Richard Musgrove
Zoologist, Dr Richard Musgrove is a science journalist based in Far North Queensland.
Dutch researchers have worked out how much and how often sea level rose after the last ice age ended around 11,700 years ago. Their research reveals more about what to expect as earth’s glaciers and icecaps melt in the face of climate change.
Oceans have risen by about 22cm since 1880, as a result of anthropogenic climate change. The US National Oceanic and Atmospheric Administration (NOAA) estimates that 2m of sea level rise is possible by 2100 and 3.9m by 2150, caused by meltwater from glaciers and ice sheets and thermal expansion of seawater as it warms.
Looking back helps us prepare for what’s coming — the inexorable rise of the tide.
Our distant ancestors lived and hunted and survived the last great ice age — the Pleistocene— which started about 2.6 million years ago and ended around 11,700 years ago. At about that time, ice sheets covering much of Asia, Europe and North America stopped their advance. Why this happened is uncertain, but it may have been that the Earth’s tilt changed, producing longer and stronger summers in the Northern Hemisphere.
Now researchers at Utrecht University in the Netherlands have worked out what happened to sea level at the end of the Ice Age.
Lead author, Dr Marc Hijma and team looked at sediment cores from the North Sea, off the Netherlands, Germany and Denmark. These cores were from now-submerged Ice Age coastal wetlands; so much water was caught up in ice back then, that sea levels were around 122m lower, globally.
As the ice melted between 11,000 and 3,000 years ago, the North Sea reclaimed those marshes. The now-flooded wetlands became buried in brackish and marine sediments, forming a 10-30cm layer of decayed organic matter — compressed to ‘peat’ by the increasingly deep mud.
It was a treasure trove of plant material awaiting a sediment corer.
The cores revealed the paleoenvironment before submergence, says Hijma, signalled by the types of microalgae (diatoms) and other plants. Different diatom communities form, depending on where they are in relation to sea level, which means that height above sea level could be worked out. Radio carbon dating gave sea level changes over thousands of years, and X-ray fluorescence analysis told them what elements were present.
From this data researchers estimated how fast sea level rose as ice sheets thawed.
They found that sea level rise happened twice. The first about 10,300 years ago, was fast, at about 9mm per year, similar to that expected under the high greenhouse gas scenario for present-day climate change. The second, about 8,300 years ago, was slower — about 8mm per year, and Hajimi, says was triggered by the release of meltwater from huge glacial lakes that formed at the bases of the melting ice sheets.
Sea level rose almost 40m, higher than a 10-storey building, until about 3000 years ago.
Hijma says that the study will help policymakers and scientists better understand what to expect, and to prepare, as the earth’s icesheets and glaciers melt, driven by anthropogenic climate change. Impacts in the now much larger human population will be orders of magnitude more severe than those our Ice Age ancestors faced, given 15% of Anthropocene humans live in fixed infrastructure near the coast — 87% in Australia.
The paper is published in Nature.
The University of Utrecht also has a “sea level game” to create awareness about sea level rise among young people.
Coastal cities not safe from sea level rise – oceanographer
