Need some technical details for a story.
The scene revolves around a deep water upwelling of water, often helped by underwater currents in deep-sea trenches, but more often accounted for by temperature variants (similar to air currents allowing birds to hover in place). Assuming there is a substantial temperature difference, what would be the effect at the surface, seeing as how the oceans are warmer at the surface and extremely cold deep underwater. Would the water at the surface be freezing, or warmer than usual (assuming there are no volcanic vents involved).
I'm assuming the temperatures are different deep underwater, but the effect is negated as the water rises. In which case, the water continues rising because it's being pushed by the uprising water beneath it.
Any oceanographers among us?