Preprints
https://doi.org/10.5194/egusphere-2024-835
https://doi.org/10.5194/egusphere-2024-835
18 Apr 2024
 | 18 Apr 2024
Status: this preprint is open for discussion.

Tracing rate and extent of human induced hypoxia during the last 200 years in the mesotrophic lake Tiefer See (NE Germany)

Ido Sirota, Rik Tjallingii, Sylvia Pinkerneil, Birgit Schroeder, Marlen Albert, Rebecca Kearney, Oliver Heiri, Simona Breu, and Achim Brauer

Abstract. The global spread of lake hypoxia, [O2] < 2 mg/l, during the last two centuries has a severe impact on ecological systems and sedimentation processes. While the occurance of hypoxia was observed in many lakes, a detailed quantification of hypoxia spread remained largely unquantified. We track the evolution of hypoxia and its controls during the past 200 yrs in lake Tiefer See (TSK; NE Germany) using 17 gravity cores, recovered between 10 and 62 m water depth in combination with lake monitoring data. Lake hypoxia was associated by the onset of varve preservation in the TSK, and has been dated by varve counting to 1918±1 at 62 m water depth and reached a lake-floor depth of 16 m at 1997±1. This indicates oxygen concentration to fell below the threshold for varve preservation at the lakefloor (>16 m). Sediment cores at 10–12 m depth do not contain varves indicating well oxygenation of the upper water column. Monitoring data show that the threshold for hypoxia at the depocenter is a period of five months of [O2] < 5 mgl   and two months of [O2] < 2 mgl . Detailed TOC, δ13Corg and XRF core scanning analyses of the short cores indicate that the depletion in DO started several decades prior to the varve preservation. This proves a change in the depositional conditions in the lake following a transition phase of several decades during which varve preservation was not accomplished. Furthermore, varve preservation does occur at seasonal stratification and not necessarily requires permanent stratification.

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Ido Sirota, Rik Tjallingii, Sylvia Pinkerneil, Birgit Schroeder, Marlen Albert, Rebecca Kearney, Oliver Heiri, Simona Breu, and Achim Brauer

Status: open (until 31 May 2024)

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Ido Sirota, Rik Tjallingii, Sylvia Pinkerneil, Birgit Schroeder, Marlen Albert, Rebecca Kearney, Oliver Heiri, Simona Breu, and Achim Brauer
Ido Sirota, Rik Tjallingii, Sylvia Pinkerneil, Birgit Schroeder, Marlen Albert, Rebecca Kearney, Oliver Heiri, Simona Breu, and Achim Brauer

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Short summary
Hypoxia has spread in lake Tiefer-See (NE Germany) due to the increased human activity. The onset of hypoxia indicated by varve preservation is dated to ~1920 at the lake’s depocenter, which respond faster and more severely to the reduction in oxygen level. The spread of hypoxic conditions is a gradual process that lasted for nearly one hundred years, and the chemistry of the sediments shows that the depletion in oxygen in the lake started several decades before the onset of varve preservation.