"Seawater is toxic because your body fails eventually when it has to try to get rid of the salt that comes from sea water. Your body normally gets rid of excess salt by having the kidneys produce urine, but it needs freshwater to dilute the salt in your body for the kidneys to work properly. Normally that is not a problem, as you are always drinking water and eating food with water. Tissue in your body also contains freshwater that can be used. But if there is too much salt in your body, you kidneys cannot get enough freshwater to dilute the salt and your body will fail." Why can't we drink seawater Link.
Ocean currents influence climate patterns in many different ways:
In a way, ocean currents control the temperature.
All the oceans are helpful to marine life because they provide necessary nutrients for underwater animals.
"Larger ocean currents bring warmer water towards the poles and colder waters towards the equator, modifying temperatures across the planet...The movement and exchange of water in all currents influences ocean and air temperature and cycles nutrients through the ocean system."