[lenticular]

No, speaking as a former glaciologist, that's not likely to be true. The parent poster is correct. Younger Dryas featured multiple advances and retreats, which is inconsistent with an impact. Multiple impact over many centuries just isn't that statistically likely, and we would see better evidence of it.

Instead, the most probably cause is freshwater pulses coming out of the melting Laurentide ice sheet changing circulation in the Atlantic. This is actually quite well supported.

Younger Dryas was also confined to the parts of the northern hemisphere, mainly in higher latitudes. A large enough impact to significantly alter climate would see the resulting particulates globally mix in the atmosphere, resulting in more uniform cooling.

Instead, the fact that it was confined to parts of the northern hemisphere also supports the freshwater pulse hypothesis, since it is only a change in the transport of heat from the tropics to the pole, not a change in total heat.

The fact that freshwater pulses from the Laurentide ice sheet caused so much cooling is actually a concern with climate change. It's possible that it could happen again with melting of the Greenland Ice Sheet, at least a weakened version of it (the Laurentide Ice Sheet dwarfed the GIS).

[pmayrgundter]

A report was published in Nature in spring of this year showing multiple lines of evidence for impact-related effects in the YDB layer in southern Chile:

"In the most extensive investigation south of the equator, we report on a ~12,800-year-old sequence at Pilauco, Chile (~40°S), that exhibits peak YD boundary concentrations of platinum, gold, high-temperature iron- and chromium-rich spherules, and native iron particles rarely found in nature. A major peak in charcoal abundance marks an intense biomass-burning episode, synchronous with dramatic changes in vegetation, including a high-disturbance regime, seasonality in precipitation, and warmer conditions. This is anti-phased with northern-hemispheric cooling at the YD onset, whose rapidity suggests atmospheric linkage. The sudden disappearance of megafaunal remains and dung fungi in the YDB layer at Pilauco correlates with megafaunal extinctions across the Americas. The Pilauco record appears consistent with YDB impact evidence found at sites on four continents."

https://www.nature.com/articles/s41598-018-38089-y

[lenticular]

That just means that there was an impact at around the same time. There's been numerous impacts like this that have been claimed to be the cause of Younger Dryas in the past. However, just because there was an impact doesn't mean it had anything to do with YD.

The Atlantic meridional overturning current shutdown from a freshwater pulse is much more parsimonious, and is exactly what we would expect from the physics of the Laurentide melt going into the Atlantic.

Impacts still don't explain the multiple advance and retreats during the Laurentide, but it is obvious why that would occur with the AMOC shutdown explanation:

Melting causes the AMOC to shut down, causing nothern hemisphere cooling. The cooling reduces melting, inducing the AMOC to start back up, increasing melting once again.

[pmayrgundter]

I accept part of what you're saying, which I believe is that the Laurentide melt was probably happening anyways, with the associated effects on the AMOC. Glacial oscillation are their own cycle, clearly.

But the YD impact scenario hardly seems irrelevant to the YD. I'm curious what other impacts you're aware of that you deem irrelevant.

The best candidate I'm aware of for the YD impact would possibly/probably be related to the Hiawatha crater [1], which is 31km after likely boring through a km or so of ice. This puts it amongst the largest impacts on Earth, e.g. since back to the Chesapeake/Siberian impact around 35mya, (if not beyond after the ice impact is taken into account, e.g. to Chicxulub) [2]. It's not solidly dated yet, but according to the authors the evidence at the site is consistent with an impact during the Pleistocene, and they even say it may still be hot, despite being packed in ice!

If we're talking about the same event, with evidence across 24-53 sites on 4 continents that includes continent-wide fires, impact winter and floral and megafaunal extinction, then I'd be hard-pressed to see how this doesn't have to do with the main climate change event of that period; that's the definition of what makes the YD significant: the drastic floral changes (e.g. of Dryas octopetala) at the boundary. The impact seems a more likely candidate cause for the abrupt global changes.

Or put another way, I think the question is back to you of how changes in the AMOC during the YD somehow caused the characteristic extinctions and charcoal residue observed in southern Chile at the YDB.

The contemporaneous, global inferno and impact winter going seems too much to chalk up to coincidence. That's where I see the parsimony breakdown for a simple Laurentide melting/AMOC change being responsible for the YDB.

[1] https://advances.sciencemag.org/content/4/11/eaar8173

[2] https://en.wikipedia.org/wiki/List_of_impact_craters_on_Eart...