シュウホクセイ ケイソウ Navicula streckerae Lange-Bert. & Witk. トクニ テンモン ニ ツイテ

Navicula streckeraeはドイツ北部の2地点と北極海で記録されている種であるが,今回フブスグル(Khovsgol)湖(モンゴル)とカムチャッカで見出した(図1).本種はユーラシア大陸の北緯50度以北に分布する周北性珪藻である.また,本種はその形態より北極海型,Weser川型,Kinzig川型に3区分できる.ヨーロッパとカムチャッカの三つの型について形態と計測値の比較を行う. 条線を構成する点紋の密度は1980年代に入ってから種を区分する特徴の一つとして重要視されてきた.しかし,珪殻の部位による点紋密度の変化の調査はどの種についても行われていないようである.今回ヨーロッパとカムチャッカ産の試料で詳しく調査を行った結果,中心域を形成する短い条線と先端部,Voigtの欠落付近の点紋密度の変化は大きく,その他では比較的安定していることが判明した.点紋密度の計測はこの部分で行うべきである.Navicula streckerae was recorded in two locations of northern Germany and the Arctic Ocean. According to the findings of this taxon from Lake Khovsgol (Mongolia) and Kamchatka (Russia) by our investigations, this taxon distributed northward from latitude 50°N. on the Eurassian Continent and is considered to be a circumboreal diatom. This taxon is divided into three types, namely the Arctic Ocean type, the Weser River type and the Kinzig River type according to the valve morphology. In this study we compare these three types in the samples from Europe and Kamchatka focusing on the valve form and sizes. Though the density of lineolae composing striae is one of the important characteristics to classify the species, there are few records of this point. We investigate this point in detail in the specimens from Europe and Kamchatka. Consequentry the two extreme values, short striae forming the cental area and the area including Voigt discontinuities, should be excluded when measuring the density of lineolae to obtain a stable value

Holocene environmental history of a small coastal lake from north-eastern Kamchatka Peninsula.

AbstractA radiocarbon and tephra-dated sediment core from Lifebuoy Lake, located on the north-east coast of Kamchatka Peninsula, was analysed for pollen, spores, diatoms, chironomids and tephra in order to uncover regional environmental history.The 6500-year environmental history of Lifebuoy Lake correlates with the broad regional patterns of vegetation development and climate dynamics with both diatoms and chironomids showing near-synchronous changes.Between ca. 6300 and 3900calyrBP, the lake ecosystem was naturally enriched, with several Stephanodiscus species dominating the diatom plankton. This natural eutrophication state is likely to be due to a combination of the base-rich catchment geology, the fertilisation effect of several fires in the catchment, silica input from tephra layers and, possibly, nitrogen input from seabirds. The substantial tephra deposit at about 3850calyrBP might have stopped sedimentary phosphorus from entering the lake water thus decreasing the trophic state of the lake and facilitating the shift in diatom composition to a benthic Fragiliariaceae complex.Both diatoms and chironomids showed simultaneous compositional changes, which are also reflected by statistically significant changes in their rates of change 300–400years after the arrival of Pinus pumila in the lake catchment. The rapid increase in both total diatom concentration and the percentage abundance of the large heavy species, Aulacoseira subarctica might be a response to the change in timing and intensity of lake spring turn-over due to the changes in the patterns of North Pacific atmospheric circulation, most notably westward shift of the Aleutian Low.The two highest peaks in A. subarctica abundance at Lifebouy Lake occurred during opposite summer temperature inferences: the earlier peak (3500–2900calyrBP) coincided with warm summers and the latter peak (300calyrBP–present) occurred during the cold summer period. These imply that A. subarctica shows no direct response to the changes of summer air temperature. Instead, it appears to thrive during the periods of increased winter precipitation, thicker ice and late spring turn-over periods, i.e., shows indirect response to climate.The clearest effect of tephra deposition on the lake ecosystem is above 908cm (ca. 3800calyrBP) where the tephra deposit might have caused the shift from Stephanodiscus-dominated planktonic assemblages to the Fragilariaceae complex of benthic species. Tephra deposits might have also contributed towards the development of eutrophic plankton from about 6300calyrBP. It is not certain if several tephra deposits influenced diatom and chironomid changes during the last 300years

Global data set of long-term summertime vertical temperature profiles in 153 lakes

peer reviewedClimate change and other anthropogenic stressors have led to long-term changes in the thermal structure, including surface temperatures, deepwater temperatures, and vertical thermal gradients, in many lakes around the world. Though many studies highlight warming of surface water temperatures in lakes worldwide, less is known about long-term trends in full vertical thermal structure and deepwater temperatures, which have been changing less consistently in both direction and magnitude. Here, we present a globally-expansive data set of summertime in-situ vertical temperature profiles from 153 lakes, with one time series beginning as early as 1894. We also compiled lake geographic, morphometric, and water quality variables that can influence vertical thermal structure through a variety of potential mechanisms in these lakes. These long-term time series of vertical temperature profiles and corresponding lake characteristics serve as valuable data to help understand changes and drivers of lake thermal structure in a time of rapid global and ecological change. © 2021, The Author(s)

Circumboreal diatom Navicula streckerae Lange-Bert. & Witk., especially on lineolae

Navicula streckerae was recorded in two locations of northern Germany and the Arctic Ocean. According to the findings of this taxon from Lake Khovsgol (Mongolia) and Kamchatka (Russia) by our investigations, this taxon distributed northward from latitude 50°N. on the Eurassian Continent and is considered to be a circumboreal diatom. This taxon is divided into three types, namely the Arctic Ocean type, the Weser River type and the Kinzig River type according to the valve morphology. In this study we compare these three types in the samples from Europe and Kamchatka focusing on the valve form and sizes. Though the density of lineolae composing striae is one of the important characteristics to classify the species, there are few records of this point. We investigate this point in detail in the specimens from Europe and Kamchatka. Consequentry the two extreme values, short striae forming the cental area and the area including Voigt discontinuities, should be excluded when measuring the density of lineolae to obtain a stable value