variation was the amount of sediment input. The Constant rate of supply (CRS) model results showed good agreement with the varve counting. The model results showed that the 210Pb deposition has been constant over the last 80 years and no effect of climate change to the 210Pb deposition was observed.

Plateaus and jumps in the atmospheric radiocarbon record – potential origin and value as global age markers for glacial-to-deglacial paleoceanography, a synthesis

Abstract. Changes in the geometry of ocean meridional overturning circulation (MOC) are crucial in controlling past changes of climate and the carbon inventory of the atmosphere. However, the accurate timing and global correlation of short-term glacial-to-deglacial changes of MOC in different ocean basins still present a major challenge. The fine structure of jumps and plateaus in atmospheric and planktic radiocarbon (14C) concentration reflects changes in atmospheric 14C production, ocean–atmosphere 14C exchange, and ocean mixing. Plateau boundaries in the atmospheric 14C record of Lake Suigetsu, now tied to Hulu Cave U∕Th model ages instead of optical varve counts, provide a stratigraphic “rung ladder” of up to 30 age tie points from 29 to 10 cal ka for accurate dating of planktic oceanic 14C records. The age differences between contemporary planktic and atmospheric 14C plateaus record the global distribution of 14C reservoir ages for surface waters of the Last Glacial Maximum (LGM) and deglacial Heinrich Stadial 1 (HS-1), as documented in 19 and 20 planktic 14C records, respectively. Elevated and variable reservoir ages mark both upwelling regions and high-latitude sites covered by sea ice and/or meltwater. 14C ventilation ages of LGM deep waters reveal opposed geometries of Atlantic and Pacific MOC. Like today, Atlantic deep-water formation went along with an estuarine inflow of old abyssal waters from the Southern Ocean up to the northern North Pacific and an outflow of upper deep waters. During early HS-1, 14C ventilation ages suggest a reversed MOC and ∼1500-year flushing of the deep North Pacific up to the South China Sea, when estuarine circulation geometry marked the North Atlantic, gradually starting near 19 ka. High 14C ventilation ages of LGM deep waters reflect a major drawdown of carbon from the atmosphere. The subsequent major deglacial age drop reflects changes in MOC accompanied by massive carbon releases to the atmosphere as recorded in Antarctic ice cores. These new features of MOC and the carbon cycle provide detailed evidence in space and time to test and refine ocean models that, in part because of insufficient spatial model resolution and reference data, still poorly reproduce our data sets.

Impact of hydrological conditions on the radiocarbon reservoir effect in lake sediment 14C dating: the case of Kusai Lake on the northern Qinghai-Tibet Plateau

Abstract The hydrological conditions of a lake system strongly influence the reservoir effect in the radiocarbon dating of endogenic organic and inorganic carbon in lake sediments. In this paper, we compare 14C dating with varve counting results for cores from Kusai Lake to determine the temporal changes in 14C reservoir ages during the last 2000 years. Based on the 14C budget equation for a lake system, the characteristics of geomorphology, topography, and river systems in the catchment, and the physical and chemical properties of modern water in Kusai Lake, the hydrological conditions and the reservoir effect age are discussed. The reservoir age of the sediment core from northwestern Kusai Lake (i.e., deep water area) fluctuates slightly between 2980 and 3310 years, while that from southeastern Kusai Lake (i.e., shallow water area) fluctuates greatly between 3130 and 4010 years. Under the relatively steady conditions of atmospheric 14C levels for the past 2000 years, the 14C level in the dissolved inorganic carbon (DIC) of Kusai Lake is mainly related to carbon influxes from river and glacial meltwater and carbon outfluxes in lake water. The water in the shallow water area is more affected by the Kusai River, glacier meltwater, and lake outflow than the water in the deep water area, which has caused larger temporal changes in the radiocarbon reservoir ages in the shallow water area than in the deep water area during the last 2000 years.

New insights into lake responses to rapid climate change: the Younger Dryas in Lake Gościąż, central Poland

The sediment profile from Lake Gościąż in central Poland comprises a continuous, seasonally resolved and exceptionally well‐preserved archive of the Younger Dryas (YD) climate variation. This provides a unique opportunity for detailed investigation of lake system responses during periods of rapid climate cooling (YD onset) and warming (YD termination). The new varve record of Lake Gościąż presented here spans 1662 years from the late Allerød (AL) to the early Preboreal (PB). Microscopic varve counting provides an independent chronology with a YD duration of 1149+14/–22 years, which confirms previous results of 1140±40 years. We link stable oxygen isotopes and chironomid‐based air temperature reconstructions with the response of various geochemical and varve microfacies proxies especially focusing on the onset and termination of the YD. Cooling at the YD onset lasted ~180 years, which is about a century longer than the terminal warming that was completed in ~70 years. During the AL/YD transition, environmental proxy data lagged the onset of cooling by ~90 years and revealed an increase of lake productivity and internal lake re‐suspension as well as slightly higher detrital sediment input. In contrast, rapid warming and environmental changes during the YD/PB transition occurred simultaneously. However, initial changes such as declining diatom deposition and detrital input occurred already a few centuries before the rapid warming at the YD/PB transition. These environmental changes likely reflect a gradual increase in summer air temperatures already during the YD. Our data indicate complex and differing environmental responses to the major climate changes related to the YD, which involve different proxy sensitivities and threshold processes.

Varve microfacies and chronology from a new sediment record of Lake Gościąż (Poland)

The varved sediment of Lake Gościąż (Central Poland) is one of the most detailed and complete climate archives of the Late Glacial and the Holocene in Central Europe. Here, we present microfacies analyses in combination with μXRF core scanning and a detailed varve chronology of a new and continuous GOS18 sediment record.This record presents six lithozones that mark the most prominent depositional and geochemical changes during the Holocene and Late Glacial. Varve boundaries and five main varve microfacies types were distinguished under petrographic microscope. Analysis provides detailed insights into depositional processes and its changes since the Late Glacial. Microfacies components were used to interpret processes leading to varve formation. A new and independent chronology is obtained by triple varve counting on petrographic thin sections that is complemented by 137Cs measurements and 14C AMS dating of terrestrial plant remains. The age-depth model consists of three parts: (1) the upper part (0–520 cm) that is primarily based on varve counting, (2) the middle part (520–758 cm) obtained through age-depth modelling and (3) the lower part (758–1897 cm) developed by varve counting. The bottom of the composite profile coincides with the onset of lacustrine sedimentation in the late Allerød at 12,834 +134/-233 varve yr BP.The largest shift in geochemistry, expressed by log(Ca/Ti) and log(Si/Ti) ratios show a rapid increase of calcite precipitation and primary productivity at 7940 +112/-168 varve yr BP. Possible triggers for this include local changes in hydrology as the formation of “Na Jazach” system due to the Ruda River development and fluctuations of lake water level.

The first Holocene varve chronology for the UK: Based on the integration of varve counting, radiocarbon dating and tephrostratigraphy from Diss Mere (UK)

Abstract The British Isles lack long high-precision and independent chronologies to reconstruct Holocene environmental and climatic conditions at sub-decadal timescales. This paper reports the first Holocene varved chronology for the lacustrine sediment record of Diss Mere in the UK. The record of Diss Mere is 15 m long, and shows 4.2 m of finely-laminated sediments, which are present between ca. 9 and 13 m of core depth. The microfacies analysis identified three major seasonal patterns of deposition (microfacies 1–3), which corroborate the annual nature of sedimentation throughout the whole interval. The sediments are diatomaceous organic and carbonate varves with an average thickness of 0.45 mm. Microfacies 1 consists of a pale layer of authigenic calcite crystals and diatom frustules, and a dark layer composed of a planktonic diatoms and filaments of organic matter. Microfacies 2 is similar but includes a mono-specific diatom bloom layer preceding the calcite layer. Microfacies 3 consists of varves with an occasional very thin calcite layer and mono-specific diatom blooms in spring and autumn. A total of 8473 varves were counted with maximum counting error of up to 40 varves by the bottom of the varved sequence. To tie the resulting floating varve chronology to the IntCal20 radiocarbon timescale, we used a Bayesian Deposition model (P_Sequence with outlier detection) on all available chronological data from the core. The data included five radiocarbon dates, two known tephra layers (Glen Garry and OMH-185) with calendar ages based on Bayesian modelling of sequences of radiocarbon ages, and the relative varve counts between dated points. The resulting age-depth model (DISSV-2020) dates the varved sequence between ca. 2100 and 10,300 cal BP and age uncertainties are decadal in scale. The immediate implication of this new UK Holocene chronology is the updated precise ages for the Glen Garry tephra at 2073 ± 39 cal BP and the OMH-185 tephra at 2617 ± 29 cal BP. DISSV-2020 will also enable Holocene research at high time resolution and comparisons to other annually-resolved records on absolute timescales supporting climatic investigations at the regional level.

Chronology of Laurentide glaciation in New Jersey and the New York City area, United States

AbstractDeposits of at least three glaciations are present in New Jersey and the New York City area. The oldest deposits are magnetically reversed. Pollen and stratigraphic relations suggest that they are from the earliest Laurentide advance at ~2.4 Ma. Deposits of a second advance are overlain by peat dated to 41 ka and so are pre-Marine Isotope Stage (pre-MIS) 2. Their relation to marine deposits indicates that they predate MIS 5 but postdate MIS 11 and may postdate MIS 7 or 9, suggesting an MIS 6 age. The most recent deposits are of MIS 2 (last glacial maximum [LGM]) age. Radiocarbon dates and varve counts tied to glacial-lake events indicate that LGM ice arrived at its terminus at 25 ka, stood at the terminus until ~24 ka, retreated at a rate of 80 m/yr until 23.5 ka, and then retreated at a rate of 12 m/yr to 18 ka. At 18 ka the retreat record connects to the base of the North American Varve Chronology at Newburgh, New York. The 25–24 ka age for the LGM is slightly younger than, but within the uncertainty of, cosmogenic ages; it is significantly older than the oldest dated macrofossils in postglacial deposits in the region.

Seasonal deposition processes and chronology of a varved Holocene lake sediment record from Chatyr Kol lake (Kyrgyz Republic)

Abstract. Microfacies analysis of a sediment record from Chatyr Kol lake (Kyrgyz Republic) reveals the presence of seasonal laminae (varves) from the sediment base dated at 11 619±603 BP (years Before Present) up to ∼360±40 BP. The Chatvd19 floating varve chronology relies on replicate varve counts on overlapping petrographic thin sections with an uncertainty of ±5 %. The uppermost non-varved interval was chronologically constrained by 210Pb and 137Cs gamma spectrometry and interpolation based on varve thickness measurements of adjacent varved intervals with an assumed maximum uncertainty of 10 %. Six varve types were distinguished, are described in detail, and show a changing predominance of clastic-organic, clastic-calcitic or clastic-aragonitic, calcitic-clastic, organic-clastic, and clastic-diatom varves throughout the Holocene. Variations in varve thickness and the number and composition of seasonal sublayers are attributed to (1) changes in the amount of summer or winter/spring precipitation affecting local runoff and erosion and/or to (2) evaporative conditions during summer. Radiocarbon dating of bulk organic matter, daphnia remains, aquatic plant remains, and Ruppia maritima seeds reveals reservoir ages with a clear decreasing trend up core from ∼6150 years in the early Holocene, to ∼3000 years in the mid-Holocene, to ∼1000 years and less in the late Holocene and modern times. In contrast, two radiocarbon dates from terrestrial plant remains are in good agreement with the varve-based chronology.

Miniature radiocarbon measurements ( < 150 µg C) from sediments of Lake Żabińskie, Poland: effect of precision and dating density on age–depth models

Abstract. The recent development of the MIni CArbon DAting System (MICADAS) allows researchers to obtain radiocarbon (14C) ages from a variety of samples with miniature amounts of carbon (<150 µg C) by using a gas ion source input that bypasses the graphitization step used for conventional 14C dating with accelerator mass spectrometry (AMS). The ability to measure smaller samples, at reduced cost compared with graphitized samples, allows for greater dating density of sediments with low macrofossil concentrations. In this study, we use a section of varved sediments from Lake Żabińskie, NE Poland, as a case study to assess the usefulness of miniature samples from terrestrial plant macrofossils for dating lake sediments. Radiocarbon samples analyzed using gas-source techniques were measured from the same depths as larger graphitized samples to compare the reliability and precision of the two techniques directly. We find that the analytical precision of gas-source measurements decreases as sample mass decreases but is comparable with graphitized samples of a similar size (approximately 150 µg C). For samples larger than 40 µg C and younger than 6000 BP, the uncalibrated 1σ age uncertainty is consistently less than 150 years (±0.010 F14C). The reliability of 14C ages from both techniques is assessed via comparison with a best-age estimate for the sediment sequence, which is the result of an OxCal V sequence that integrates varve counts with 14C ages. No bias is evident in the ages produced by either gas-source input or graphitization. None of the 14C ages in our dataset are clear outliers; the 95 % confidence intervals of all 48 calibrated 14C ages overlap with the median best-age estimate. The effects of sample mass (which defines the expected analytical age uncertainty) and dating density on age–depth models are evaluated via simulated sets of 14C ages that are used as inputs for OxCal P-sequence age–depth models. Nine different sampling scenarios were simulated in which the mass of 14C samples and the number of samples were manipulated. The simulated age–depth models suggest that the lower analytical precision associated with miniature samples can be compensated for by increased dating density. The data presented in this paper can improve sampling strategies and can inform expectations of age uncertainty from miniature radiocarbon samples as well as age–depth model outcomes for lacustrine sediments.

Reanalysis of the Atmospheric Radiocarbon Calibration Record from Lake Suigetsu, Japan

ABSTRACTTerrestrial plant macrofossils from the sedimentary record of Lake Suigetsu, Japan, provide the only quasi-continuous direct atmospheric record of radiocarbon (14C) covering the last 50 ka cal BP (Bronk Ramsey et al. 2012). Since then, new high precision data have become available on U-Th dated speleothems from Hulu Cave China, covering the same time range (Cheng et al. 2018). In addition, an updated varve-based chronology has also been published for the 2006 core from Lake Suigetsu (SG06) based on extended microscopic analysis of the sediments and improved algorithms for interpolation (Schlolaut et al. 2018). Here we reanalyze the radiocarbon dataset from Suigetsu based on the new varve counting information and the constraints imposed by the speleothem data. This enables the new information on the calendar age scale of the Suigetsu dataset to be used in the construction of the consensus IntCal calibration curve. Comparison of the speleothem and plant macrofossil records provides insight into the mechanisms underlying the incorporation of carbon into different types of record and the relative strengths of different types of archive for calibration purposes.

Evidence of giant earthquakes and tsunamis of the seventeenth-century type along the southern Kuril subduction zone, eastern Hokkaido, northern Japan: a review

Abstract Large earthquakes of magnitude 7–8 occur at intervals of about 70–100 years in the southern Kuril Trench off eastern Hokkaido, northern Japan. However, especially large giant earthquakes (M w c. 8.8) have recurred at 300–500 year intervals, and the most recent of these was in the early seventeenth century. Surveys on the Pacific coast of eastern Hokkaido have documented field evidence that includes sharp contacts of peat and mud layers, indicative of coseismic coastal uplift, and large tsunami sand layers. Several proposed fault models of the seventeenth-century giant earthquake have been tested with numerical tsunami simulations. The best of these models incorporates a multi-segment interplate earthquake (M w 8.8) with large slip near the trench axis. The seventeenth-century giant earthquake and the 1611 Keicho Sanriku tsunami appear to have had different sources because varve counts from Lake Harutori suggest that the seventeenth-century giant earthquake occurred at c. 1637. Moreover, a consideration of regional tectonics suggests that convergence of the Kuril forearc sliver controls the current topography of eastern Hokkaido. Further progress in understanding the seismicity of this region will benefit from the combined insights of both geologists and seismologists.

Chronology and sedimentology of a new 2.9 ka annually laminated record from South Sawtooth Lake, Ellesmere Island in this NOAA depository: https://www.ncdc.noaa.gov/paleo/study/33214

Few annually laminated (varved) lacustrine records exist in the Arctic, but these high-resolution climate archives are needed to better understand abrupt climate change and the natural mode of climate variability of this sensitive region. This paper presents a new high-resolution 2900-year long varved lake sediment record from the Fosheim Peninsula, Ellesmere Island. The varve chronology is based on multiple varve counts made on high-resolution scanning electron microscope images of overlapping sediment thin sections, and is supported by several independent dating techniques, including 137Cs and 210Pb analysis, one optically stimulated luminescence age located close to the bottom of the composite sequence, and comparison between paleomagnetic variations of this record and the longest High-Arctic varve record, Lower Murray Lake, which confirms the reliability of the Sawtooth chronology. High-resolution backscattered images examined under a scanning electron microscope (SEM) were crucial to giving a more detailed view of sedimentation processes in the lake and thus help to delineate varves more precisely than in conventional image analysis. Fine-scale geochemical analysis reveals that lake sedimentation is mainly clastic and that elemental geochemistry is influenced by grain-size. Principal component analysis of multiple proxies and the coarse grain-size fraction of South Sawtooth Lake display similar fluctuations to the nearby Agassiz Ice Cap ∂18O record, including lower values during the Little Ice Age cold period. These results show this new high-resolution and continuous record has a reliable varve chronology and is sensitive to temperature variability. South Sawtooth Lake's mean sedimentation rate of 1.67 mm a−1 is higher than any other sedimentary sequence in the High Arctic providing a unique opportunity for extracting new, high-resolution paleoclimatological and paleoenvironmental record in a region where few other records currently exist.

Two twentieth-centuryMLH= 7.5 earthquakes recorded in annually laminated lake sediments from Sary Chelek, western Tian Shan, Kyrgyzstan

AbstractCentral Asia is highly vulnerable to large earthquakes, yet existing records of past seismic activity in this area are still insufficient to reliably assess regional earthquake hazard on longer timescales. Within this study, the sediments of Sary Chelek, a mountain lake in the western Kyrgyz Tian Shan, were investigated to explore its potential as a natural paleoseismic archive. The lacustrine deposits are characterized by a succession of annually laminated (varved) sediments overlying event deposits that consist of large-scale turbidites and distorted lake sediments, similar to earthquake-related deposits described from other lake sediment records. Microscopic sediment analysis furthermore revealed distorted varves in the laminated sequence that closely resemble earthquake-related soft-sediment deformation structures. Varve counting and radiometric dating determine the formation of the distorted varves and the emplacement of the large-scale event deposits to the early 1990s and mid-1940s, respectively. This is in good temporal agreement with the occurrence of two large earthquakes that struck western Kyrgyzstan in AD 1992 and AD 1946. These results and particularly the precise age control of the Sary Chelek sediment record highlight its potential for establishing a long and precisely dated record of regional earthquake activity.

A local clay-varve chronology of Onega Ice Lake, NW Russia

Onega Ice Lake developed in front of the receding Late Weichselian ice margin in Russian Karelia. Glacial varves that formed in Onega Ice Lake have been earlier studied by means of varve counts, palaeomagnetism and 14C AMS dates from small lakes north of modern Lake Onega and from Lake Onega proper. Synchronous changes in magnetic parameters and similar stratigraphy of these varve records together with the existence of basin-wide marker interval of pink-coloured varves have been used for core-to-core correlation and palaeogeographic interpretations. Unfortunately, there are missing varve-to-varve correlations between these cores. We present a 1155 yr long local varve chronology based on 3 parallel overlapping cores from two small lakes in the Zaonezhsky Peninsula at the northern coast of Lake Onega. Varve counts and matching of varve series were made from digital images. Following the textural, structural, colour and thickness changes of varves within Onega Ice Lake varve series, six characteristic varve units are identified. These clay units reflect changing sedimentary conditions at the time of accumulation that in general can be interpreted as a progressively increasing distance to the retreating ice margin. Variations in varve thickness superimposed on that overall trend, namely two episodes of abrupt and consistent decrease in varve thickness, do not correspond to known lake-level changes or shifts in outflow directions. AMS chronology for deglaciation of Lake Onega basin gives some evidences for correlation of above intervals of decreased varve thickness with the GI-1c2 and GI-1B cold events in NGRIP δ 18O event stratigraphy but further age estimations are needed to confirm presented correlations. Interval of reddish-brown varves – earlier described also as the ‘pink horizon’ – was observed in all studied sequences, and according to varve correlation, at the same stratigraphical level, which proves its basin-wide synchronous appearance. Ca 100 km south of our study area, Saarnisto and Saarinen (2001) reported ca 200 more varves compared to our results. Visual correlation of varve thickness graphs places these extra varves to the proximal part of the series and indicate a rapid ice recession from the main lake basin to the northern Lake Onega area with the ice recession rate ca 500 m per year.

Glacial and climate history of the last 24 000 years in the Polar Ural Mountains, Arctic Russia, inferred from partly varved lake sediments

We present a well‐dated, high‐resolution and continuous sediment record spanning the last c. 24 000 years from lake Bolshoye Shchuchye located in the Polar Ural Mountains, Arctic Russia. This is the first continuous sediment succession reaching back into the Last Glacial Maximum (LGM) ever retrieved from this region. We reconstruct the glacial and climate history in the area since the LGM based on sedimentological and geochemical analysis of a 24‐m‐long sediment core. A robust chronology was established using a combination of AMS 14C‐dating, the position of the Vedde Ash and varve counting. The varved part of the sediment core spans across the LGM from 24 to 18.7 cal. ka BP. We conclude that the lake basin remained ice‐free throughout the LGM, but that mountain glaciers were present in the lake catchment. A decrease in both glacial varve preservation and sedimentation rate suggests that these glaciers started to retreat c. 18.7 cal. ka BP and had disappeared from the catchment by 14.35 cal. ka BP. There are no indications of glacier regrowth during the Younger Dryas. We infer a distinct climatic amelioration following the onset of the Holocene and an Early to Middle Holocene thermal optimum between 10–5 cal. ka BP. Our results provide a long‐awaited continuous and high‐resolution record of past climate that supplements the existing, more fragmentary data from moraines and exposed strata along river banks and coastal cliffs around the Russian Arctic.

An extended and revised Lake Suigetsu varve chronology from ∼50 to ∼10 ka BP based on detailed sediment micro-facies analyses

Lake Suigetsu (Japan) is a key site for radiocarbon (14C) calibration and palaeo-environmental reconstruction in East Asia. Here we present a description of the sediment (micro)facies, which in combination with a new approach to varve interpolation allows construction of a revised varve based chronology that extends the previous 2012 varve based chronology by ∼10 ka, back to ∼50 ka BP. Challenges in varve counting and interpolation, which were previously discussed in detail only for the Last Glacial-Interglacial Transition, are described here back to ∼50 ka BP. Furthermore, the relative merits of varve counting by μXRF scanning and by thin-section microscopy are discussed. Facies analysis reveals four facies zones, their transitions driven by both local and climatic controls. The lamination quality of the sediment is highly variable and varve interpolation reveals that in the analysed time interval, on average, only 50% of the annual cycles are represented by seasonal layers. In the remaining years seasonal layers are indistinguishable, i.e. either did not form or were not preserved. For varve interpolation an advanced version of the Varve Interpolation Program was used, which enabled the construction of the longest, purely varve dated chronology published, despite long intervals of poor lamination quality. The calculated interpolation uncertainty is +8.9% and −4.6%, which is well within expectations considering the high degree of interpolation and the length of the record.

Multiple varve chronologies for the last 2000 years from the sediments of Lake Żabińskie (northeastern Poland) – Comparison of strategies for varve counting and uncertainty estimations

Abstract This study compares different methods to count biogenic varves in Lake Żabinskie in northeastern Poland. To perform this comparison, we used 2000 years-long varved sediment record from this lake because of the well-preserved laminations as well as the independent age controls, i.e. 29 AMS14C dates, 137Cs activity peaks and volcanic glass shards (1875 AD Askja cryptotephra). Microscopic investigations of thin sections allowed us to identify six major varve microfacies along the sediment profile. Using these microfacies, we tested three counting methods and different approaches of counting uncertainty estimation. These methods provided comparable numbers of varves (1943 ± 30, 2034 ± 34, 2028 +34/-53) and similar shapes in the age-depth relations. However, in two methods, we found possible disadvantages in arbitrary assumptions and subjective decisions in the process of chronology building, procedures leading to age underestimation as well as problems with reliable and objective estimations of counting uncertainty. Based on these results, we propose the counting method which include analyses of major varve microfacies and three independent countings without the need for varve-by-varve microscopic investigations. This method provided acceptable results (

Late Holocene high resolution multi-proxy climate and environmental records from Lake Van, eastern Turkey

We present the multi-proxy records of centennial scale climate and environmental changes over the last 3.5 ka from a varved sediment core in Lake Van, eastern Turkey. The multi-proxy analyses include ostracod counts, μ-XRF elemental, total organic (TOC) and inorganic carbon, C-N elemental and stable isotopes. For the age model of the core, we use radionuclide (210Pb and 137Cs) analysis and varve counting. Large differences between Accelerator Mass Spectrometry (AMS) radiocarbon dates from TOC and varve ages indicate reservoir ages of 1.2–3.8 ka calBP. Average sedimentation rate for the last 170 years (top 75 mm of the core) ranges between 0.42 and 0.54 mm/yr according to 210Pb dating.Multi-proxy parameters show that Lake Van experienced more arid conditions during the 3.5–1.6 Ka calBP than those during the last 1.6 ka BP. 16 periods of alternating cold/dry and warm/wet intervals with 100–350 years duration are observed over the last 3.5 ka. The Lake Van climate records are conformable with the Lake Nar and the Sofular speleothem records as well as the European historical climate periods including Roman Warm Period (RWP), Dark Age Cold Period (DACP), Medieval Warm Period (MWP) and Little Ice Age (LIA), indicating teleconnections with the North Atlantic system. Human influence is reflected by high detrital influx in the last 700 years.

Sedimentary laminae in muddy inner continental shelf sediments of the East China Sea: Formation and implications for geochronology

The sedimentary rhythm is well developed in the environment which is controlled by strong seasonal climate changing condition. This rhythm is important for sediment core dating purpose. In this study, we examine muddy sediments on the inner continental shelf of the East China Sea that are influenced under seasonal change of the East Asian monsoon. We use Ensemble Empirical Mode Decomposition (EEMD) method to process sediment grain size and X-radiograph negatives grayscale value data in three sediment cores from this area and use the results to analyze the patterns of sedimentary variability and the causes of cyclic variability of the sedimentary process. The variability in the grain size and grayscale values of the core sediments has three components: the high-frequency variability, low-frequency variability and a secular trend. Among these components, the high-frequency component reflects variability on annual time scale can be well recognized, we suggest that the annual variability is derived from seasonal variation in the sediment flux from the Yangtze River to the sea, as well as the East Asian monsoon's impact on the sedimentary dynamics of the East China Sea's inner continental shelf. However, the other variability is hard to identify which cycles there are. This variability may reflect decadal winter monsoon oscillation and human activity of dam construction in the Yangtze River. Each annual variability presents a varve in the sediment sequence, which can be used to determine the sediment deposition rate and accurately date the core sediment. We found that the average deposition rates of the three cores from north to south on the inner shelf were 3.1 cm/yr, 1.0 cm/yr, 0.9 cm/yr, indicating that the Yangtze-derived sediment decreased with the increasing distance from the Yangtze estuary to the shelf. The deposition rate of each core varies over time, and the maximum deposition rate can be 3–5 times greater than the minimum rate. The sediment ages obtained from varve chronology and radiometric dating are fairly consistent on a centennial scale, differing only by 2–5 years. Thus, varve counting is a useful supplementary approach to radiometric age dating for constructing chronologies for core sediment in shelf seas influenced by monsoons.