any major consequences of really large objects striking the oceans?

Tsunamis can carry the energy of an impact thousands of miles from the point of impact within a few hours of the impact. This is more rapid than the slower dispersal of dust through the atmosphere, but would not reach very far into the centre of continents.

major impact events all refer to landing on the continents

I saw a theory that a large impact would leave a hole in the atmosphere - vacuum reaching the ground behind the descending meteorite. This would carry dust and rock from the impact out of the atmosphere into a suborbital trajectory, falling back into the atmosphere all over the planet for the next few hours.

Calculations suggested that the entire surface of the planet could be subjected to temperatures similar to a pizza oven for hours after the impact, leading to immediate global sterilisation of the surface.

Only plants and animals protected by a reasonably thick layer of soil or water would be able to survive these conditions, to emerge into a blighted and unrecognisable landscape.