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The study says that the sea can grow faster than thought

The fifth year of Ph.D. Molly Keogh filmed this photograph near Bohemia, looking northeast across the Breton Sound Wetland in southeast Louisiana. Credits: Tulane University

The new Tulane University study questions the reliability of how sea levels rise in low coastal areas, such as southern Louisiana, and suggests that the current method underestimates the seriousness of the problem. This research is at the center of the news release this week in the journal Science.

Relative sea level rise, which is a combination of rising water and soil drift, is traditionally measured by tide and tide meters. But researchers Molly Keogh and Torbjörn Törnqvist claim that in coastal Louisiana, measuring instruments for the tide speak only of the part of the story.

Tests in such areas are anchored on an average of 20 meters in the ground, not on the surface of the ground. "As a result, the tide scales do not record the slippage occurring in the shallow underground and underestimate the relative rise in sea levels," said Keogh, the fifth year of PhD. student and principal author of the study.

"This study shows that we have to think about how we measure the rise of sea levels in the fast growing coastal lowlands," said Törnqvist, Professor of Vocation Geology at the School of Science and Engineering Tulane.

Study, published in the open access journal Ocean Science, says that although tachimeters can accurately measure the slippage that is happening under their foundations, they miss a shallow tune. With at least 60 percent of the landfall occurring in the first 5 meters of sedimentary columns, tidal meters do not include the primary contribution to rising sea levels.

An alternative approach is to measure shallow gauges using surface elevation charts, cheap mechanical instruments that record changes in surface height in swampy areas. Coastal Louisiana already has a network of more than 300 of these instruments in place. The data can then be combined with deep-metered GPS measurements and satellite sea level measurements, said Keogh.

The relative levels of sea level gained by this approach are considerably higher than the rates established in the sea level measurement data. "So we conclude that coastal areas of low elevation may be at a higher risk of flooding in a shorter period than previously assumed," said Keogh.

She said research has implications for coastal communities around the world.

"Throughout the world, communities in the low coastal areas can be more vulnerable to flood than we have understood, with implications for coastal zone management, urban planners and emergency planners, planning based on a certain time line, and rising sea levels faster than planned it will be a problem. "

Explore further:
A new map highlights the sinking coast of Louisiana

More information:
Molly E. Keogh et al., Measurement rates of today's relative rise in sea levels in coastal areas of low elevation: critical assessment, Ocean Science (2019). DOI: 10.5194 / os-15-61-2019

Journal reference:

Tulane University

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