Varve Microfacies Research Articles

Limnological responses to environmental changes during the last 3,000 years revealed from a varved sequence of Lake Lubińskie (western Poland)

Sediments from Lake Lubińskie, western Poland, were investigated to determine the limnological responses to environmental changes during the last 3,000 years. To identify the mechanisms driving the eutrophication in the lake, we distinguished six lithozones along with five major varve microfacies. An age-depth model based on varve counting and radiometric measurements was established resulting in final age of 946 +113/-144 before the Common Era at the bottom of the composite profile. Varve microfacies as well as geochemical, pollen, and diatom data was used to determine major phases of landscape and lake ecosystem transformations. Our data shows that until the 4th century of the Common Era, conditions in the lake were stable. Several shifts occurred before the first millennium, when changes were observed in every proxy as a response to the increased agricultural activity in the area as well as climate fluctuations. The highest frequency of shifts was observed from the 17th century onward and mirrored further deforestation (decrease in arboreal pollen), accelerated erosion (increase in Ti), increased nutrient delivery (increased total nitrogen content), and better ventilation of the water body (higher Mn/Fe ratio). Simultaneously, the lake became more eutrophic as a response to changes in the lake catchment area. Our study suggests that inferred lake-level changes are primarily related to human activity in the catchment area.

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 micromorphology of glaciolacustrine varve sediments and their use for reconstructing palaeoglaciological and palaeoenvironmental change

Former glaciolacustrine systems are an important archive of palaeoglaciological, palaeoenvironmental and palaeoclimatic change. The annually laminated (varved) sediments that, under certain conditions, accumulate in former glacial lakes, offer a rare opportunity to reconstruct such changes (e.g. glacier advance and retreat cycles, glacier ablation trends, permafrost melt, nival events) at annual or even sub-annual temporal resolution. Data of this kind are desirable for their ability to guide and test numerical model simulations of glacier dynamics and palaeoclimatic change that occur over rapid time intervals, with implications for predicting future glacier response to climatic change, or the effects of weather and climate events on lake sedimentation. The most valuable records preserved in glaciolacustrine systems are continuous varved sequences formed in the distal parts of glacial lakes, where microscale lamination structures can accumulate relatively undisturbed. Technological advances, in the last few decades, have enabled improved characterisation of glaciolacustrine varve microfacies and the precise measurement of varve thickness at the micrometre scale. However, unlike in cognate fields (e.g. soil science), protocols for the robust and consistent description and interpretation of glaciolacustrine varve sediments are lacking. To fill this gap, and to provide a resource for future studies of glaciolacustrine varved sediments, this paper reviews the processes of sedimentation in glacial lake basins, and presents the defining microfacies characteristics of glacial varves using a descriptive protocol that uses consistent examination of grain size, sorting, structure, nature of contacts, development of plasmic fabrics and features such as dropgrains and intraclasts within individual laminations. These lamination types are then combined into lamination sets, whose structures can be interpreted as glaciolacustrine varves. Within this framework, we define five principal assemblages of glaciolacustrine varve microfacies which, if clearly identified in palaeoglaciolacustrine settings, enable more detailed palaeoenvironmental interpretations to be made. Finally, we discuss the utility and complexities of reconstructing the evolution of former glacial lake systems using varve microfacies and thickness datasets.

Grain-Size Distribution and Structural Characteristics of Varved Sediments from Lake Żabińskie (Northeastern Poland)

Typically, the description of varve microfacies is based on microscopic sedimentary structures, while standard grain-size analysis is commonly applied with lower resolution. Studies involving a direct comparison of varve microfacies and particle-size distributions, common for clastic environments, are scarce for biogenic varves. In this study, we analyzed nine-year resolution grain-size data from Lake Żabińskie (northeastern Poland) to detect differences between varve microfacies. Six varve microfacies were differentiated using grain-size distributions and sedimentological attributes (calcite layer thickness, dark layer thickness, mass accumulation rate). However, changes in particle-size distributions between different varve types are relatively small and indicate a similar source for the material deposited. Decomposition of grain-size distributions with the end-member approach allows recognition of relative changes for the deposition of allochthonous (mineral) and autochthonous (carbonates, (hydr)oxides) components. Grain-size data suggest that sources of allochthonous material remained constant, while varve formation was controlled mostly by in-lake processes.

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 (

Varve microfacies and varve preservation record of climate change and human impact for the last 6000 years at Lake Tiefer See (NE Germany)

The Holocene sediment record of Lake Tiefer See exhibits striking alternations between well-varved and non-varved intervals. Here, we present a high-resolution multi-proxy record for the past ~6000 years and discuss possible causes for the observed sediment variability. This approach comprises microfacies, geochemical and microfossil analyses and a multiple dating concept including varve counting, tephrochronology and radiocarbon dating. Four periods of predominantly well-varved sediment were identified at 6000–3950, 3100–2850 and 2100–750 cal. a BP and AD 1924–present. Except of sub-recent varve formation, these periods are considered to reflect reduced lake circulation and consequently, stronger anoxic bottom water conditions. In contrast, intercalated intervals of poor varve preservation or even extensively mixed non-varved sediments indicate strengthened lake circulation. Sub-recent varve formation since AD 1924 is, in addition to natural forcing, influenced by enhanced lake productivity due to modern anthropogenic eutrophication. The general increase in periods of intensified lake circulation in Lake Tiefer See since ~4000 cal. a BP presumably is caused by gradual changes in the northern hemisphere orbital forcing, leading to cooler and windier conditions in Central Europe. Superimposed decadal- to centennial-scale variability of the lake circulation regime is likely the result of additional human-induced changes of the catchment vegetation. The coincidence of major non-varved periods at Lake Tiefer See and intervals of bioturbated sediments in the Baltic Sea implies a broader regional significance of our findings.

Calibrating 210Pb dating results with varve chronology and independent chronostratigraphic markers: Problems and implications

Varved lake sediments provide a unique opportunity to validate results of isotope dating methods. This allows testing of different numerical models and constraining procedures to produce reliable and precise chronologies. Here we present results of the model testing and validation by multiple dating approaches for the varved sediment record from Lake Żabińskie (northeastern Poland). Our goal was to assess possible deviations of 210Pb-derived ages from true sediment ages provided by varve chronology and to check how different numerical procedures can improve the consistency of the chronologies. Different methods for age estimation were applied including varve counting, 210Pb, 137Cs, 14C and tephra identification. Microscopic analysis of the varve microfacies revealed that laminations found in Lake Żabińskie were biogenic (calcite) varves. Three independent counts indicated a good preservation quality of laminae in the sediment profile which contained 178+4/−8 varve years. The calendar-year time scale was verified with two maxima of 137Cs activity concentrations in the sediments (AD 1963 and 1986) and a terrestrial leaf dated to AD 1957–1958 by the 14C method. Additionally, geochemical analysis of the glass shards found in the sediments indicated a clear correlation with the Askja AD 1875 eruption of Iceland which provided an unambiguous verification of the varve chronology. For testing 210Pb dating we used two routinely applied models: Constant Flux Constant Sedimentation (CFCS) and Constant Rate of Supply (CRS). None of the models in their standard forms produced a chronology consistent with varve counts and independent chronostratigraphic markers. Both models yielded ages much younger than the calendar age with a difference of ca. 50 years at the bottom part of the profile. However, a significant improvement was introduced after using the composite CFCS model with sediment accumulation rates calculated for different zones of the sediment profile. This provided highly consistent values along the time scale with deviations <5 yrs compared with calendar ages. Also constraining the CRS model with 137Cs peaks as well as testing the correction values for incomplete 210Pb inventory provided results that finally deviated from the calendar age only by ≈ 10 yrs for the 120 years old sediments.

Comparing Varve Counting And &lt;sup&gt;14&lt;/sup&gt;C-Ams Chronologies In The Sediments Of Lake Żabińskie, Northeastern Poland: Implications For Accurate &lt;sup&gt;14&lt;/sup&gt;C Dating Of Lake Sediments

Varved lake sediments from Lake Zabihskie (northeastern Poland) provide a high- resolution calendar-year chronology which allows validation of &lt;sup&gt;14&lt;/sup&gt;C dating results. Microscopic analy­sis of the varve microfacies revealed that laminations found in Lake Zabihskie were biogenic (calcite) varves. Three independent counts indicated a good preservation quality of laminae in the 348 cm long sediment profile which contained 1000&lt;sup&gt;+12&lt;/sup&gt;/&lt;sub&gt;-24&lt;/sub&gt; varves. The varve chronology was validated with the &lt;sup&gt;137&lt;/sup&gt;Cs activity peaks, the tephra horizon from the Askja eruption at AD 1875 and with the timing of major land-use changes of known age inferred from pollen analysis. 32 AMS &lt;sup&gt;14&lt;/sup&gt;C dates of terrestrial macrofossils distributed along the profile were compared with the varve chronology. After identifica­tion of outliers, the free-shape model performed with 21 &lt;sup&gt;14&lt;/sup&gt;C dates provided the best possible fit with the varve chronology. We observed almost ideal consistency between both chronologies from the present until AD 1250 while in the lower part (AD 1000-1250) the difference increases to ca. 25 years. We demonstrate that this offset can be explained by too old radiocarbon ages of plant remains trans­ported to the lake by the inflowing creek. Results of this study highlight that careful interpretation of radiocarbon age-depth models is necessary, especially in lakes where no annual laminations are ob­served and no independent method are used for cross-validation.

An abrupt wind shift in western Europe at the onset of the Younger Dryas cold period

The Younger Dryas cold reversal during the last glacial termination is one of the most abrupt climate change events observed in the Northern Hemisphere. Analyses of varved lake sediments from western Germany suggest that storminess in the North Atlantic region increased within a single year at this time, providing a mechanistic link between a decrease in the meridional overturning circulation and western European cooling. The Younger Dryas cooling 12,700 years ago is one of the most abrupt climate changes observed in Northern Hemisphere palaeoclimate records1,2,3,4. Annually laminated lake sediments are ideally suited to record the dynamics of such abrupt changes, as the seasonal deposition responds immediately to climate, and the varve counts provide an accurate estimate of the timing of the change. Here, we present sub-annual records of varve microfacies and geochemistry from Lake Meerfelder Maar in western Germany, providing one of the best dated records of this climate transition5. Our data indicate an abrupt increase in storminess during the autumn to spring seasons, occurring from one year to the next at 12,679 yr BP, broadly coincident with other changes in this region. We suggest that this shift in wind strength represents an abrupt change in the North Atlantic westerlies towards a stronger and more zonal jet. Changes in meridional overturning circulation alone cannot fully explain the changes in European climate6,7; we suggest the observed wind shift provides the mechanism for the strong temporal link between North Atlantic Ocean overturning circulation and European climate during deglaciation.

Palaeoclimatic implications from micro-facies data of a 5900 varve time series from the Piànico interglacial sediment record, southern Alps

Varve micro-facies analyses have been carried out on a 405-cm-thick annually laminated sediment sequence from the Piànico palaeolake in the southern Alps considered to correlate with the MIS 11 interglacial. This varve counted interval represents the uppermost 5900 yr of a ca 400 kyr old interglacial lacustrine deposit with a minimum length of 16,000 varve years. Intercalated in the varve succession are: (i) detrital layers, (ii) debris flows (slump deposits), and (iii) micritic calcite layers. The annual couplets are composed of a dominant light summer layer of biochemically precipitated calcite and a thin dark winter layer consisting of organic and minerogenic detritus. Microscopic correlation of individual couplets in two outcrops 130 m apart demonstrated basin-wide continuity of varve deposition. Summer layers have been found to be composed of up to four sub-layers differing in grain size, most likely reflecting discrete pulses of calcite precipitation. Two long periods of pronounced decreases in varve thickness occur within the interglacial (1100 varve years) and during the decline of full interglacial conditions (480 varve years) suggesting colder climatic conditions. The decreases in varve thickness are further accompanied by changes in the pattern of summer sub-layering. The first cold interval reflects an exceptionally long intra–interglacial climatic fluctuation indicating a mode of climatic variability different from the present interglacial. Wavelet analyses of seasonal layer thickness data revealed that periodic variations of solar activity (88-yr and 208-yr cycles) and probably of thermohaline circulation (512-yr cycle) impact on varve formation at certain intervals of the studied time window.

Biogeochemical and micro-facial fingerprints of ecosystem response to rapid Late Glacial climatic changes in varved sediments of Meerfelder Maar (Germany)

The response of a lacustrine ecosystem to climatic changes from 13,500 to 10,800 BP was studied in a varve dated sediment profile of Lake Meerfelder Maar, western Germany. Bulk biogeochemical parameters, stable carbon and nitrogen isotopes of sedimentary organic matter and micro-facies analysis are used for a detailed investigation of the lake's development from the Allerod interstadial (AL) to the Younger Dryas stadial (YD) and into the early Holocene (Preboreal). Varve micro-facies reveal rapid changes in composition and seasonal structure of the depositional environment mainly in temporal accordance with changes of terrestrial biozones. The respective responses of bulk proxy parameters (∼bi-decadal resolution) indicate different sensitivities to diverse climatic changes. A prominent transition took place within two decades at the AL/YD boundary (12,690–12,670 BP). Increased flux of nutrients released from redeposited littoral sediments and shorter YD summer seasons led to an acceleration and concentration of lacustrine primary production with reduced discrimination against 13C. High lacustrine primary production was further favored by relatively warm YD summer temperatures. At 12,240 varve years BP, from 1 year to the next, a regular deposition of detrital layers in spring set in which is related to local hydrologic threshold processes amplifying the response to increased snowmelt discharge. This distinct change in the middle of the YD is clearly detected by varve micro-facies but not equally recorded in organic bulk proxy data. Especially, carbon isotope ratios remain constant and indicate a negligible effect of this process on the productivity of lacustrine algae. The YD/Preboreal transition (11,645–11,585 BP) is marked by a characteristic change in micro-facies. Throughout this transition, stable carbon isotope ratios strongly decline while the accumulation of opal and organic matter (OM) remained constant. This is seen as an increasing importance of spring and autumn for gross primary production at the onset of the Holocene.

Biogeochemical and micro-facial fingerprints of ecosystem response to rapid Late Glacial climatic changes in varved sediments of Meerfelder Maar (Germany)

The response of a lacustrine ecosystem to climatic changes from 13,500 to 10,800 BP was studied in a varve dated sediment profile of Lake Meerfelder Maar, western Germany. Bulk biogeochemical parameters, stable carbon and nitrogen isotopes of sedimentary organic matter and micro-facies analysis are used for a detailed investigation of the lake's development from the Allerød interstadial (AL) to the Younger Dryas stadial (YD) and into the early Holocene (Preboreal). Varve micro-facies reveal rapid changes in composition and seasonal structure of the depositional environment mainly in temporal accordance with changes of terrestrial biozones. The respective responses of bulk proxy parameters (∼bi-decadal resolution) indicate different sensitivities to diverse climatic changes. A prominent transition took place within two decades at the AL/YD boundary (12,690–12,670 BP). Increased flux of nutrients released from redeposited littoral sediments and shorter YD summer seasons led to an acceleration and concentration of lacustrine primary production with reduced discrimination against 13C. High lacustrine primary production was further favored by relatively warm YD summer temperatures. At 12,240 varve years BP, from 1 year to the next, a regular deposition of detrital layers in spring set in which is related to local hydrologic threshold processes amplifying the response to increased snowmelt discharge. This distinct change in the middle of the YD is clearly detected by varve micro-facies but not equally recorded in organic bulk proxy data. Especially, carbon isotope ratios remain constant and indicate a negligible effect of this process on the productivity of lacustrine algae. The YD/Preboreal transition (11,645–11,585 BP) is marked by a characteristic change in micro-facies. Throughout this transition, stable carbon isotope ratios strongly decline while the accumulation of opal and organic matter (OM) remained constant. This is seen as an increasing importance of spring and autumn for gross primary production at the onset of the Holocene.

High resolution sediment and vegetation responses to Younger Dryas climate change in varved lake sediments from Meerfelder Maar, Germany

This work focuses on a 1900-year section of varved sediments from Lake Meerfelder Maar (MFM) extending from the Late Allerød to the Preboreal. Varve counting provides the chronological framework and determines the length of Younger Dryas to 1025–1090 years. A strong relation between climate change, environment response and depositional processes has been found. In consequence, varve microfacies variations are a sensitive proxy for environment changes. These are reflected, for example, in erosion processes within the lake’s catchment (minerogenic input) and lake productivity (diatom blooms). The observed varve changes have been quantified by multiproxy analyses of physical and chemical sediment parameters with a resolution of between 8 and 40 years depending on sedimentation rate. In addition, high resolution palynological investigations provide the biostratigraphical subdivision based on changes in the vegetation occurring during the same time interval. Varve observations reveal that environment changes at the beginning and the end of the Younger Dryas occurred within 20–50 years. Furthermore, sediment and vegetation changes were synchronous. Within the actual precision of the MFM and GRIP chronologies (divergence of only a few decades) terrestrial responses in Western Europe occurred quasi-synchronous to temperature changes in Greenland.