Elemental analysis
Mn and Fe concentrations in Lake Fryxell carbonates range from tens to
thousands of ppm; in samples from four depth points within the oxycline,
[Mn] ranges from 44–8972 ppm, and [Fe] from 36–2182 ppm. The
ratio of [Mn] to [Fe] also displays a broad range from
0.24–20.31. [Mn] and [Fe] display a rough covariance; the
shallowest carbonates contain the lowest concentrations of both metals,
while in deeper samples, the ablation sites yielding the highest
[Mn] also yield the highest [Fe] (Figure 5). The minimum values
of both [Mn] and [Fe] increase with depth. Carbonate [Mn]
and [Fe] vary widely at 9.3 and 9.7 m, with [Mn] ranging from
52–4173 ppm and [Fe] from 178–2418 ppm at these depths. The
highest values of both [Mn] and [Fe] represent dark brown to
black spots in carbonates interpreted as oxide minerals (Figure 5).