Below I post the original inquiry about the dissolution of diatoms. In the case of inadvertent changes in meaning, I apologize and will correct the error as soon as I'm notified. I can also add new messages if that is warranted. One of the longest and most interesting cores only has diatoms near the top, but sponge spicules throughout. There are fragments of diatoms on the slides, but these too become more common upcore.
Dissolution is clearly a major factor.
I think this is a real problem for us under these circumstances. Also, one other comment. In a few instances we had all broken fragments, but the scaled chrysophyte scales were in great shape - thus, no dissolution problem here. I think that in our case it has something to do with organic acids. I know that it is not strictly a pH problem in our case.