May 29, 2013
Researchers Map New Jersey Sea-Level Changes Over Last 10,000 Years
April Flowers for redOrbit.com - Your Universe Online
The public and policymakers alike were caught off guard when Hurricane Sandy hit the east coast of the US last fall. The majority of the destruction came from the storm surge and flooding that followed the storm, leading researchers to pay attention to how climate change and sea-level rise may have played a role in the disaster, and how those same factors may impact the shoreline in the future.
Benjamin P. Horton, an associate professor in the Department of Earth and Environmental Sciences at the University of Pennsylvania (UPenn), led a new study that relied on fossil records of marshland to reconstruct the changes in sea level along the New Jersey coast going back 10,000 years. The findings of this study were published in the Journal of Quaternary Science.
The state´s sea level has risen continuously during the last 10,000 years, the study confirms. The analysis also reveals that there have been times of very high rates of sea-level rise coinciding with periods of glacial melting. This finding is particularly relevant to conditions today as a warming climate has caused large ice sheets of Antarctica and Greenland to melt into the sea.
The research team says that even if climate change is left out of the equation, sea levels will continue to rise over time, increasing the chances of disruptive flooding, such as the flooding that followed Sandy.
“We´re trying to better understand past sea-level changes because they are key to putting the future in context,” Horton said in a statement.
The team compiled and standardized data from multiple studies conducted during the last few decades to gain insight into the variations in New Jersey´s past sea levels. Fossil evidence of marsh vegetation was used by all of the studies to estimate sea level at various points during the Holocene, with data points from 10,000 years ago through the year 1900.
“We knew that the sea level across the whole of the U.S. Atlantic Coast, including New Jersey, has been rising for the last 10,000 years,” Horton said. “But it´s been rising at different rates. We wanted to find out the reasons for the different rates of rise and the processes that control them.”
Three distinct time periods were revealed by the analysis in which the rate of sea-level rise varied. The sea level rose an average of 0.16 inches per year from 10,000 to 6,000 years ago; 0.08 inches per year from 6,000 to 2,000 years ago; and 0.05 inches per year from 2,000 years ago until 1900.
The rise from 2,000 years ago to 1900 is due to the fact that the land along the coast is naturally subsiding, or sinking, over time. The team says that this rate may also serve as a baseline to incorporate into future flood-risk planning. Horton says that the 0.16 inch rate last seen thousands of years ago might be relevant to the future of New Jersey´s shoreline.
“If you look at what was happening 6 to 10,000 years ago, the ice sheets were melting on Earth, both from northwest Europe and North America, contributing to those high rates of rise,” Horton said. “Now what´s happening? Greenland and Antarctica are melting and could trigger similar rates of sea-level rise.”
The scientists warn that the 0.16 inch rate might not be the ceiling for sea-level rise, because it was higher than that earlier than 10,000 years ago and might reach those levels again if climate change triggers catastrophic melting of ice sheets.
“Ice sheets don´t respond linearly to temperature rise; they go through thresholds,” Horton said. “That could lead to far higher rates of sea-level rise if they reach one of these tipping points.”
The study points out that local factors could also drive the rate of rise much higher than 0.16 inches per year. Although the findings did not suggest that tidal ranges have changed significantly in the time range they studied, the researchers say anthropogenic factors, such as dredging in the Delaware Bay or groundwater extraction in the Atlantic City region, could serve to increase tides or sediment compaction. This would effectively drive sea level higher in those areas.
“To model what the ocean is doing, you have to incorporate what the land is doing, too,” Horton said. “This is the way we´re starting to go from global to regional projections of sea level.”