Guest Post by Wim Röst
Introduction
The creation of ‘Hot Worlds’ and ‘Glacial Worlds’ during past geological periods was only made possible by warm and cold deep oceans, respectively, that were created by specific configurations of continents and oceans. Without warm deep oceans, no warm global climate state is possible. Without cold deep oceans, no glacial periods are possible.
The temperature of the oceans is mainly created by the kind of downwelling water. When warm very salty water is downwelling, warm oceans are created. When cold salty waters are downwelling, cold oceans are created.
What is oceanic downwelling?
Oceanic downwelling is the sinking of more dense seawater into a layer of less dense water. ‘More dense’ means: more weight (or mass) per unit volume.
Reasons for ‘density’
There are two reasons for seawater to be more dense than other seawater:
- the seawater is colder
- the seawater is saltier
We can expect downwelling to occur in areas with the highest density of surface waters. The following map shows where we find surface waters with the highest density.
Figure 1: Sea-surface density [kg m-3]. Annual mean sea surface seawater density calculated from World Ocean Atlas 2005 fields of temperature and salinity using the SEAWATER toolbox. Density here is in kg m-3. Blue and red squares are added.
The higher the density, the more chance there is for downwelling. The densities in the map above are annual densities. Because downwelling can occur every moment, this map only gives an indication of the annual potential for downwelling. In our current cold Quaternary Period, most downwelling potential is found in the North Atlantic and around Antarctica.
Two types of downwelling
There are two main types of downwelling:
- Warm and very salty
- Cold and salty
In the above map of figure 1 we find present warm and very salty downwelling in the red squares. The cold and salty downwelling areas are indicated by the blue squares.
(Nota bene, downwelling also occurs in the Pacific but the exact location(s) are unknown by the author)
Cold downwelling
As warm surface waters are transported to the poles they mostly have a higher salt content (a higher salinity) than other local waters because of the higher evaporation at the time the transported waters still were residing in the tropics and subtropics. But because this salty tropical or subtropical water also is very warm, it continues floating until it cools in polar areas. The now cold and salty water will sink into less dense water until it reaches equally dense water. We find this cold downwelling both in Arctic and Antarctic areas. Depending on the density of the downwelling waters, intermediate water (cold but shallower water) or deep ocean water is formed. The higher the density, the deeper the water will sink.
Warm downwelling
We don’t often find warm downwelling today, but warm downwelling does happen. Warm waters will also sink into colder waters when they are salty enough. Very salty warm water is that dense, and can sink into colder waters that have a lower salinity.
The role of salt
It is because the ocean water contains salt that this type of downwelling – warm downwelling – exists. As will be explained, this simple physical fact (the salinity of the oceans) is of decisive importance for the average background temperature of the Earth’s climate in different geological periods.
Jacuzzi
Simply said: if you only turn on the warm water tap of the big Jacuzzi in your bathroom, all bathwater will be warm. When you, after filling the bath close the door and return half a day later, the atmosphere in the bathroom will be warm.
But if you only turned on the (very) cold water tap and after filling the bath closed the door and returned half a day later, not only the bath will be very cold but you will also experience an unpleasant cold atmosphere in the bathroom.
If the Jacuzzi fills 71% of the bathroom, that situation would resemble the Earth whose surface is 71% ocean water. Cold water taps in our oceans are filling the deep ocean with ice cold water. We have two big chillers: one in the Arctic and one in the Antarctic. In recent geologic time, they have been perfectly positioned for cooling. Both are receiving more saline than average water from the Atlantic.
In our present Earth, unfortunately, our ‘warm water taps’ hardly function. We have ‘warm water taps’ in the Mediterranean, the Red Sea and the Persian Gulf. Also in the Pacific Ocean, there is some production of warm downwelling water. But as we will see, the total deep warm water production is minimal compared to the deep-and-cold water production which is, by far, dominating downwelling. Therefore, our Earth has a very, very cold Jacuzzi.
And because of the cold oceans, we experience very cold climates. Historically cold.
Every second around 40 million cubic meters (40 Sv, one Sv = one million cubic meters per second) are downwelling into the depth of the Earth’s oceans. Ninety percent of that 40 million cubic meters is very cold.
Cold downwelling: the downwelling in the Thermohaline Circulation
In the Thermohaline Circulation (THC) cold downwelling plays a significant role. Warm salty water from the Gulf Stream flows to the North Pole area, cools and sinks. This water flows as deep cold water to all of our oceans. All the deep oceans are connected to each other.
The deep ocean flow is not in the form of a simple ‘transport belt’ as is often shown in graphics like figure 2 below. Imagine that all deep and surface water is moving, sometimes more slowly, sometimes faster.
Figure 2: A popular image of the Thermohaline Circulation. Shown are the cold downwelling areas near the poles and the direction (not: quantity) of transport of deep waters (blue) and surface waters (red).
Less known: examples of warm downwelling. First: the Mediterranean
After the smaller Red Sea and the Arabian Gulf, the Mediterranean Sea has the highest salinity of all sea surface waters. In summertime in the Mediterranean evaporation is high and precipitation is nearly absent. Salt remains in the sea after evaporation and after some time all Mediterranean water will become very salty.
Figure 3: Surface salinity of the Mediterranean. Entering in the west at Gibraltar, surface waters become saltier after evaporation as we move to the east of the Mediterranean.
When this very salty and very warm Mediterranean water is cooling, it will sink below the less dense waters that enter at Gibraltar. The less dense water from the Atlantic overflows the dense, still warm and very salty waters that we find eastwards.
The warm deep water that is formed in the Mediterranean finally has a temperature of 12 – 14 °C (figure 4), which is warm compared to much colder deep water in the North Atlantic where temperatures below 1000 meter nearly always are less than five degrees C.
Figure 4: Temperature and salinity of Mediterranean water. The Y axis (depth) is logarithmic. The distance east- west is 3,700 kilometres. To compare with other oceans: the average salinity of all oceans is 34.9 PSU
At Gibraltar, the deep very salty warm water flows out of the Mediterranean into the Atlantic Ocean. In doing so, the Mediterranean creates a huge underwater waterfall: the dense very salty warm water sinks into the colder but less salty layers of the Atlantic Ocean. Figure 5.
Figure 5: The Mediterranean underwater waterfall at Gibraltar. Very salty and warm water (dark blue) dives deep down into colder Atlantic waters. The speed of the outflow can reach 2 metres per second: 7.2 kilometres an hour.
(Original: Marine Geology, Kuenen, p. 43, with a slight enhancement)
The warm downwelling water flows to a depth around 1000-1100 meter where it meets and mixes with colder but less saline waters. The inflow of Mediterranean water results in an estimated final temperature effect for the North Atlantic of between 0.1 and 0.3 °C.
The effect of the spreading and mixing of the Mediterranean water in the North Atlantic is also visible in the salinity map of figure 6.
Figure 6:
The tongue of saline water from the Mediterranean outflow in the observations of Levitus, Burgett, and Boyer [1994] at 1100 m depth. Contours show the salinity anomaly (practical salinity units)
Even deeper downwelling of very salty waters: Red Sea water
The Red Sea is not only warmer but also has a higher salinity than the Mediterranean: 40 – 41 PSU. Because of that high salinity, the outflow reaches far deeper waters in the Indian Ocean than the Mediterranean waters do in the Atlantic: we can find the warm Red Sea Intermediate Water at a depth of around 3 kilometres, see figure 7.
Figure 7: Very salty and warm Red Sea Intermediate Water at 3 km depth in the Indian Ocean: red oval
Source: Slide 47
Present downwelling: the numbers
In the present configuration of the Earth we find both warm and cold downwelling, but cold downwelling dominates. See table 1, red = warm downwelling, blue = cold downwelling. Based on estimations by Ganachaud and Wunsch (2000)
Source: Data from Plate 4b
Not mentioned in table 1 is the Mediterranean outflow of 1-2 Sv. If added, the total present warm deep-water production will be at least 3.5 Sv, still far less than the 36 Sv produced as ice cold Arctic and Antarctic deep waters. Ten times as much ice cold deep water is produced compared to warm deep-water production. As a result, present deep oceans are ice cold.
The present situation of ice cold oceans results in the historical cold climate state in the period we are living in, the Quaternary.
Figure 8: Phanerozoic Global Temperatures according to Christopher Robert Scotese The added red arrow indicates our present relatively warm interglacial temperature: but it is still an ‘Icehouse’ temperature.
Upwelling
Because yearly more than a million cubic kilometres of very cold deep waters are upwelling into the warm surface layer, the new surface water has a low starting temperature and diminishes the average temperature of the sea surface waters. Warmer upwelling waters would have a warming effect. As described in Cooling Deep Oceans – and the Earth’s General Background Temperature the cooled deep ocean cools the atmosphere, enabling our present very cold Quaternary, characterized by glacial periods.
Next post
In the next post, more about the development of the present configuration of the Earth that has led to our present ice cold oceans. As an introduction to the next posts some maps are presented in figures 9 and 10.
Figure 9: Two different configurations of the Earth’s continents and oceans. The map on the left has led to our present icehouse state, the situation shown on the map to the right would have led to a hothouse state.
Figure 10: Configuration of the Earth’s continents and oceans 65 million years ago, creating the warm deep oceans and the warm climates that were present at the start of the Eocene. Notice the Eurasian situation around 30N – the arid subtropics – where we presently find the relatively small warm and salty deep water producing seas (Mediterranean, Red Sea) described above. Light blue is ‘shallow’.
Conclusions
Surface water will become deep water when it is either cold and salty or when it is warm and very salty.
It is the special quality of salty seas that warm water can also downwell to great depths, due to a very high salt content. Because of the high salinity the density of the warm very salty water equals the density of much colder but less salty water. The very saline water will sink to the same depth as colder but less salty water, raising the average temperature of the deep ocean.
In the present configuration of the Earth the downwelling deep cold water dominates. As a result, the oceans and therefore the Earth’s climate are historically cold. As deep water wells up into the surface layer, the surface layer becomes relatively cold and because of the cold surface layer our present global atmosphere and climate is historically cold.
The present absence of large warm deep water producing seas, in combination with the large and well-functioning cold deep water production areas at the poles, ensure that our Earth is experiencing one of the coldest periods of the last 500 million years: the Quaternary Period. This is the very cold era we now live in, the glacial era.
With regards to commenting: please adhere to the rules known for this site: quote and react, not personal.
In commenting: please remember you are on an international website: for foreigners, it is difficult to understand abbreviations. Foreigners only understand words and (within the context) easy to guess abbreviations like ’60N’ or ‘SH’.
About the author: Wim Röst studied human geography in Utrecht, the Netherlands. The above is his personal view. He is not connected to firms or foundations nor is he funded by government(s).
Andy May was so kind to read the original text and improve the English where necessary. Thanks Andy!
Take a break Wim, for you greatly deserve it. There is a great need for the study of ocean heat/salinity to understand Earth’s climate. Thank you.
Chad Jessup: thank you! Yep, and there is a lot to discover. And area (71% of the Earth’ surface) that stayed out of sight hides a lot of things to reveal.
Google the words: Sea Level NOAA Battery. The graph shows no trend change back to 1850-The onset of the Industrial Revolution. Such a linear trend implies the absence of any pronounced influence on climate outside of nature. If there were a correlation between warming and CO2 in the atmosphere, an obvious disturbance of this linear trend would be present.
http://linkis.com/noaa.gov/WREJm
A Dutch geology professor, Salomon Kroonenberg, last year published an interesting book about sea level rise, unfortunately just in Dutch. The name: “Spiegelzee”. He concludes that nothing unusual is happening so far. After the Little Ice Age we see a moderate sea level rise of around 20 cm or so per century. Not dramatic at all.
While most of us Dutch are living below sea level, we would be the first to know about dangerous sea level movements. The images Al Gore showed in his first movie about a disappearing Netherlands because of sea level rise were fake: he just showed what happens as you remove the dikes that protect us. I remember that at highschool I saw the same map: the Netherlands without dikes. The West and the North of the country under water.
As a geologist, I often consider what we know/surmise about the Earth’s changes over 4.5 billion years. Much of what went before likely won’t happen again, or if it does, it will be at a slower pace (sort of like me). Vast quantities of heat of whatever source – radioactive decay, impact related, core formation – have been dissipated to space. Never again will we see komatiites erupted on the face of the Earth. Plate tectonics is slowing down, and our north-south continental arrangement is going to be here for a looooong time. The Antarctic continent – now a two-mile high pile of ice covering a few million square miles – seems happy where it is, giving us a free-flowing Southern Ocean for perhaps the first time in the globe’s history (mostly, the continental masses have been at the southern pole). CO2 is in danger of being entirely consumed by a voracious Earth. The outlook for life – as we know and enjoy it – becomes tenuous. We really DO need to start thinking about Terraforming – in this case Terra. Without CO2, we all die. Another Ice Age will reduce us to primitives. This is the stuff of science fiction, but in 5-10 kilo years will be upon us (assuming we survive 2018).
Jimmy Finley, “Plate tectonics is slowing down, and our north-south continental arrangement is going to be here for a looooong time.”
WR: there seems to be some controversy about the question whether plate tectonics is slowing down or is accelerating: https://www.newscientist.com/article/mg22329843-000-earths-tectonic-plates-have-doubled-their-speed/
But a fact is that our north-south continental arrangement as you call it (Atlantic Ocean configuration) is going to stay for a very long time. And the Atlantic is our big salt water producer. So we are going to keep it cool. More about this in the following post.
This sure blows Trenberth’s “the missing global warming heat is hiding in the deep oceans” (BS) theory out of the water ! Pun intended.
Wim, GW raises a point here… A while back you had a post on the effect of wind speeds on ocean mixing. It seems we have two trains running here. On the one hand, more sinking cold water than warm water (for reasons pointed out in this post). And on the other more downwelling warm surface waters due to greater vertical mixing. Which of the two is greater and by how much? (one would think that higher SSTs overall would mean a warming ocean on the whole rather than a cooling ocean from sinking saline enriched waters)…
post script~ let me know where any of my thought processes have jumped track here (☺)
Afonzarelli, the first one you mention, the more cold water sinking than warm deep water is by far the most important process. We are speaking about a quantity of 36 million cubic meters every second! Meant is downwelling which cools the deep sea and has important long term effects.
The second one you mention is mixing of warm surface (!)water with lower colder surface water what is mentioned in the commentaries of the first post about upwelling. Upwelling cools the surface because the upper layer is blown away and colder water from below wells up. Another cooling process is the by you mentioned mixing, that cools the surface because the top surface layer becomes mixed with the colder layer just below. In both cases the surface cools. So in the second case I was talking about the cooling of the surface (!) waters by the deep or ‘deeper’ waters.
The last one, upwelling has a very direct effect on surface temperatures: cool seas surfaces cool the atmosphere. The first one, downwelling cools the deep sea and has a long term cooling effect. A cold deep sea finally (!) will cool the surface as well, because deep sea water will well up and will be become part of the surface layer.
‘Down’ and ‘up’ are different processes that listen to different mechanisms and most time are localized at different places. Upwelling is orchestrated by wind. Downwelling by salt and temperature. Although all water that goes down once will go up, the drivers for both processes are different. Downwelling can diminish in the same time upwelling grows or vice versa.
-Wim. I certainly don’t disagree with your remarks on up/down welling but I am trying to think of the oceans as a separate heat engine from the atmosphere with some similar general characteristics. In the atmosphere, cold, dense volumes of air tend to fall in cells, often virtually right beside rising columns of warmer air. Is something like that not possible in the oceans? Perhaps especially where warm water is more concentrated in salinity?
Wim, A criticism of your figure 9
You have used a “Tobler’s rescaling in a circle of Mollweide’s Projection” to illustrate your point.
http://progonos.com/furuti/MapProj/Normal/ProjPCyl/Img/mp_MollweideCircle-s37.5.png
Unfortunately the two axes are not equivalent in angle; the Y-axis is 180 degrees of latitude while the X-axis is 360 degrees of longitude.
A better display would be to choose the Great Circle of Longitude 90E & 90W as the new equator with the North Pole at the modern Pacific Ocean location of 0N 90W to tilt the Atlantic Ocean into the Northern Hemisphere as a Meridional Ocean.
A minor quibble but a projection that it would be fun to try 😉
Phili Mulholland: “You have used a “Tobler’s rescaling in a circle of Mollweide’s Projection” to illustrate your point.”
WR: Well, perhaps I was that intelligent to do so, but personally I think I produced a “Röst rescaling in a circle of Mollweide’s Projection”. You have seen it well, it was a Mollweide projection but I needed an image that I could turn without losing the idea of ‘our Earth’. Therefore I produced this image myself.
Of course the goal was to show the right part of fig. 9 in the post, the turned earth. That same world, but with a 90 degrees turning of the continents creates a complete other climate system. That is what I wanted to show. It shows that you can not only make calculations and think you have an ‘ever true answer’. You always do so within a certain setting. Another setting, another result. In this case: a fundamentally other ‘background temperature’. Just by turning the same Earth.
Of course I am interested in better projections which make it possible to show the same, without losing the idea of an Earth. But I am not enough technically skilled to produce such a one myself.
For educational purposes mine will do, I think. And even for myself the final result of the turned world was rather funny and ‘stimulating for the mind’.
If we want to turn the climate world ‘upside down’, it is a good first step to start with 90 degrees!
Wim,
Yes I agree that your diagram works for illustrative purposes, however key point is that on “Planet Ocean” the sun tracks everyday across a hemisphere of water, the Pacific Ocean. We need to remember this and that the continental land masses of Planet Earth only subtend an angle of about 180 degrees (half of the sun’s daily track).
Sorry I got that wrong. Choose the Greenwich Meridian as the new equator with North Pole at the modern Pacific Ocean location of 0N 90W.
Wim,
If you have access to ESRI ArcMap then the following workflow will produce the required globe of Planet Ocean:-
Starting with a Spherical transverse Mercator plot with the Greenwich Meridian as the central zone
1. Save the image to your computer and load it into your favourite image display tool for resampling as a jpeg (I use IrfanView).
2. Rotate the globe clockwise by 90 degrees to turn the Greenwich Great Circle line into the equator and to place the Americas to the north and the rest of the world to the south, then save to file.
3. Open ArcMap using a Blank Map Template and set the Layer Coordinate System (I used a Geographic Coordinate System – World WGS 1984).
4. Load the rotated jpeg image and georeference it with the South Pole at 90 West, 0 North and the North Pole at 90 East, 0 North (the new equator line).
5. Rectify the current warp to create a new geolocated image and update the georeferencing.
6. Load the newly rectified geolocated image into ArcMap and change the layer coordinate system to a Projected Coordinate System Mollweide (world)
7. Export the Mollweide Map of Planet Ocean
Planet Ocean has a number of interesting features. Antarctica is of course on the equator which would really would make it habitable (now that’s what I call climate change!). Planet Ocean also has the Galapagos Islands at the North Pole and the South Pole is in the eastern Indian Ocean. It is a nice looking water-world, maybe we should ask Slartibartfast to build it for us!
Thank you Philip! I will have a try!
WM; No problem, it was an interesting challenge. Here is my result on LinkedIn that you are welcome to use.
Philip Mulholland August 22, 2017 at 11:30 am: “Here is my result on LinkedIn”
WR: Very funny result and a great view of our Water World! Thank you Philip!
Just one question: does the surface of the oceans reflect the real ocean surface share (71%)? It seems to be so. But if not, what could be the difference, any idea?
Wim: I am not sure is the simple answer. I started with a UTM map based on the Greenwich Meridian. As we know Mercator always exaggerates the areal extent of high latitudes (e.g. Greenland versus India) and in this case of course it is the far longitudes that get exaggerated. Rotation by 90 degrees turns the UTM based on Greenwich into a standard equatorial Mercator. A Mollweide projection of this may not be technically accurate, but it does produce a great looking globe.
Philip, by ‘copy and paste’ I have put nearly all land of the right map in the right half of that map. On view it looks like if the total ‘land area’ comes close to the 30%. So I think you produced a great map! Water World.
Wim
Way back in another life when I did oceanography at university (Southampton) we were told that the Norwegian sea was globally the biggest site of downwelling and source of deep water. But I can’t help feeling that Antarctica must be at least as important if not more so.
Here is a graphic showing the multilayer circulation at Antarctica indicating its strong connection to all the oceans. Have you seen this – or do you have a better resolution version of it? It suggests that Antarctica is the “Grand Central Station” of ocean deep circulation:
http://arizonaenergy.org/WaterEnergy/Soceanracetrack.jpg
+10
Ptolemy2: “Have you seen this – or do you have a better resolution version of it?”
WR: In the comments of this article by Willis Eschenbach https://wattsupwiththat.com/2016/02/25/the-warmer-the-icier/ I found a better resolution graph:
http://www.nat.vu.nl/environmentalphysics/SIMULATION%20Experiments/newpage/Two-Dimensional%20Oceans%20Model_old/general/3D%20ocean%20circulation/scan100dpi.jpg
At least the numbers in table 1 in the text of the post suggest that the Antarctic has a higher deep cold water production. But I also think the influence of the Antarctic on the total production of cold water is much more massive than the numbers in table 1 presented suggest. I suppose in the table only the production of the ‘deepest water’ is shown. In the figure above the Antarctic Bottom Water, AABW. The coldest water we find in the oceans. But the next figure shows that we find more cold water production in the Antarctic region:
http://www-odp.tamu.edu/publications/177_IR/CHAP_01/Output/ch_01a12.htm
AABW we find here on the most southern part, in this figure on the right. But ‘other’ cold water production is shown as CDW and AAIW. From the Northern Hemisphere the NADW, the North Atlantic Deep Water enters.
As we see the production of CDW (Circumpolar Deep Water) is high.
But there is also Antarctic Intermediate Water (AAIW) produced and I think this water (!) could play an important role in cyclic movements of climates.
The reason is, that I read in the study of Rosenthal et al., talking about Intermediate Waters (450 to 1000 m. depth) reaching Indonesia, the following very important sentence: “likely reflects the fact that it takes several decades for the intermediate water masses [AAIW] to reach the western equatorial Pacific from their high-latitude origins (7).” http://www.ldeo.columbia.edu/~blinsley/Dr._B._K_Linsley/Indonesia_&_Pacific_Intermediate_Water_files/Rosenthal.Linsley.Oppo%202013%20Pac.Ocean.Heat.pdf
Cold Antarctic Intermediate Water is produced at 46S to 50S. It only takes tenths of years to reach Indonesa and to become mixed there with other waters. My guess is that this AAIW will play a role in climate after mixing, but that is just a guess. Anyway the intermediate water will be closer to the surface as it was before.
The production region of AAIW (see the above figure) is in the “Polar Front Zone”. The zone where I expect the mass of the huge and powerful Low Pressure areas surrounding the Antarctic. Worlds’ ‘biggest mixer’. Changes in the northward/southward movement of the polar front will influence this kind of cold deep water production. This is where changes in the atmosphere have a strong influence on the formation of deeper ocean waters and tenths of years later (my guess) that ocean waters become influential for climate. My guess.
Unfortunately this link does not show up, but it is worth to open it:
http://www-odp.tamu.edu/publications/177_IR/CHAP_01/Output/ch_01a12.htm
ptolemy2 August 21, 2017 at 7:22 am
This graphic nicely shows the THC (thermohaline circulation). Very cold, dense water crashing down into the deep oceans around Antarctica (AABW) and crawling over the ocean floor towards and beyond the equator.
The geothermal flux (GF) warms this water making it less dense. Without GF there would be no THC, the deep oceans would simply fill up with cold dense water.
From the North Pacific and Indian Ocean comes no bottom water. For the Atlantic this graphic nicely shows the process:
http://www.uib.no/sites/w3.uib.no/files/styles/content_main/public/w2/at/atlantic-det4.jpg
It should be obvious that the solar heated warm surface layer and/or an ice layer prevent bottom heated water from reaching the surface.
“In the present configuration of the Earth the downwelling deep cold water dominates. As a result, the oceans and therefore the Earth’s climate are historically cold. As deep water wells up into the surface layer, the surface layer becomes relatively cold and because of the cold surface layer our present global atmosphere and climate is historically cold.”
A very interesting article but I don’t understand the conclusion. In the deep ocean solar heating and heating from the earth’s interior are neglible. I divide the ocean into two layers: cold water at the bottom and a transition layer from this cold basin to the warm surface. When the deep layer is filled with cold surface water the layer gets thicker and the surface will be warmer. On the other hand downwelling warm water cools the surface and makes the deep layer thinner. In the steady state there will be a constant thickness of the deep layer. The interesting question is: “Which processes can perturb the steady state?”
P. Berberich: “A very interesting article but I don’t understand the conclusion.”
WR: P. Berberich, if you change ‘cold’ into ‘warm’ in the same sentence that you mention, you will get the following:
“In the present configuration of the Earth the downwelling deep WARM water dominates. As a result, the oceans and therefore the Earth’s climate are historically WARM. As deep water wells up into the surface layer, the surface layer becomes relatively WARM and because of the WARM surface layer our present global atmosphere and climate is historically WARM.”
By doing so, you see the importance of the temperature of the deep ocean. The quantity of warm deep water producing seas is of the utmost importance for the final temperature of the oceans.
Secondly, your remark “When the deep layer is filled with cold surface water the layer gets thicker and the surface will be warmer.” can not be correct in my opinion. A million cubic kilometres of deep sea water is upwelling into the surface layer every year (see: https://wattsupwiththat.com/2016/12/26/warming-by-less-upwelling-of-cold-ocean-water/) and the temperature of the upwelling water will influence the temperature of the sea surface layer and so the temperature of the atmosphere. In present times, the surface will become COLDER because of upwelling COLD deep water. Your idea about stratification of ocean waters is an old idea, it is a rather common idea, but it does not reflect the dynamics of the ocean. See my remark under: https://wattsupwiththat.com/2017/08/20/oceanic-downwelling-and-our-low-surface-temperatures/comment-page-1/#comment-2586657
I hope this clarifies.
So if we nuke the Gibraltar Sill, that would, at first glance, appear to increase the warm saline downwell, but in actuality simply result in the entire Med becoming significantly less salty in the first place, REDUCING overall downwell and thus helping to cool things off?
Am I missing the mechanism, or is this grounds for Dr. Strangelove in action?
“So if we nuke the Gibraltar Sill, that would, at first glance, appear to increase the warm saline downwell, but in actuality simply result in the entire Med becoming significantly less salty in the first place, REDUCING overall downwell and thus helping to cool things off?”
WR: I like to think ‘out of the box’. After opening the Gibraltar Sill (and the other sill in the Mediterranean itself, the Straits of Sicily) a huge well of warm salty water would change the temperature of the North Atlantic. But indeed, that is only one time, although it could have a warming effect for many years.
But then, what changes? But first, what will NOT change?
What not will change, is the capacity of the Mediterranean to make seawater more salty. Net evaporation contimues, surface waters will become saltier and sink. But the rate of refreshment is higher, so the sinking water did not have the time to become much saltier. Also temperatures might lower because the raising influx of colder Atlantic water.
Is there more downwelling warm water produced? Yes, but both salinity and temperature are more moderate. The lower salinity will diminish density, the lower temperature will enhance density. Some calculations are needed to get the total effect.
Is the effect of the outflowing warm saline water different? Yes, it will not flow to the same depth in the Atlantic Ocean because of a different density. Therefore it will influence surface waters sooner or later, depending on the depth and direction of the final horizontal flow. Plus, the quantity of the outflow is raised.
So if I’m Dr. Strangelove, I’d need to try to calculate that flow BEFORE setting off the nukes. Thanks, Wim.