Surface currents, the Ekman spiral, and Ekman transport

Summary

This video explains how wind drives surface ocean currents through friction and energy transfer, as first explored by Walford Ekman in 1905. It details how energy moves from the surface to deeper water layers, creating a spiral pattern called the Ekman spiral. The resulting movement, called Ekman transport, occurs at a 90-degree angle to the wind direction, influencing coastal environments and nutrient cycling. It also covers upwelling, downwelling, and how these processes impact ocean productivity and the formation of gyres. The video highlights the role of Ekman transport in both coastal areas and the open ocean.

Takeaways

• 😀 Wind causes surface ocean currents through friction between the moving air and the water's surface.
• 😀 Some of the energy from wind-driven surface currents is transferred to deeper water layers, affecting depths of 50 to 100 meters.
• 😀 Walford Ekman, in 1905, studied the movement of water layers under wind influence, building a model for how energy transfers from the surface to deeper layers.
• 😀 The Coriolis effect causes water layers to move at an angle to the wind, creating a spiral pattern known as the Ekman spiral.
• 😀 The deflection caused by the Coriolis effect leads to net water movement at a 90-degree angle to the wind direction.
• 😀 In the Northern Hemisphere, water moves to the right of the wind, while in the Southern Hemisphere, it moves to the left.
• 😀 Ekman transport explains how surface currents are displaced by wind and can cause upwelling or downwelling depending on the wind direction.
• 😀 In coastal areas, offshore winds can lead to upwelling, bringing nutrient-rich deeper waters to the surface, increasing biological productivity.
• 😀 On the other hand, wind blowing toward the coast causes downwelling, leading to less nutrient availability and reduced productivity.
• 😀 Ekman transport also impacts open ocean currents. Trade winds near the equator push water away, causing upwelling and stimulating primary productivity.
• 😀 In mid-latitudes, converging currents from easterly and westerly winds cause downwelling, contributing to the formation of ocean gyres.

Q & A

How does wind affect surface ocean currents?

Wind causes surface ocean currents by transferring energy through friction between the moving air and the surface of the water, which causes the water to start moving.

What is the role of Ekman in understanding surface currents?

Walford Ekman developed a mathematical model in 1905 to explain how energy from wind moves from the surface to deeper layers of the ocean and how the Coriolis effect influences water movement.

How did Nansen's observations contribute to the understanding of surface currents?

Nansen observed that windblown sea ice moved differently than the wind direction, leading him to speculate that Earth's rotation influenced the movement of water, which Ekman further investigated.

What is the Ekman spiral?

The Ekman spiral is a pattern where water moves in a spiral as energy from wind moves from the surface to deeper layers, with each layer moving at an angle to the one above it due to the Coriolis effect.

Why does the movement of water decrease with depth?

As energy is transferred to deeper layers, some of it is lost, causing the speed of water movement to diminish rapidly with depth.

How does the Coriolis effect influence water movement in the Ekman spiral?

The Coriolis effect causes each layer of water to deflect to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, creating the spiral pattern.

What is Ekman transport and how is it influenced by the Coriolis effect?

Ekman transport refers to the net movement of water at a 90-degree angle to the direction of the prevailing wind, influenced by the Coriolis effect, which causes the deflection to the right in the Northern Hemisphere and left in the Southern Hemisphere.

How does Ekman transport influence coastal areas?

In coastal areas, when wind blows along the coast and causes Ekman transport offshore, deeper water rises to replace it, creating upwelling. Conversely, when the wind blows towards the coast, surface water piles up, leading to downwelling.

What is the significance of upwelling and downwelling in ocean productivity?

Upwelling brings nutrient-rich water to the surface, stimulating high productivity in these regions, while downwelling pushes nutrient-poor surface water downward, resulting in lower productivity.

How do trade winds affect ocean currents along the equator?

Trade winds, blowing from east to west, cause water to move away from the equator, leading to a lowering of the water level at the equator. This creates a region of divergent currents that causes deeper water to upwell.