Guest essay by Wim Röst
The best kept secret in the ‘climate world’ probably is: the cooling capacity of the deep sea. Some attention is paid to the heat uptake by the oceans, but there is no attention for the cooling capacity of the deep sea. That capacity is huge and might be (and might have been) of decisive importance in climate and climate change.
Fig. 1. Temperatures in a North South section of the Atlantic Ocean
The oceans are on the average 3.688 meter deep. The surface layer, directly connected to the atmosphere, is only 100-200 meter thick. Below this layer we find cold to very cold water. And, as we know, water has an enormous capacity to absorb heat. Which means that it also has an enormous capacity to cool.
The temperature of the top surface layer is on average 18 ºC. There is a big difference in temperature between the surface layer and the layer 200 meters deeper. According to AR5 (fig. 3.1d) the surface layer on the average is 6,3 ºC warmer than the layer 200 meters below. Nearly all upwelling will affect the temperature of the surface layer in a way that it is cooling the surface strongly.
Below a 1000 meter temperatures are only 5 degrees ºC or lower.
Fig. 2. Thermocline in a tropical ocean
The total water content of the oceans is enormous. One cubic kilometre contains a billion m3. And there are nearly 1,3 billion cubic kilometres of water in the ocean. But, with a surface area of 362 million km2 the top layer of the oceans (the upper 200 meters) ‘only’ has a content of 72.4 million km3. Most ocean water (95%) is cold ‘deep water’.
There is a considerable mixing of water masses in the top layer of the ocean. Mostly driven by wind.
Fig. 3 Areas with upwelling waters
The coldest and deepest ocean water takes (at the most) an estimated 1000 years to reach the surface layer. Which means that other less deep ocean layers are welling up faster.
Every year the [average] surface layer is cooled down by a huge quantity of cold ocean water welling up. When reaching the surface, that cold water is heated by the sun.
In the ‘climate world’ it is assumed that there is a constant cooling of the surface layer by upwelling waters.
At least one million cubic kilometres of cold ocean water is welling up every year*. If this one million cubic kilometres in any year would become two million cubic kilometres or, only half a million cubic kilometres, this change would have a substantial effect on the surface temperature of the Earth’ oceans. And therefore on the temperature of the atmosphere.
Upwelling is driven by wind and because wind is not constant – being dependent on changes in pressure – the changes in upwelling quantities might be considerable. Variations in pressure exist.
The most simple calculation is the following. Heat content is measured in ºC/million km3
After year 1 the total heat content of the surface layer will be 1303,2 minus 18 plus 5 = 1290,2. The temperature of the surface layer (this example excludes the effect of heating by the sun) will be 1290,2 / 72,4 = 17,84 ºC after one year. The surface of the ocean cooled substantially by 0,18 degrees C in only a year.
In case the heating by the sun remains the same every year, a doubling of the upwelling in one year will result in a net cooling of 0,18 ºC of the ocean surface. And, on the other hand, half of the upwelling will cause a warming of the ocean surface by 0,09 ºC in one year.
Of course upwelling can diminish (or increase) during a number of years by smaller percentages as well. A century with a two percent decrease of upwelling results in 2 x 0,18 = 0,36 ºC warming of the ocean surface waters, all other things remaining the same.
The cooling potential of the oceans is huge. Even with minor changes in water flows.
Therefore, all warming of the ocean surface since the Little Ice Age could have been the result of a relatively small diminished upwelling of cold deep ocean water.
To judge ‘warming’, we must first know everything there is to know about cooling.
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)
* Some data on ocean water volume, deep water and bottom water (sinks) production and upwelling of deep water
Abrupt Climate Change – National Research Council (2002)
PLATE 4b (…) representation of the global ocean circulation (…) simplified from Ganachaud and Wunsch (2000), as estimated from modern oceanographic data.
From the above figure:
Data in Sv (Sverdrup). One Sverdrup is equivalent to a flow of 1 million m3 in a second. Which makes one cubic kilometre in 1000 seconds. There are 31 556 926 seconds in a year.
Total ocean volume: 1.335 million km3 (1,3 billion km3)
(source NOAA: https://www.ngdc.noaa.gov/mgg/global/etopo1_ocean_volumes.html )
One Olympic Swimming Pool has a water content of 2.500.000 L = 2.500 m3
One cubic kilometre has a water content of 1.000.000.000 : 2.500 = 400.000 Olympic Swimming Pools
A million cubic kilometers have a total water content of 400.000.000.000 (400 billion) Olympic Swimming Pools.
Total Ocean content is 1.335 million km3 of Ocean Water, 95% of which is cold Deep Water