It’s a simple thing. There are these maps. They say where the ocean water wanders. Authoritative. Well reasoned. Based on the best science. Centuries of observations and wisdom.
One Small Problem: They have arrows going in the same places on some maps, different directions on others.
What does it mean? I donno….
Are the old maps wrong? Are some maps showing surface currents and others deep flow? Are some smaller currents, others larger? One season vs another? Again, I don’t know.
My guess would be some of each. Then again, maybe some of the new maps are just wrong too.
Now, since ocean tides and currents are strongly likely to be the determinant of our weather and longer term climate effects, perhaps some of these just show what was happening at different lunar / tidal states. In any case, if we only have a loose grip on what the oceans are doing, not going to get much right about the effect it has on the air and weather.
With no further ado, and in no particular order, some maps for you to contemplate, with sporadic comments and snideitude scattered through.
The “big lumps”. Supposedly this is the most major layer of circulation. The core basic movement.
https://en.wikipedia.org/wiki/Thermohaline_circulation has some nice maps.
And from a quasi south pole view:
“This is one example of what oceanographers call thermohaline flow. The large-scale flow pattern that results from the sinking of water in the Nordic and Greenlans Seas and around Antartica is called the oceanic conveyor belt (figure 2a). Another example of thermohaline flow occurs in the Meditterean Sea in summer when water gets heavier due to strong evaporation that transports fresh water into the atmosphere, feeding the hydrological cycle, and leaves salts behind that make the water denser and it sinks. This salty water, produced in the Meditterean Sea, can be found in the Atlantic Ocean at depths of 1000 to 1500 m (figure 2b). ”
Nice, but in addition to some spelling errors, they don’t have the circumpolar current going all the way around the south pole:
Though the more interesting thing from that link is the Mediterranean Salt Tongue.
Now, the description of Ocean Gyres has some different ideas what the currents might be:
Notice that they do not connect, and the part near Spain heads south, but turns west toward north America where it runs into North Africa. While long before reaching Africa, the Thermohaline map above has it flowing west in the middle of the Atlantic. Nearly nothing near Africa. Similarly, the south Atlantic gyre doesn’t show much in the thermohaline map.
Some Other Currents
Has a bunch of things, including this alternate view of the salt tongue. Seems it really breaks up into salty “lenses” called “meddes” that drift around the Atlantic for a while…
The caption says:
Coupling data collected by NASA/JPL by several different satellite-borne sensors, researchers have been able to “break through” the ocean’s surface to detect “Meddies” — super-salty warm-water eddies that originate in the Mediterranean Sea and then sink more than a half-mile underwater in the Atlantic Ocean. The Meddies are shown in red in this scientific figure.
So we have “chunks” of water drifting around the Atlantic. Flowing out and sinking. Wonder if that counts as a “current”…
But wait, there’s more…
Somehow I think I trust this older map more than most. It also shows the limits of ice flow, ice berg sightings, and more. The full sized image is huge, and very detailed.
NOAA has a view that is much more “disjoint” and conceptual… useful not so much:
It seems to be lacking the North Atlantic Gyre as well as any current going from Iberia down to Africa. It does have a nice equatorial current toward North America, but doesn’t show much of where that water comes from.
This one likes to have arrows run into each other, though it does have some hint of the gyres. There is also a tendency to have arrows start nowhere and end running into things. So the current headed south along the east (asian) side of Africa seems to start from nowhere and the one in the Indian Ocean next to it starts from Indonesia, makes a U turn and runs back into Indonesia, but not where it starts. Ending as mysteriously as it begins.
So where do the ocean currents go? The Ekman Sprial implies many different directions depending on depth and surface winds:
The diagram above attempts to show the forces associated with the Ekman spiral as applied to the Northern hemisphere. The force from above is in red (beginning with the wind blowing over the water surface), the Coriolis force (which is shown at right angles to the force from above when it should in fact be at right angles to the actual water flow) is in dark yellow, and the net resultant water movement is in pink, which then becomes the force from above for the layer below it, accounting for the gradual clockwise spiral motion as you move down.
The first documented observations of an oceanic Ekman spiral were made in the Arctic Ocean from a drifting ice flow in 1958.[
So… what’s a current to do. Lenses of salty water drifting sideways. Spirals of water shifting direction as depths advance. Major Gyers spanning oceans. But supposedly with steady currents crossing entire oceans. Some starting nowhere and ending nowhere.
Then a thermal picture of the Gulf Stream sure looks like reality is a whole lot more complicated. Rather like clouds. Eddies and swirls. Wisps wandering into other areas. Size dramatically changing. Full motion video is even more dynamic. I have no idea how one could begin to program that behaviour into a computer model.
All of which leads me to really wonder just how well the “climate codes” model oceans and currents. How much do those various “conceptual maps” above reflect anything real? With what resolution? On what time scales? With what dynamics over time?
To me, it looks like a real fools errand to try to explain how those “currents” move heat around the planet and impact weather and climate. It is a huge, fine grained, and somewhat chaotic system.
If, as I expect, a lunar influence on tides and currents determines the very long cycles of weather and climate, the 79, 350, 1470, and even 1800 and 5000 year cyclical changes: It is going to be nearly impossible to figure out how they change the currents of today. We have essentially zero record of real past currents (especially at depth) to work from in figuring out what will happen in lunar / tidal regimes that have not been seen for 1500 to 5000 years.
We can’t model it. Heck, we don’t even have a consistent “story” about where currents move today (if that above muck of maps is any guide). Unexpected changes in something we poorly understand and can’t reliably describe are not going to be easily predicted.
It is also certainly the case that one can not look at that kind of system and say any “heat” is being reliably carried down into any particular depth of the oceans. Horizontal currents are barely covered, vertical hardly at all. There is no mass flow size nor temperature profiles to apply to that unknown mass. Any assertion we know what volume and temperature is flowing in the vertical is just insane. Then add a bunch of changes to tides on an 18.6 year cycle. And on a 56 year harmonic of that when any given face of the earth finally returns to being under the moon at the same part of the 18.6 year cycle.
To me, it just looks a lot like a poorly understood system.
But you look at the maps and see if you can make some sense out of them. Some kind of consistent understanding.