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I would like to understand why any of the following conditions in a layer of a lacustrine sediment core appear to imply that the lake level was low at the relevant time:

  1. low C/N ratio
  2. low δ13C
  3. low concentration of magnetic particles

All papers I've come across assume prior knowledge about these relationships, and basic sources like Wikipedia haven't helped me either. My background is mathematics, with little to no chemistry knowledge.

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    $\begingroup$ The concentration of magnetic particles is an indication of whether the sediments were oxic or anoxic - shallow waters are likely to be oxygenated, deeper waters anoxic. In oxygenated waters any iron is likely to be in the form of Iron oxides, while in anoxic conditions there are biogeochemical pathways for the formation of ferrous minerals, some of which are ferromagnetic,. $\endgroup$
    – Andy M
    Commented Feb 24, 2022 at 9:58
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    $\begingroup$ @AndyM You could turn this comment into a (partial) answer. $\endgroup$ Commented Feb 24, 2022 at 20:06
  • $\begingroup$ @AndyM, thank you this is very helpful indeed. $\endgroup$
    – qr597
    Commented Mar 4, 2022 at 2:35

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That delta C13 values are useful proxies for lake level because carbon isotope ratios are relevant to organic carbon deposited by lacustrine plants and, critically, for relatively shallow lakes. Past a certain lake depth and those isotope ratios make increasingly less sense.

Other chemistries: nitrogen, iron oxidation state are useful indicators of organic growth rates as well as deposition environment, which, incidentally, would tell you if the lake is too deep for using (organically derived) C13 isotopes. One would also want to know if that organic carbon is the result of nitrogen loading, oxygenation, or both, or neither.

Check out this paper: Evaluation of lacustrine organic δ13C as a lake-level indicator: A case study of Lake Qinghai and the satellite lakes on the Tibetan Plateau.

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