Guest essay by Phillip Mulholland
Late Carboniferous to Early Permian time (315 mya — 270 mya) is the only time period in the last 600 million years when both atmospheric CO2 and temperatures were as low as they are today (Quaternary Period ). Temperature after C.R. Scotese http://www.scotese.com/climate.htmCO2 after R.A. Berner, 2001 (GEOCARB III)
In a previous thread on WUWT published on 13 September titled Claim: atmosphere heats the oceans, melts Antarctic ice shelf, Sridhar Anandakrishnan, Professor of Geosciences, at Penn State is reported as saying:-
“Eventually, with all that atmospheric heat, the oceans will heat up.”
Well, that statement may or may not be true, but one thing we can be certain about, it does not apply to the seas around Antarctica.
A former colleague of mine had on the wall of his office a standard map of the World with the continents coloured by surface elevation. Unusually his map showed the icecaps of Greenland and Antarctica, not as featureless white regions, but instead coloured by the true elevation of the ice surface. What his map showed is the dramatic height of this surface, both over the bulk of Greenland and also over the vast majority of Antarctica, with layers of ice piled high into the atmosphere forming a plateau as tall as the mountain ranges of other continents.
His map demonstrated why Antarctica at 2,500m has the greatest average surface elevation of all the continents. With its high surface elevation that reaches a plateau maximum at Dome A of just over 4,000 metres, Antarctica stands taller in the atmosphere than any other landmass. With thin dry transparent air above it and the long months of the Austral winter, the ice surface of Antarctica acts as a gigantic thermal radiator that short circuits the atmospheric greenhouse effect and exhausts surface radiant energy directly into Space.
Throughout the winter season of darkness in Antarctica the thermal cooling of the ice surface generates copious amounts of cold dry dense air, this bitterly cold tropospheric air flows north off the icecap towards the Southern Ocean, descending to sea level as a gale force katabatic wind. The wind that Captain Scott referred to when he wrote “Great God this is an awful place”.
When the dense cold air reaches the coast at the Weddell Sea, its temperature is sufficiently low to flash freeze any open surface sea water, but the wind’s continuous force directs any newly formed ice north, away from the coast, creating a permanent open water gap The Latent Heat Polynya.
Oxygen is a reactive gas vital for the survival of animal life. In the oceans, oxygen can only be created either by biological activity in the surface waters of the photic zone or be directly dissolved from the atmosphere by the turbulent mixing of surface waves. In the planetary ocean sea water is layered by density and cold dense water is found throughout the bulk of the modern deep ocean. One of the challenges for Oceanography is to explain the presence and distribution of dissolved oxygen gas in the ocean deeps, given that it cannot have been formed there.
The explanation for the presence of this deep ocean oxygen lies in the existence of the Latent Heat Polynya in the Weddell Sea and elsewhere along the coast of Antarctica. Here, in the polynya, cold dense sea water is created, chilled and oxygenated by the katabatic winds of Antarctica and salted by the key process of brine rejection – dense salty water expelled from the continuously formed sea ice. This chilled sea water descends into the ocean as a gravity driven flow of high salinity brine that carries the dissolved oxygen vital for deep marine life down into the ocean depths. Truly it can be said that the polar icecaps are the lungs of the deep ocean.
The current climate paradigm recognises two distinct and separate states for world climate, the Icehouse World and the Greenhouse World. The Icehouse World is characterised by low atmospheric carbon dioxide levels, cold ocean deeps with high levels of dissolved oxygen and of course, polar continental icecaps with consequent low global sea levels. The Greenhouse World by contrast is characterised by high atmospheric carbon dioxide levels, warm ocean deeps with low levels of dissolved oxygen, no polar continental icecaps and therefore high global sea levels.
Geology shows us that in the past during the Cretaceous period, at a time when the world did not have any polar continental icecaps and global sea levels were high, the ocean deeps were filled with warm +15C dense salty oxygen-poor water creating the required conditions for global marine anoxia and the deposition of Sapropel, (biological carbon) in deep ocean muds of, for example, the Cretaceous Boreal Ocean. The implication here is clear, because warm sea water has a low dissolved gas carrying capacity, anoxia is preferentially associated with warm world conditions and the presence of sapropel in the Geological record is considered to be diagnostic of a Greenhouse World.
This dichotomy is a fundamental tenet of climate science. That climate can be in one state, either global cold – the Modern world, or global warmth – the Cretaceous world, but not in both states simultaneously. However this tenet is wrong and Geology proves that it is wrong. It is indeed possible to have a world with a massive continental polar ice cap, an Icehouse World diagnostic, and simultaneously anoxic prone warm water ocean deeps, a Greenhouse World diagnostic, and that world was the Carboniferous period.
Imagine a world with no South Atlantic Ocean, instead South America is joined directly to Africa, a world with no Southern Ocean, instead Antarctica is joined directly to Australia and also no Indian Ocean with instead the Indian landmass (along with Madagascar) filling the jigsaw puzzle gap between South America/Africa/Arabia and Australia/Antarctica. This southern continent is called Gondwana by Geologists. Imagine this gigantic Gondwana continent covered with an ice sheet that at its maximum extended from the South Pole across an area equivalent to all of Antarctica, Southern Australia, India, Madagascar, south & east Africa and southern South America combined. This continental icecap existed throughout the Carboniferous period. The modern world’s single polar ice continent of Antarctica is puny in size compared to this ice monster.
Victorian geologists were very interested in the Carboniferous period; the coal won from these rocks powered their industrial world. Studies of the Carboniferous strata in north Yorkshire demonstrated the existence of Cyclothems, repeated patterns of marine sedimentation that start with a coal seam, the remains of an equatorial forest being drowned and then often overlain by marine limestone. The limestones were then in turn overlain by river delta sediments as the coast moved seaward and the shallow sea retreated. Eventually the swamp forests regrew and another coal seam was created. The Victorians recognised that this rhythmic depositional cycle seen in the Yoredale deposits of Yorkshire was controlled by eustatic sea level change. That is global sea level variations controlled by the waxing and waning of a major continental icecap. We now know that the icecap responsible for the Carboniferous cyclothems was located on the Gondwana continent.
So the deep oceans of the Carboniferous world were filled with cold oxygenated seawater created by the katabatic winds of the Gondwana icecap, just like those from the modern world’s Antarctica? Well no actually the deep ocean of the Carboniferous world was anoxic just like the later Cretaceous ocean. Again thanks to the Victorian geologists who studied the Culm deposits of Devon they recognised that the Carboniferous Culm contained radiolarian chert, pseudomorphs of calcite and abundant organic carbon. They concluded correctly that Culm was a deep ocean deposit, and although they did not recognise the true size of the ocean they were studying, we know because of their work, that the muds were bathyal sediments deposited below the carbonate compensation depth far from land. The carbon content of Culm proves that the Carboniferous world ocean was anoxic and that abundant marine sapropel was created and deposited in Carboniferous marine sediments which now form part of the oil and gas shale resource which supplies the hydrocarbon fuel used to power our modern industry and commerce.
So how can we resolve this paradox of the Carboniferous with its simultaneous continental icecap of Gondwana and an anoxia prone global ocean? In Geology, the present is often the key to the past, and we have a key to unlock this conundrum. That key is the modern Red Sea.
The Red Sea is situated in the northern hemisphere tropics between Africa and Arabia. Under modern climatic conditions, located beneath the Hadley Cell, the Red Sea experiences high insolation, high evaporation and low fresh water input. These features combine to produce a Red Sea marine bottom water with the highest temperature (21.7C) and salinity (40.6 psu) in the modern world, even with its current low carbon dioxide atmospheric conditions.
Although the outflow volume of Red Sea high temperature bottom water into the Indian Ocean does not impact the modern deep water temperatures of the World Ocean, the key point is that Red Sea deep water produced under a modern tropical climate has a higher density at 1028.579 kg/m3 than any of the cold deep water currently produced in Antarctica by the modern world’s polar climate. For example Antarctic Bottom Water has a minimum temperature of -0.8C, a peak salinity of 34.6 psu and a consequent density of 1027.880 kg/m3.
If these two bottom waters, cold oxygenated polar deep water and warm high salinity low-oxygen carrying tropical bottom water, were allowed to meet, the density stratification principle requires that the densest marine water will occupy the deepest part of the ocean. Red Sea bottom water is denser than the coldest water Antarctica can produce. In a straight contest between the Red Sea and the Weddell Sea, the Red Sea wins every time.
So consider now the Carboniferous period with its shallow tropical seas and vast coastal equatorial coal swamps and remember that half of the surface area of our planet is located between 30 degrees North and 30 degrees South. The shallow seas of the tropics are huge solar energy collectors producing warm dense marine brines. Even in the Carboniferous with its gigantic Gondwana icecap the world was warm because in Oceanography marine water salinity trumps marine water temperature every time.
The Carboniferous shows us that with open ocean conditions the natural state of the world’s climate is as follows-
A polar continental icecap that produces cold oxygenated mid-level ocean water. This sea water is less dense and therefore is layered above the warm dense saline and anoxia-prone tropical water of the bathyal ocean depths.
I leave you with this conclusion. The Carboniferous was a warm ocean world, with low gas solubility in the deep sea. This produced an atmosphere suitable for land plants as they had an abundance of carbon dioxide gas to consume. Not for nothing does this period of Earth’s geological history have as its name the Carboniferous and yet in the mid-ocean above the deep abyssal anoxia, the pelagic fish also had an abundance of dissolved oxygen to breathe thanks to the presence of the Gondwana icecap and its coastal latent heat polynya.
This essay proposes that a fundamental tenet of climate science, that the world’s climate can be in one of two separate and distinct modes, either the Icehouse world or the Greenhouse world, is false.