Ocean circulation act as conveyor belt which transport warm water from the tropics towards poles from where cold water sinks to the deep ocean. It is also known as the thermohaline circulation because it is driven by salinity and temperature.
However, change in climate causing these ocean's thermohaline current to slow down because influx of cold and melting fresh water from the polar region is disrupting these circulation as influx of fresh water making the water less saline and less dense and hence it become harder to sink to deep ocean.
