[flyGuyOnTheSly]

I don't think it's the carbon dioxide that is killing the phytoplankton, they probably love it like most plants love a little extra CO2.

I imagine it's other chemicals like herbicides making their way into the oceans and killing the tiny plants.

[geedy]

The general problem is that the warmer waters are trapping the cooler waters below. Upwelling is an attempt to fix it!

[petre]

It's the temperature, not the CO2. I have fresh water shrimp and some fish. If you raise the temperature over 30°C, less oxygen dissolves into the water and there's not enough for the critters to breathe. It's basically asphyxiation. Labyrinth fish are adapted, since they can breathe air as well, but they do it merely for survival, they too become stressed and die after a while. Also some types of algae grow faster when the water is warmer. More algae = more O2 uptake during daytime.

[tedivm]

A little extra CO2 sure, but the rising CO2 in the oceans is actually changing the PH balance.

https://news.mit.edu/2015/ocean-acidification-phytoplankton-...