The Vostok, Antarctica ice core is a high altitude, inland ice core.
It formed from snow, that came from water vapor, that originally came from all of the Southern Hemisphere oceans, so should represent the average Southern Hemisphere temperature.
A Russian team has been establishing a chronology of deuterium from snow-cores near the Vostok, Antarctica station.
Deuterium (2H) concentrations in ice cores are used as a proxy of the temperature at the time the ice formed.
Deuterium is a heavy hydrogen isotope that is considered stable.
It does not decay.
Below are explanations of how D2, and other isotopes, are used as temperature proxies in ice cores:
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The connection between deuterium and atmospheric temperature:
(1) Isotopic ratios of oxygen-18 (18O) and deuterium (2H) in snowfall are temperature-dependent.
A strong correlation exists between the average temperature and the average isotopic ratio of 18O to 2H in precipitation.
Vostok ice cores tell us two things:
(1) At times it’s been hotter in the past, and
(2) At times temperatures in the past have risen faster than they have since the 1800’s.
Deuterium measurements from 8 meters to 3,310 meters deep, of the Vostok ice-core, indicate the temperature of the nearby atmosphere from 1800 back to 421,000 BC.
Deuterium in the most recent layers of the Vostok Ice Cores reveal no unusual warming in the past 8,000 years, in spite of the CO2 rise in the last century.
Marcott 2013 shows temperatures dropping -- more than a 1 degree C. drop from 5000 BC to about 1800 -- while CO2 levels barely changed.
From 1800-2000, the Marcott 2013 reconstruction shows only a +0.2 degree C. increase in temperature in spite of over a 100+ ppm increase in CO2.
CO2 rises from a minimum level of 180 ppm in the Vostok ice core record, to 400 ppm today, with no significant warming effect.
From the Vostok data, our present climate is about 2 ⁰C below the warmest of the last 420,000 years, and about +6 ⁰C above the coldest.
There is strong evidence from ice cores that the global temperature drives the atmospheric CO2 level, with a lag of hundreds of years, rather than the atmospheric CO2 level driving the global temperature, as the global warmunists claim today.