The mainstream chronologies and temperature reconstructions derived from the Greenland ice cores are primarily based upon the analysis of “δ18O” [aka “delta 18O”] values.
The first step towards calculating a “δ18O” value is to determining the ratio of Oxygen18 to Oxygen16 found in a sample of water extracted from the ice core.
The “δ18O” value then calculated as a relative deviation from a selected standard value.
A four year benchmarking exercise clearly shows the annual variability in “δ18O” values and their close association with temperature on the Greenland ice cap at an altitude of about 3,200 metres.
This very limited benchmark clearly establishes for the early 1990s:
1) A normal range of “δ18O” values between -45.5 and -25.5
2) A minimum “δ18O” value of -45.5 during the winter.
3) A maximum “δ18O” value of -25.5 during the summer.
4) A midpoint “δ18O” value of -35.5 for an average year.
A ten metre sample from the Central Greenland ice core Crête [which is deemed to cover the period 1939 to 1956] is very supportive of the benchmark midpoint “δ18O” value of -35.5 that was established for the early 1990s.
However, the minimum and maximum values are less extreme and this indicates that annual ice core samples tend to merge towards their midpoint “δ18O” value with depth.
Having established benchmark values for “δ18O” and completed a reality check on the Greenland Crête ice core we are now equipped to analyse the premier ice core from Greenland: NGRIP.
The most surprising aspect of the NGRIP “δ18O” values [graphed in black above] is that they fall almost entirely within the GRIP benchmark “normal range” of -45.5 to -25.5.
Initially the NGRIP ice core “δ18O” are close to the benchmark midpoint “δ18O” value of -35.5.
The subsequent plunge into an oscillating range between [roughly] -45 and -37 has been deemed by the mainstream to represent the last “ice age” with a midpoint annual temperatures [based upon the benchmark] ranging from -34C to -50C.
However, the NGRIP data does also allow for an alternative hypothesis where the plunge in “δ18O” values is associated with a “warmer climate” where snowfall was predominately limited to winter.
The two opposing scenarios should create signatures that are easy to differentiate in the ice core.
The mainstream “ice age” scenario is associated with huge annual ice accumulations that fed the vast ice sheet covering parts of North America. This implies that any dust entrapped within the snow during the “ice age” would be sparsely distributed and the associated ice core should be visibly “clear”.
The alternative “warmer climate” hypothesis is associated with an ice core that is visibly “dirty” because any entrapped dust would become concentrated in the remnant icecap during the summer melt season. The remnant ice cap may have partially retreated to the uplands of Greenland or have been confined in Greenland’s central lakes as residual multiyear ice.
The NGRIP “δ18O” data indicates that the climate transition occurred approximately halfway down the ice core at a depth of about 1,500 metres.
Surprisingly, the Greenland GISP2 ice cores provide a visual clue that the NGRIP ice core might be “dirty” below 1,500 metres.
The Greenland GRIP ice core from 3,029 metres also suggests that the NGRIP ice core might be “dirty” below 1,500 metres.
The following radar image of the Greenland ice cap shows that [roughly] the lower half of the ice cap is “dirty” because it produces a stronger radar reflection [lighter in the image].
The following radar image of the Greenland NGRIP ice cap definitively confirms that the lower half of the NGRIP ice core is “dirty” because it produces a strong radar reflection.
This 150 km long section of radar data collected around NorthGRIP shows a flat bedrock (the thick dark line close to the bottom of the picture is the bedrock echo) but undulating internal layers. The shape of these layers is created by changing basal melt rates along the sections. Where the layers dip down the basal melt rate is highest. Credit: CReSIS
Unfortunately, for the mainstream, the evidence is firmly stacked against any “ice age” being recorded in the Greenland ice cap because the “dirty” evidence shows the climate was warmer before the Holocene.
Anybody left wonder about the final upturn in the NGRIP “δ18O” to -32 should remember that NGRIP drilled to a depth of about 135 metres below sea level and encountered water. The “δ18O” of -32 indicates that this was melt water with an appropriate “δ18O” for mid-July 2003.
Unusually, there is melting at the bottom of the NGRIP core – believed to be due to a high geothermal heat flux locally.
On July 17th 2003 the drilling at NorthGRIP reached bedrock at a depth of 3084.99 m , and the drilling was terminated.
Therefore, the NGRIP ice core “δ18O” data does not provide any supporting evidence of an “ice age” and the NGRIP ice core data does not terminate in the Eemian interglacial.
Overall, the mainstream narrative represents a massive “confirmation bias” failure.
The density of ice approaches a peak of 917 kg/m3 in ice cores at a depth of about 200 metres and [therefore] can be disregarded as an issue when analysing the radar images below this depth.
When a density of 830 kg/m3 is reached at a depth of approx. 80 m, all air passages between the crystals are sealed off so that air only exists in closed bubbles. This defines the transition from firn to ice. With increasing depth, the air in the bubbles is compressed and the density approaches 917 kg/m3 which is the density of glacier ice. It is impossible to compress the ice any further, and at greater depths, the thinning of the layers only happens through deformation of ice by ice flow.
Chronology: 1 – Ice Cores