[TheWasteLand]

I know nothing about ice cores and temperature measurement, but a quick google turned up this NASA link which you might find interesting:

Paleoclimatology The Ice Core Record

The relevant bit seems to be this:

"As with marine fossils, the ratio of oxygen isotopes in the snow reveals temperature, though in this case, the ratio tells how cold the air was at the time the snow fell. In snow, colder temperatures result in higher concentrations of light oxygen."

There is another article on the subject of oxygen isotopes:

Paleoclimatology The Oxygen Balance

[Pearls Before Swine]

"...the ratio of oxygen isotopes in the snow reveals temperature..."

They aren't measuring trapped gas in the sense of dissolved gas. They are measuring the isotope ratios of the oxygen in the ice, which can't diffuse away from its original location, because its solid, not gaseous.

You had me wondering for a moment, though.

[y2gordo]

Okay, so they use the oxygen isotope ratio in the snow to reveal the temperature, which makes sense, and look at the levels of dissolved gasses within ice layers to get a picture of the atmosphere at that moment in time. Diffusion would still throw off results, and unless they account for this, they have a significant error to deal with as they attempt to relate that atmosphere to today. Furthermore, as the ice compacts, the layers become indistinguishable which means there is probably some exchange of oxygen isotopes between layers, not to mention what would occur as the ice very slowly flows over 100,000 years or if there was a period of warming that melted some layers away.

I'll have to read more about this, but something about ice core drilling never seemed right to me.

///@\\\