Isotopic Indications of Meromixis in Separated Lakes on the White Sea Coast

Studies of lakes at different stages of separation from the sea have been carried out on the northwestern coast of Kandalaksha Gulf of the White Sea. At the end of the winter period, from March 16 to 29, 2013, the lakes Kislo–Sladkoe, Trekhtzvetnoe, Nizhnee Ershovskoe, Ermolinskaya Bay and snow near the pier of Pertsov White Sea Biological Station of Moscow State University (WSBS MSU) were studied. The isotope characteristics of the water of lakes, ice and snow, the distribution of salinity, temperature, and hydrogen sulfide content were studied.

     

Late Holocene moisture balance variability in the southwest Yukon Territory,Canada

Analyses of sediment cores from Marcella Lake, a small, hydrologically closed lake in the semi-arid southwest Yukon, provides effective moisture information for the last ∼4500 years at century-scale resolution. Water chemistry and oxygen isotope analyses from lakes and precipitation in the region indicate that Marcella Lake is currently enriched in ¹⁸O by summer evaporation. Past lake water values are inferred from oxygen isotope analyses of sedimentary endogenic carbonate in the form of algal Charophyte stem encrustations. A record of the δ¹⁸O composition of mean annual precipitation at Jellybean Lake, a nearby evaporation-insensitive system, provides data of simultaneous δ¹⁸O variations related to decade-to-century scale shifts in Aleutian Low intensity/position. The difference between the two isotope records, Δδ, represents ¹⁸O-enrichment in Marcella Lake water caused by summer effective moisture conditions. Results indicate increased effective moisture between ∼3000 and 1200 cal BP and two marked shifts toward increased aridity at ∼1200 and between 300 and 200 cal BP. These prominent late Holocene changes in effective moisture occurred simultaneously with changes in Aleutian Low circulation patterns over the Gulf of Alaska indicated by Jellybean Lake. The reconstructed climate patterns are consistent with the topographically controlled climatic heterogeneity observed in the coastal mountains and interior valleys of the region today.     

羊卓雍湖流域湖水稳定同位素循环过程研究

基于卓雍错流域2004年降水、河水、湖水中δ¹⁸O的监测结果,结合内陆湖水循环稳定同位素蒸发分馏模型,探讨了青藏高原南部羊卓雍湖水中稳定同位素的变化过程.研究表明:羊卓雍现代湖水中-5.9‰的δ¹⁸O平均值,相对应于当地相对湿度介于54%~58%的气候条件下,这是湖水蒸发分馏作用的最后结果.此外,入湖河水中δ¹⁸O变化也对湖水中平衡δ¹⁸O有一定的影响,而湖水温度的直接影响可以乎略.湖水中δ¹⁸O对入湖水δ¹⁸O的波动的调节能力很强,对于入湖水中δ¹⁸O大的波动,只有不到50 a的时间,湖水中稳定同位素会重新达到平衡.     

Carbon and Oxygen Isotopic Composition of Surface‐Sediment Carbonate in Bosten Lake (Xinjiang,China) and its Controlling Factors

Bosten Lake is a mid-latitude lake with water mainly supplied by melting ice and snow in the Tianshan Mountains. The depositional environment of the lake is spatially not uniform due to the proximity of the major inlet and the single outlet in the western part of the lake. The analytical results show that the carbon and oxygen isotopic composition of recent lake sediments is related to this specific lacustrine depositional environment and to the resulting carbonate mineralogy. In the southwestern lake region between the Kaidu River inlet and the Kongqi River outlet, carbon isotope composition (δ13C) values of the carbonate sediment (?1‰ to ?2‰) have no relation to the oxygen isotope composition of the carbonate (δ18O) values (?7‰ to ?8‰), with both isotopes showing a low variability. The carbonate content is low (<20%). Carbonate minerals analyzed by X-ray diffraction are mainly composed of calcite, while aragonite was not recorded. The salinity of the lake water is low in the estuary region as a result of the Kaidu River inflow. In comparison, the carbon and oxygen isotope values are higher in the middle and eastern parts of the lake, with δ13C values between approximately +0.5‰ and +3‰, and δ18O values between ?1‰ and ?5‰. There is a moderate correlation between the stable oxygen and carbon isotopes, with a coefficient of correlation r of approximately 0.63. This implies that the lake water has a relatively short residence time. Carbonate minerals constitute calcite and aragonite in the middle and eastern region of the lake. Aragonite and Mg–calcite are formed at higher lake water salinity and temperatures, and larger evaporation effects. More saline lake water in the middle and eastern region of the lake and the enhanced isotopic equilibrium between water and atmospheric CO2 cause the correlating carbon and oxygen isotope values determined for aragonite and Mg–calcite. Evaporation and biological processes are the main reasons for the salinity and carbonate mineralogy influence of the surface-sediment carbonate in Bosten Lake. The lake water residence time and the CO2 exchange between the atmosphere and the water body control the carbon and oxygen isotope composition of the carbonate sediment. In addition, organic matter pollution and decomposition result in the abnormally low carbon isotope values of the lake surface-sediment carbonate.     

Investigating hydraulic connections and the origin of water in a mine tunnel using stable isotopes and hydrographs

Turquoise Lake is a water-supply reservoir located north of the historic Sugarloaf Mining district near Leadville, Colorado, USA. Elevated water levels in the reservoir may increase flow of low-quality water from abandoned mine tunnels in the Sugarloaf District and degrade water quality downstream. The objective of this study was to understand the sources of water to Dinero mine drainage tunnel and evaluate whether or not there was a direct hydrologic connection between Dinero mine tunnel and Turquoise Lake from late 2002 to early 2008. This study utilized hydrograph data from nearby draining mine tunnels and the lake, and stable isotope (δ¹⁸O and δ²H) data from the lake, nearby draining mine tunnels, imported water, and springs to characterize water sources in the study area. Hydrograph results indicate that flow from the Dinero mine tunnel decreased 26% (2006) and 10% (2007) when lake elevation (above mean sea level) decreased below approximately 3004 m (approximately 9855 feet). Results of isotope analysis delineated two meteoric water lines in the study area. One line characterizes surface water and water imported to the study area from the western side of the Continental Divide. The other line characterizes groundwater including draining mine tunnels, springs, and seeps. Isotope mixing calculations indicate that water from Turquoise Lake or seasonal groundwater recharge from snowmelt represents approximately 10% or less of the water in Dinero mine tunnel. However, most of the water in Dinero mine tunnel is from deep groundwater having minimal isotopic variation. The asymmetric shape of the Dinero mine tunnel hydrograph may indicate that a limited mine pool exists behind a collapse in the tunnel and attenutates seasonal recharge. Alternatively, a conceptual model is presented (and supported with MODFLOW simulations) that is consistent with current and previous data collected in the study area, and illustrates how fluctuating lake levels change the local water-table elevation which can affect discharge from the Dinero mine tunnel without physical transfer of water between the two locations.     

Lake-level changes during the past 100,000 years at Lake Baikal, southern Siberia

Lake-level changes inferred from seismic surveying and core sampling of the floor of Lake Baikal near the Selenga River delta can be used to constrain regional climatic history and appear to be correlated to global climate changes represented by marine oxygen isotope stages (MIS). The reflection pattern and correlation to the isotope stages indicate that the topset and progradational foreset sediments of the deltas formed during periods of stable lake levels and warm climatic conditions. During warm stages, the lake level was high, and during cold stages it was low. The drop in the lake level due to cooling from MIS 5 through MIS 4 is estimated to be 33-38 m; from MIS 3 through MIS 2, it fell an additional 11-15 m. Because the lake level is chiefly controlled by evaporation and river input, we infer that more water was supplied to Lake Baikal during warm stages.     

Images of concentrations of dissolved sulphide in the sediment of a lake and implications for internal sulphur cycling

The high-resolution mapping of dissolved sulphide in modern sediment of a permanently stratified (meromictic) lake is possible using a novel sulphide imaging technique (called a 'sulphur print'). The technique is simple, easy to use and can map a relatively large area (up to several dm²). In situ sulphur prints from anoxic fine-grained sediments are able to reveal internal structures in apparently homogeneous materials. Sulphur prints have been used to examine the formation and distribution of dissolved sulphide in the sediment and water column of the meromictic Lake Cadagno (southern Switzerland). The prints show clearly that a previously unknown laminar convective flow of sulphide-free porewater occurs across the sediment–water interface. Such convective flow out of the sediment must be accompanied by convective flow of sulphide- and sulphate-rich lake water into the sediment, and may be an important mechanism for the accumulation of sulphur in the sediment.     

Lithology and late postglacial stratigraphy of bottom sediments in isolated basins of the White Sea coast exemplified by a small lake in the Chupa settlement area (Northern Karelia)

The complex lithological, geochemical, geochronological, and micropaleontological (diatoms, spores, pollen) investigations of stratified bottom sediments that constitute facies-variable sedimentary sequences in a small isolated lake located near the upper limit of the sea on the White Sea coast made it possible to define lithostratigraphic units (LSU) forming the complete sedimentary succession in deep parts of isolated basins. It is shown that stratigraphy of heterogeneous sequences is determined by two regional transgressive–regressive cycles in relative sea level fluctuations: alternating late Glacial and Holocene transgressions and regressions. The lower part of a clastogenic clayey–sandy–silty sequence successively composed of freshwater (LSU 1) and brackish-water (LSU 2) sediments of the ice-marginal basins and marine postglacial facies (LSU 3) was formed during the late Glacial glacioeustatic marine transgression. Its upper part formed in different isolated basins at different stages of the Holocene is represented depending on its altimetric position on the coastal slope by costal marine sediments (LSU 4) and facies of the partly isolated inlet (LSU 5). The organogenic sapropelic sequence, which overlies sediments of the marine basin and partly isolated bay, corresponds to lithostratigraphic units represented by Holocene sediments accumulated in the meromictic lake (LSU 6), onshore freshwater basin (LSU 7), and freshwater basin with elevated water mineralization (LSU 8) deposited during maximum development of Holocene transgression and lacustrine sediments (LSU 9) formed in coastal environments during terminal phases of the Holocene. The defined lithostratigraphic units differ from each other in lithological, micropaleontological, and geochemical features reflected in structural and textural properties of their sediments, their composition, inclusions, and composition of paleophytocoenoses and diatom assemblages.     

Geodynamic impact on the stable isotope signatures in a shallow epicontinental sea

Analyses were made of a mollusc‐based meta dataset of 859 δ¹³C and δ¹⁸O data of Miocene nearshore settings in the European Paratethys Sea and its descendant Lake Pannon. The observed trends document a strong tie to geodynamics, which are largely decoupled from Miocene open ocean isotope curves. Semi‐ to fully enclosed, initially marine water bodies such as the Paratethys Sea are prone to switching seawater isotope signatures because they respond rapidly to changes in the evaporation/precipitation ratio. Two phases of positive deviations of oxygen isotope values of water (relative to the modern ocean value, SMOW) occurred during the Middle Miocene; both were initiated by tectonic constrictions of the seaways and became amplified by global warming and regionally decreasing precipitation. With the final disintegration of the Paratethys, the marine isotope signatures vanish. Instead, the observed isotope trends suggest a comparably simple system of an alkaline lake with steadily declining salinity. The ‘ocean‐derived’ Paratethys Sea may thus act as a key for understanding isotope trends in epicontinental seas.     

Stable isotopic compositions of Recent freshwater cyanobacterial carbonates from the British Isles: local and regional environmental controls

Recent (<50 years old) freshwater cyanobacterial carbonates from diverse environments (streams, lakes, waterfalls) throughout Britain and Ireland were analysed for their stable carbon and oxygen isotope compositions. The mean δ¹⁸O value of ?5–9‰ PDB for river and stream data represents calcite precipitation in equilibrium with the mean oxygen isotopic composition of precipitation in central Britain (?7–5‰SMOW) assuming a mean water temperature of 9°C. The mean δ¹⁸O of lake data, ?4–5‰ PDB, is statistically different, reflecting the effects of residence time and/or variations in the oxygen isotopic composition of rainfall. Carbon isotopes have wide variations in both fluviatile and lake data sets (+ 3 to ?12‰ PDB). These variations are principally controlled in the fluviatile samples by contribution of isotopically light ‘soil zone’ carbon relative to isotopically heavier carbon from limestone aquifer rock dissolution. Lake samples have the heaviest carbon isotope values, reflecting a trend toward isotopic equilibrium between atmospheric CO₂ and aqueous HCO^?₃. We infer that isotopic compositions of ancient cyanobacterial carbonates should also record environmental information, although the effects of stabilization and diagenesis on primary δ¹⁸O values will need careful consideration. Primary carbon isotope compositions should be well preserved, although in marine samples values will be buffered by the isotopic composition of aqueous marine bicarbonate.     

Environmental Geochemistry of Swan Lake Inlet,Rongcheng Bay,the Yellow Sea of China

The Swan Lake Inlet, the State Primary Wildlife Protection Area, is a lagoon-inlet system located in the Rongcheng Bay, Shandong Peninsula, China. It has been undergoing development for aquaculture and tourism. In the summer of 1999, a study on the environment of the Swan Lake Inlet was carried out. The concentrations of the major elements and trace elements Fe, Al, Pb, Zn, Cd, Cu, Cr, Mn and P have been measured by ICP-AES and graphite furnace atomic adsorption spectrometry. The sources and distribution of the elements in the Swan Lake Inlet have been discussed. It is concluded that the Swan Lake Inlet has not been subjected to significant environmental pollution. The chemical results show that the dissolved oxygen (DO) contents are generally normal. At some locations DO solubility appears to be >100 %. The BOD₅ ( five-day biochemical oxygen demand) values are generally <4 mg/L and COD (chemical oxygen demand) 3～4 mg/L. The seawater N, P and Si contents are lower than the Class I water type specified by the Chinese National Standard of Water Quality. The low nutrient distribution reflects little discharge from land, therefore lacking of nutrient supply.     

意大利上新世古生产力的轨道驱动

主要研究了意大利上新统3个剖面Punta Piccola、Cape Spertivento以及Punta Rossello蛋白石含量的变化,综合其它古环境指标对非洲季风和地中海表层生产力加以分析,研究表明,Punta Piccola剖面和Cape Spertivento剖面各古环境指标对岁差周期影响的响应明显而单纯,即岁差低值,对应氧同位素偏负,有机碳和蛋白石高值以及碳酸盐低值,说明地中海表层生产力明显受到岁差的驱动。岁差驱动下的北非夏季风导致尼罗河泛滥,带来的丰富营养元素使得生产力剧增,同时淡水注入,阻碍了水体的垂向交换,直接导致了海底的缺氧环境,硅藻利用深层营养产生勃发,并组成“藻席”,快速沉降到海底,使得有机碳迅速埋葬和保存,从而引发了腐泥层的形成。Punta Rossello剖面硅藻层证实了“藻席”的存在,但是蛋白石含量并不高。 [HT5H]关 键 词:[HT5K] [HT5H]中图分类号： 文献标识码：A[HT5SS][HK]     

青藏高原中部湖泊岩芯记录的第四纪湖平面变化及气候意义

通过对羌塘地区中部羌D1井长181·6m第四系岩芯的研究,分析湖泊沉积记录的岩相旋回和Fe/Mn和Sr/Ba等微量元素古环境参数的变化,结合样品的热释光(TL)测年数据,讨论晚更新世该区湖泊扩张和湖面升降变化过程。结果表明,晚更新世以来该区湖泊环境的演化,经历了二次湖进过程,二次湖平面上升期之间出现了一次广泛的干化低水位时期。其中15~7万年期间的湖泛事件可以在区域上进行追踪对比,它对应于深海氧同位素的第5阶段,可以作为高原中央气候转型期的标志。     

Groundwater/surface-water interactions on deeply weathered surfaces of low relief: evidence from Lakes Victoria and Kyoga, Uganda

Little is known of the interactions between groundwater and surface water on deeply weathered landscapes of low relief in the Great Lakes Region of Africa (GLRA). The role of groundwater in sustaining surface-water levels during periods of absent rainfall is disputed and groundwater is commonly excluded from estimations of surface-water balances. Triangulated piezometers installed beside lake gauging stations on Lake Victoria and Lake Kyoga in Uganda provide the first evidence of the dynamic interaction between groundwater and surface water in the GLRA. Stable isotope ratios (²H:¹H, ¹⁸O:¹⁶O) support piezometric evidence that groundwater primarily discharges to lakes but show further that mixing of groundwater and lake water has occurred at one site on Lake Victoria (Jinja). Layered-aquifer heterogeneity, wherein fluvial-lacustrine sands overlie saprolite, gives rise to both rapid and slow groundwater fluxes to lakes which is evident from the recession of borehole hydrographs following recharge events. Darcy throughflow calculations suggest that direct contributions from groundwater to Lake Victoria comprise <1% of the total inflows to the lake. Groundwater/surface-water interactions are strongly influenced by changing drainage base (lake) levels that are controlled, in part, by regional climate variability and dam releases from Lake Victoria (Jinja).     

Sulfur cycling in a stratified euxinic lake with moderately high sulfate: Constraints from quadruple S isotopes

We present a 3-year study of concentrations and sulfur isotope values (δ³⁴S, Δ³³S, and Δ³⁶S) of sulfur compounds in the water column of Fayetteville Green Lake (NY, USA), a stratified (meromictic) euxinic lake with moderately high sulfate concentrations (12-16 mM). We utilize our results along with numerical models (including transport within the lake) to identify and quantify the major biological and abiotic processes contributing to sulfur cycling in the system. The isotope values of sulfide and zero-valent sulfur across the redox-interface (chemocline) change seasonally in response to changes in sulfide oxidation processes. In the fall, sulfide oxidation occurs primarily via abiotic reaction with oxygen, as reflected by an increase in sulfide δ³⁴S at the redox interface. Interestingly, S isotope values for zero-valent sulfur sampled at this time still reflect production and recycling by phototrophic S-oxidation. In the spring, sulfide S isotope values suggest an increased input from phototrophic oxidation, consistent with a more pronounced phototroph population at the chemocline. This trend is associated with smaller fractionations between sulfide and zero-valent sulfur, suggesting a metabolic rate control on fractionation similar to that for sulfate reduction. Comparison of our data with previous studies indicates that the S isotope values of sulfate and sulfide in the deep waters are remarkably stable over long periods of time, with consistently large fractionations of up to 58‰ in δ³⁴S. Models of the δ³⁴S and Δ³³S trends in the deep waters (considering mass transport via diffusion and advection along with biological processes) require that these fractionations are a consequence of sulfur compound disproportionation at and below the redox interface in addition to large fractionations during sulfate reduction. The large fractionations during sulfate reduction appear to be a consequence of the high sulfate concentrations and the distribution of organic matter in the water column. The occurrence of disproportionation in the lake is supported by profiles of intermediate sulfur compounds and by lake microbiology, but is not evident from the δ³⁴S trends alone. These results illustrate the utility of including minor S isotopes in sulfur isotope studies to unravel complex sulfur cycling in natural systems.     

Palaeoecology of two lake basins from Disko,West Greenland

The macrofossils, lithology and chronology of two lake basins on Disko in central West Greenland have been investigated. Both lakes were isolated from the sea in the mid-Holocene as a result of relative land uplift. A marine-brackish-limnic sequence was recovered from the Qivittut Lake. The marine fauna is unusually diverse, whereas the brackish water fauna consists only of few species. Immediately after isolation the lake passed through a short-lived eutrophic phase, after which stable, mesotrophic conditions were established. From the second lake basin, the Fortunebay Lake, only limnic sediments were recovered. This lake record demonstrates that rather stable conditions have persisted since mid-Holocene times. Both lakes show anomalously high accumulation rates.     

Petroleum potential of Baikal deposits

We analyzed oils, gases, and bitumens of bottom sediments from natural shows on the southeastern shore of Lake Baikal, in the mouth of the Stvolovaya River near Capes Tolstyi and Gorevoi Utes. Based on a set of geological data, we have established that: (1) the lake oils underwent biodegradation to a variable degree: “Fresh” nondegraded paraffin oil floats up near Cape Gorevoi Utes; in the mouth of the Stvolovaya River and near Cape Tolstyi, aromatic-naphthene oil lacks n-alkanes, monomethyl alkanes, and acyclic isoprenoids; (2) Cenozoic oil originated from the organic matter of fresh-water basins with significant amounts of higher land plant remains, including angiosperm plants (oleanane), which suggests the lake or delta genesis of oil source formations of Cretaceous and younger ages. Judging from the carbon isotope composition (average δ¹³C = −43.84‰), methane from the bottom sediments near Cape Gorevoi Utes is catagenetic. The initial in-place resources in the Baikal sedimentary basins are estimated by the volumetric-statistical method at 500 mln tons of equivalent hydrocarbons.     

Dissolved silica budget in the North basin of Lake Lugano

We studied the dissolved silica cycle in the water column of the North basin of Lake Lugano, Switzerland/Italy. Lake Lugano is a meromictic, eutrophic lake, permanently stratified below 100-m depth. A one-box model was used to calculate a silica mass-balance over 1993, based on various lake measurements, such as sediment traps, sediment cores, water analysis and biota countings. We found that the North basin of Lake Lugano is at steady state as far as dissolved silica is concerned. The primary source of dissolved silica in the lake is river input (about 80%), with diffusion from bottom sediments and groundwater input also playing a role. Atmospheric input is negligible. The main export of dissolved silica occurs via biogenic uptake by diatoms and final burial of their frustules in the bottom sediment. Loss of dissolved silica through the lake outflow only represents 15% of the total output. Of the total amount of Si exported to the lake bottom through diatom sinking, less than 20% is re-supplied to the surface water by diffusion. Thus, the lake acts as an important permanent sink for silica. The long residence time of dissolved silica in the lake (7 years) is related to the strong physical stratification of the lake. Only about 10% of the standing stock are available to phytoplankton uptake.     

Geochemistry of ice-covered, meromictic Lake A in the Canadian High Arctic

The geochemical processes occurring within meromictic Lake A (maxdepth 120 m) on northern Ellesmere Island, Canada, were investigated to determinethe history of the lake and to provide a baseline for future studies. The lake contained seawaterdiluted by freshwater input that had been mixed prior to the lake's isolation from tidalaction. Input of freshwater after isolation of the lake created vertical stratification resultingin the creation of distinct oxic, suboxic and anoxic zones. Dissolved oxygen was present to 13 m,and sulphide beneath 32 m. Manganese and iron cycling dominated the redox chemistrybetween these depths. Total manganese concentrations reached 176 M, higher thanin most other natural stratified lake or marine environments.