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Oceans are a tremendous reservoir of heat. The upper 10 feet of ocean water holds more heat than the earth's entire atmosphere. Due to the formation of the Antarctic Circumpolar Current, enabled by plate tectonics, Antarctica became thermally isolated from the rest of the earth initiating 1) a permanent ice cap, 2) extensive sea ice that extruded cold brine that filled the ocean's bottom water, and 3) Intensified upwelling that increased productivity that drew down atmospheric CO2 to current levels. As a result of increasing cold Antarctic Bottom Water, oceans ventilated its its displaced ancient bottom water heat. As a result of a 50 million year cooling trend, the earth is now locked into a fluctuating balance between cold ice ages and warm interglacials
Transcript of Presentation below:
Welcome back, everybody. Thanks for all the kind comments today. I want to discuss what I call the Antarctic refrigeration effect. And if you understand that, you understand why the earth will remain in ice age mode for probably the next 200 million years. Now, climate change is a huge in complex problem, and it's akin to the, the Indian, east Indian parable of the blind men characterizing an elephant. Unfortunately, there's one cadre of scientists who are trying to force a singular viewpoint: Carbon dioxide is the climate control knob. But once you understand how important ocean circulation is, you just might be convinced that the greenhouse gas effect is really the tail wagging the elephant.
If you look at ancient climates, we'll see that 90 million years ago during the Cretaceous that the earth's continents were warm from the polar region to the equator, and Antarctica was a tropical rainforest. It had its own dinosaurs, Glacialisaurus sp. Well, the dinosaurs had a major extinction event about 66 million years ago when an asteroid collided with the earth and caused the extinction about seventy-five percent of all global species. So I'm going to skip ahead to the Eocene and the cooling trend that happened about 50 million years ago. Now temperatures back in the during the Eocene, the Arctic's Ellesmere island summer temperatures, even though it was, it was a polar place was about 68 degrees Fahrenheit.
The coldest month only dropped down to just above freezing. Yet today we look at Ellesmere Island, which is adjacent to Greenland, and the average temperature there is about 2.3 degrees C. So we've had a tremendous cooling trend since then. And along with that cooling trend was the development of polar glacial ice caps.
Now we look at around 34 million years ago, Antarctica started to have its permanent ice cap, but it then took until about two and a half million years ago for a permanent ice cap to form on Greenland. So the question becomes if CO2 is the control number of temperature and ice formation, why is this this 15 to 30 million lag between Antarctic in Arctic ice cap formations now to understand the earth climate before the great global cooling trend began, we have to go back to the age of dinosaurs back then the continents were all connected in one continuous continent, known as Pangea with the lack of glaciers.
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| 50 million year cooling trend from the Eocene to the present |
During the age of dinosaurs, there were higher sea levels which created shallow coastal seas. And there was the creation of the Tennessee, another shallow sea shallow seas heat up more quickly and evaporate water more quickly. And that causes more warm salty water to sink to the ocean floor.
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| Pangea with shallow seas (purple) |
So at the beginning of the Eocene, the oceans of the world were dominated by warm, salty, deep water (WSDW), the oceans bottom waters (WSDW) were about 10 to 13C warmer than they are today. And that warm water would also upwell around the Antarctic and be carried back to the equator by a current known as the Antarctic Intermediate Water (AAIW). But that dynamic was about to change as Pangea broke up throughout the age of dinosaurs.
And pretty soon Antarctica became isolated as it is today. When Antartica separated from south America, Australia, and Tasmania, it allowed for one continuous current to loop around Antarctica known as the Antarctic Circumpolar Current (ACC). And it had had some major impacts on the world's climate. That current blocks, the warm sub-tropical waters from entering Antartica waters and that initiated extensive sea ice growth and glaciation.
It also increased upwelling and diatom productivity, which is associated with the evolution of baleen whales that now we're able to just filter feed through the ocean. That tremendous productivity caused more CO2 sequestration, which caused the amount of atmospheric CO2 to drop.
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| Antarctic Circumpolar Current |
And now the Antarctic Circumpolar Current through the Antarctic intermediate waters would feed all the rest of the world's oceans in the Aaliyah scene lasting from 34 to 23 million years ago, the Antarctic circumpolar current deepened and strengthened the formation of sea ice now cause cold brine rejected from that sea ice to sink to the bottom and replace the warm salty water. And that began to change the temperature profile of our oceans.
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| Changing Oligocene ocean bottom waters from warm salty WSDW to cold Antarctic Bottom Water (AABW) |
And that began to change the temperature profile of our oceans.
Now due to the shape of the earth and its tilt of this axis, the sun more intensely heats the earth around the equator relative to the polar regions, which receive more diffuse sunlight. So the polar regions don't heat up much. And then due to the polar nights where there's no sun at all, it radiates all that heat back to space. The current temperatures in the polar regions are maintained by a flow of heat from the tropics into the polar regions, through ocean currents and atmospheric currents, uh, such as the Gulf stream or the Kuroshio current.
And we can see this illustrated here in this diagram where there's an excess amount of heat and the equator relative to his temperature and that excess heat is transported to the polar regions, which warm those regions.
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Heat transport from warm tropics to warm polar regions |
So based on those dynamics, I like to refer to the cooling that's been happening for the last 50 million years as the Antarctic refrigeration effect. Now every refrigerator has this compressor & fan apparatus, which removes heat from the refrigerator and blows it out the back. Now it's not quite analogous, but the polar regions remove heat away through radiation especially during the the polar nights.
Now, if a refrigerator door is left open, then the heat is blown out the back of the refrigerator just re-introduced through the front. So there is no cooling, but if you shut the door, the refrigerator cools and the Antarctic circumpolar current shuts the door on the Earth's temperature circulation Now is heat is blocked from entering the Antarctic southern waters increasing sea ice.
More extensive sea ice creates more brine ejection, which sinks to the bottom and cold salty brine replaces the warm salty waters. Now the formation of cold Antarctic bottom water sets the stage to create the profile of temperatures we see throughout the modern day oceans. We see that the bottom waters are dominated by Antarctic bottom waters and that cold water helps feed, uh, the Antarctic intermediate waters, which transports the cooler temperatures to the equator in, into the Northern hemisphere.
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| Ancient warm salty deep water replaced by AABW & North American Deep Water (NADW) |
And here's another way of looking at that profile. You have Antarctic bottom water on the bottom. You have North Atlantic deep water above that's been formed in the Arctic under the cooler conditions of today. We see the Antarctic, intermediate Water is flowing up past the equator and we still see some sinking warm salty water due to evaporation happening in the Mediterranean.
Now the sinking Antarctic bottom water, which is the coldest water in the oceans mixes and lowers the temperature of the North Atlantic Deep Water. And together that feeds the cool Antarctic intermediate waters that moves towards the equator and affects most of the upwelling regions around the world.
Now, by looking at the Pacific Ocean todeay, we can appreciate the power of upwelled cold water that changes the global temperature during the La Ninas. Warm waters are pushed over to the eastern side of the Pacific and cold waters rise from below to replace that warm water with cold water.
If we look at satellite temperature data, we see the major drops in global temperature happened during Linea events as represented by the red arrows.
The problem is the Pacific cold water upwelling didn't begin until 4 million years ago, Before the Arctic region began to form its glaciers and ice caps. And the reason for that is this Antarctic refrigeration effect had to build up the Antarctic bottom waters to a large enough volume to feed cold Antarctic Intermediate Waters, raising it close enough to the surface to allow it to be upwell and then affect the Earth's climate.
Now around 2.5 million years ago, Greenland's permanent ice cap took hold. And that correlates with the closing of the central American Seaway by the rise of the Panama isthmus connecting North America to South America. Now, some researchers say that this blockage of the central American Seaway, enabled the glaciations to begin, but others say that it delayed the glaciation. There's not enough time to talk about whether that's true or not, but the changes in ocean circulation around 2.5 million years ago, we're not just relegated to the isthmus of Panama, but happened around the Bering Strait, and around Indonesia.
So we see there was a tremendous change in circulation. Now, one result of the creation of the Panama isthmus that might be of interest, is it allowed the animal fauna between North and South America to move upwards or southwards. If you look at the brownish green silhouettes, those are all South American animals that moved into North America and the silhouettes in blue are North American animals then moved into south America. That causes one to question if temperature has anything to do with similar kinds of migrations
To summarize 50 million years of global cooling, we start with the ESC a time period 50 million years ago when carbon dioxide was a a thousand parts per million or greater in the atmosphere in global atmospheric temperatures, as well as warm salty, deep water was at least 23 degrees Fahrenheit, warmer or 13 degrees centigrade warmer than today by 34 million years ago.
The Antarctica Circumpolar Current was now blocking any kinds of flow of subtropical, warm water from reaching Antartica. And this caused three critical things. 1) it allowed the initiation of Antarctica's permanent ice cap that persists today, 2) it caused extensive sea ice to increase, which caused brine rejection, which added to the volume of the cold Antarctic bottom waters.
And 3) the current also increase upwelling. It caused high productivity from diatoms, the evolution of the baleen whales and that productivity sequestered more and more CO2 dropping CO2 down to levels of 300 parts per million to 700, depending on your models, which is lower than today in many cases. And surprisingly, as the Oligocene proceeded, the late Oligocene was warming despite the continued drawdown of carbon dioxide. By the Miocene, the CO2 was down around 400 parts per million, and, but global temperatures were seven degrees to eight degrees centigrade, 14 degrees Fahrenheit warmer than today.
And so some models said that that CO2 had to be higher in order to justify those temperatures. But we could also say that the reason we saw this warming in the late Oligocene, or we saw it in the Miocene as, as Antarctic bottom waters, increasingly, uh, replace replacing warm salty waters in the bottom, the ocean, it raised those ancient, warm waters to near the surface where that warm water could ventilate as heat back to the atmosphere by the Pliocene, which ended around 2.5 million years ago, we saw the initiation of the Greenland's permanent ice cap that was partly associated with the Panama isthmus as well as other changes in plate tectonics, which caused changes in ocean circulation. At that point, CO2 was again around 400 parts per million and upwelling of warm water. Up until that point had kept temperatures around three degrees or 5.5 degrees Fahrenheit warmer than today.
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Temperature changes between cold ice ages and warm interglacials |
Now the growing amount of cool upwelling waters caused the Pleistocene 2.5 million years ago to reach a point where it's very sensitive to any changes in energy imbalances on earth, that caused the Earth's climate to fluctuate wildly between glacial cold periods in interglacial warm periods.
We had the warm interglacial the previous one hundred thousand years ago that was warmer than today by about four to five degrees centigrade. And then the last glacial maximum temperature was down to about a minus 11 cooler than today
