Primeval Greenland lake found buried beneath a mile-thick slab of ice

Feb 19, 2020
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Back in the late Eocene (~34 Myr-ago, the climate was mild and the pCO2 was more than double what it is now. When the pCO2 dropped below a threshold value of about 750 ppm, the polar ice sheets began to form. This may have been when the now-buried lake was there.
 
Jan 3, 2020
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Back in the late Eocene (~34 Myr-ago, the climate was mild and the pCO2 was more than double what it is now. When the pCO2 dropped below a threshold value of about 750 ppm, the polar ice sheets began to form. This may have been when the now-buried lake was there.
Maybe - they will disappear within 1 kyrs [ https://www.sciencealert.com/greenland-s-ice-sheet-will-disappear-over-the-next-1000-years-nasa-model-shows ], and the man made CO2 release that forced that result has "only" pushed the CO2 from ~ 250 ppm [ http://www.realclimate.org/index.php/archives/2018/10/pre-industrial-anthropogenic-co2-emissions-how-large/ ] to 410 ppm [ https://www.climate.gov/news-features/understanding-climate/climate-change-atmospheric-carbon-dioxide ]. But of course that factor alone has a complex dynamic, since the global warming is 1,000 times faster than other observed.

Mostly, plate tectonic and so circulation regimes differed between now and then. And the casues and timing differed between the two land ice sheets (which contains the water that will increase sea levels and make more acute problems).

The Eocene is not only known for containing the warmest period during the Cenozoic, but it also marked the decline into an icehouse climate and the rapid expansion of the Antarctic ice sheet. The transition from a warming climate into a cooling climate began at around 49 million years ago. Isotopes of carbon and oxygen indicate a shift to a global cooling climate.[25] The cause of the cooling has been attributed to a significant decrease of >2,000 ppm in atmospheric carbon dioxide concentrations.
Global cooling continued until there was a major reversal from cooling to warming indicated in the Southern Ocean at around 42–41 million years ago.[26] Oxygen isotope analysis showed a large negative change in the proportion of heavier oxygen isotopes to lighter oxygen isotopes, which indicates an increase in global temperatures. This warming event is known as the Middle Eocene Climatic Optimum. The warming is considered to be primarily due to carbon dioxide increases, because carbon isotope signatures rule out major methane release during this short-term warming.
Cooling continued throughout the rest of the late Eocene into the Eocene-Oligocene transition. During the cooling period, benthic oxygen isotopes show the possibility of ice creation and ice increase during this later cooling.[20] The end of the Eocene and beginning of the Oligocene is marked with the massive expansion of area of the Antarctic ice sheet that was a major step into the icehouse climate.[29] Along with the decrease of atmospheric carbon dioxide reducing the global temperature, orbital factors in ice creation can be seen with 100,000-year and 400,000-year fluctuations in benthic oxygen isotope records.[40] Another major contribution to the expansion of the ice sheet was the creation of the Antarctic Circumpolar Current.[41]
[ https://en.wikipedia.org/wiki/Eocene#Greenhouse_to_icehouse_climate ]

The presence of ice-rafted sediments in deep-sea cores recovered from northwest Greenland, in the Fram Strait, and south of Greenland indicated the more or less continuous presence of either an ice sheet or ice sheets covering significant parts of Greenland for the last 18 million years. From about 11 million years ago to 10 million years ago, the Greenland Ice Sheet was greatly reduced in size. The Greenland Ice Sheet formed in the middle Miocene by coalescence of ice caps and glaciers. There was an intensification of glaciation during the Late Pliocene.[3] Ice sheet formed in connection to the uplift of the West Greenland and East Greenland uplands. The Western and Eastern Greenland mountains constitute passive continental margins that were uplifted in two phases, 10 and 5 million years ago, in the Miocene epoch.[A] Computer modelling shows that the uplift would have enabled glaciation by producing increased orographic precipitation and cooling the surface temperatures.[4] The oldest known ice in the current ice sheet is as much as 1,000,000 years old.[5]
[ https://en.wikipedia.org/wiki/Greenland_ice_sheet ]
 
Feb 19, 2020
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Professor Larsson has collected, accumulated and itemized an abundant pile of "google" type evidence that does not negate the fact that the polar ice sheets began forming when the geological and geochemical evidence shows that the pCO2 began dropping about 34 Myr ago. The climate back then was not devastatingly hot. The marine carbonate plankton were thriving and life on land was lush. A fact?

The question asked here was about when this lake formed. If Professor Larsson has another suggestion he should tell us what it is and not go off in another direction for another purpose.
 

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