Thermohaline Currents

For an introductory college-level oceanography class. Review of the basic causes and behaviors of density-driven currents.
**This video comes near the middle of the semester, so there may be terms with which the audience is unfamiliar. For a full playlist, refer to the Oceanography playlist on the Earth Rocks! KZbin Channel.
Content within this video is based on information available in any standard introductory college oceanography textbook, such as Essentials of Oceanography -- Trujillo and Thurman - Pearson Publishing.
Ocean Circulation Series:
Part 1: Thermohaline Currents
Part 2: Surface Currents
Part 3: Ocean Mixing & Pollution
Part 4: ENSO
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Note: this is version 2. Version 1 had 10409 views and was updated to simplify a chart and fix audio problems.

[@jesalasbahamon]

Ohh! It has been a really good video!, very clear and illustrative, thank you! I will definitely see the whole series.

[@garyha2650]

"ocean slowing" over time is another fascinating area related to this

[@wieslawkruczala3205]

It is very interesting. However I lack the bonding with the global conveyor belt. So far I have not been able to find anywhere how in details the conveyor belt works, how it divides and changes at different seasons. In some pictures I see the deep cold current going between Madagascar and Africa and in others it flows near the eastern edge of the island. It seems to me that the idea of the belt is usually extremally simpified. Would you please tell me where it is possible to find precise knowledge on the topic. I think that the video above is a great introduction.

[@grindupBaker]

There's a ring of water around Antarctica that is 1.2m lower sea surface height than the Pacific Ocean (this 2.2m lower sea surface height than the global average). This is because the heavy column of water is literally shoving down and north and below much other waters of the oceans like a wedge, forming the AABW. I read that it's 9 Sv. Reason it's lower sea surface height must be because surface water can't run there to fill it in as fast as it pushes down and northward.

[@grindupBaker]

At 7:56 "being pulled away". Incorrect. There is no such force as "pulled". That water is flowing down hill under gravity (I don't know whether prevailing winds there assist, probably not). On this topic, Pacific Ocean water enters the Arctic Ocean at Bering Strait into the Chuckchi Sea because it is flowing down hill to the Atlantic Ocean.

[@grindupBaker]

Oops I over-simplified. S.B. "For a fluid (liquid or gas) there is no such force as "pulled" because the molecular bonding is too weak"

[@grindupBaker]

This is for another video so the speaker references & times are not for here. 2 things that Peter & all WG1 climate scientists I've ever heard say incorrectly (though most are very vague) about thermohaline circulation (THC) even though they do the analysis are: ------------- At 23:10 "the salt goes into the water. The salt makes the water more dense and the water sinks". Incorrect Peter. The actual mechanism is shown perfectly in your own pictorial from "A Deep Convective Chimney in the Greenland Sea" and the descriptions of events in "A Farewell to Ice" such as p150 "carrying water downwards", p152 "Underneath this cap the chimney continued to exist as a rotating submerged cell". Yes, the chimney continued to exist as a rotating submerged cell because "makes the water more dense and the water sinks" is incorrect. It's a partial reversal of cause and effect. Here it is. The surface water doesn't "sink", it "descends" or a better descriptive word is "lowers" because neither gives the incorrect implication that it somehow moves into the water below it, not the same thing at all as "sinks" (which does mean moves into the water below it). The surface water descends because the entire water column descends and the entire water column descends because if it didn't then there'd be a big hole in the ocean (in the Odden) at 75.05N0.83W at 2500 m geodepth because a bunch of water was shoved south from there by Sir Isaac Newton's a=f/m Law operating horizontally because the pressure at 2500 m geodepth at 75.05N0.83W is greater than the pressure at 2500 m geodepth in the south Atlantic Ocean where the NADW literally lifts the ocean above it by brute force, and there's a continuous route there at 2500 m geodepth that's scenic, takes in all the sights and has continually decreasing pressure at 2500 m geodepth, where "geodepth" is a word I just now made up because I can make up words if I like if Wally Broecker can (or rather, could) make up whole phrases. ------------- At 21:00 "the ice forms in very small cakes". I know why that's crucial to salinity helping the THC force. I'm not clear that Peter has ever twigged. His "A Farewell to Ice" gives no clue that he's twigged. Wiki "In the Southern Ocean, strong katabatic winds blowing from the Antarctic continent onto the ice shelves will blow the newly formed sea ice away, opening polynyas along the coast". And do you know what's blown away when the newly formed sea ice is blown away. Low-salinity solid water is what's blown away and then do you think salty water moves in to replace it or do you think the ice gone leaves big dents in the ocean surface. "A Farewell to Ice" p147 "ice-free water exposed to further intense cooling from a cold atmosphere, especially in winter, particularly during phases of the climate when the prevailing winds in winter are westerly blowing off the Greenland ice cap". Those prevailing winds are also blowing ice pancakes and if they weren't then ice formation would have no effect on the THC. At 21:27 "they can't freeze together to form a sheet because there's too much wave action". That's right and ice pancakes can be blown by wind out of the dense water formation area, and also do you know what causes too much wave action, too much winds is what. And do you know what else too much winds do. Drive frozen low-salinity water away from a circle 30 km diameter where the surface water is getting denser is what. And do you know what happens when low-salinity frozen water pancakes are driven out of the circle. Nice salty water runs in to fill the big dents is what. That's how ice formation drives the THC, not at all in the slightest by making the water just below it saltier as all WG1 climate scientists incorrectly say but by leaving the surface-water densifying region letting some more salty water in to get a crack at freezing. If the ice can be driven away by strong winds or by being in pancakes then more ice can form and get driven away by strong winds too and that's how salinity increases the water weight above a 2500 m geodepth, or any geodepth below the surface. It's not done by making the surface water saltier so it sinks, it's done by making the surface water saltier so it's denser/heavier, not at all the same thing as "so it sinks". The surface water does not "sink". Please stop saying that it sinks except for vertical circulations with a horizontal component that's less than the ocean depth.

[@edthoreum7625]

5:30 oceans/currents

[@tejsinghlodhi9698]

With hindi

[@grindupBaker]

Thanks. The THC driving force description given here and by all climate scientists whenever I've heard them mention it, is incorrect. Sir Isaac Newton has a Law that something accelerates if an unbalanced force is applied to it and does not accelerate if an unbalanced force is not applied to it. The deep ocean does not have an exception granted by the Law Of The Sea. Since there is friction (a force) opposing fluid flow and since friction increases with velocity (the idea of "terminal velocity" of a falling object) then "accelerates" can be simplified to "moves" for an easier picture. The THC driving force description given here and by all climate scientists whenever I've heard them mention it, is incorrect because it has cause and effect reversed at the starting location (deep water formation). There is no "deep water formation" but rather the entire column of water drops down else the water departing south (Greenland example) would leave a bloody great hole in the ocean at ~2,500, depth ----------------------------------------------- This means, obviously, that the pressure at the NADW depth range must be continuously reducing from the place near Greenland where the column drops all the way along the path it takes to Antarctica. The water would not move otherwise. Water does not randomly move. There is the Coriolis effect and the presence of the Americas (i.e. sea surface height) causing this deep ocean current path to be what it is , not just the temperature/salinity profile above the depth of movement, but primarily it's going to be because temperature/salinity is on a decreasing pressure gradient and the water follows that gradient. I say depth range for simplicity but I don't actually mean depth as the distance from the sea surface above. I mean something close within a couple of metres though. I mean depth relative to Earth's centre of gravity (I think from memory it's called a "geoid"). The distinction is important because changing sea surface height changes pressure (more water above = more pressure) for a depth relative to Earth's centre of gravity but obviously changing sea surface height makes no change to pressure for a depth relative to the sea surface above. ----------------------------------------------- Then the entire column of water drops down at the place with the highest density (temperature/salinity) to that depth. The surface water doesn't "get cold & salty and sink", the entire column of water drops down else the water departing south would leave a bloody great hole in the ocean at ~2,500, depth, so there's no choice. Since the column of water dropped down its surface is now lower than elsewhere, hence the surface current is simply water running down hill under gravity to this low spot. In this case the route taken is whatever route is down hill but again modified by the Coriolis effect and the presence of land in the way, plus the new item of air currents that drive surface water. Note that land in the way is the same thing as "whatever route is down hill". So if you have a moderately-good science brain and education (university not needed) and you actually think about this you'll realize that I cannot possibly be incorrect unless Sir Isaac Newton's 1st Law is incorrect. The over-simplified "gets cold & salty and sink" is incorrect and with perhaps the optional "forms ice which rejects brine making the water saltier" is still incorrect as a driving force unless the ice departs and is replaced by ocean water because that's describing surface water getting heavier than the water below and thus sinking with the less-dense (warmer or less salty) water below coming up to replace it. That's just water overturning near Greenland (using AMOC/NADW example). That wouldn't drive any deep ocean current.

[@grindupBaker]

The animated pictorial at 7:37 is correct. Notice that the movement is not caused by water at or near the top becoming dense & sinking (it doesn't move down past the water that was below it). What's shown there is that that entire column of water is literally shoving the ocean ahead of it at its lowest depth shown. It's shoving the ocean ahead of it in a horizontal pipe some 15,000 km long to Antarctica (or however long that circuitous route is). This is not the same thing as the "surface water gets cold & salty and sinks" that climate scientists say in talks. That would only cause the water at various depths at the place shown near Greenland to swap places between the shallow & the deep. It wouldn't cause any horizontal flow.

[@EarthRocks]

Thanks for all the commentary. Good addition for watchers to read! :)