[jeffreyH (OP)]

Deuterium in the ice cores. Note that this is an indicator of CO2 levels.
http://earthguide.ucsd.edu/virtualmuseum/climatechange2/07_2.shtml

[jeffreyH (OP)]

Virtually nobody makes the connection with deuterium. Strange that. Of course we can't put a tax on heavy water trading, can we?

[jeffreyH (OP)]

Depends upon the heavy water vapour concentration in the atmosphere.

[chiralSPO]

Depends upon the heavy water vapour concentration in the atmosphere.

The heavy water vapor concentration in the atmosphere depends on the temperature. Not the other way around. That is why deuterium content is used to measure temperature indirectly.

[chiralSPO]

Depends upon the heavy water vapour concentration in the atmosphere.

The heavy water vapor concentration in the atmosphere depends on the temperature. Not the other way around. That is why deuterium content is used to measure temperature indirectly.

Are you saying that when temperature increases the lighter hydrogen rises leaving the deuterium at lower levels and so at a greater concentration?

My understanding is that the H/D isotope ratio of the snow is determined by the H/D ratio of the water evaporating from the oceans, lakes and rivers. D₂O and HDO have slightly lower vapor pressures than H₂O, but the difference is diminished as temperatures increase. I have attached a screenshot of a figure from Journal of Chemical and Engineering Data, Vol. 26, No. 3, 798 7. This shows that at at 15°C the vapor pressure of H₂O is about 18% higher than that of D₂O. At 19°C, this drops to about 17% (small but statistically very robust). At the extreme ends reported in the diagram the difference is more than 20.4% at 6.5°C, and just over 6% at 89°C.

[chiralSPO]

So what causes the ratios in the oceans, rivers and lakes to change?

Very little. Living organisms may have enriched the D% of surface waters ever-so-slightly, because photosynthesis consumes H₂O slightly faster than it does D₂O, but there is SO MUCH water on Earth, and SO LITTLE of it contains D, that I wouldn't think this is a major factor.

[jeffreyH (OP)]

You missed the point. The ratio changes. What causes the ratio to change.

[chiralSPO]

You missed the point. The ratio changes. What causes the ratio to change.

I thought I addressed that.

The ratio is effectively unchanged within the sea. However, the ratio in the water vapor in the atmosphere is determined by the surface temperature. It is this water vapor that forms the snow that forms the ice that is measured in the ice core as a proxy for the surface temperature.

See here for a better descriptions than I can give myself:
https://www.scientificamerican.com/article/how-are-past-temperatures/
http://www.antarcticglaciers.org/glaciers-and-climate/ice-cores/ice-core-basics/
http://www.iceandclimate.nbi.ku.dk/research/strat_dating/annual_layer_count/ice_core_dating/
http://www.iceandclimate.nbi.ku.dk/research/past_atmos/past_temperature_moisture/fractionation_and_temperature/

[puppypower]

How does this explain the cycles in the ice cores?

The ice in the cores is from compressed snowfall. So you can think of it like sedimentary rock: the earliest snow has become the deepest ice, and the most recent snow became the ice near the top (so this establishes the timeline). Then, because the ice was deposited as snow, we know that the water had become vaporized, redistributed and then fell as snow. Therefore the ratio of the H/D isotopes in a given part of the ice core is reflective of the H/D ratio in the atmosphere at a given point in time, and this serves as an indication of the temperature of the surface water around the globe when the snow formed.

One problem with this is the vapor pressure of heavy water is lower than that of regular water, with tritium having a lower VP than deuterium. For each layer of snow the heavy water tends to accumulate.

H2O: 3.165 kPa (25 °C) [808]; 611.657 Pa (273.16 K, M.Pt.)
D2O: 2.734 kPa (25 °C) [808]; 659.893 Pa (276.95 K, M.Pt.)
T2O: 2.639 kPa (25 °C) [808]; 662.388 Pa (277.64 K, M.Pt.)

[jeffreyH (OP)]

If we freeze heavy water it will sink in H2O. As oceans cool there is likely to be less heavy water at the surface. This is just buoyancy. Also there will be less of it available for evaporation. So then what is it about water vapour as a whole that makes it a greenhouse gas?

[alancalverd]

The molecular weight of H2O and the hydrogen bond make it uniquely important.

As the lightest major constituent of the atmosphere, water appears at all levels with a maximum concentration that increases with temperature - an inherent positive feedback in the heating cycle.

The H-O-H bond angle allows the monomer to absorb infrared radiation over a vast and almost continuous spectrum compared withthe other gases, and it can form temporary dimers, trimers and hexamers with further absorption bands.

Uniquely among atmospheric gases it can exist in all three phases simultaneously at every level, with enormous energy inputs and outputs associated with each phase change.

As a liquid (cloud, rain, fog) water has a specific heat capacity around ten times that of any other constituent of air, so it is the principal means of heat distribution around the globe.

75% of the earth's surface is liquid water  and all the rest is either wet to some extent,or covered with frozen water.

So the entire process of solar heating, radiative cooling, reflection from cloud and ice albedo, and distribution of atmospheric energy around the planet, is dominated by water.  And the specific heat capacity of the oceans is about 5 times that of dry land surface.
 

[chiralSPO]

If we freeze heavy water it will sink in H2O. As oceans cool there is likely to be less heavy water at the surface. This is just buoyancy. Also there will be less of it available for evaporation.

While it is true that D₂O ice is denser than water, I don't think that this proposed mechanism of D₂O depletion at the surface is likely. Fewer than 0.02% of hydrogen atoms in the ocean are deuterium, and HDO and D₂O have nearly identical physical and chemical properties with H₂O, so you would never find spontaneous generation of a pure D₂O iceberg out of >99.9% H₂O. I can't say too much more about this because I do know that the ocean is not perfectly mixed (there are salinity and temperature-related density gradients throughout), but I am quite confident that there is no significant separation of D₂O in the oceans due to density or crystallization etc.

So then what is it about water vapour as a whole that makes it a greenhouse gas?

Water vapor absorbs strongly in the infrared region, which is where most of the blackboday radiation coming from the Earth is (by energy). This is the same reason that CO₂, CH₄, SF₆ etc. are greenhouse gases. See the attached diagrams.

[jeffreyH (OP)]

Where did I mention spontaneous D2O icebergs? That would be ridiculous.

[puppypower]

Where did I mention spontaneous D2O icebergs? That would be ridiculous.

When I mentioned the vapor pressure of light and heavy water, I was thinking more in terms of ice core samples. Each spring thaw, the light water will evaporate and sublime easier, than the heavy water. This should cause a slight concentrating affect where heavy water accumulates and then gets covered by a new layer.


Another consideration with water, is water has been found in very large pockets, beneath the crust of the earth; upper mantle. One such deposit, the size of the Arctic ocean, was found under SE Asia. There is a continuity of water from the upper mantle, through the crust, into the oceans and then into the atmosphere. In my opinion, these are integrated. A seepage of sub-crustal water could heat the oceans and create an El Nino affect causing shifts in climate.

Based on research into even more extreme phases of water, it also appears likely that water exists, from the surface, all the way into the metallic core of the earth. Water at the conditions of the earth's core; temperature and pressure, form an exotic metallic water phase. This metallic water has a density of 3-4 times normal water.

As we lower pressure and temperature, moving outward from the metallic core, into the outer core and lower mantle,  water changes phase into an ionic phase. Metallic water would be a good conductor of the currents flowing through the iron core. But as an ionic phase, water becomes a resistor. Studies have shown that the core of the earth rotates faster than the surface. The metallic to ionic water phase boundary, by going from electron conductor to resistor, generates enough heat to overcome the viscoelastic adhesion, allowing the faster core rotation to perpetuate.

As we move up the mantle toward the crust, conditions change and the ionic water phase become a superionic phase. This is a nasty phase of water, that is very explosive, when subjected to sudden changes of pressure. It may play a role in allowing the crust to slide on the mantle and vent pressure via volcanoes.

In the crust, water exists as a hydrothermal phase, where water becomes an excellent solvent for all minerals and all organic materials. In fact, hydrothermal water can decompose complex organics into CO2. Hydrothermal could be a large source of natural CO2. The surface water exists in the standard phases of solid, liquid and gas.

The impact of the sun is to cause surface heating and water evaporation. This result of water evaporation is positive charge accumulates in the atmosphere. This is connected to hydrogen bonding. The net affect is a solar induced potential, in the atmosphere, all the way to the iron core, mediated by the various phases and continuity of water. The solar induced potential will oxidize the iron in the core to form iron oxide(s); loadstone. The conduction of electrons, to the surface (and hydrogen protons downward), is reflected in the slight alkaline pH of the oceans; ocean has a slight negative charge.

The impact of CO2 is more localized to the surface. While the impact of the water goes from the atmosphere to the core. The CO2 can also impact the oceans, since CO2 dissolved in water forms carbonic acid. The impact of the carbonic acid, added to the oceans, is to enhance the potential with the core. Bigger green house gas induced storms can help discharge electrons via lightning.

Seismic studies of the earth have shown that the earth is denser north-south, compared to ease-west. The bulge of the earth at the equator, is composed of less dense materials (as well as centrifugal forces).  The equator is the maximum solar heating zone, where the electron conduction to the surface (hydrogen proton inward)  is at a maximum.

The two most abundant elements of the earth are iron and oxygen. The iron is mostly localized to the core. The oxygen is continuous from the atmosphere to the core; from O2 in the atmosphere to H2O on the surface, to oxides in the crust and deeper inside the earth.

The impact of O2 in the atmosphere is the same as solar heating; electro-positive impact.  The formation of life and photosynthesis amplified the potential with the core by adding O2 to the atmosphere. Photosynthesis will also remove CO2 which limits the acid impact on the oceans, moderating the impact of the O2.

I will not go into how life is integrated to the sun and earth via the water.
 

[chiralSPO]

Where did I mention spontaneous D2O icebergs? That would be ridiculous.

Sorry, that's how I interpreted this:

If we freeze heavy water it will sink in H2O. As oceans cool there is likely to be less heavy water at the surface. This is just buoyancy. Also there will be less of it available for evaporation.

I'm glad we agree that D2O icebergs would be ridiculous

[jeffreyH (OP)]

Where did I mention spontaneous D2O icebergs? That would be ridiculous.

Sorry, that's how I interpreted this:

If we freeze heavy water it will sink in H2O. As oceans cool there is likely to be less heavy water at the surface. This is just buoyancy. Also there will be less of it available for evaporation.

I'm glad we agree that D2O icebergs would be ridiculous

LOL