Freshwater diatoms as indicators for Holocene environmental and climate changes on Kamchatka, Russia

Bernhard.Diekmann [ at ]


The functionality of the climate controlling system of the Kurile‐Kamchatka‐Aleutean‐ Sea‐Island‐Arc and its adjacent regions in the north‐western Pacific and the Bering Sea is yet not well understood. Factors that influence the climate of this high‐latitude region comprise changes in volcanic activity, modifications of ocean circulation in the northern Pacific realm, or variations in the prevailing modes of atmospheric teleconnections. The German‐Russian joint venture project KALMAR aims to assess these climate controlling features by palaeoenvironmental reconstructions inter alia. One aspect of KALMAR was the reconstruction of climate‐related past terrestrial environmental changes from faunal and floral remains in lake sediments. In this thesis, changes in the composition of fossil freshwater diatom assemblages are used as palaeoecological indicators. Another approach invokes the palaeolimnological interpretation of the stable oxygen isotope composition of the siliceous diatom cell walls (δ18Odiatom). This combination of taxonomical and geochemical methods was applied for the first time on lake‐sediment records from Kamchatka. The studied lakes were selected to cover different environmental boundary conditions. They comprised a hydrologically closed seepage lake (Lake Sigrid) at a moderate elevation of about 280 m above sea level next to an open through‐flow lake (Two‐Yurts Lake) in central Kamchatka and an open through‐flow lake at an elevation of almost 500 m above sea level (Lake Sokoch) in south Kamchatka. A total of 133 diatom taxa were identified within the fossil records, whereof one taxon could be identified as an up‐to‐now unknown species. It is referred to as Fragilaria flexura sp. nov. U. HOFF et LANGE‐BERTALOT, of which a detailed description was conducted during this thesis. The composition of the diatom assemblages differs between the three studied lakes, dependent on several parameters, such as water temperature and the geochemical character of the host water, stratification of the water column, turbulence, trophy, or the amount of available nutrients. Two‐Yurts Lake reveals highest biological productivity (diatoms), due to a steady input of nutrients and diluted silica by its inflows, additionally supported by frequent occurring strong turbulences, enabling for a reworking and hence recycling of deposited nutrients/silica from the lake bottom surface sediments. Lake Sokoch shows less intense biological productivity, most likely caused by minor nutrient and diluted silica input into the lake and a geographical setting which is less exposed to fall winds than Two‐Yurts Lake is. The closed seepage Lake Sigrid in turn reveals lowest numbers of diatoms per gram sediment (biological productivity) most likely due to its lacking inflows. For the diatom assemblage of Lake Sigrid being not predominantly affected by strong fluctuations in the availability of nutrients originating in the lakes hinterland, changes within the assemblage are most reasonably indicators for temperature changes. Therefore, the diatom assemblages could be used to infer warm, temperate and also cold periods of the Holocene history of Kamchatka. Diatom assemblages of Lake Sokoch are suggested to document the often world‐wide observed Holocene temperature trend with a mid‐ Holocene climate optimum and late Holocene cooling. A similar overall trend towards colder conditions could also be inferred from δ18Odiatom values in sediment cores from Two‐Yurts Lake. However, diatom assemblages from Two‐Yurts Lake as well as from Lake Sigrid are assumed to indicate short‐term temperature fluctuations overprinting the long‐term trend of a Holocene cooling.

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Thesis (PhD)
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Hoff, U. (2010): Freshwater diatoms as indicators for Holocene environmental and climate changes on Kamchatka, Russia , PhD thesis, Universität Potsdam, Mathematisch-Naturwissenschaftliche Fakultät.

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