How cold is the arctic ocean?

My research question is "How is the ocean explored?" One of the topics I'm researching about are the challenges that scientists face when exploring the ocean, such as the extreme cold. But how cold is it at the ocean floor, generally speaking...

I like swimming in the ocean but I've heard the water temperature in the Aegean sea is cold. Anyone knows how "cold" the ocean is in July, August and September? .... at Santorini/Mykonos/Paros?

I seem to get colder than most people when I swim. I shake and shiver uncontrollably sometimes, which my friend tells me is the beginning stages of hypothermia. It's not that the water is that cold, because other people don't seem to notice. Could it...

If the ocean advances not only at the beach areas, but also advances up rivers, due to the rivers being the lowest lying features, I would like to know what areas along beaches and rivers will be inundated. What would be the highest water level expected...