It should also be pointed out that at the time of Noah's flood (roughly 4,300 years BP), there is no large spike of volcanic markers.
If our Bible is true when it tells us Noah's flood was a real and global event that, according to the Biblical chronology, happened about 2,345 B. (roughly 4,300 years BP), and if the GISP2 and GRIP data are also true, the only possible explanation is that the bulk of the material which constitutes the basement of the present Greenland Ice Sheet somehow survived that flood.
Actually, it would have needed to survive two floods, as the Earth was also flooded before the six-day regeneration.
Whether the ice was floated off its anchor rock by Noah's flood, or remained stuck fast to the rock and was submerged by the flood waters, would make no difference.
In either scenario the top layers would have been washed over by fresh (not salt) water, resulting in a "melt" layer or hiatus in accumulation, in the former case by rains; in the latter case through inundation by a rapidly rising fresh water lens.
The establishment of this 100,000 year BP record of Earth's atmospheric history in the ice has been fairly well calibrated with proxy dating methods.
The annual layer counting of visible ice stratification, when compared to radiocarbon extracted from the CO2 gas trapped within the ice and other measurement techniques, has yielded an age error factor of about 2% from present to 11.64 years BP; about 5% to 17.38 years BP; and 10% to about 40,000 years BP.
For what it is worth, even with all the millions of tons of so called "greenhouse gases" that have been added to the atmosphere over the last two centuries, the measured greenhouse effect has so far only increased average global temperatures by less than about half a degree C of what it was before Noah's flood.
So it is safe to conclude that the world between Adam and Noah was relatively much warmer compared to our world today.
The ion concentrations reflect relative levels of global volcanic activity at given intervals across the time line.
The information on the composite graphic reveals several very important things.
The top portion of the next graphic shows the global temperature trends across 18,000 years BP, determined by Paleoclimate proxy data.