After the last ice age, the sea level rose an inch every year and Doggerland disappeared

During the tail of the last ice age and the millennia after that, between 13,700 and 6,200 years ago, the sea level rose to almost one centimeter a year at speeds. That is what researchers write from the Dutch Knowledge Institute Deltares this week Nature. The periods with extra rapid rise were caused by the melting of the North American and Antarctic ice sheets. Those speeds give a glimpse into what may await us in the coming centuries.

Right now that the climate is increasingly warming up, accurate methods to predict sea level rise are crucial. The Intergovernmental Panel on Climate Change expects to see an increase in the coming centuries that has not been observed since the early Holocene, around 11,700 years ago. But data on how fast that increase went at the time are scarce, because the changes in ice volume and the exact timing are unknown.

For reliable reconstructions you need measuring points on land that provide insight into the former sea level level. Coral reefs, peat layers or archaeological settlements, for example that say something about where the sea was or not. The tricky thing is that it is precisely the points from the early Holocene, when the sea was lower, now often under water and are therefore difficult to sampled.

A location where such slips (Sea-Level Index Points) can be reached relatively easily (and therefore cheaply), the North Sea is due to the low depth. And there is exactly a peat -rich, archaeologically interesting location: the ‘drowned’ Doggerland.

Grassy plain with mammoths

The North Sea was not always the North Sea. During the last ice age, the Weichsel time-from 116,000 years ago to 11,700 years ago-you could walk from the Netherlands to Great Britain over a vast grassy area. Mammoths and woolly rhinos grazed there, people hunted there. And when sea level began to rise, one high -lying area continued to protrude above the water, up to 8,000 years ago: Doggerland. At that time it was also inhabited by people.

Thanks to SLIPs from Doggerland, the current research team has now managed to construct the speeds of the former sea level rise, says main author Marc Hijma van Deltares. “In some phases, the water rose around 1 meter per century.” In the Netherlands, the current rise is around 3 millimeters per year, or 30 centimeters per century. In their calculation, the researchers also took into account the ‘glacial seesaw’: the fact that the Netherlands and the North Sea still fall by a few millimeters per year and northern countries such as Norway and Sweden rise. The latter countries were hidden during the Weichsel age time during kilometers-thick ice packages, pushing the country down. Since the ice has melted, they are still gradually back, while the area on the south side of the seesaw is falling.

The researchers also calculated how much the sea rose in total in the period from 11,000 years ago to 3,000 years ago: the estimates vary widely. Based on the slips, they arrived at about 38 meters.

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