Surface currents are created by wind and the Earth's rotation. What creates deep water currents?
Deep water currents are primarily created by differences in water density and temperature. Specifically, there are two main processes that drive deep water currents: thermohaline circulation and upwelling.
1. Thermohaline Circulation: This process is driven by differences in water density caused by variations in temperature (thermo) and salinity (haline). Colder and saltier water is denser and tends to sink, while warmer and less salty water rises. This vertical movement of water creates a conveyor belt-like circulation pattern on a global scale. The sinking of dense water masses (such as in the North Atlantic and Antarctica) drives the deep water currents that flow along the ocean floor.
To understand the concept, you can follow these steps to explore an example of thermohaline circulation:
Step 1: Identify regions of high evaporation and intense cooling. For example, in the North Atlantic, water near the poles experiences intense cooling, causing the surface water to become colder and denser.
Step 2: Observe the formation of sea ice. The intense cooling in regions like the North Atlantic leads to the formation of sea ice, leaving behind highly saline water from which the salt doesn't freeze.
Step 3: Note the increased density and sinking of colder, saltier water. The dense water produced in these regions sinks down to the ocean depths, creating a deep water current.
Step 4: Understand the global-scale circulation. The sinking of dense water in the North Atlantic creates a pulling force, which leads to the inflow of warmer surface water from the equatorial regions. This causes a global-scale circulation where surface water moves toward the poles, and deep water flows back toward the equator.
2. Upwelling: While thermohaline circulation drives global-scale deep water currents, upwelling occurs in certain regions where cold, nutrient-rich water rises to the surface. Upwelling is usually driven by wind patterns and ocean currents pushing surface water away from a coastline. As the surface water moves away, it is replaced by cold, deep water welling up from below.
Understanding the drivers of deep water currents, such as thermohaline circulation and upwelling, helps us comprehend the complex mechanisms behind the ocean's circulation system.