Havn't you gone over to SI units yet Iains?

I bar (standard atmospheric pressure) = 750 torr.

1 torr is not significantly different from the old unit of pressure, the mm of mercury.

The density of mercury is 13.534 times that of fresh water.

Keith is right. I think he is also right in that the reduction of the sea level due to atmospheric pressure increases precisely cancels out this increase when calculating the pressure on the sea bed. The effect of atmospheric pressure changes on the sea bed is not just miniscule, it is zero.

Dinosaurs are a different matter. Having one of them wade through a shallow lagoon would definitely cause pressure changes, and may well trigger seismic activity.