The Maths – LGM total ice volume

Extract from the book: The Post-Glacial Flooding Hypothesis

In a later paper, Lemieux (2017) had constructed a model to calculate the amount of LGM ice volume that is absorbed into the ground to become groundwater.

“Glaciations are known to have a large and long-lasting impact on groundwater flow. Several geochemical and isotopic studies have shown that water of glacial origin is still present in basins in North America and northern Europe that were formerly covered by ice-sheets. The presence of glacial water is commonly identified by low salinity, depletion in heavy isotopes such as 18O and 2H, high excess air, cold recharge temperature inferred from noble gases, and old groundwater age”.

Moreover, what the research article also provides is the evidence that the meltwater will recharge the groundwater under the landmass as it recharges it throughout the glaciers life-cycle and not just the end during the glaciers retreat.

 “Subglacial recharge of meltwater is the prevailing hypothesis of recharge of water of glacial origin during the Pleistocene. Ice-sheets can be partially wet-based due to basal friction and can release large volumes of subglacial meltwater. If the permeability of the ground is sufficient, it was put forward that meltwater could infiltrate into the subsurface under pressure exerted by the ice sheet showed that recharge of supraglacial meltwater could also occur below ice-sheets due to the presence of crevasses”.(Lemieux,2017)

The paper also concluded that “By the end of the glacial maximum (15 ky B.P.), the meltwater contents in the intermediate and lower aquifers are about 10 and 12.5%, respectively and in the same aquifers, meltwater has travelled about 50 and 75 km”.

Therefore, even BEFORE the ice cap retreated and completely melted, meltwaters had moved tens of kilometres into the surface and had partly recharged the aquifers.

The conclusion by Lemieux indicates that “The average infiltration/exfiltration fluxes range between 1 and 12 mm/a. Using mixed, ice sheet thickness-dependent boundary conditions for the subglacial environment, it was estimated that 15–70% of the meltwater infiltrated into the subsurface as recharge, with an average of 43%.”

Therefore, we can now return to our original meltwater calculation of 8.42 quadrillion tonnes of water for the Fennoscandia & U.K. Ice Sheet to give us an estimate of groundwater in the land at the end of the last ice age.

According to ‘Table 1’ The Fennoscandian and Great Britain ice sheet covered 9.18 106 KM2, which is equivalent to: 

  • 8.42 106 Gigatonnes of water / 9.18 106 km2, which gives us 0.92 Gt per km2
    • 0.92 Gt of water at a penetration rate of 43%, give us 0.4 Gt of water per km2
    • 0.4 Gigatonnes of water by U.K. landmass 242,495 km² give us 96,998 Gt of groundwater in the ground even BEFORE the start of the Meltwater pulses

Moreover, this water will be released at a rate of 1 – 12mm per annum and be at a depth of possibly 75km. Therefore, to release groundwater at a depth of 75km at an average rate of 6mm per annum would take 12,500 years – not the 1,200 years previously believed, which is just the surface meltwater from the latter stages of last ice age.

Location of Aquifers and recharge time depending on depth

More information on LGM Ice Volume can be found: https://youtu.be/j5LJ2sGcKOA