What of Molybdenum, Uranium and Vanadium concentrations? Try their enrichment factors as well. If you have rare earth elements as part of your geochemical data, you can also use them as part of the redox proxies particularly cerium anomaly.

I agreed; I can use these proxies as a redox indicator. But my question was, why does the majority of anoxic proxies not indicate anoxic lake bottom? Could it be because:

Thank you

Okay. Since you are dealing with surface samples, their geochemical signatures may have been altered. To compliment your geochemical data, you may want to look at other proxies such as the microfossils ( e.g. arcellaceans also known as thecameobians) in the sediments. It may also worth it to obtain some core samples to see the changes below the sediment /water interface. The absence or presence of laminations, microfossils and the geochemical data in the core sediments will tell a lot of stories. The lake may not be completely anoxic throughout its sediments deposition.