An international team of scientists discovered a surprisingly strong regional sea-level rise which occurred during the onset of Antarctic glaciation about 34 million years ago, while the global sea-level on average lowered. In an article, published today in Nature Geoscience, scientists of the Royal Netherlands Institute for Sea Research (NIOZ), Utrecht University and TU Delft explain why.
'We already knew gravity has an important role by sea-level changes due to glaciation or deglaciation. But this is stunning,' said Paolo Stocchi (NIOZ), leader of the international team of researchers of the article published today.
About 34 million years ago the climate at Antarctica changed from temperate without much ice to a polar climate. The ice-sheet grew geologically fast. Worldwide the sea-level dropped by 60-80 meters, since the water was extracted from the oceans, forming the first large ice-sheet on Antarctica. The researchers were surprised to find that the sea-level around Antarctica didn't drop, but rose with about 150 meters.
This regional sea-level rise can be explained by combining several geophysical models. The weight of the growing ice-sheet lowered the Antarctic crust which in turn caused the uplift of the immediate surroundings, under water. But even more important is that the enormous mass of ice has a huge attraction (gravity) to the seawater. Mass attracts mass. Even today, there are immense regional differences in sea-level. It's impossible to speak of a worldwide uniform sea-level rise or -fall.
Consequences for climate research
This finding can have large consequences for climate research in the geological past. And thereby also for future climate-scenarios. This study demonstrates that ice models and ocean currents that are based on worldwide uniform sea-level changes will be different from those based on regional-variable models. It marks the end of the often accepted assumption of uniform 'eustatic' sea-level changes in paleo-research.
This research is based on analyses of sediment cores near the coast of Antarctica during IODP-expedition 318 in 2010 with the Joides Resolution.
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Stocchi, P. et al. Relative sea-level rise around East Antarctic during Oligocene glaciation, Nature Geoscience, 21 April 2013.