@article{DraegerPlessenKieneletal.2019,
  author    = {Dr{\"a}ger, Nadine and Plessen, Birgit and Kienel, Ulrike and Siowinski, Michat and Ramisch, Arne and Tjallingii, Rik and Pinkerneil, Sylvia and Brauer, Achim},
  title     = {Hypolimnetic oxygen conditions influence varve preservation and delta C-13 of sediment organic matter in Lake Tiefer See, NE Germany},
  series = {Journal of paleolimnolog},
  volume    = {62},
  journal   = {Journal of paleolimnolog},
  number    = {2},
  publisher = {Springer},
  address   = {Dordrecht},
  issn      = {0921-2728},
  doi       = {10.1007/s10933-019-00084-2},
  pages     = {181 -- 194},
  year      = {2019},
  abstract  = {Stable carbon isotopes of sediment organic matter (delta C-13(OM)) are widely applied in paleoenvironmental studies. Interpretations of delta C-13(OM), however, remain challenging and factors that influence delta C-13(OM) may not apply across all lakes. Common explanations for stratigraphic shifts in delta C-13(OM) include changes in lake productivity or changes in inputs of allochthonous OM. We investigated the influence of different oxygen conditions (oxic versus anoxic) on the delta C-13(OM) values in the sediments of Lake Tiefer See. We analysed (1) a long sediment core from the deepest part of the lake, (2) two short, sediment-water interface cores from shallower water depths, and (3) OM in the water column, i.e. from sediment traps. Fresh OM throughout the entire water column showed a relatively constant delta C-13(OM) value of approximately -30.5 parts per thousand. Similar values, about -31 parts per thousand, were obtained for well-varved sediments in both the long and short, sediment-water interface cores. In contrast, delta C-13(OM) values from non-varved sediments in all cores were significantly less negative (-29 parts per thousand). The delta C-13(OM) values in the sediment-water interface cores from different water depths differ for sediments of the same age, if oxygen conditions at the time of deposition were different at these sites, as suggested by the state of varve preservation. Sediments deposited from AD 1924 to 1980 at 62m water depth are varved and exhibit delta C-13(OM) values around -31 parts per thousand, whereas sediments of the same age in the core from 35m water depth are not varved and show less negative delta C-13(OM) values of about -29 parts per thousand. The relation between varve occurrence and delta C-13(OM) values suggests that delta C-13(OM) is associated with oxygen conditions because varve preservation depends on hypolimnetic anoxia. A mechanism that likely influences delta C-13(OM) is selective degradation of OM under oxic conditions, such that organic components with more negative delta C-13(OM) are preferably decomposed, leading to less negative delta C-13(OM) values in the remaining, undegraded OM pool. Greater decomposition of OM in non-varved sediments is supported by lower TOC concentrations in these deposits (similar to 5\%) compared to well-varved sediments (similar to 15\%). Even in lakes that display small variations in productivity and terrestrial OM input through time, large spatial and temporal differences in hypolimnetic oxygen concentrations may be an important factor controlling sediment delta C-13(OM).},
  language  = {en}
}
@article{KienelPlessenSchettleretal.2013,
  author    = {Kienel, Ulrike and Plessen, Birgit and Schettler, Georg and Weise, Stephan and Pinkerneil, Sylvia and Boehnel, Harald and Englebrecht, Amy C. and Haug, Gerald H.},
  title     = {Sensitivity of a hypersaline crater lake to the seasonality of rainfall, evaporation, and guano supply},
  series = {Fundamental and applied limnology : official journal of the International Association of Theoretical and Applied Limnology},
  volume    = {183},
  journal   = {Fundamental and applied limnology : official journal of the International Association of Theoretical and Applied Limnology},
  number    = {2},
  publisher = {Schweizerbart},
  address   = {Stuttgart},
  issn      = {1863-9135},
  doi       = {10.1127/1863-9135/2013/0405},
  pages     = {135 -- 152},
  year      = {2013},
  abstract  = {The hypersaline crater lake and its catchment on seabird island Isabel (Pacific, off Mexico) was studied to explore the influence of strong seasonal variations in rainfall/evaporation and guano contribution on its limnology. The hypersaline lake water (HSW, 78 \%) is up to 2.2-times enriched in inert ions relative to mean seawater. Rainfall during summer dilutes the HSW to form a less saline rainwater body (RWB) above a chemolimnion between 2 and 4 m water depth. The RWB is inhabited first by diatoms and ostracods followed later on by cyanobacteria and ciliates. Evaporation of > 1.5 m depth of lake water over the dry season increases the salinity of the RWB until the water column becomes isohaline at HSW concentrations in the late dry season. Differences in the stable isotope composition of water and primary producers in RWB and HSW reflect this development. Introduction of seabird guano and the decrease of salinity fuel a high primary production in the RWB with higher delta(CDIC)-C-13 and delta(13)Corg of particulate organic matter than in the HSW. The high N supply leads to high delta N-15 NH4 values (+ 39 \% in the HSW) as the consequence of ammonia volatilization that is strongest during guano maturation and with evaporative salinity increase from the HSW. Precipitation of carbonate (calcite and aragonite) from the RWB and the HSW is hindered by the high concentration of guano-derived P. This inhibition may be overcome with evaporative supersaturation during particularly dry conditions. Carbonate may also precipitate during particularly wet conditions from the dilute RWB, where the P-concentration is reduced during an active phytoplankton production that raises the pH. Differences in the stable isotope signatures of carbon and oxygen in HSW and RWB (+ 5 \% delta(CDIC)-C-13 and -3 \% d18OH2O) suggest the processes of carbonate precipitation can be distinguished based on the isotope signature of the carbonates deposited. Changes in the lake system are indicated when lower temperatures and higher rainfall in the 2006 wet season introduced more and less mature guano to the lake. The lower pH was accompanied by lower ammonia volatilization and carbonate precipitation as indicated by an increased concentration of NH4, Ca, Sr and DIC, while delta H-2, delta(NNH4)-N-15, and salinity were lower. According to our results, the observed sediment laminations should reflect the introduction of catchment material (including guano) with runoff, the RWB plankton production, and the carbonate precipitation in relation to its origin and seasonality.},
  language  = {en}
}