Observed trends of climate and land cover changes in Lake Baikal basin

Land cover and vegetation in Lake Baikal basin (LBB) are considered to be highly susceptible to climate change. However, there is less information on the change trends in both climate and land cover in LBB and thus less understanding of the watershed sensitivity and adaptability to climate change. Here we identified the spatial and temporal patterns of changes in climate (from 1979 to 2016), land cover, and vegetation (from 2000 to 2010) in the LBB. During the past 40 years, there was a little increase in precipitation while air temperature has increased by 1.4 °C. During the past 10 years, land cover has changed significantly. Herein grassland, water bodies, permanent snow, and ice decreased by 485.40 km², 161.55 km² and 2.83 km², respectively. However, forest and wetland increased by 111.40 km² and 202.90 km², respectively. About 83.67 km² area of water bodies has been converted into the wetland. Also, there was a significant change in Normalized Difference Vegetation Index (NDVI), the NDVI maximum value was 1 in 2000, decreased to 0.9 in 2010. Evidently, it was in the mountainous areas and in the river basin that the vegetation shifted. Our findings have implications for predicting the safety of water resources and water eco-environment in LBB under global change.     

新疆阿尔泰山喀纳斯湖冰层温度变化规律试验研究

2014年12月-2015年4月期间,新疆布尔津县喀纳斯湖举行了冰上旅游项目。为监测冰层生长、发育和融化状况,分别对喀纳斯湖（湖边、湖中）A、B、C三点进行温度监测,利用监测得到的冰层温度数据绘制湖冰从上到下温度分布状况图。根据湖边与湖中的冰层结构特点,从冰层的天然结构角度分析湖冰结构对温度分布的影响。结果表明：天然冰层中温度传递系数并不是一致不变的,既受冰上气温、冰下湖水温度的影响,也受到冰层自身结构状况的影响,并进一步阐述了湖面冰层的温度分布规律与变化成因,为分析温度对冰层强度的影响奠定了基础。     

Natural ring structures on the Baikal ice cover: Analysis of experimental data and mathematical modeling

Hydrophysical studies and mathematical modeling of ring structures during ice cover on Lake Baikal have shown that their existence at the stage of ice cover degradation is due to anticyclonic currents. Such currents can be generated as a result of local upwelling, which we associate with the rise of methane hydrates from the top layer of bottom sediments and their dissociation. Analysis of satellite images shows that the radii of ice rings range from 1300 to 2400 m, which is close to the baroclinic Rossby radius. The measured ice thicknesses in the area of the rings are in agreement with model calculations. Deep water renewal in Lake Baikal can also be associated with the rise of hydrates.     

Upwellings in Lake Baikal

Based on shipboard and satellite observations, the characteristics of upwelling in Lake Baikal in the period of direct temperature stratification have been determined for the first time. Coastal upwellings appear annually under the effect of run-down and alongshore winds and are traced along the coast to a distance of up to 60–100 km and up to 250 km in North Baikal. Analogous to the way it occurs in seas, water rises from the depths of 100–200 m (350 m as a maximum) at the velocity of 0.1 × 10⁻²−6.5 × 10⁻² cm/s. Divergence in the field of intràbasin cyclonic macrovortices produces upwelling in the Baikal pelagic zone and downwelling in the vicinity of shores; this lasts from 7 to 88 days and covers the depth interval of 80–300 m in August and up to 400–800 m in early-mid November. The area of upwellings occupies up to 20–60% of the separate basins of the lake. Vertical circulation of water in the field of pelagic upwellings leads to intensification of coastal currents and to formation of the thermobar with a heat inert zone in the central part of the lake in November, and this thermobar is not observed in other lakes, at that.     

Sorption of P by ferric hydroxide film, cover particles of sediments of Lake Baikal

We investigated in more detail the adsorption phenomenon which was described earlier. It was clearly established that the hydroxyl apatite was not participated in P adsorption. This phenomenon takes place because of ferric hydroxide film. Modem sediments from the Southem Basin of Lake Baikal were taken and stirred with Baikal water. Carrier-free [^32p]-orthophosphate was added in this system. Similar experiments were made with carrier-free [^35S]-sulphate. Sulphate stayed in supematant completely. The influence of pH on the system with inorganic phosphate was also studied. In low alkali conditions phosphate migrated in supematant, in low acid, in sediments. Baikal sediment was stripped of iron-hydroxous film by treatment with 1% oxalic acid. Investigation of striped sediment shown that phosphate stays in supematant only. Hence, hydroxyl apatite cannot be the phase of the sediments of Lake Baikal which binds phosphate. This all showed by our group before. Now we have found the limit of phosphate sorption in Lake Baikal sediments and the stehiometry of the sorption. The sorption limit of Lake Baikal sediments was studied. An experiment with inorganic ^31P phosphate was made. 0.025% K2HPO4 solution with adding ^32P radioactive mark into it was prepared. 100 μL of mixture of ^31PO4^3- and ^32PO4^3- seven times were added in a ＂Baikal water-Baikal sediment＂ system and blank （100 ml BW only）. Concentrations of inorganic ^31PO4^3- were very low so the bend dot on the diagram was found and sorption limit of sediment was estimated. Baikal sediment stopped assimilating phosphate in the bend dot. The stehiometry of sorption was estimated by supematant-sediment radioactive ratio, which equals 3, that is, three Fe （Ⅲ） atoms associate one PO4^3- anion. The only Fe （Ⅲ） substance which could associate P is -Fe-O-Fe- polymer film. It also dissolves in acid conditions.     

Deep seismic investigations in the Baikal rift zone

The largest rift zone of Europe and Asia is located in the region of Lake Baikal. In 1968–1970 deep seismic measurements were carried out along a number of profiles with a total length of about 2000 km within the rift zone and in the adjacent parts of the Siberian platform and the region of the Baikal Mountains. These investigations were of a reconnaissance nature, and therefore the point sounding method was used.A low-velocity region for compressional waves (7.6–7.8 km/sec) has been found and could be traced over a large area in the upper parts of the mantle. The width of this anomalous zone is 200–400 km. The Baikal rift lies in its northwestern part. Within the studied part of the Siberian platform the thickness of the earth's crust is 37–39 km, while in the rift zone it is 36 km, and further to the southeast the crust-mantle boundary lies at a depth of 45–46 km. The Baikal rift proper is bounded in the northwest by a deep fracture zone and does not seem to be associated with any significant “root” or “antiroot” in the relief of the Mohorovi?i? discontinuity.The reduced compressional velocity in the upper parts of the mantle beneath the Baikal zone is considered to correspond to the same phenomena found under the mid-oceanic ridges and the extended rift system in the Basin and Range province of North America. The Baikal rift in the narrow sense of the word lies over the northwestern edge of the anomalous mantle region. This asymmetric position seems to be its main peculiarity.     

Mercury in the sedimentary deposits of Lake Baikal

Mercury distribution was examined in the sediments of Lake Baikal that were sampled within the scope of the Baikal Drilling International Project in 1996–1999. The Hg concentrations in the ancient sediments are close to those in the modern sediments with the exception of a few peak values, whose ages coincide with those of active volcanism in adjacent areas. Mercury was demonstrated to be contained in the sediments in the adsorbed Hg⁰ mode, predominantly in relation with organic matter. When the organic matter of the bottom sediments is decomposed in the course of lithification, Hg is retained in the sediments adsorbed on the residual organic matter, and the concentration of this element corresponds to its initial content in the bottom sediments during their accumulation. Mercury concentrations in lithologically distinct bottom sediments of Lake Baikal and its sediments as a whole depend on the climate. Sediments that were formed during warm periods of time contain more Hg than those produced during cold periods or glaciation. Periodical variations in the Hg concentrations in the bottom sediments of Lake Baikal reflect the variations in the contents of this element in the Earth’s atmosphere in the Late Cenozoic, which were, in turn, controlled by the climatic variations on the planet and, thus, can be used for detailed reconstructions of variations in the average global temperature near the planet’s surface.     

Lake Hoare, Antarctica: sedimentation through a thick perennial ice cover

Lake Hoare in the Dry Valleys of Antarctica is covered with a perennial ice cover more than 3 m thick, yet there is a complex record of sedimentation and of growth of microbial mats on the lake bottom. Rough topography on the ice covering the lake surface traps sand that is transported by the wind. In late summer, vertical conduits form by melting and fracturing, making the ice permeable to both liquid water and gases. Cross-sections of the ice cover show that sand is able to penetrate into and apparently through it by descending through these conduits. This is the primary sedimentation mechanism in the lake. Sediment traps retrieved from the lake bottom indicate that rates of deposition can vary by large amounts over lateral scales as small as 1 m. This conclusion is supported by cores taken in a 3 × 3 grid with a spacing of 1.5 m. Despite the close spacing of the cores, the poor stratigraphic correlation that is observed indicates substantial lateral variability in sedimentation rate. Apparently, sand descends into the lake from discrete, highly localized sources in the ice that may in some cases deposit a large amount of sand into the lake in a very short time. In some locations on the lake bottom, distinctive sand mounds have been formed by this process. They are primary sedimentary structures and appear unique to the perennially ice-covered lacustrine environment. In some locations they are tens of centimetres high and gently rounded with stable slopes; in others they reach ～ 1 m in height and have a conical shape with slopes at angle of repose. A simple formation model suggests that these differences can be explained by local variations in water depth and sedimentation rate. Rapid colonization and stabilization of fresh sand surfaces by microbial mats composed of cyanobacteria, eukaryotic algae, and heterotrophic bacteria produces a complex intercalation of organic and sandy layers that are a distinctive form of modern stromatolites.     

Bottom temperature monitoring in Lake Baikal

We report results of bottom temperature monitoring of 2003–2004 in the deepwater South Baikal basin (Lake Baikal) near active gas-fluid methane vents at lake depths of 1020 and 1350 m. Sediments and water temperatures were measured using an autonomous temperature recorder designed at the Institute of Geophysics (Novosibirsk). Experiments implied short-duration recording and pioneering continuous 350 day-long monitoring near the Staryi vent. Measurements within a 1 m thick layer above and below the bottom showed notable variations in water (up to 0.07 °C) and sediment temperatures and in geothermal gradient. The long temperature records include a relatively steady period (mid-June 2003-early February 2004) with smooth temperature variations (especially in sediments) and two transient unsteady periods. The steady season is the best time for heat flow studies in the South Baikal basin. The 0.04–0.05 °C drop in bottom water temperature during the unsteady periods may result from intrusion of cold surface water. A positive temperature anomaly of ∼0.04 °C recorded in April 2003 may be caused, among other reasons, by active gas venting.     

Elements of the iron and manganese cycles in Lake Baikal

Using data obtained in recent years, we considered the external mass balance and characteristics of internal iron and manganese cycles in Lake Baikal (biological uptake, remineralization, sedimentary and diffusive fluxes, accumulation in sediments, time of renewal, etc.). Some previous results and common concepts were critically reevaluated.     

冰盖下的输冰量计算分析

冰塞或冰盖下输冰受热力、水力以及边界条件等影响,计算河道在稳封期的冰流量对计算冰塞厚度及冰期水位具有重要的意义。根据对实验室试验数据的分析,提出平衡输冰形式的回归公式。同时对比了黄河河曲段稳封期的实测资料,结果显示这一计算输冰量公式的结构形式是合理的,可为天然河道稳封期输冰流量计算提供参考。     

Oxidation of methane in the water column of Lake Baikal

The rate of aerobic oxidation of methane was calculated based on average profiles of the tritiumhelium age of the Baikal waters and concentrations of the dissolved methane in the water column. In the deep lake zone (>200 m), the intensity of oxidation vertically decreases and is (2–0.3) × 10^?2 nl CH₄l^?1 days^?1 in southern and central Baikal and (2.8–1.0) × 10^?2 nl CH₄ l^?1 days^?1 in northern Baikal. The effective coefficient of the oxidation rate in the lake depressions is 3.6 × 10^?4, 3.3 × 10^?4, and 3.7 × 10^?4 days^?1, respectively. At current methane concentrations in the water column, about 80 t of methane is oxidized per year. Oxidation of the dissolved methane in the water column was estimated at a possible increase of its concentration.