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The deep oceans drive the atmosphere

Posted By JoNova On June 12, 2010 @ 1:28 am In Global Warming | Comments Disabled

IMAGE: Warm layer of the pacific ocean rests on cold water

Ever wondered how the whole planet could suddenly “get warmer” during an El Nino, and then suddenly cool again? William Kininmonth has the answer. As I read his words I’m picturing a major pool of stored “coldness” (bear with me, I know cold is just a lack of heat) which is periodically unleashed on the surface temperatures. The vast deep ocean abyss is filled with salty and near freezing water.  In years where this colder pool is kept in place we have El Ninos, and on years when the colder water rises and mixes up near the surface we have La Ninas. The satellites recording temperatures at the surface of the ocean are picking up the warmth (or lack of) on this top-most layer. That’s why it can be bitterly cold for land thermometers but at the same time the satellites are recording a higher world average temperature, due to the massive area of the Pacific.

In other words, just as you’d expect, the actual temperature of the whole planetary mass is not rising and falling within months, instead, at times the oceans swallow the heat on the surface and give up some “coldness”. At other times, the cold stays buried deep down and the heat can collect and loll about on the surface.

William Kininmonth was chief of Australia‘s National Climate Centre at the Bureau of Meteorology from 1986 to 1998. Below, he describes how a vast pool of cold water filled the deep ocean abyss over 30 million years, and why this water and the currents that shift it have a major impact our climate. The so-called Bottom Layer is not just pockets or pools, it forms around Antarctica, then sinks and flows along the bottom all the way across the equator and into the Northern Hemisphere. Bear in mind the average depth of the ocean is around 4 kilometers, and yet almost all the water below a depth of 1000 m is around 4°C  or colder. The Antarctic Bottom Water itself is close to 0°C. The equivalent heat energy of the entire atmosphere is stored in just the top few meters of water. It gives us all some perspective on the relative importance of different factors affecting the climate. His thoughts are in response to the latest debate essay from Dr Andrew Glikson, so the figures 1 and 2 come from that article.

Kininmonth points out that small changes in the rate of the Thermohaline Circulation (also known as the Ocean’s Conveyor Belt)  makes a huge difference to all corners of the globe, and that the climate models make large assumptions about the flow of energy. Since the cold bottom layer was created by a kind of “Antarctic Refridgerator” (set into play by the circumpolar current) this colossal cold pool of water will presumably hang around until the continents shift. That’s quite a few election cycles.

Jo

Guest post by William Kininmonth

The deep cold abyss

IMAGE: Deep Ocean Abyss with cold bottom water

The deep ocean abyss forms as cold salty water sinks from Antarctica

Of particular interest to me was the second panel of his Figure 1(see below). It shows that the temperature of the deep ocean fell from 12°C  to 0°C ,  but without explanation.  Bob Foster has spoken of this regularly – the opening of Drake Passage and the isolation of the Antarctic continent from the warmer tropical surface temperatures by the Antarctic Circumpolar Current. This means that winter sea ice forms around the Antarctic coastline, and expels salt into the surrounding sea water which increases the salinity and density of the near freezing water under the sea ice. There is only one way for that cold saline water to go and that is down to form Bottom Water.

The diagram identifies the commencement of cold Bottom Water as about 50 million years ago and near 0°C temperatures being achieved about 30 million years ago as permanent glaciation appeared over Antarctica. Gradually the cold Bottom Water filled the ocean abyss because it is thermally isolated from the energy supply at the surface.

By 3 million years ago (see his Figure 6) the ocean below the mixed surface layer was filled with cold water and thereafter formation began to cool the surface temperature. Even today the cold ocean interior is being replenished as cold Bottom Water continues to form and the cold subsurface water is entrained or mixed into the surface mixed layer to regulate tropical surface temperatures. There is very little mixing of cold subsurface water under the western Pacific Warm Pool and surface temperatures are generally in the range of 30-31°C; over the eastern equatorial Pacific the rate of entrainment varies with upwelling and temperatures vary from as low as 22 °C (strong La Nina) to nearly 30 °C (El Nino).

Figure 1

Figure 1 (from Glikson’s post): Atmospheric CO2 and continental glaciation 400 Ma to present. Note the upper limit of glacial periods under atmospheric radiative forcing levels of ~500 ppm CO2. Top. Vertical blue bars mark the timing and palaeolatitudinal extent of ice sheets. Middle. Global compilation of deep-sea benthic foraminifera 18O isotope records from 40 Deep Sea Drilling Program and Ocean Drilling Program sites updated with high-resolution records for the Eocene through Miocene interval. Most data were derived from analyses of two common and long-lived benthic taxa, Cibicidoides and Nuttallides. Bottom. Detailed record of CO2 for the last 65 Myr. See Glikson’s original post for more detail and also IPCC AR4 Ch 6)

The importance of the ocean conveyor belt

The Antarctic Circumpolar Current is a central part of the global circulation pattern

Figure 2 (see below) is also of interest. At winter time in the poles, more infrared radiation is emitted to space than the solar radiation absorbed during summer. So the high latitudes are regions of net radiation  deficit. To maintain this condition requires continual transport of energy from the tropics by way of the ocean and atmospheric circulations.

Trenberth and Caron (J of Climate) have estimated that about 80% of the transport is by the atmosphere and the remainder by the oceans. If this ratio were to vary then the climate would be very different over middle and high latitudes. For example, if the Thermohaline Circulation were to decline in intensity then there would be less transport by the oceans and the polar seas would become colder; at the same time there would be less mixing of cold subsurface water into the tropical mixed surface layer and the western Pacific Warm Pool would expand causing more energy exchange with the atmosphere and more poleward transport of energy to warm the high latitude land surfaces.

Conversely, an increase in the Thermohaline Circulation would result in more warm water penetrating through the North Atlantic and Bering Seas to the Arctic Ocean but also more tropical upwelling of cold subsurface water, less energy exchange with the tropical atmosphere and cooler high latitude land surfaces as atmospheric transport declined.

The atmosphere and oceans are interacting fluids and it would be naive to expect the partitioning of poleward energy transport between the atmosphere and ocean circulations to remain constant.

Figure 2

Figure 2: Global temperature projections for mean September 1990-2009 relative to NASA’s baseline of 1951-1980, displaying concentration of warming in H2O vapour-low polar and desert regions. NASA GISS

Image Sources: Antarctic Currents Avsa. Small Globe in the first picture adapted from Oceania Maps.

ADDENDUM (from comments)

George suggests an interesting way of thinking about the ocean as only an electrical engineer could. It’s a novel model…

Comment #6  co2isnotevil : June 12th, 2010 at 5:35 am

If you examine the nominal temperature profile of the ocean, there are 2 inflection points, one near the warm surface waters and another about 1km down at about 4C. The region between them is the thermocline. The temperature profile is consistent with the thermocline acting as a layer of insulation between the deep ocean cold and the warm surface waters. At northern and southern latitudes, the thermocline breaks through to the surface and at the N pole and around Antarctica, the deep ocean cold breaks through to the surface. The 2 poles and their corresponding ice packs are thermally connected through the deep ocean, i.e. isotherms at temperatures of between 0 and 4C connect the poles through the deep ocean.

I like to think of the planet as storing energy in a similar way to energy storage in a capacitor. There is a cold plate (the deep ocean cold and polar ice caps) and a warm plate (the warm tropical surface waters) and a dielectric separating them (the thermocline). Energy is stored as a differential temperature between these plates and the average temperature of these 2 plates is the average temperature of the planet. This is more or less confirmed by noting that the temperature at the middle of thermocline is very close to the average surface temperature. There is a secondary boundary between the hot and cold pools of energy, which we observe as weather fronts and is where most of the energy transfer between these pools occurs.

An important consideration is that energy is stored as equal and opposite amounts of hot energy and cold energy, each relative to the average temperature of the planet, which in a way offset each other. It also means that the ocean can respond quickly to changes in incident energy as only the boundary (inflection point) between the warm plate and the thermocline needs to change. The temperature at the lower inflection point seems fixed by pressure and density considerations.

George

Michael Hammer adds:

A very interesting post. One thing which strikes me very pointedly is the negative feedback implied. If ocean current heat transport declines then that directly leads to an increase in atmospheric heat transport and vice versa. Yet again, what we see in naturally stable systems is a dominance of negative feedback loops. This contrasts so strongly with the warmists who see posiive feedback in everything to do with climate. Without the claimed positive feedback there is no AGW crisis.

UPDATE 2

Carl writes to tell me that he’s done a Danish Translation of this. Thanks Carl!

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