sea levels on the other side of N America

1 Aug 2015

We learnt yesterday, that sea level was surprisingly stable in northern British Columbia over the last 13,000 years - but we now have a new study that claims it is a lot different on the eastern coast of N America. It is said to be anything but stable.

At and ... which concern the same study and is derived from 70 boreholes drilled in a wildlife refuge in Maryland - at the back end of Chesapeake Bay. In addition, LiDAR imaging was used and GPS mapping data. A 3D portrait of current and previous post-glacial geology was produced going back millions of years. The latter is the rub - the point of weakness in the study. We know that in the Late Glacial Maximum (or at some point in the last Ice Age) the continental shelf off the eastern states was dry land. We also know that many millions of years ago it was submerged - and a large part of what is now the mainland (or that is the geological interpretation).

The study was published this month by GSA (the Geological Society of America) (Aug, 2015) and the claim is that sea level is rising twice as fast in the Chesapeake Bay area than elsewhere - some 3.4mm rather than 1.7mm a year. This is of course interpreted as a catastrophe and in looking around for a reason it is suggested glacio-isostatic adjustment of the land is taking place as a result of loading and unloading of the ice sheet (many moons ago). Their boreholes indicate the bay was once 40 to 80 metres lower than it is today. This is dated to marine isotope stage 3 (30 to 60 million years ago) - so it is way back. Today, these former submerged areas are above sea level, raised by what they claim was a forebulge (a raised section of land abutting on the ice sheet during the Late Glacial Maximum (which it is known reached as far south as the Great Lakes). The land once below the ice sheet has bounced back up which implies the forebulge should also realign itself - going down. They continue by saying that glacial isostacy controlled sea level in the mid Atlantic region (a reference to the big difference between sea level in the Ice Age and afterwards) by backing up ocean water as ice (how else would there have been such a massive hypothetical ice sheet). 

In the same process, Washington DC is threatened by the Chesapeake Bay and Maryland sinking of the land - and the doomsaying here is that it will be flooded (or those bits below the Hill).