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<p>The global spread of lake hypoxia, [O<span class="inline-formula">₂</span>] <span class="inline-formula"><i>&lt;</i></span> 2 mg L<span class="inline-formula">⁻¹</span>, during the last 2 centuries has had a severe impact on ecological systems and sedimentation processes. While the occurrence of hypoxia was observed in many lakes, a detailed quantification of hypoxia spread at centennial timescales remained largely unquantified. We track the evolution of hypoxia and its controls during the past 200 years in a lake, Tiefer See (TSK; NE Germany), using 17 gravity cores recovered from between 10 and 62 m water depth in combination with lake monitoring data. Lake hypoxia was associated with the onset of varve preservation in the TSK and has been dated by varve counting to 1918 <span class="inline-formula">±</span> 1 at 62 m water depth and reached a lake floor depth of 16 m in 1997 <span class="inline-formula">±</span> 1. This indicates that oxygen concentration fell below the threshold for varve preservation at the lake floor (<span class="inline-formula"><i>&gt;</i></span> 16 m). Sediment cores at 10–12 m depth do not contain varves indicating good oxygenation of the upper-water column. Monitoring data show that the threshold for hypoxia, and the intensity and duration of hypoxia which are sufficient for varve preservation, is a period of 5 months of [O<span class="inline-formula">₂</span>] <span class="inline-formula"><i>&lt;</i></span> 5 mg L<span class="inline-formula">⁻¹</span> and 2 months of [O<span class="inline-formula">₂</span>] <span class="inline-formula"><i>&lt;</i></span> 2 mg L<span class="inline-formula">⁻¹</span>. Detailed total organic carbon (TOC), <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M13" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mrow class="chem"><msup><mi mathvariant="italic">δ</mi><mn mathvariant="normal">13</mn></msup><mi mathvariant="normal">C</mi></mrow><mi mathvariant="normal">org</mi></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="38pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="57f48634cede70c6f48ef51699358c5a"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-21-4317-2024-ie00001.svg" width="38pt" height="17pt" src="bg-21-4317-2024-ie00001.png"/></svg:svg></span></span>, and X-ray fluorescence (XRF) core scanning analyses of the short cores indicate that the decline in dissolved oxygen (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 varves were not preserved. Furthermore, varve preservation does occur at seasonal stratification and does not necessarily require permanent stratification.</p>