The aim of this work is to elucidate the specifics of recent sedimentation in the Chukchi Sea, based on the study of the material composition of Late Holocene bottom sediments. Analytical methods included grain size and mineralogical analyses. The results of 210Pb and 137Cs dating were used. The sediments are clayey silt and silty clay containing sand admixture and single gravel grains and pebble. The content of coarse-grained material increases slightly in the upper parts of the studied sections. This is probably due to the greater contribution of ice rafting to the recent Chukchi Sea sedimentation as a result of climate warming. The ultrafine- and fine-grained (0.25-0.05 mm) sandy material is dominated by light-fraction minerals. Volcanic glass was discovered in the sediments sampled in the southern and central areas of the Chukchi Sea. It might have been transported from the volcanoes of Alaska, the Aleutian Islands, and the Kamchatka Peninsula through the Bering Strait by the Pacific currents directed from south to north. The sediments collected in the southern, central, and northern areas of the Chukchi Sea differ in grain size and mineral composition. This is probably due to their remoteness from the coastline and provenance areas and is also caused by different rates of sedimentation.

Authigenic phases in lake sediments hold the potential to record changes in the isotope compositions of past lake water, potentially yielding valuable information on secular changes in continental weathering patterns and rates, including over past glacial cycles. Here, different leaching approaches are investigated with the aim of extracting Sr, Nd, Pb, and Be hosted in authigenic Fe-Mn (oxy)hydroxide sediment phases for precise isotope measurements. Elemental Al/Mn, Ca/Mn, and P/Mn ratios obtained via a mild reductive leach agree well with the composition of marine authigenic Fe-Mn phases. For core top sediments, leached Sr isotope compositions obtained with this leach agree well with the composition of lake water. The Be and Nd isotope compositions of core top leachates are consistent with the spatial variability observed in the water column. Due to high concentrations in Fe-Mn phases, leachate compositions are dominated by authigenic Be, Sr, Nd, and Pb, even in cases when as much as 40% of leached phases (by mass) are non-authigenic. These lines of evidence suggest that the mild reductive leach successfully extracts the modern lake isotope composition from modern sediments in terms of the isotope systems investigated. We further show that the leaching method is also reliable for older sediments (<340 ka): leached paleo-Sr isotope compositions are consistent between the current and previous interglacial periods, as well as for glacial periods. This suggests that reconstructed water isotope compositions are not affected by early diagenetic processes, instead reflecting environmental factors around the lake that determine the composition of weathering fluxes. Although more difficult to assess for Be, Nd, and Pb due to the heterogeneity of modern lake water, the data we present indicate the overall robustness of the leaching approach. These promising results open up lakes as archives for paleo-weathering reconstructions. Given that marine reconstructions face some important limitations (e.g., integration of basin-wide changes in weathering processes, long residence times for Sr, etc.Fe), lake records provide an avenue to improve our understanding of changes in regional weathering processes over glacial-interglacial timescales. The mild reductive leach used here may also be useful for meteoric Be studies in marine shelf settings, to prevent leaching of terrestrial sedimentary Fe-Mn oxy(hydroxide) phases.

This paper describes an approach assuming that already in the sea, based on the express analysis of visually similar cores of Arctic Holocene sediments and their comparison with dated and studied in detail cores of the regional sediments, it is possible to select a material that is promising for sequence stratigraphic correlation and paleoreconstructions. The range of lithological, colorimetric (CIE L*, CIE a*, and CIE b*), geophysical (magnetic susceptibility), and geochemical (Fe/Rb, Mn/Rb, and Ti/Rb) parameters is analyzed. The most informative characteristics include the CIE b* color coordinate, magnetic susceptibility, and Fe/Rb.

The objective of the work was a comprehensive study of Late Holocene bottom sediments from the southern Chukchi Sea and reconstruction of their accumulation conditions. Analytical methods included macroscopic description with smear slides, 210Pb dating of sediments, determination of biogenic components, magnetic susceptibility measurements, and grain size distribution, palynological, and mineral analyses. The modern sedimentation rate established at the study point is 8–10 mm/year. Sediments are mainly represented by silts. In the upper part of the core, there are elevated concentrations of SiO2biog, Corg, and Ntot and decreased magnetic susceptibility values. This is probably due to the increased bioproductivity of the Chukchi Sea in recent years, caused by current climate warming. The palynological composition of the studied deposits reflects the tundra and forest–tundra vegetation on land adjacent to the Chukchi Sea. The presence of Neogene pollen in Late Holocene sediments is evidence of their transfer from eroded ancient sediments.

Late Holocene sediments have been recovered in a core from the central Chukchi Sea to reconstruct their accumulation conditions. The sediments consist mainly of terrigenous and just partly of biogenic material. Fine sand is dominated by up to 99.8

—The paper provides the results of experiments with sediment traps in the deep-water part of the South Basin of Lake Baikal (depth of 1366 m), installed from March 2015 to March 2016 in order to study recent sedimentation within the lake. We present new data on total fluxes of particulate matter and fluxes of biogenic components (SiO2biog, Сorg, and Ntot) at different depths of the water column both for the whole year and for individual periods of the year. Diatom analyses were carried out for all obtained samples. The total flux of sedimentary material averaged 94.9 g/m2/y; the average fluxes of SiO2biog, Сorg, and Ntot were 23.9, 11.6, and 0.94 g/m2/y, respectively. The molar C/N ratio varies from 11 to 21 and indicates a predominance of allochthonous material in almost all samples. Maximum fluxes of sedimentary matter were recorded from 20 June to 20 July 2015. This period corresponds to the bloom of diatoms of the species Synedra acus. This species amounts to >94% of the total diatom content in all samples taken during this year. The recent predominance of Synedra acus in the water column, as well as in the surface bottom sediments of South Baikal, is probably due to the climate warming.

We present a detailed analysis of weathering fluxes at Lake Baikal, the largest lake in the world, using the major element, trace element and isotope geochemistry of major inflowing rivers, the lake itself, and its sediments. Our objective is to assess how lake records could be used to understand river-catchment-scale denudation and weathering processes. Total denudation rates at Lake Baikal, as obtained from meteoric Be-10/Be-9, are an order of magnitude lower than the global average, at 16-35 t km(-2) yr(-1). Chemical weathering rates obtained from the riverine dissolved load and discharge are, on the other hand, in the same range as global values, at 6-29 t km(-2) yr(-1). Chemical weathering rates are higher in the north of the catchment than in the south, consistent with higher runoff in the north. In contrast, Be-10/Be-9-derived denudation rates are higher in the south. We hypothesize that this pattern of variation may be due to the stabilizing effect of permafrost soils preventing erosion in the north. An inverse model shows that the Selenga River, Lake Baikal's major tributary, has a silicate weathering contribution to riverine dissolved cation fluxes of 42 mol%; this and other characteristics are representative of large rivers globally. Many trace elements have much lower concentrations in the lake than in inflowing rivers (Be (5%), Mn (3%), Fe (0.4%) and REE (1-2%)). We suggest, based on REE patterns and Mn, Fe-depth profiles in the lake, that this removal is the result of pH induced changes in dissolved-adsorbed partitioning at the river-lake interface, and the incorporation of trace elements into authigenic Fe-Mn (oxyhydr)oxide phases forming within the lake. Strontium is isotopically uniform within the lake, demonstrating that the whole lake mixes on a timescale shorter than its residence time (< 330 years). Neodymium and Be, in contrast, show isotopic variability between the basins. While the Sr isotope budget of the lake is largely consistent with observed riverine Sr fluxes, an unradiogenic Nd source is needed to explain lake Nd isotope compositions, especially in the Northern Basin. This source appears to derive from old crustal rocks in this part of the catchment and could be hydrothermal, or small rivers that were not sampled here. Similarly, elevated Be-10/Be-9 ratios in the lake basins relative to the river input imply variable but significant atmospheric inputs of Be-10 into the lake.Overall, this study demonstrates that records of the paleo-chemistry of lakes, and Lake Baikal in particular, hold promise for understanding denudation and weathering on the continents, in ways that are more directly relatable to the environmental conditions of the catchment than is possible with marine records. (c) 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/ licenses/by/4.0/).

We provide an extended Sr-87/Sr-86 database for the water of Lake Baikal collected along the lake and within its bays at a depth range from the surface down to 1366 m, the major tributary rivers, lake animals, and atmospheric precipitation. The water of open Lake Baikal, the Little Sea (Maloe More) Strait, and large bays are characterized by a uniform Sr-87/Sr-86 = 0.7086266 +/- 0.0000045 (n = 44, uncertainty at 95% confidence interval). Major volumetric contributors of water to the lake (the eastern rivers and precipitation) are only slightly different from the lake value in terms of Sr-87/Sr-86. In the western rivers, Sr-87/Sr-86 is much higher, but due to their small incoming volume, their contribution is rapidly diluted by the water currents of the lake. The exception is water with high Sr-87/Sr-86 from isolated Mukhor Bay at the inland end of the Little Sea Strait and water above the underwater discharge of hydrothermal springs. Benthic and pelagic Lake Baikal animals have Sr-87/Sr-86 similar to the values of the open lake, supporting lake water homogenization. The modelled budget of Sr suggests that 86 +/- 14% of input Sr is stored in the waters of Lake Baikal. In other words, according to the estimations some Sr (from 0 to 28%) may be precipitated at the lake bottom by chemical and biochemical processes.

Lake Baikal is the world’s largest (by volume), deepest, and oldest (30-40 Ma) lake. Climate varies from arid to semi-arid to arctic-boreal with extreme seasonal and spatial differences in temperature and precipitation 1 . The catchment has also been affected by periodic Quaternary glaciations 2 . Although the geology of the catchment is diverse, the most prominent lithologies are granitoids and gneisses 1 . Lake Baikal is therefore a promising site to study the effect of climate on silicate rock weathering. Here we present new insights into the modern weathering regime and, in anticipation of a paleo-weathering study, we evaluate how these weathering signals are transferred into the lake. Chemical weathering rates are higher in the northern part of the catchment, possibly due to the weathering of fine sediments produced during the last glaciation. Total denudation rates derived from dissolved riverine 10 Be/ 9 Be are, however, higher in the southern than in the northern river catchments, possibly due to more widespread permafrost 3 preventing soil erosion. For most rivers, Be-derived denudation rates exceed the summed estimates for chemical and physical erosion, pointing to the potential importance of sediment storage in floodplains. Preliminary results of an inverse model that apportions riverine dissolved loads to silicate, carbonate and evaporite weathering suggest that 74-94% of the Na flux and 19-42% of the total dissolved fluxes are derived from silicate weathering. From

Sedimentation in Lake Baikal is significantly affected by continuous seismic activity in the Baikal Rift Zone. Our study shows that historical earthquakes, as well as recent seismic events, considerably influenced sedimentation in this deep tectonic basin. Here we present some of the results of extensive international research activities during the period of 1996–2019. To identify traces of seismic events in the uppermost sediments (<1.5 m), short cores were recovered from many coring stations throughout the entire lake. Based on lithological descriptions, measurements of magnetic susceptibility, and concentration of inorganic and organic components, we identified earthquake indicators in the sediment cores. Impacts of historical earthquakes were traced within South Baikal (near the Sharyzhalgai Station and the Station 106-km of the Circum-Baikal railway, hereafter CBR) and Proval Bay (near the Selenga River delta).

Mercury (Hg) loading in Lake Baikal, a UNESCO world heritage site, is growing and poses a serious health concern to the lake's ecosystem due to the ability of Hg to transform into a toxic form, known as methylmercury (MeHg). Monitoring of Hg into Lake Baikal is spatially and temporally sparse, highlighting the need for insights into historic Hg loading. This study reports measurements of Hg concentrations from water collected in August 2013 and 2014 from across Lake Baikal and its main inflow, the Selenga River basin (Russia, Mongolia). We also report historic Hg contamination using sediment cores taken from the south and north basins of Lake Baikal, and a shallow lake in the Selenga Delta. Field measurements from August 2013 and 2014 show high Hg concentrations in the Selenga Delta and river waters, in comparison to pelagic lake waters. Sediment cores from Lake Baikal show that Hg enrichment commenced first in the south basin in the late-19th century, and then in the north basin in the mid-20th century. Hg flux was also 20-fold greater in the south basin compared to the north basin sediments. Hg enrichment was greatest in the Selenga Delta shallow lake (Enrichment Ratio (ER) = 2.3 in 1994 CE), with enrichment occurring in the mid-to late-20th century. Local sources of Hg are predominantly from gold mining along the Selenga River, which have been expanding over the last few decades. More recently, another source is atmospheric deposition from industrial activity in Asia, due to rapid economic growth across the region since the 1980s. As Hg can bioaccumulate and biomagnify through trophic levels to Baikal's top consumer, the world's only truly freshwater seal (Pusa sibirica), it is vital that Hg input at Lake Baikal and within its catchment is monitored and controlled.

Results of high-resolution research of recent bottom sediments from south, central and north Chukchi Sea reveal striking data on environmental changes during the last decades. The composition of surface sediments from the Arctic Sea gives evidence of the decrease of ice cover and an increase of biogenic elements, caused by higher bioproductivity.

Lake Baikal, lying in a rift zone in southeastern Siberia, is the world's oldest, deepest, and most voluminous lake that began to form over 30 million years ago. Cited as the "most outstanding example of a freshwater ecosystem" and designated a World Heritage Site in 1996 due to its high level of endemicity, the lake and its ecosystem have become increasingly threatened by both climate change and anthropogenic disturbance. Here, we present a record of nutrient cycling in the lake, derived from the silicon isotope composition of diatoms, which dominate aquatic primary productivity. Using historical records from the region, we assess the extent to which natural and anthropogenic factors have altered biogeochemical cycling in the lake over the last 2,000 y. We show that rates of nutrient supply from deep waters to the photic zone have dramatically increased since the mid-19th century in response to changing wind dynamics, reduced ice cover, and their associated impact on limnological processes in the lake. With stressors linked to untreated sewage and catchment development also now impacting the near-shore region of Lake Baikal, the resilience of the lake's highly endemic ecosystem to ongoing and future disturbance is increasingly uncertain.

Here we present new data of bottom sediments, which were collected in March 2018 in the deep water of Southern Baikal. The deposits consist of pelagic mud, intercalated by three turbidites. The uppermost 2 cm of the core are formed by the light layer of a diatomite, consisting mainly of valves of Synedra acus (up to 219 million cells / g). We attribute the increased content of this diatom species in the upper part of the core to warmer climatic conditions.

Lake Baikal is the world’s largest (by volume), deepest, and oldest (30-40 Ma) lake. In the catchment, climate varies from arid to semi-arid to arctic-boreal with extreme seasonal and spatial differences in temperature and precipitation1. Elevation ranges from 450-3000m, resulting in a large range of geomorphic settings. The catchment has also been affected by periodic Quaternary glaciations2. Although the geology of the catchment is diverse and contains igneous, metamorphic and sedimentary rocks of Archean to Cenozoic ages, the most prominent lithologies are granitoids and gneisses with only minor carbonate contributions1. Continuous lake sediment cores are available recording the Quaternary glacial cycles, and even dating back into the Miocene. Lake Baikal is therefore a promising site to study variation of silicate rock weathering in both space and time. In preparation for paleo-studies, we constrain the present-day budget of the lake with respect to radiogenic weathering tracers (Nd, Pb, and Sr) and meteoric 10Be/9Be isotope ratios. Nd, Sr, Pb, and their radiogenic isotope systems show different behaviors in Lake Baikal. Sr concentrations in the lake are similar to riverine inputs, reflecting conservative behavior of Sr and resulting in a uniform isotopic composition that is slightly higher than the average of riverine inputs (possibly due to loess inputs3). Pb concentrations are higher in the lake than in the major tributaries. The isotopic composition of both lake and rivers point to anthropogenic sources of Pb. In contrast, Nd concentrations in the lake are much lower than in the rivers. Nd isotopic compositions are similar in the central and southern basin but less radiogenic in the northern basin. Both 10Be and 9Be concentrations are much lower in Lake Baikal than in its tributaries, possibly indicating removal due to pH induced changes in dissolved-particulate partitioning4. This may also explain the contrast in Nd concentrations between rivers and the lake. 10Be/9Be ratios in the lake are slightly elevated compared to riverine inputs, suggesting a potential role for dust and/or precipitation as a source for 10Be5. We will also compare silicate weathering fluxes derived from meteoric Be isotope ratios with those derived from major element concentrations and riverine discharges. Taken together, these results highlight the importance of assessing modern processes at sediment core locations prior to interpreting variation in the past, and the benefits of using a suite of weathering proxies rather than relying on one: while Sr isotopes at any core location record changes to the chemistry of the whole lake (and the processes in its catchment), Be and Nd isotopes are likely biased to the inputs of the nearest rivers. 1. Zakharova et al. Chem. Geol. 214, 223–248 (2005). 2. Karabanov et al. Quat. Res. 50, 46–55 (1998). 3. Yokoo et al. Chem. Geol. 204, 45–62 (2004). 4. You et al. Chem. Geol. 77, 105–118 (1989). 5. Aldahan et al. Geophys. Res. Lett. 26, 2885–2888 (1999).

Removal of riverine trace elements from solution is well known for marine estuaries, resulting in dramatically lower concentration in seawater for elements like Fe, Mn, REEs, Al, and Be compared to rivers. Traditionally, this is often attributed to salinity induced coagulation and removal of colloidal matter and associated particle reactive elements1. Although Lake Baikal has a lower ionic strength than its tributaries, a similar drop in concentration from riverine values is observed for many of the same elements (like Fe, Mn, REEs, Al, Be, Cu, Y). Based on comparable Ce anomalies of lake surface waters and tributaries, the drop in concentration at the river-lake interface is mostly due to adsorption of solutes onto existing particulates. REE concentrations (as well as Fe, Mn, Be) in the lake also decrease with depth while Ce anomalies get more negative, indicating the ad-/absorption of REEs by newly formed authigenic FeMn phases2. The resulting short residence time of Nd in the lake leads to a non-uniform distribution of Nd isotopes. In contrast, Sr concentrations are similar in lake and rivers and Sr isotopes show a uniform distribution within the lake. The controlling parameter for the drop in concentrations of these trace elements across the river-lake interface appears to be pH, which is elevated in the lake (8.3-8.5 at the lake surface) compared to riverine values (7.8, flow weighted average). This finding is consistent with observed correlations between pH and the concentrations of some of these elements in river waters3. Together, these results call into question our understanding of the processes occurring in marine estuaries. Possibly, pH rather than salinity is also the dominant driver in the marine context.

This paper presents the first results of the quantitative reconstruction of ice conditions in the Arctic based on a comparison of the data for periods of meteorological observations with variations in the chemical compositions of the sediments accumulated during the same times. The biogenic elements (Br, Ca, and Sr) and some redox-sensitive (As and Fe) elements are the most informative for the reconstruction of changes in ice conditions with positive correlations, and the lithogenic elements (K and Ti) are predominantly negatively correlated. The reconstruction results for the last 300–400 years of average annual air temperature anomalies for all cores in general terms coincide with the reconstruction for the Northern Hemisphere. The common features of all reconstructions are low temperatures during the Little Ice Age (LIA) and a rapid warming in the middle of the 19th century and in the last decades of the 20th and first decades of the 21st centuries. The results of the reconstruction of the duration of the ice-free period generally coincide with the temperature changes for the last two centuries, although for LIA there is an inverse correlation between the variations in temperature and the duration of the ice-free period. A possible reason for this may be changes in the structure of the surface currents in the Chukchi Sea and the northern part of the Bering Sea, because of which the inflow of warm and freshened waters through the Bering Strait to the Arctic increased occasionally.

Представлены данные минералогического анализа тонкого и мелкого песка в составе осадков, накопленных в южной части Чукотского плато за четвертичное время. Рассмотрены ассоциации и распределение по разрезу породообразующих и акцессорных минералов, их связь с другими характеристиками. Выявленные минералогические особенности, обусловленные климатическими изменениями — периодами потепления и похолодания, могут быть использованы в решении ряда генетических вопросов, стратификации, палеореконструкциях.

The paper presents mineralogical analysis data on very-fine- and fine-grained sand in the composition of Quaternary sediments in the southern part of the Chukchi Plateau. The associations and downcore distribution of rock-forming and accessory minerals in relation to other characteristics are considered. The established climatically controlled mineralogical features, i.e., periodicity of warmings and coolings, can be used to solve a number of genetic problems, stratigraphic subdivision of sediments, and paleoreconstructions.