Unusual biogenic calcite structures in two shallow lakes, James Ross Island, Antarctica

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Authors

ELSTER Josef NEDBALOVÁ Linda VODRÁŽKA Radek LÁSKA Kamil HALODA Jakub KOMÁREK Jiří

Year of publication 2016
Type Article in Periodical
Magazine / Source Biogeosciences
MU Faculty or unit

Faculty of Science

Citation
Web Biogeosciences online
Doi http://dx.doi.org/10.5194/bg-13-535-2016
Field Ecology
Keywords Antarctica; James Ross Island; lakes; photoautotrophic mat; calcite spicules
Description The floors of two shallow endorheic lakes, located on volcanic surfaces on James Ross Island, are covered with calcareous organosedimentary structures. Their biological and chemical composition, lake water characteristics, and seasonal variability of the thermal regime are introduced. The lakes are frozen down to the bottom for 8–9 months a year and their water chemistry is characterised by low conductivity and neutral to slightly alkaline pH. The photosynthetic microbial mat is composed of filamentous cyanobacteria and microalgae that are considered to be Antarctic endemic species. The mucilaginous black biofilm is covered by green spots formed by a green microalga and the macroscopic structures are packed together with fine material. Thin sections consist of rock substrate, soft biofilm, calcite spicules and mineral grains originating from different sources. The morphology of the spicules is typical of calcium carbonate monocrystals having a layered structure and specific surface texture, which reflect growth and degradation processes. The spicules’ chemical composition and structure correspond to pure calcite. The lakes’ age, altitude, morphometry, geomorphological and hydrological stability, including low sedimentation rates, together with thermal regime predispose the existence of this community. We hypothesise that the precipitation of calcite is connected with the photosynthetic activity of the green microalgae that were not recorded in any other lake in the region. This study has shown that the unique community producing biogenic calcite spicules is quite different to any yet described.
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