I've already discussed the backstory of the Paleocene-Eocene Thermal Maximum more than once already, so let me shorten this into a list of notes:
- 56 million years ago
- 5-9-degree-Celsius rise in temperature in 20-50 millennia
- A duration of roughly 200 millennia
In an alternate timeline, the only difference in the PETM is that it lasted three to four times longer than in our timeline. It poses so many questions, but because of the SE's "one-at-a-time" policy, this would have to work as a series. The first question concerns a little something called the lysocline. What, exactly, is that? Here is how the Wikipedia article on the PETM described it:
The lysocline marks the depth at which carbonate starts to dissolve (above the lysocline, carbonate is oversaturated): today, this is at about 4 km, comparable to the median depth of the oceans. This depth depends on (among other things) temperature and the amount of CO2 dissolved in the ocean. Adding CO2 initially raises the lysocline, resulting in the dissolution of deep water carbonates. This deep-water acidification can be observed in ocean cores, which show (where bioturbation has not destroyed the signal) an abrupt change from grey carbonate ooze to red clays (followed by a gradual grading back to grey). It is far more pronounced in north Atlantic cores than elsewhere, suggesting that acidification was more concentrated here, related to a greater rise in the level of the lysocline. In parts of the southeast Atlantic, the lysocline rose by 2 km in just a few thousand years.
In that context, would a longer PETM raise the lysocline, and to how much of an extent?