#thermohaline

[th3-0bjectivist]

“Thermohaline” - Animated painting

Original acrylic painting currently on sale for peanuts on Poshmark at https://poshmark.com/closet/galleryofluke

[drondskaath]

Thermohaline | Maelström | 2021

International Avant Garde Black Metal

From members of The Order Ov The Black Arts

https://thermohaline.bandcamp.com/

[bizarrobrain]

"Shipwrecked" by Thermohaline - From "Maelström" (2021)

[earthstory]

Swim with a Viking

The ocean is in constant motion. Forget about waves and tides here - in the grand scheme of things, they don't move that much water. We're talking about the 'global ocean conveyor belt'. A vast, global circulation system driven by the Sun and the spin of the Earth, which moves water from surface to the deep and back, and between every ocean basin on the planet.

This cycle is big and slow. Water that sinks into the depths in the North Atlantic won't come back to the surface for 1300-1500 years. This means that if you were to go swimming in the North-East Pacific, there's a fairly good chance that the last person in that water was a Viking. The image above shows us how old the deep water (2500 m) is in different parts of the world.

This system is more correctly called 'thermohaline circulation'. It is mainly driven by changes in temperature ('thermo' = heat) and salinity ('haline' = salt), which determine where water sinks, and where it rises to the surface. Once water sinks or rises, the path of the currents is determined by the rotation of the earth, and the shape of the continents. This global cycling of the oceans determines long-term climate, fuels the productivity of the ocean, and maintains global chemical cycles that keep the planet in balance.

This circulation process is... complex, but here are the basics: the density of seawater is determined by its salinity and temperature. Hot, fresh water is less dense, and cold, salty water is more dense. Imagine a bucket of seawater at the equator - the hot sun will heat it up, and cause a lot of evaporation, which will make the water more salty, and more dense. However, if you poured your bucket into the ocean in the Carribean, it wouldn't sink because it's warmer, and therefore less dense, than the water underneath. Now take that bucket on a long journey North, let's say Iceland. It's much cooler up there, and your warm, salty bucket of water gets cold. If you poured this cold, salty water into the sea off Iceland, it would sink. This cold, salty liquid is about as dense as seawater can get.

Once it gets moving, the water has momentum. Dense, sinking water pushes the water underneath out of the way, and shunts it along the ocean floor, directed by the shape of the ocean floor, and the spin of the Earth. As the Earth spins, there's a tendency for water to be 'left behind' - think about what happens if you suddenly move a glass of water (don't try this near your computer!) - the water wants to stay still, and sloshes up the side of the glass. This is basically what happens to an ocean current: as a current moves South in the Northern Hemisphere, it will gradually bend to the right, as the movement of the Earth 'leaves it behind'. This is known as the Coriolis Effect, [and is the reason that water going down a plug-hole spins clockwise in the Northern Hemisphere, and anti-clockwise in the Southern Hemisphere - we originally put this in here, but it's NOT TRUE! The Coriolis effect is far too weak at this small sale to have an effect - the design of the basin is more important in which way your pughole-water spins. Thanks to our readers for correcting this.

An ocean current will flow along, affected by Coriolis, until it hits a barrier (i.e. a continent) and is deflected. This sets the path of global thermohaline circulation.

Our bucket analogy, while ridiculous, is pretty much what happens. Ocean circulation is mainly driven by warm salty water zooming North up the Gulf Stream, cooling and eventually sinking in the North Atlantic. There is a constant 'underwater waterfall', as this dense water sinks and begins to flow South. This deep current hugs the East coast of America (Coriolis, remember?), and eventually joins the Antarctic Circumpolar Current, which flows round and round the South Pole. Tongues of this circular current lick up into the Indian ocean, and into the South Pacific. The South Pacific current heads North East until it hits North America, where the water has nowhere else to go, and is forced to the surface. This is why the Pacific Coast of the USA has such delightfully cold water, and it's somewhere around here that you might be able to swim with the Vikings. Once on the surface, The water starts its slow journey back to the North Atlantic, via the Indian Ocean, round the Horn of Africa, in the ferocious Agulhas current, and back up the Western Atlantic to form the Gulf Stream, which keeps Western Europe warm. These currents are unimaginably vast. The largest one, the Antarctic Circumpolar Current, flows at 125 Sverdrups. That's 125,000,000 cubic meters per second. Or 50,000 Olympic swimming pools per second. Or 600 times the flow of the Amazon (largest river on Earth, by discharge). And yet, despite the size of these currents, one complete circulation can take up to 3000 years.

The picture above is complex, but doesn't begin to scratch the surface of these global ocean processes. Oceanographers spend their entire lives trying to work out the peculiarities of ocean currents, and how they tie in to climate and our daily lives. A pressing question at the moment concerns the flow of the Gulf Stream: melting of ice sheets have the potential to disrupt a lot more than Polar Bears. The worry is that as the Greenland Ice Sheet melts, it will dump a huge amount of fresh water into the North Atlantic. As we know, fresh water is less dense, and could mix with North Atlantic water and stop it sinking, and take away the main driving force behind the 'conveyor belt' circulation. It's almost impossible to work out what this would do to ocean circulation. The world is as we know it because the ocean currents move the way they do.

OB

Image Credit: http://goo.gl/FBMrdr

, via http://goo.gl/TRNhc

NASA

Further Information: - The ocean currents in action (video):http://goo.gl/UHsJ6m

Watch the Gulf Stream flowing and cooling (video):http://goo.gl/xvIXXH

More detail on thermohaline circulation (NOAA):http://goo.gl/m2HMZm

And a lot of detail (Scientific paper):http://goo.gl/FBMrdr

[th3-0bjectivist]

“Thermohaline” - Acrylic paint on canvas

[earthstory]

Radiation in the oceans

These 2 images are cross sections of the Atlantic ocean, running from the equator to the North Pole. They show the formation of North Atlantic Deep Water - cold water in the north Atlantic is denser than the warm water at the equator and gradually sinks, forming water that moves along the bottom of the ocean. Scientists have managed to track the formation of deep water in recent decades due to an act of humans.  In the 1950s and 1960s, the United States and the Soviet Union set off hundreds of nuclear weapons in the Earth’s atmosphere. These tests scattered the unstable, radioactive debris reactions over planet at small amounts, and that radioactive debris allowed tracking of this Deep Water. One part of that debris is tritium, a hydrogen atom with 2 neutrons. Its half-life is 12 years, so over time it decays into Helium-3, but before it decays its chemical properties are the same as hydrogen. It can bond with oxygen and form water, so the pulse of tritium released in these airborne nuclear tests largely went into the oceans.

The water molecules containing that tritium mixed rapidly in the upper layers of the ocean, but took much longer to sink to depth. The contours in this plot show how the tritium released in the late 1950s gradually moved deeper as cold waters from the North Atlantic sank towards the Atlantic Ocean bottom.

This tritium allowed us a signal that we could track as the oceans mixed. Shallow waters are mixed around the world in a matter of years to decades by the winds, but the bulk of the oceans, the deep water, takes much longer, centuries to millennia, to overturn completely. Once water sinks to the ocean bottom, it can take thousands of years before it fully comes back to the surface. The presence of this tritium pulse allowed scientists to watch waters as they moved from the surface to the deeper parts of the Atlantic.

-JBB

Image credit: Toggweiler, 1994 https://www.gfdl.noaa.gov/bibliography/related_files/jrt9401.pdf

[allsortsoffuckedup]

Oh look New Apocalypse just dropped. Sixth Extinction here we come

[mikeo56]

The global conveyor belt is a strong, but easily disrupted process. Research suggests that the conveyor belt may be affected by climate change.

Winds drive ocean currents in the upper 100 meters of the  ocean’s surface. However, ocean currents also flow thousands of meters below  the surface. These deep-ocean currents are driven by differences in the water’s  density, which is controlled by temperature (thermo) and salinity (haline). This process is known as thermohaline circulation.

In the Earth's polar regions ocean water gets very cold, forming sea ice. As a consequence the surrounding seawater gets saltier, because when sea ice forms, the salt is left behind. As the seawater gets saltier, its density increases, and it starts to sink. Surface water is pulled in to replace the sinking water, which in turn eventually becomes cold and salty enough to sink. This initiates the deep-ocean currents driving the global conveyor belt.

Thermohaline circulation drives a global-scale system of currents called the “global conveyor belt.” The conveyor belt begins on the surface of the ocean near the pole in the North Atlantic. Here, the water is chilled by arctic temperatures. It also gets saltier because when sea ice forms, the salt does not freeze and is left behind in the surrounding water. The cold water is now more dense, due to the added salts, and sinks toward the ocean bottom. Surface water moves in to replace the sinking water, thus creating a current

This deep water moves south, between the continents, past the equator,      and down to the ends of Africa and South America. The current travels around      the edge of Antarctica, where the water cools and sinks again, as it does      in the North Atlantic. Thus, the conveyor belt gets "recharged." As it moves      around Antarctica, two sections split off the conveyor and turn northward.      One section moves into the Indian Ocean, the other into the Pacific Ocean.

 These two sections that split off warm up and become less dense as they travel northward toward the equator, so that they rise to the surface (upwelling). They then loop back southward and westward to the South Atlantic, eventually returning to the North Atlantic, where the cycle begins again.

The conveyor belt moves at much slower speeds (a few  centimeters per second) than wind-driven or tidal currents (tens to hundreds of  centimeters per second). It is estimated that any given cubic meter of water  takes about 1,000 years to complete the journey along the global conveyor belt.  In addition, the conveyor moves an immense volume of water—more than 100 times  the flow of the Amazon River (Ross, 1995).

The conveyor belt is also a vital component of the global ocean nutrient and carbon dioxide cycles. Warm surface waters are depleted of nutrients and carbon dioxide, but they are enriched again as they travel through the conveyor belt as deep or bottom layers. The base of the world’s food      chain depends on the cool, nutrient-rich waters that support the growth of algae and seaweed.

The global conveyor belt is a strong, but easily disrupted process. Research suggests that the conveyor belt may be affected by climate change. If global warming results in increased rainfall in the North Atlantic, and the melting of glaciers and sea ice,  the influx of warm freshwater onto the sea surface could block the formation of  sea ice, disrupting the sinking of cold, salty water. This sequence of events   could slow or even stop the conveyor belt, which could result in potentially  drastic temperature changes in Europe.