If you were swimming/floating within a body of water experiencing upwelling due to sea-surface thermal fronts, would you be able to physically feel the water that is being up-welled or is it on a different scale not sensed by humans?
There is a sea-surface thermal front at the northwest tip of Scotland. On the western side is water from the Gulf Stream Drift - cool, but sufficiently comfortable to swim in. On the north side is Arctic water which is horribly cold and which nobody in their right mind would swim in. I write from personal experience!