Thickness record of varves from glacial Ojibway Lake recovered in sediment cores from Frederick House Lake, northeastern Ontario

The thicknesses of 384 rhythmic couplets were measured along a composite sequence of glacial Lake Ojibway glaciolacustrine deposits recovered in two sediment cores from Frederick House Lake, Ontario. The visual comparison of distinctive couplets in the CT-scan radiographs of the Frederick House core samples to photographs of core samples from Reid Lake show a match of ±1 varve number from v1656-v1902, and ±5 varve numbers between v1903-v2010, relative to the regional numbering of the Timiskaming varve series. There are two interpretations for the post-v2010 couplets that fall within the Connaught varve sequence of the regional series. In the first, the interpreted numbering spans from v2066-v2115, which produces a gap of 55 missing varves equivalent to v2011-v2065, and corresponds to the original interpretation of the Connaught varve numbering. The second spans v2011a-v2060a, and represents alternative (a) numbering for the same varves. Varve thickness data are listed in spreadsheet files (.xlsx and .csv formats), and CT-Scan radiograph images of core samples are laid out on a mosaic poster showing the interpreted varve numbering and between-core sample correlations of the varve couplets.

Supplemental Material: A new glacial varve chronology along the southern Laurentide Ice Sheet that spans the Younger Dryas–Holocene boundary

Varve thickness data and ¹⁴C-date metadata.<br>

Supplemental Material: A new glacial varve chronology along the southern Laurentide Ice Sheet that spans the Younger Dryas–Holocene boundary

Varve thickness data and ¹⁴C-date metadata.<br>

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

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.

Constructing paleoclimate networks from annually laminated lake sediments – the VARDA database

&lt;p&gt;Reconstructing global patterns of past climate change requires large-scale networks of paleoclimatic archives. Generating paleoclimatic networks relies on precise synchronization of individual records with robust age control. The detailed age constrains of continuous varved lake sediments and the good preservation of isochrones from supra-regional extreme events make these records ideal for constructing large scale continental paleoclimatic networks. Yet, a global synthesis of varved lake archives is missing.&lt;/p&gt;&lt;p&gt;Here we present the VARved sediments DAtabase 1.0 (VARDA 1.0), the first global data compilation for varve chronologies and associated palaeoclimatic proxy records. VARDA 1.0 uses a connected data model provided by a state-of-the-art graph database, enabling custom generations of synchronized paleoclimatic networks. We report on compilation strategies for the identification of varved lakes and assimilation of high-resolution chronologies. Existing chronologies have been re-assessed and harmonized using a novel approach that infers information on sedimentation rates enclosed in varve thickness records. This information provides detailed information on the priors required for Bayesian age-depth modelling and strongly improves these results. Additionally, a synthesis of tephra layers from volcanic eruptions provides supra-regional isochrones for synchronizing even distant varved lake records. The current version (VARDA 1.0) comprises 261 datasets from 95 varved lake archives, including chronological information from &lt;sup&gt;14&lt;/sup&gt;C dating and varve thickness measurements, but also palaeoclimatological proxy data. We further explore potential applications of such networks in paleoclimatic studies, such as identifying leads and lags of regional climate change, large-scale model-data comparisons or differentiated proxy responses between archives. The VARDA graph-database and user interface can be accessed online at https://varve.gfz-potsdam.de.&lt;/p&gt;

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

A finely laminated lake sediment record with a basal age of 11,619 ± 603 years BP was retrieved from Lake Chatyr Kol (Kyrgyz Republic). Microfacies analysis reveals the presence of seasonal laminae (varves) from the sediment basis to ~ 360 ± 40 years BP. The Chatvd19 floating varve chronology covers the time span from 360 ± 40 years BP to the base and 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 γ-spectrometry and interpolation based on varve thickness measurements of adjacent varved intervals with an assumed uncertainty of 10 %. Six varve types were distinguished, are described in detail and show a changing predominance of clastic-organic, clastic-calcitic or -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 reveal reservoir ages with a clear decreasing trend up core from ~ 6,150 years in the early Holocene, to ~ 3,000 years in the mid-Holocene, to ~ 1,000 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.

Solar activity expressed in a modern varve thickness sequence

Annually laminated sediments (varves) form in particular depositional settings, e.g., where seasonal climate produces fluctuations in runoff volume; variations in runoff affect the amount and type of sediment delivered to a catchment. Prior studies confirm that variations in selected varve traits correlate with inter-annual climate signals. In some locations, solar activity also appears to be expressed in varve characteristics, either through a direct effect or indirectly via influence of solar activity on climate. Evidence from proglacial Iceberg Lake, Alaska, indicates that solar activity may have directly contributed to varve deposition. A varve thickness sequence is compared to sunspot observations from 1610–1995 CE. Maunder and Dalton minima are clearly expressed in a varve power spectrogram; varve signal amplification beginning ca. 1950s CE coincides with increasing activity evident in a sunspot spectrogram, features that are only vaguely discernible in the raw time-series plots. Spectral relationships at sunspot periodicities are consistent with direct solar forcing of varve thickness, independent of any effect solar activity might otherwise have on climate. Simulations based on a meltwater model indicate that direct forcing could result from amplified ultraviolet (UV) emission during solar maxima, combined with lower UV albedo of glacial ice. The plausible forcing mechanism bolsters epistemology for concluding a cause–effect relationship: solar variability likely contributed directly to inter-decadal patterns in Iceberg Lake varve thicknesses. The putative effect could be enhanced at higher latitudes, where Earth’s atmosphere absorbs less of the UV energy emitted by the Sun; periods of lowered ozone concentration near the poles would exacerbate the natural abetting UV phenomena, potentially linking human activity to recent and accelerated polar ice cap melting.