Alan Cannel,
Thank you for your reply. Our reasons for our interest in paleo climate and biosphere productivity versus temperature over geological time are clearly quite different. You appear to be mostly interested in the last glaciation and Holocene. My interest in this discussion is about the period since complex life began, biosphere productivity versus GMST, and the causes of the mass extinction events.
Yes, there is recent evidence that the Permian-Triassic Boundary was a short ice age and a mass extinction event. Baresel et al (2017) https://www.nature.com/articles/srep43630 , give the timing as ~89 ka in the Permian and ~14 ka in the Triassic.
I can’t comment on the impact of drowned forests on atmospheric CO2 and GMST. However, my suspicion is that it is trivial. We’d need to see the estimated quantities and compare these with the masses of C in the biosphere, oceans and calcareous sediments – e.g. as given by Mike Jonas in this comment above https://judithcurry.com/2019/01/04/sea-levels-atmospheric-pressure-and-land-temperature-during-glacial-maxima/#comment-887416 . We’d also need to understand the emissions rates and sequestration rates (oceans, vegetation and weathering) and compare these with the rates from all other sources.