Lake Ladoga ice phenology: Mean condition and extremes during the last 65 years

Winter conditions play an important role for the largest lake in Europe—Lake Ladoga. The ice cover lasts for 171 ± 3 days on average from the early November until the mid‐May. We investigated the ice regime of Lake Ladoga using a constructed ice database of aircraft surveys and satellite images. More than 1250 surveys of the lake's ice cover from 1943 to 2010 were collected and analysed to determine mean and extreme ice conditions for winters of different types of severity. The time series of ice cover percentage over the lake was plotted. On average, 18 observational ice charts were made every winter. Individual ice phenology records show considerable year‐to‐year variation. For this reason, records typically have been combined and analysed as groups (categories). Extremely cold winters were determined as winters with complete ice cover that lasts more than three months which is approximately 90% quartiles from all winters with complete ice cover. The lake surface was completely covered with ice for more than three months during 5 seasons. Extremely warm winters when the maximum ice cover was less than 70% of the lake area occurred during 5 seasons as well. A basic relationship between the winter severity as winter maximum of accumulated freezing degree‐days (AFDD) and the earlier derived Relative Ice Cover Index (RICI) was established. We have used teleconnection indices such as North Atlantic Oscillations (NAO) and Arctic Oscillation (AO) for the period from October to May for estimation of different types of Lake Ladoga's ice conditions. The AO index in winter months and local winter maximum of AFDD explained much of the interannual variation in ice cover. Copyright © 2011 John Wiley & Sons, Ltd.     

Evidence for an Hesperian-aged South Circum-Polar Lake Margin Environment on Mars

A broad pitted plain and an elongated low rise occur near the south pole of Mars between a region of major cavi (Cavi Angusti) and a regionally smooth and broad valley (Argentea Planum). Viking, Mars Global Surveyor (MGS), and Odyssey data reveal a densely pitted plain covering ∼6750 km², and containing >300 irregularly shaped, steep-walled and flat-floored depressions with a mean diameter of ∼3.5 km. At the southernmost (poleward) extent of this plain are 12 north/south trending linear valleys that are characterized by theater-shaped heads abutting a major cavi within Cavi Angusti. The pitted plain, which abuts Cavi Angusti to the southwest, is separated from the floor of Argentea Planum by a smooth, elongated low rise that extends parallel to the plain for ∼200 km. These unusual features are all found within the Hesperian-aged circumpolar Dorsa Argentea Formation, which has been interpreted by some workers to be an ice-rich glacier-related deposit. We interpret the pitted plain to represent the maximum northern extent of the Angusti lobe ice deposit. The pits are analogous in morphology and distribution to terrestrial kettle holes, which form from the melting of isolated ice-blocks surrounded and partly buried by sediment, to leave hollows. The linear valleys are consistent with sapping valleys formed from the release of an elevated groundwater table, fed by meltwater lakes. On the basis of these characteristics, relationships and analogs, we interpret the marginal facies to represent an ice-sheet/lake contact environment that existed during Hesperian time.     

Late glacial and Holocene environmental change in the Lake Baikal region documented by oxygen isotopes from diatom silica

We investigate late glacial and Holocene climate change recorded in Lake Baikal using the oxygen isotope composition of diatom silica (δ¹⁸O_DIAT). Evaporation from the lake is minor, and the temperature fractionations of δ¹⁸O are unable to explain variations in the δ¹⁸O_DIAT record alone. Isotopically, low meltwater input from glaciers may have some influence on δ¹⁸O_DIAT, but the assumed periods of climatic warming and wastage do not coincide with large shifts in δ¹⁸O_DIAT. There is a gradual oxygen isotope lowering from 27.0‰ to 20.6‰ over the late glacial, while, during the Holocene, δ¹⁸O_DIAT values return to relatively high values. Previous studies of the modern oxygen and hydrogen isotope composition of Lake Baikal's inputs reveal that fluvial input to the lake's North Basin are isotopically lower than fluvial input from South Basin rivers. This north–south gradient of river δ¹⁸O and δD is mainly due to the greater input from isotopically low winter precipitation in the north and isotopically higher summer precipitation in the south. As a result, the δ¹⁸O_DIAT record from Lake Baikal can at least in part be explained by varying input from these sources related to seasonal changes in precipitation. Changes in atmospheric conditions may have a role in altering seasonality and the distribution of precipitation over Lake Baikal's catchment. A feedback mechanism is well known linking higher Eurasian spring snow cover extent (ESSC) to the development of anticyclonic conditions and low precipitation the following summer in the areas south of Lake Baikal. A simultaneous increase in the importance of depleted water (snowmelt) input from the north and decreased enriched summer precipitation in the south is needed to explain depletions in δ¹⁸O of lake water and subsequently δ¹⁸O_DIAT during colder periods. The opposite of this situation is required to enrich lake water during warmer periods. The analysis of δ¹⁸O from diatom silica is a useful proxy for environmental change, especially in lakes, like Lake Baikal, where carbonates are absent or diluted. However, analysis must be based on near pure diatom samples as even trace amounts of silt can have a dominating effect on δ¹⁸O_DIAT values.     

ENCLOSURE EXPERIMENTS ON AND LACUSTRINE PRACTICE FOR ELIMINATING MICROCYSTIS BLOOM

Microcystis bloom, one of the most objectionable characteristics of eutrophication in tropical and subtropical waters, occurred in Donghu Lake (East lake) of Wuhan every summer from the 1970s up to 1984, but from 1985 up to now failed to occur there. The cause of its disappearance rema-ined in obscurity until recently. In situ enclosure experiments in the lake for three years showed that the stocking of the filter-feeding silver carp ( Hypophthalmichthys molitrix ) and big-head carp (Aristichthys nobilis ) played a decisive role in eliminating Microcystis bloom from the lake; but that recurrence of the bloom is possible under certain conditions. This paper presents the details and the results of enclosure ex-periments. The authors‘ analysis of fish biomass data obtained by echo-sounding and the fishery produc-tion of the lake over the years, revealed that the recurrence of Microcystis bloom can be prevented so long as the combined biomnss of silver carp and big-head carp remains at or exceeds 50 g per cubic meter of lakewater, as was the case in the lake‘s 1985 fish yield of 1015 t.     

The applicability of research on flood-drought tendency —an analysis on disastrous flood of Taihu Lake basin in June-July, 1991

In Taihu Lake basin during June–July in 1991, there happened a catastrophic flood, the precipitation reached that of 1954 and the water level was the highest in the history in Taihu Lake. This heavy flood, happening in the relatively humid period and being well accord with flood-drought change tendency, was early precautioned. The occurrence of the flood illustrated that using records of historical climate to predict flood-drough tendency is practically significant for hazard-reduction project.     

A 3600 years paleoclimatic change inferred from organic δ13C and TOC/TN of the Gucheng Lake sediments, southeast China

A 6.2 m thick core of Gucheng Lake sediment provided a 3600 years record of climate change. The contents of the TOC in the core changed from 2.63% to 8.48%, and the δ¹³C values of organic matter were from −21.54% to −27.3%. The TOC/TN ratios indicated that the organic materials in sediments were from lake plankton and land-derived plants. The 2.9–22 m core interval with high TOC/TN ratios, low δ¹³C values and low contents of TOC indicated a cold climate stage. The 6.2–5.5 m and 0.4–0.1 m intervals were characterized by low TOC/TN ratios, high δ¹³C values and high contents of TOC, and reflected temperate climate stages. Project 49372129 supported by NSFC.     

THE HOLOCENE SEDIMENTAL CHARACTERISTIC AND PALEOCLIMATIC EVOLUTION OF EBINUR LAKE，XINJIANG

ＴＨＥＨＯＬＯＣＥＮＥＳＥＤＩＭＥＮＴＡＬＣＨＡＲＡＣＴＥＲＩＳＴＩＣＡＮＤＰＡＬＥＯＣＬＩＭＡＴＩＣＥＶＯＬＵＴＩＯＮＯＦＥＢＩＮＵＲＬＡＫＥ，ＸＩＮＪＩＡＮＧ吴敬禄，王苏民，吴艳宏ＴＨＥＨＯＬＯＣＥＮＥＳＥＤＩＭＥＮＴＡＬＣＨＡＲＡＣＴＥＲＩＳＴ...     

Glacial Lake Victoria,a high‐level Antarctic Lake inferred from lacustrine deposits in Victoria Valley

We present evidence of a large lake (Glacial Lake Victoria) that existed in Victoria Valley in the dry valleys region of Antarctica between at least 20 000 and 8600 ¹⁴C yr BP. At its highstands, Glacial Lake Victoria covered 100 km² and was ca. 200 m deep. The chronology for lake‐level changes comes from 87 AMS radiocarbon dates of lacustrine algae preserved in deltas and glaciolacustrine deposits that extend up to 185 m above present‐day lakes on the valley floor. The existence of Glacial Lake Victoria, as well as other large lakes in the dry valleys, indicates a climate regime significantly different from that of today at the last glacial maximum and in the early Holocene. Copyright © 2002 John Wiley & Sons, Ltd.     

Microscale Simultaneous Measurement of Carbon and Nitrogen Isotopes on Natural Diamond

Simultaneous analysis of carbon and nitrogen isotope ratios by SIMS was applied for the first-time to a natural diamond from the Kelsey Lake kimberlite, State Line Distinct, Colorado (UWD-1). This in situ procedure is faster, reduces sample size for analysis, and measures both isotope ratios from a single ~ 10 μm diameter pit, a critical advantage for zoned diamonds. The carbon isotope ratio (expressed as δ¹³C_VPDB) of the bulk UWD-1 crystal, determined by the conventional combustion method in the present study, is -5.9‰ ± 0.2‰ (VPDB, 2s). Nitrogen mass fraction ([N]) and isotope ratio (expressed as δ¹⁵N_Air) were determined by stepwise combustion and gas-source mass-spectrometry, resulting in 553 ± 64 μg g^-1 and -6.7‰ ± 1.1‰ (Air, 2s), respectively. Secondary ions of ¹²C₂^-, ¹²C¹³C^-, ¹²C¹⁴N^-, and ¹²C¹⁵N^- were simultaneously measured by SIMS using three Faraday cups and one electron multiplier. The spot-to-spot reproducibility of δ¹³C and δ¹⁵N values for the UWD-1 (178 spots on sixteen chips, 10 μm spots), were 0.3‰ and 1.6‰, respectively (2s). While ¹²C¹⁴N^-/¹²C₂^- ratios, which are an indicator for [N], varied up to 12% among these sixteen chips, such variation did not correlate with either δ¹³C or δ¹⁵N values. We propose that UWD-1 is a suitable reference sample for microscale in situ analysis of δ¹³C and δ¹⁵N values in diamond samples.     

Historical variations in autochthonous and allochthonous sediment supplies to the largest freshwater lake in Central India

Lacustrine sediment preserves high-resolution biogeochemical records of past variations in watershed processes controlling lake sedimentation. The current study explores historical variations in autochthonous and allochthonous sediment supplies to a large tropical freshwater lake system (Upper Lake, Bhopal) protected under the international Ramsar Convention of 2002 against anthropogenic pressures. For this purpose, multi-proxy biogeochemical data are presented for organic matter (total organic carbon, total nitrogen, phosphorous, and loss on ignition [LOI] at 550 °C), carbonate (LOI at 950 °C), lithic sediment (aluminum, titanium, iron, calcium, magnesium, sodium, potassium, manganese, zirconium, niobium, hafnium, tantalum, thorium, uranium, and rare earth elements), and anthropogenic inputs (lead) measured in a 38 cm long sediment core retrieved from the lake. In addition to the lacustrine sediment core, the samples of catchment bedrock, surface soils, major stream sediment, and eolian dust collected from the lake periphery also are analyzed. The systematic biogeochemical excursions in the upper core section (top ～8 cm) indicate increased anthropogenic inputs, watershed denudation by agricultural activities, artificially reduced fluvial sediment supply, relatively increased dust inputs and lake eutrophication in the last few decades. The current study underscores the roles of anthropogenic land-use and wetland conservation practices in the rapid alteration of autochthonous and allochthonous sediment supplies to open aquatic ecosystems. Further, rising lake eutrophication levels despite a managed reduction in allochthonous sediment supplies seem challenging to control due to dissolved nutrient supply from urban sewage discharge and runoff from agricultural land in the watershed.