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OceansScience

Southern Hemisphere Sea Levels Have Risen Dramatically

Sea levels have risen approximately 20 centimetres in the South West Pacific Ocean since the end of the 19th century, a dramatic increase according to a new study released this week.

Scientists found that sea levels in Tasmania remained relatively stable for most of the previous 6,000 years but that around 1880 they started to rise dramatically. Between 1900 and 1950 the sea level rose at an average rate of 4.2 millimetres per year. The highest rates of sea level rise occurred in the 1910s with an increase of .3 to .8 millimetres per year, followed by a second peak in the 1990s.

“The rise in 1910 probably reflects the end of the little ice age, when temperatures were about one to two degrees cooler in the northern hemisphere than today,” Dr Moss said. “The 1990s peak is most likely indicative of human-induced climate change.”

The study indicates that the size of the sea level rise is much higher in the South West Pacific than elsewhere on the planet, possible due to the ice-melt from sources in the northern hemisphere.

“A large ice-melt is like a fingerprint,” Dr Moss said. “When such a significant mass shifts around the earth’s surface we can detect its movement.

“Based on this, it appears likely that the primary source of sea level rise in the Southern Hemisphere is the Greenland Ice Sheet, but also mountain glaciers in Alaska, western North America and the Canadian Arctic.”

Published in the journal Earth and Planetary Science Letters and written by scientists from The University of Queensland, Plymouth University, the Victoria University of Wellington, Queens University Belfast, the University of Tasmania and University of Southampton, the report looked at sediments taken from Tasmania’s salt marshes to create a record of past ea levels.

“The surface of the marshes builds up over time in response to tidal inundation, providing an accurate record for sea level change,” Dr Moss said. “Sea level observations in Australia only go back as far as European settlement. By comparing our measurements to official observations we can look at long-term changes in sea levels.”

The sediment layers in the core extracted from the Tasmanian marshes also provided physical evidence of the start of logging in Tasmania, when nuclear testing was at its peak globally, and the introduction of unleaded petrol. Dr Moss said an accurate measurement of past sea levels had significant implications for understanding sea level rise under a changing climate.

“Any drastic changes from the norm, which persist for several decades and over a wide area, represent important climate signals,” Dr Moss said. “This in turn has implications for where we build our cities and infrastructure.”

Source: The University of Queensland, Australia
Image Source: Simon Helle Nielsen




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