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dismallyOriented
@dismallyOriented

Howdy cohost. Saw folks out there posting science facts and decided to throw my hat into the ring.

Global map of ocean deepwater circulation. The cycle begins in the Arctic, which is captioned "Sea to Air Heat Transfer" and "Sinking Cold, Salty Water". A blue arrow labeled "North Atlantic Deep Water" travels south from the Arctic, all the way down to Antarctica, where it transitions into "Antarctic Bottom Water". This arrow then splits into two, one which travels north into the Indian Ocean, and another labeled "Deep Cold Current" which runs along Antarctica and then up into the Pacific. Both these arrows loop back around to a new red arrow, labeled "Shallow Warm Current". The red arrow travels through South East Asia, around Africa, and then back up to the Arctic to complete the cycle.

Today's marine science fact: the global ocean conveyor belt!

You may know that all the oceans are connected to each other, but did you know that there's a 1500 year long water circulation cycle happening between them? It's all driven by the formation of deep ocean water in the Arctic Ocean.

When ocean water enters the Arctic, it cools down and starts to freeze. This does two things. One, the water that freezes solid gets pulled out of the liquid water at the surface. This makes the remaining liquid water extra salty, as the ice leaves but the salt it used to carry stays behind. Two, because the water is extra salty, its freezing point gets even lower. So now you have really cold, really salty water. And this cold salty surface water is denser and heavier than the regular seawater it's on top of. And if you know anything about density, you'll know that this dense water is gonna sink all the way to the bottom.

That formation of new deep-ocean water in the Arctic starts this whole global conveyor belt. That deep water takes whatever was at the surface when it formed (oxygen, organic matter from living things) and takes it all the way to the bottom. And all that stuff slowly makes its way through the oceans. You can actually track the movement of the water by comparing the oxygen, CO2, and nutrient levels in water from the North Atlantic, to water in the North Pacific. North Atlantic water is super well oxygenated and full of organic matter. Whereas North Pacific water has had ~1500 years for everything in it to get consumed and broken down by deep sea bacteria. It is full of CO2 and nutrients, and very oxygen-depleted.

This CO2 and nutrient heavy bottom water eventually comes back up, where it becomes really, really important for the oceanic food cycle. But that will be a topic for another time.

Happy Monday, and I'll sea you all next week!

For the image source, and more detail: https://www.e-education.psu.edu/earth103/node/686


FoxgirlFoamer2816
@FoxgirlFoamer2816
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in reply to @dismallyOriented's post:

Here's where my knowledge fails me a little; I'm not sure how much that curve is a stylized depiction or representing an actual pattern! My very tentative guess is that it has something to do with upwelling, which is sort of the opposite of the downwelling that started the cycle.

Short version is, when global winds push water against the coast of a continent, the waters at the surface will get diverted to the side as they bump up against the continent. There are physics reasons that make it move that way, though I can't exactly remember why that is. Would have to look it up. Anyway, the surface water getting repeatedly pulled aside produces a bit of a vacuum - there is Supposed to be volume there, so when the volume is displaced, more water comes up to replace it. And this pulls the deep water up to the surface. Because this happens on the West coast of the Americas in the Pacific, I assume that's why the water comes up where it does.

Those coastal upwelling zones end up being really really really good places for fishing, because they bring up all the nutrient and CO2 rich water. That stuff fuels phytoplankton which eventually means loads and loads of fish for food chain reasons. Coincidentally I'd been thinking about talking about that next Monday 😂

ohhh neat! i never even would have thought of that but it makes a lot of sense. perhaps i should have considered that this map was a simplification and not totally representative of the complex 3d movement of water 🤔

id def be interested to read more about that if you do end up posting about that next week!

OH duh I fully forgot that the Gulf Stream is part of this circulation too. Of course it affects the weather.

Yeah! It's kind of wild to think that Scotland and other pretty temperate parts of Europe are on equal latitude with Canada and could in theory be Just as cold

I remember seeing this exact image (translated to my mother tongue ofc) in my high school geography text books. :) iirc this whole current system is being deeply affected by the northern ice caps melting due to global warming... The water being transported south is colder than normal because of the melted ice in it, which then has ripple effects on the rest of the chain (though I can't say I remember which, other than "they're not good"...)

Aww, that's really cool! Yeah, the whole start of the conveyor belt depends on the freezing and formation of sea ice - if the water at the poles is less cold and less salty, then it's not gonna sink as far or as quickly bc the change in density/weight wouldn't be as strong. Your bit with the cold meltwater traveling south has to do with the Gulf Stream, that warm current that runs across the Atlantic to Europe. The heat from the Gulf Stream is what keeps western Europe from getting as cold as Canada, and if cold water disrupts that current then things get real weird. You're not gonna get like, an ice age tomorrow, but that's definitely a piece of concern re: climate change