[jpsb]

sounds reasonable, but alot of the ice would melt(fast) and pour in (but not like ocean water). One other thing, this cater is 200D miles and the gulf crater 60D, seems like a lot more energy (but can't say for sure without knowing density).

The major difference I can see is one hit near (relatively) the equator (better mixing) and the other at a pole, I would guess that if major impact caused extinctions this impact should have caused at least an extinction in the southern hemisphere.

[null and void]

One other detail. In both cases the top one mile of target was blasted into ballistic trajectories.

In the Chicxulub case this was rock, which was heated to incandescence by the impact and subsequent reentry into the earth's atmosphere. As vast numbers of white hot rocks passed overhead it was like turning the atmosphere into a broiler element. Animals were scorched and vegetation withered. Wherever the rocks fell they started fires. Vast areas were burned in an instant.

In the antarctic case it was ice, flashed to steam and lost to space. The effects were mercifully limited to the immediate area.

Good thing, since the antarctic impact was ~4X larger. (~200 mile Ø, vs Chicxulub's ~120 mile Ø).