dismallyOriented

@dismallyOriented

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Marine Science MTuesday 🦈🦦🦐🐚

Howdy folks,

Forgive the week 2 schedule slip, a smarter man than me would have banked a couple of topics and draft posts instead of just freewheeling it. But also sometimes your Monday is a Tuesday. It happens.

Diagram of coastal upwelling. A coastline is depicted in 3D isometric perspective, with the seafloor sloping downward from the land, and water layered over it in transparent blue. An orange arrow labeled "Wind" runs south, parallel to the coastline and over the water. A blue arrow labeled "Upwelling" curves up from the deep water, pointing towards the shallows, and then up and away from the coastline.

Today's marine science fact: upwelling zones!

You may be aware of the Coriolis Effect, where the rotation of the Earth causes wind and water to curve in certain directions, depending on which side of the equator you're on. Aside from driving wind and sea currents, the Coriolis effect also drives vertical water movement by combining with the wind.

When wind blows over the ocean, the movement of the air starts to pull the water with it. However, due to the Coriolis effect, the water ends up getting pulled perpendicular to the direction of the wind - in the Northern Hemisphere, it goes to the right, while the Southern Hemisphere water goes to the left. In addition to the Coriolis Effect, there is another physical phenomenon occurring, known as Ekman Transport.

Diagram of Ekman transport in the northern hemisphere. A white wind arrow travels over the ocean surface, pulling the surface water 45 degrees to the right. Meanwhile, other arrows project outward beneath the surface layer, each at greater angles from the wind and shorter distances, in a spiral down to the seafloor.

Just like the surface water is pulled by wind, all other water layers underneath are pulled with the same 45-degree deflection from the motion above it. Friction reduces the speed and force of the pull as you go further from the surface. When you average all these forces together, the overall motion equals to a 90-degree deflection from the wind direction.

This produces interesting effects at coasts. Because the water is being moved, but the overall volume is the same, conservation of mass means that more water will be pulled from elsewhere to replace the water that moved away. In downwell zones, the surface water is pulled toward the coastline and the pileup against the land pushes the surface water downward. Whereas upwelling zones form when water is pulled away from the coastline, drawing up water from beneath to the surface.

A map of global upwelling zones. Coastlines with upwelling are highlighted in red. Major areas include the west coast of North and South America, the west coast of Africa, the North Sea in Europe, parts of Southeast Asia, and the waters between China & Japan, Russia & Alaska, and Canada & Greenland.

Coastal upwelling zones are extremely productive and prolific because they are constantly drawing up cold, CO2 and nutrient-rich water from the deep. These are ideal conditions for large amounts of photosynthesis by phytoplankton - provided enough sun, they can churn out enough organic matter to feed everything from the smallest sardine to the biggest blue whale. The biggest ocean fisheries are all located in upwelling zones for this reason - 25% of all ocean fisheries landings come from just 5 zones.

We'll come to those phytoplankton next week, but for now, have a happy M'Tuesday, and I'll sea you next time.

Rundown of sources, which I may reformat into citations later:
https://en.wikipedia.org/wiki/Upwelling
https://en.wikipedia.org/wiki/Ekman_transport
https://oceanservice.noaa.gov/education/tutorial_currents/03coastal4.html
http://oceanmotion.org/html/background/ocean-in-motion.htm

 
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