[meteorite-list] WHAT OCCURS IN A LARGE HYPERVELOCITY IMPACT ON AN ICE SHEET? PART 3

[E.P. Grondine]

Hola Listeros -

Four weeks ago, we pointed out that a major rise in sea levels and a major change in climate occurred well before the dates for what is widely and mistakenly called the Younger Dryas Boundary impact event. 

Three weeks ago we pointed out a geobleme in Canada that may or may not be associated with the Holocene Start Impact Event.

Two weeks ago we returned to consideration of the question of "What occurs in a large hypervelocity impact on an ice sheet?", and traced the water release.

This week we take a look at other climatic effects.

First off, there was not a persistent atmospheric dust load.
The larger mega-fauna survived the Holocene Start Impact Event, 
only to die from starvation due to the much later impact dust loading ca. 10,850 BCE.

As ice appears to have been hit and not the ground, it is to be expected that what would be released would be water, and not dust from the ground.
That would leave the dust from the impactor(s), but this would have been precipitated out of the atmosphere by the water vapor released in the impact(s).

The best current map of impactites from this cometary encounter may be found here:
http://www.uc.edu/news/NR.aspx?id=17831

Which map most likely elides the data from the impacts of several comet fragments, 
impacts which occurred at different times during the Holocene Start Impact Event.

Of course, the initial impacts of the Holocene Start Impact Event would have covered a fair part of the ice sheet with black dust,
which would have absorbed sunlight and led to ice melting.

Those melting waters, both initial and later, would have led to the further dispersal of the impactite dust.
Without further coring and detailed studies, the map of impactites shown above is known a priori to be of very limited use.

Which leads us back to consideration of the missing Grondine Minima, which we discussed earlier:

"We can see that the last ice age lacked a maxima of cold:
http://www.climate4you.com/images/VostokTemp0-420000%20BP.gif

Let us call this missing minimal temperature the "Grondine Minima". 
The discontinuity with earlier glacial cycles begins at about the same time as the first spike in neutrons between 20,000-10,000 BP."

Global Temperature:
http://www.ncdc.noaa.gov/paleo/pubs/alley2000/alley2000.gif
http://s90.photobucket.com/user/dhm1353/media/Holocene-1.png.html

Since atmospheric dust lading from an ice sheet impact 
could not account for continued melting, 
What accounts for the continued ice sheet melt, 
and the creation of Glacial Lake Agassiz?

The best hypothesis we have been able to come up with involves this mechanism:
http://www.chesapeakequarterly.net/images/uploads/siteimages/CQ/V12N4/p-7a.png

When cold water was released into the Pacific Current,
it lead to less warm moist air over the ice sheet.
That in turn led to less snow and ice,
which led to more sunlight being absorbed,
which led to further melting.

Later impacts may have released meltwater:
see slide 18 here for the timing of meltwater pulses:
http://slideplayer.com/slide/2808821/
Especially and carefully note that these are PULSES, and not continuous processes. 

se also slide 34 for a detailed pollen series for Eastern North America, in particular the data for the Ohio paleoclimates.

(For your viewing pleasure - an introduction to isolation and precession:
https://www.youtube.com/watch?v=oRdyNn1tB-E&index=1&list=PLmen0eQI4-Lof_GS8Amc9sysdRMrRYzps)


good hunting, all - 
E.P. Grondine
Man and Impact in the Americas