nikkii

Why does ferrous iron (+2) only exist in anoxic, and Fe(+3) Ferric exist in oxic environments?

I have recently been reading a lot of papers of different paleothermometers. The Calcium in calcium carbonate can get replaced by Mg and Sr and people use the ratios of Mg/Ca and Sr/Ca to predict past ocean surface temperatures. What I can't seem to understand is why the Mg/Ca and Sr/Ca show opposite trends with temperature such that as temperature increases Mg/Ca increases while Sr/Ca decreases. I would have thought they would both increase. Could someone please explain this to me? Thank you

I have recently been reading a lot of papers of different paleothermometers. The Calcium in calcium carbonate can get replaced by Mg and Sr and people use the ratios of Mg/Ca and Sr/Ca to predict past ocean surface temperatures. What I can't seem to understand is why the Mg/Ca and Sr/Ca show opposite trends with temperature such that as temperature increases Mg/Ca increases while Sr/Ca decreases. I would have thought they would both increase. Could someone please explain this to me? Thank you