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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 10Be/9Be, 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, 10Be/9Be-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 (, Geochimica et Cosmochimica Acta, 321, ISSN:0016-7037, ISSN:1872-9533

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.Zakharova et al. Chem. Geol. 214, 223–248 (2005). Karabanov et al. Quat. Res. 50, 46–55 (1998). Yokoo et al. Chem. Geol. 204, 45–62 (2004). You et al. Chem. Geol. 77, 105–118 (1989). Aldahan et al. Geophys. Res. Lett. 26, 2885–2888 (1999).

The water column of Lake Baikal (Siberia) is pervasively oxic and O2 penetrates several cm into the sediment, followed by distinct layers of Fe/Mn oxide that undergo reductive-dissolution/oxidative-precipitation cycles. Uranium (U) contents of the oxic surface sediment layers were ~ 15 μg g− 1, which is unparalleled in oxygenated lakes. To understand the processes leading to this enrichment we investigated the geochemical composition of the particulate matter and pore water of four sediment cores from different locations in the lake and performed mass balance calculations based on sediment mass accumulation rates and published loads from major tributaries. The comparison of loads and export of U in Lake Baikal suggested that current estimates of loads are too low by a factor of about 3 compared to sediment mass accumulation rates. Peak loads during spring ice melt in tributaries that are difficult to monitor and quantify might be the main cause for the deviation. The high U concentrations in the lake sediments originated from the scavenging of U in the water column through association with settling organic particles and particulate Fe(III)- and, to a lesser extent, Mn(IV)-oxides. We outline the hypothesis that two distinct U phases, lithogenic and non-lithogenic U reach the lake sediment and that authigenic U is subsequently formed under reducing conditions within the sediment. In some cores we found that most U was remobilized during the degradation of organic matter, in particular within the top oxygenated layer of the sediment. Significant enrichments prevailed due to U adsorption to and/or co-precipitation with Fe-oxides. When Fe-oxides and, to a lesser extent, Mn-oxides were reductively dissolved, they released U to the pore water, leading to peak dissolved U concentrations in the anoxic sediment, which in turn, precipitated as authigenic U under predominantly sulphate-reducing conditions. The onset of the accumulation of authigenic U coincided with the formation of distinct Fe/Mn oxide layers above. We argue that the resilience of Fe-oxides (especially crystalline goethite and hematite), in association with phosphate, even within reducing (but non-sulfidic) sediments support the burial of substantial amounts of U.

Lake Baikal is the deepest and probably oldest lake on Earth. Its water column is pervasively oxic and sedimentation rates are very low which leads to the formation of a dynamic iron (Fe) and manganese (Mn) enrichment below the Mn(II)/O2 boundary. These often massive accumulations can be buried within the reducing part of the sediments and give rise to complex and cryptic redox cycles. The mobility of rare earth elements (REEs) is influenced by the dissolution and reduction dynamics of the ferromanganese oxides. The present study offers an overview of the REE chemistry in Lake Baikal and its catchment area and more specifically REE distribution in five 11- to 26-cm-long sediment cores situated across the lake at different water depths. We analysed and discussed normalised REE patterns and their consequential cerium (Ce) anomalies. While particulate REE concentrations are mainly influenced by processes above or near the surface of Lake Baikal, such as the development of a widespread negative Ce anomaly, processes occurring during early diagenesis in the sediment are most reflected in pore water REEs. The dissolution of ferromanganese oxides at the Mn(II)/O2 boundary remobilizes significant amounts of REE into the pore water whereby some are likely adsorbed onto colloidal Fe oxides. However, besides the tendency of Ce being associated with Mn-oxides, pore water REEs fractionate predominantly around the buried Fe/Mn accumulation where light REEs preferentially adsorb onto Fe-oxides.

[This corrects the article DOI: 10.1371/journal.pone.0208765.].

Lake Baikal is the deepest and oldest lake on Earth. Extraordinary features of the lake are manganese and iron‐enriched layers and crusts occurring at different depths within the sediment. They can be broadly subdivided into an upper accumulation at the O 2 /Mn(II) redox boundary and one or more layers buried within the reducing part of the sediment. The processes leading to their formation and peculiar distribution within the sediment have remained subject of debate, in particular whether the burial of vast amounts of Mn and Fe-oxides results from a steady-state process or if it is the consequence of singular events, such as changes in sedimentation rate, bottom water oxygen concentrations, or the mass accumulation rate (MAR) of organic carbon (C org ), Mn or Fe. We retrieved short cores from the South basin, the North Basin, and Academician Ridge, determined sedimentation rates, contents of C org , Mn and Fe, and estimated pore‐water fluxes from concentration profiles of O 2 , NO 3 − , Mn(II), Fe(II), SO 4 2 − and CH 4 . A consistent picture emerged from the data showing that the upper Fe/Mn layer formed at the lower end of the oxygen penetration depth as a dynamic pattern, moving upward with the growing sediment. Thereby, reductive dissolution of Mn(IV) occurred at the lower margin. Upward diffusing Mn(II) was oxidized with O 2 forming the upper boundary of the Fe/Mn accumulation. The buried Fe/Mn layers were immobilized within the sediment and underwent slow reductive dissolution mainly driven by the anaerobic oxidation of CH 4 . The process leading to the detachment of the ‘active’ Fe/Mn layer from the top redox interface is not unambiguously clear. However, we suggest a cyclic pattern where the burial of a Fe/Mn layer is accompanied by the generation of a new enrichment at the O 2 /Mn(II) redox boundary, which is subsequently nourished by the slowly dissolving old layer.

The late Cretaceous-Cenozoic sediments of fossil soils and weathering crusts of the Baikal rift have been subject to long-term studies. Based on our research results, it is possible to distinguish the following litho-stratigraphic complexes which are related to particular stages of the rift development: the late Cretaceous–early Oligocene (crypto-rift Arheo-baikalian), the late Oligocene–early Pliocene (ecto-rift early orogenic Pra-baikalian), and the late Pliocene-Quaternary (ecto-rift late orogenic Pra-baikalian – Baikalian) complexes. Changes of weathering modes (Cretaceous-quarter), soil formation (Miocene-quarter) and differences of precipitation by vertical and lateral stratigraphy are analysed with regard to specific features of climate, tectonics and facial conditions of sedimentation. Tectonic phases are defined in the Cenozoic period of the Pribaikalie.

Results of investigations of Baikal bottom sediments from a long core (BDP-97) and several short (0–1 m) cores are presented. It has been shown that the Holocene sediments in the Baikal basins consist of biogenic-terrigenous muds, accumulated under calm sedimentation conditions, and of turbidites, formed during catastrophic events. The turbidites can be distinguished from the host sediments by their enrichment in heavy minerals and thus their high magnetic susceptibility. Often, Pliocene and Pleistocene diatom species observed in the Holocene sediments (mainly in the turbidites) point to redeposition of ancient offshore sediments. Our results indicate that deltas, littoral zones, and continental slopes are the source areas of turbidites. The fact that the turbidites occur far from their sources confirms the existence of high-energy turbidity currents responsible for long-distance lateral-sediment transport to the deep basin planes of the lake.

The internal cycles of carbon, silica, nitrogen, and phosphorus in the South and North Basins of Lake Baikal were quantified in the frame of a multidisciplinary collaboration. Fluxes of particulate organic matter from the epilimnion to the deep water were quantified with integrating sediment traps deployed at 200- to 250-m water depth and compared with fluxes measured in near-bottom traps to reveal mineralization in the water column. Sedimentation rates were determined with dated sediment cores to calculate mass accumulation rates of elements in the sediment. Advective and turbulent transport of dissolved nutrients in the water column was based on a set of monitoring data, which included temperature and current data, as well as hydrochemical data of the water column. Diffusive fluxes from the sediment to the overlying water column were determined by applying different porewater sampling techniques. The combination of these data resulted in consistent internal budgets for carbon, nitrogen, and phosphorus in Lake Baikal: the new production in the South Basin was 1730 mmol C m(-2) year(-1) and the mass accumulation rate in the sediment 220 mmol C m(-2) year(-1), whereas in the more secluded North Basin, new production was only 1220 mmol C m(-2) year(-1) and mass accumulation rate 125 mmol C m(-2) year(-1). Fluxes of particle-bound nitrogen, phosphorus, and biogenic silica were by about 30% smaller in the North Basin than in the South Basin. Export fluxes of nitrogen from the surface zone to the deep water were 150 mmol N and 100 mmol N m(-2) year(-1). Denitrification rates in the sediment were estimated from mass-loss calculation to 38 and 53 mmol N m(-2) year(-1) for the South and North Basin, respectively, corresponding to 25% and 52% of the total nitrogen input to the hypolimnion. Nitrogen (19 and 13 mmol m(-2) year(-1)) was finally buried in the sediments of the South and North Basins; 10.1 and 3.5 mmol P m(-2) year(-1), and 1830 and 1400 mmol Si m(-2) year(-1) were transferred to the deep water in the South and North Basin where 28% and 70% P, and 64% and 54% Si were retained in the sediments. A diatom bloom occurred during our sampling period of 2 years, which usually occurs only every 3 to 5 years. Accordingly, Si flux data from sediment traps were increased by an estimated 50% compared with the long-term average illustrating the necessity of several years of field measurements to compensate for the natural dynamics of Lake Baikal. (C) 2004 Elsevier B.V. All rights reserved.

Distinct layers of iron(III) and manganese(IV) (Fe/Mn) oxides are found buried within the reducing part of the sediments in Lake Baikal and cause considerable complexity and steep vertical gradients with respect to the redox sequence. For the on-site investigation of the responsible biogeochemical processes, we applied filter tube samplers for the extraction of sediment porewater combined with a portable capillary electrophoresis instrument for the analyses of inorganic cations and anions. On the basis of the new results, the sequence of diagenetic processes leading to the formation, transformation, and dissolution of the Fe/Mn layers was investigated. With two exemplary cores we demonstrate that the dissolution of particulate Fe and Mn is coupled to the anaerobic oxidation of CH4 (AOM) either via the reduction of sulphate (SO42−) and the subsequent generation of Fe(II) by S(−II) oxidation, or directly coupled to Fe reduction. Dissolved Fe(II) diffuses upwards to reduce particulate Mn(IV) thus forming a sharp mineral boundary. An alternative dissolution pathway is indicated by the occurrence of anaerobic nitrification of NH4+ observed at locations with Mn(IV). Furthermore, the reasons and consequences of the non-steady-state sediment pattern and the resulting redox discontinuities are discussed and a suggestion for the burial of active Fe/Mn layers is presented., Environmental Science: Processes & Impacts, 16 (4), ISSN:2050-7887, ISSN:2050-7895

The ancient Lake Khubsugul in North Mongolia is situated at the far reach of moisture from the North Atlantic into continental Asia [Kuznetsova, 1978]. It is remote from the Pacific Ocean and shielded from the China Sea and the Indian Ocean by high mountains. Information on the paleoclimates in this territory is scarce and sometimes controversial. In winter of 2003, due to a joint project (Khubsugul Drilling Project or KDP) of the Siberian Branch of the Russian Academy of Sciences and the Academy of Sciences of Mongolia, a 53-m drilling core (KDP-1) of sediments of Lake Khubsugul was obtained. This article describes the first results of paleomagnetic and geochemical studies of this core, which was found to span the time interval of the last 1.05 Myr. The data suggest that global climate oscillations manifested themselves in repeated desiccation and filling of the lake due to changes in humidity.