My personal theory is that these underwater volcanoes and other steam vents, when very active, cause El Nino. I don’t have any proof, but it makes sense to me. It would take a tremendous amount of volcanic activity just to heat the Pacific Ocean to the point that an El Nino occurs. If this is true, it would be enough to heat the Pacific enough.
About 15 yrs ago I was having an argument with a liberal foe regarding the impending doom of global warming.
He declared that sea temperatures were indisputably increasing and that this was conclusive proof of global warming. Because this around the time that geothermal vents were being popularized, I asked him how he could discount newly discovered underwater volcanic activity.
He quickly dismissed my query as nonsense in that way that the close-minded do in the face of unexpected ideas - very satisfying.