Editing Downwelling (section)

== Wind-forced downwelling ==
[[File:Oceanic gyres.png|thumb|320x320px|Map showing the five subtropical ocean gyres.]]

=== Subtropical gyres ===
[[Ocean gyre|Subtropical gyres]] act on the largest scale that we observe downwelling. Winds to the north and south of each ocean basin blow opposite each other such that [[Ekman transport]] moves water toward the basin's center. This movement piles up water, creating a high-pressure zone in the center of the gyre, low pressure on the borders, and deepens the [[mixed layer]]. The water in this zone would diffuse outward if the planet weren't spinning. However, because of the [[Coriolis force]], the water rotates clockwise in the Northern Hemisphere and counterclockwise in the southern, creating a gyre. While it spins, the rotating high-pressure zone forces water downward, resulting in downwelling.<ref name="www.sciencedirect.com" /> Typical downwelling rates associated with ocean gyres are on the order of 10’s of meters per year.<ref>{{Cite journal |last1=Froyland |first1=Gary |last2=Stuart |first2=Robyn M. |last3=van Sebille |first3=Erik |date=September 2014 |title=How well-connected is the surface of the global ocean? |url=http://dx.doi.org/10.1063/1.4892530 |journal=Chaos: An Interdisciplinary Journal of Nonlinear Science |volume=24 |issue=3 |pages=033126 |doi=10.1063/1.4892530 |pmid=25273206 |bibcode=2014Chaos..24c3126F |hdl=10044/1/21883 |issn=1054-1500|hdl-access=free }}</ref> 

=== Coastal downwelling ===
Coastal downwelling occurs when winds blow parallel to the shore. With such winds, Ekman transport directs water movement towards or directly away from the shore. If Ekman transport moves water towards the shore, the shoreline acts as a barrier causing surface water to pile up onshore. The piled-up water is forced downwards, pumping warm, [[nutrient]]-poor, oxygenated water below the mixed layer.<ref name="Webb-2023" /><ref name="www.sciencedirect.com" />

=== Langmuir circulation ===
[[Langmuir circulation]] develops from the wind, which, through Ekman transport, creates alternating zones of convergence and divergence at the ocean surface. In convergent zones, marked by long strips of floating debris accumulation, such as the [[Great Pacific Garbage Patch]], coherent vortices transport surface waters to the base of the mixed layer develop. Also, direct wind stirring and current [[Shear stress|shear]] at the base of the mixed layer can create instabilities and [[turbulence]] that further mix properties within and at the base.<ref>{{Citation |last=Foltz |first=Gregory R. |title=Wind- and Buoyancy-Forced Upper Ocean |date=2019 |url=http://dx.doi.org/10.1016/b978-0-12-409548-9.11336-3 |encyclopedia=Encyclopedia of Ocean Sciences |pages=113–121 |access-date=2023-11-26 |publisher=Elsevier|doi=10.1016/b978-0-12-409548-9.11336-3 |isbn=9780128130827 |s2cid=232350491 }}</ref>