Coastal upwelling occurs where Ekman transport moves surface waters away from the coast; surface waters are replaced by water that wells up from below. Where Ekman transport moves surface waters toward the coast, the water piles up and sinks in the process known as downwelling.
What factors contribute to upwelling?
Upwelling is a process in which currents bring deep, cold water to the surface of the ocean. Upwelling is a result of winds and the rotation of the Earth. The Earth rotates on its axis from west to east. Because of this rotation, winds tend to veer right in the northern hemisphere and left in the southern hemisphere.
What is the Ekman flow?
The Ekman spiral is a structure of currents or winds near a horizontal boundary in which the flow direction rotates as one moves away from the boundary. It derives its name from the Swedish oceanographer Vagn Walfrid Ekman.
Where does Ekman upwelling occur?
Ekman suction occurs both along coastlines and in the open ocean, but also occurs along the equator. Along the Pacific coastline of California, Central America, and Peru, as well as along the Atlantic coastline of Africa there are areas of upwelling due to Ekman suction, as the currents move equatorwards.
What happens when Ekman transports converge?
Ekman transport convergence and divergence in the Northern Hemisphere due to variations in a zonal (eastward) wind. Ekman transport is southward, to the right of the wind. Divergent transport causes downwelling, denoted by circles with a cross. Convergent transport causes upwelling, denoted by circles with a dot.
What does the Ekman spiral describe?
Ekman spiral, theoretical displacement of current direction by the Coriolis effect, given a steady wind blowing over an ocean of infinite depth, extent, and uniform eddy viscosity. According to the concept proposed by the 20th-century Swedish oceanographer V.W.
How do upwellings affect phytoplankton growth?
The upward movement of this deep, colder water is called upwelling. The deeper water that rises to the surface during upwelling is rich in nutrients. These nutrients “fertilize” surface waters, encouraging the growth of plant life, including phytoplankton.
How are the Coriolis effect and the Ekman transport related?
The Ekman spiral is a consequence of the coriolis effect. When the surface water moves by the wind, they drag the deeper layers with them. Each layer of water is moved by friction from the shallower layer and each deeper layer moves more slowly than the layer above it. This creates a spiral called the Ekman spiral.
What causes Ekman divergence?
Coastal Upwelling In the northern hemisphere, Ekman divergence occurs when the wind blows parallel to a coastline on its left. For example, during spring and summer the mean winds along the west coast of North America are southward. Associated with these winds is a net westward Ekman transport.
What is the relation of wind flow and Ekman transport to coastal upwelling and downwelling?
Downwelling can also occur, if the winds were to reverse. Ekman transport and the Coriolis effect would cause the water to basically “pile up” on the coast and eventually sink to the bottom. Upwelling is important for coastal communities because deep water has more nutrients.
What causes equatorial upwelling due to Ekman transport?
Equatorial upwelling due to Ekman transport results from the westward wind stress (trade winds). These cause northward Ekman transport north of the equator and southward Ekman transport south of the equator.
What are the implications of Ekman transport and pumping?
Ekman transport and pumping have far-reaching implications, from the mechanism of momentum transfer from wind to water to the maintenance of the large-scale wind-driven oceanic current gyres. Dr.Antony Joseph, in Investigating Seafloors and Oceans, 2017
What is Ekman pumping in the northern hemisphere?
Therefore, in the Northern Hemisphere (f > 0), upwelling into the Ekman layer results from positive wind stress curl, and downwelling results from negative wind stress curl. Downwelling is referred to as Ekman pumping.
Why is the Ekman transport to the right of the wind?
In Figure S7.12, with varying zonal (west to east) wind, the Ekman transport is to the right of the wind, and is convergent because the zonal wind varies with latitude. Note that it is not necessary for the Ekman transports to be in opposite directions to have divergence or convergence, just that the transports change. FIGURE S7.12.
