Younger Dryas - Still Looking for a Cause 

The Younger Dryas was an episode of frigidity, lasting about a millenium (12.9 to 11.7ka). I presume there was a cause but so far, nothing examined has proved to be robust.

The latest cause to be examined was the impact crater beneath the Hiawatha Glacier in the northwest of Greenland. It had been proposed that a cometary impact could be a cause. This did not meet universal approval!

The Hiawatha impact site had its proponents, but dating the impact was difficult - it lies beneath a kilometer of ice. The crater was only discovered using airborne radar in 2018. 

Obviously the age of the impact is crucial and THIS ARTICLE tells of two different age determining methods which both give dates of about 58 million years BP. So no connection with the Younger Dryas.

The comet cause people are suggesting an airburst of an incoming projectile, similar to the Tunguska event of 1908. But proving this might be more difficult than dating a meteror impact.

FIG. 1 Geomorphological and glaciological setting of Hiawatha Glacier, northwest Greenland.(A) Regional view of northwest Greenland. Inset map shows location relative to whole of Greenland. Magenta box identifies location of (B) to (D). (B) A 5-m ArcticDEM mosaic over eastern Inglefield Land. Colors are ice surface velocity. Blue line illustrates an active basal drainage path inferred from radargrams. (C) Hillshade surface relief based on the ArcticDEM mosaic, which illustrates characteristics such as surface undulations. Dashed red lines are the outlines of the two subglacial paleochannels. Blue lines are catchment outlines, i.e., solid blue line is subglacial and hatched is supraglacial. (D) Bed topography based on airborne radar sounding from 1997 to 2014 NASA data and 2016 Alfred Wegener Institute (AWI) data. Black triangles represent elevated rim picks from the radargrams, and the dark purple circles represent peaks in the central uplift. Hatched red lines are field measurements of the strike of ice-marginal bedrock structures. Black circles show location of the three glaciofluvial sediment samples described in table S1. Copied from HERE.