I’m Felicity Williams and I study how sea level changes when the amount of ice on land either grows or melts.
It is very tempting to think of our earth as one large bath tub in which the water level goes up and down uniformly across the entire surface. The real world is far more interesting!
Every location around the world experiences a different sea level for the same amount of water being added to or taken away from the oceans.
Figure 1: Mountainside scoured by a retreating glacier –the Moiry Glacier – which can be seen to the left of the image.
Figure 2: A view down the valley scoured by the Moiry Glacier. Here you can see the edge moraines formed by the ice when it surged down the valley.
This is because when ice grows it squishes down the land underneath it. This causes sea level to effectively rise in that location even though ice is building up on land and so taking water out of the ocean. Conversely when the ice melts, the land springs back and sea level falls, even though more water is being added to the ocean. This process is called Glacial Isostatic Adjustment – and we feel it even today in the British Isles as a result of the great British and Irish Ice Sheet that was centered over Scotland around twenty thousand years ago.
Figure 3: Beautiful corals on the Great Barrier Reef in Australia. We can reconstruct past sea levels using fossil corals that were once alive.
We have some clues as to how sea level changed in the past gained from evidence like fossil corals, and we have some clues as to how much ground the ice sheets covered in past times as the ice sheets can push huge mounds of earth and rubble in front of them as they advance – these are known as moraines.
My job is to pull these clues together, so that we get a better idea of just how variable sea level was in past times – with the intention of applying it to the present day. If we know how fast sea level changed in the past, we have a better idea as to just how variable sea level could be in the future.