Ocean currents are acting the same way as rivers. They are the ongoing, predictable, and directional movement of seawater. Currents are moved by gravity, wind (the Coriolis Effect), and water density. Ocean currents are also affected by nearby landmasses. Water in the ocean can move in two different directions: vertically and horizontally. Horizontal movement is called currents, and vertical movement is called either upwelling or downwelling. Ocean currents travel long distances, and all together they form the global conveyor belt. By doing this, it affects the climate of many places on Earth.
Ocean currents transport water. They either transport warm or cold water. Oceans get their heat from the atmosphere. Since the temperature of the atmosphere is getting higher, the temperature of the water is also getting higher, which changes the circulation patterns. If the circulation patterns shift, then it means that places that used to be colder are becoming warmer, or the other way around. Oceans store a huge amount of heat, so even the smallest changes make a big difference. For example, a higher water temperature affects the amount of water vapour in the atmosphere, and as earlier mentioned, water vapour is also a greenhouse gas. And if the water temperature is higher, they can’t absorb so much carbon dioxide from the atmosphere. Oceans are the biggest carbon dioxide holders, and CO2 in water doesn’t absorb heat like it does in the atmosphere.

Oceans cover 71% of Earth, and they hold 97% of the water. Ocean currents are located on the surface, and they can also be 300 meters deep. Surface currents can occur on both local and global scales. They are usually moved by the wind. Surface currents are usually short-term, and they include rip currents, longshore currents, and tidal currents. In upwelling currents, the colder water is brought to the surface, and the less dense, warm water is pushed downward. It creates a cycle of upwelling and downwelling.
Deep ocean currents are driven by density, and they differ from surface currents by their speed, scale, and energy. The density of water is affected by temperature, saltiness, and the depth of the water. Water is denser if it is colder and saltier. Since the density of the ocean is different around the globe, it contributes to a global-scale circulation system called the global conveyor belt.
The global conveyor belt includes both surface and deep ocean currents that circulate on the Earth’s 1000-year cycle. It is caused by two processes: warmer water is less dense and carries the water away from the Equator, while colder, more dense water carries the water from the poles towards the Equator.
These processes regulate the weather and climate. They are also regulating the thermal energy, and they cycle the nutrients and gases.

Oceans have a major impact on forming the climate. Oceans transfer roughly the same amount of heat around the Earth as the atmosphere. The only difference is that the oceans are restricted by landmasses, and therefore their heat transport is more region-specific.
Under normal conditions in the Pacific Ocean, trade winds blow westward along the equator, carrying warm water from South America to Asia.
El Nino and La Nina are two climate patterns during which the weather is different than normally. They both have a global impact on weather, wildfires, ecosystems, etc. El Nino and La Nina can last from nine months to several years. During the El Nino trade, winds are weaker, and therefore the warm water is pushed back to the east. Warmer waters push the Pacific jet streams to move south. It causes the northern U.S. and Canada to have a dryer and warmer climate than usual. And at the same time, in the south, they have increased flooding. La Nina is opposite to El Nino. During La Nina, warm water is pushed towards Asia. In the North U.S. and Canada, they experience now floods.

Oceans have an effect on climate, but climate is causing a change in oceans as well. Ocean temperatures are rising because of climate change. It causes an effect called thermal expansion that leads to a rise in sea level and also changes the ocean currents. Bigger amounts of CO2 in the atmosphere mean that more of it is going to dissolve in water, and it makes the oceans more acidic.

Sources:
https://education.nationalgeographic.org/resource/resource-library-ocean-currents/
https://en.wikipedia.org/wiki/Ocean_current
https://www.bgs.ac.uk/discovering-geology/climate-change/what-causes-the-earths-climate-to-change/
https://education.nationalgeographic.org/resource/ocean-currents-and-climate/
https://www.pik-potsdam.de/~stefan/Lectures/ocean_currents.html
https://oceanservice.noaa.gov/facts/ninonina.html
https://www.nhm.ac.uk/discover/quick-questions/how-does-climate-change-affect-the-ocean.html