Figure 3: Ice core records show atmospheric CO2 was lower than today for last 800,000 years. (niskanencenter.org)
Ice core records show there was a sharp rise in carbon dioxide in the atmosphere — a nearly 50 % increase — at the end of the last ice age. (sciencemediacentre.co.nz)
That would make ice cores a record of those specific locations rather than a broader measure of the sea where the evaporation occurred. (theinconvenientskeptic.com)