A sediment core (LS-1) collected from Long Lake in King George Island, South Shetland Islands (West Antarctica) was analyzed for a variety of textural, geochemical, isotopic and paleontological properties together with 14C age dates. These data combined with published records of other studies provide a detailed history of local/regional postglacial paleoproductivity variation with respect to terrestrial paleoclimate change. The lithologic contrast of a lower diamicton and an upper fine-grained sediment demonstrates glacial recession and subsequent lake formation. The upper fine-grained deposit, intercalated by mid-Holocene tephra-fallout followed by a tephra gravity flow, was formed in a lacustrine environment. Low total organic carbon (TOC) and biogenic silica (Sibio) contents with high C/N ratios characterize the diamicton, whereas an increase of TOC and Sibio contents characterize the postglacial lacustrine fine-grained sediments, which are dated at c. 4000 yrBP. More notable are the distinct TOC maxima, which may imply enhanced primary productivity during warm periods. Changes in Sibio content and δ13C values, which support the increasing paleoproductivity, are in sympathy with these organic matter variations. The uniform and low TOC contents that are decoupled by Sibio contents are attributed to the tephra gravity flows during the evolution of the lake rather than a reduced paleoproductivity. A very recent TOC maximum is also characterized by high Sibio content and δ13C values, clearly indicating increased paleoproductivity consequent upon gradual warming across King George Island . Comparable with changes in sediment geochemistry, the occurrence and abundance of several diatom species corroborate the paleoproductivity variations together with the lithologic development. However, the paleoclimatic signature in local terrestrial lake environment during the postglacial period (for example the Long Lake) seems to be less distinct, as compared to the marine environment.
The main goal of the presented research was to investigate spatial distribution of surface sediments and to recognize relationships between chemical composition of water and sediments in a coastal Lake Sarbsko (northern Poland). The Lake Sarbsko is a freshwater basin. The water column is well oxygenated and waters exhibit only minor spatial variability of chemical composition indicating rapid and good mixing. Surface sediments of Lake Sarbsko are strongly diversified with respect to chemical composition. The sediments of Lake Sarbsko are characterized by elevated content of terrigenous silica indicating enhanced input of clastic material from the watershed and/or increased dynamics of the lake waters. Moreover, SiO2ter is strongly negatively correlated with SiO2biog, organic matter and element contents, which argues for diluting effect of the former towards authigenic components of sediments. Basically, terrigenous silica (quartz) content is highest in the lake shores and declines towards the lake center. Biogenic silica, organic matter and most of elements display reversed tendency. CaCO3 was encountered in three isolated areas, where it co-occurs with FeS. It is anticipated that precipitation of calcite in Lake Sarbsko resulted from postdepositional processes. Spatial distribution of Fe, Mn, Ca, Mg, Na and K in Lake Sarbsko is also governed by their geochemical affinities to organic matter (Fe), Fe/Mn oxides (Fe, Mn), sulphides (Fe), clay minerals (Na, K, Mg, Mn) and carbonates (Ca, Mn).