Ice

This is a great rebuttal of the whole YDIH.

Specifically regarding the possibility of air bursts, (0) says this:

The firestorm began in 2007 when Richard Firestone and numerous colleagues proposed that it was a comet strike of “multiple ET [extraterrestrial] airbursts along with surface impacts” that occurred at 12,900 years ago that initiated the YD.”23 The paper was full of impressive evidence gathered from 10 sites where a carbon-rich layer (referred to as the “black mat”) marked what they claimed was the end of the Clovis culture in North America: “The in situ bones of extinct Pleistocene megafaunas, along with Clovis tool assemblages, occur below this black layer but not within or above it.” They reported that sediments directly below the black mat were enriched in magnetic grains, iridium, magnetic microspherules, charcoal, soot, carbon spherules, glass-like carbon containing nanodiamonds and fullerenes containing extraterrestrial helium. They explained that the soot, charcoal, spherules, etc. were the result of extensive and intense forest fires initiated by the airbursts. Melting of the Laurentide Ice Sheet would have dumped copious quantities of melt water into the Atlantic, thereby disrupting the density currents and bringing on the cooling.

Over the years, however, support for the YDIH has been undermined. Nearly every aspect of the original evidence has been challenged by a host of scientists in various fields. Only one of the indicators, iridium, has been commonly used as an impact marker, and the iridium data have not always been reproducible. The iridium concentrations can also be explained by terrestrial origins.24, 25 Nor do nanodiamonds require extraterrestrial events. The absence of any impact craters at the beginning of the YD worldwide is the most disconcerting evidence against YDIH, as is the lack of control for the age of sediments/black mat at or near the YD boundary.

Elsewhere it remarks that even should air bursts be the case, from a massive comet breaking up or multiple comets breaking up, there still must be corresponding craters of the size of Meteor crater to correspond to the scale of the proposed devestation

In addition to these arguments against the YDIH, it is difficult to imagine how an airburst/impact could annihilate the North American mammal megafauna and Clovis culture and initiate huge wild fires, without leaving any evidence in the way of massive flooding or impact features. Vance Holliday and his colleagues argue that “no physical mechanism is known to produce an airburst that would affect the entire continent.”27 They also point out that any comet strike large enough to affect an entire continent would leave a detectable crater even if it struck the ice sheet. To get around this glaring problem, the Firestone group proposed that the comet broke up upon entry into earth’s atmosphere. But according to physicist Mark Boslough and his colleagues,28 that would produce “more than a million Meteor craters” (the size of the crater in central Arizona) based on the comet size postulated by Firestone and his cohorts.29, 30

While the Firestone group claims that the comet strike was responsible for the disappearance of the 37 mammal megafauna genera specifically in North America, extinctions occurred on other continents, most notably South America, where at least 52 mammal genera disappeared. And not all those genera disappeared synchronously at the YD boundary! Instead, megafauna extinctions on continents and islands seem to correlate with the arrival of humans. The thinking goes that these huge megafauna would have had no reason to fear humans, and were probably easy pickings for the newly arriving hunter-gatherers. Scientists have also been a bit incredulous that a comet strike could wipe out all the megafauna as far south as Patagonia, while leaving mammoths alive and well on St. Paul Island, Alaska until 3,700 years ago

(0) https://www.skeptic.com/reading_room/defant-analysis-of-hanc...

It is a circular argument that extinctions coincide with arrival of humans: that humans arrived at that time is an assumption, and one that is losing credibility. Anyway, as noted, you also need to explain why humans didn't wipe out African megafauna (no, wariness doesn't), and also why Clovis culture disappeared suddenly across the continent. One may doubt they starved immediately after wiping out the last of their prey.

You can quibble all you like about nanodiamond crystallography and carbon granules, but sharp platinum peaks at 200x above background, found at dozens of sites, need better explanation. It is curious--telling, even--that critics dwell on osmium isotope ratios and never mention platinum.

As was explained in connection with the K-T extinction event that attracted similar derision from geologists who had to retire before it got a fair hearing, anything that happened, can.

Another possibility is abrupt changes in the flow of large bodies of waters affecting ocean circulation causing climate changes. One hypotheses is as the glaciers retreated the waters of the Missisppi river switched to flowing out of the St Lawrence river affecting North Atlantic currents.

This article seems to combine the lost civilization pseudo-science of Randall Carlson and Graham Hancock with the myopia of catastrophic climate change alarmists that ignore paleoclimate evidence. This evidence is captured in the LR04 Benthic Stack data and is fully supported by ice core and other data sources.

Modelling the fluid dynamics following the termination of the last glacial maxima is non-trivial but the broad strokes are well understood. The 120 meter change in sea levels during the 100-kyr glacial cycles are associated with predictable ice sheets, post-glacial rebound, glacial lakes, and meltwater pulses. Something similar to Glacial Lake Missoula occurred after each termination.

What we should expect to see moving forward is the start of the re-accumulation of glacial ice timed to the Milankovich Cycles. The question is how big a monkey wrench does human forced atmospheric CO2 throw into the established cycles.