Marshes in the Mississippi Delta are drowning
The researchers found that coastal marshes have a tipping point, where a small increase in sea-level rise could create a domino effect that is detrimental to marshes across the region.
Over the past century, an estimated 2,000 square miles of wetlands have been lost in coastal Louisiana.
Scientists are now faced with the daunting task of predicting what will happen to the remaining 6,000 square miles of marsh in the Mississippi Delta.
For the current study, the Tulane team used hundreds of sediment cores collected since the early 1990s to investigate how marshes have responded to sea-level rise over the past 8,500 years.
Study lead author Torbjörn Törnqvist is a professor of Geology in the Tulane Department of Earth and Environmental Sciences.
“Previous investigations have suggested that marshes can keep up with rates of sea-level rise as high as half an inch per year, but those studies were based on observations over very short time windows, typically a few decades or less,” said Professor Törnqvist.
“We have taken a much longer view by examining marsh response more than 7,000 years ago, when global rates of sea-level rise were very rapid but within the range of what is expected later this century.”
The study revealed that once sea-level rise exceeds about one-tenth of an inch per year, most Mississippi Delta marshes drown in a few centuries.
If the rate of sea-level rise surpasses a quarter of an inch per year, the marshes are submerged in much less time – about five decades.
“The scary thing is that the present-day rate of global sea-level rise, due to climate change, has already exceeded the initial tipping point for marsh drowning,” said Professor Törnqvist.
“And as things stand right now, the rate of sea-level rise will continue to accelerate and put us on track for marshes to disappear even faster in the future.”
Despite the grim forecast for coastal marshes along the Mississippi Delta, it is not too late to prevent the worst possible outcomes.
According to Professor Törnqvist, the most important action is to drastically curb greenhouse gas emissions to prevent sea-level rise from ramping up to rates where marshes will drown within a matter of decades.
The next important step is to implement major river diversions as quickly as possible. This way, some portions of the Mississippi Delta have a better chance for survival.
However, the window of opportunity for these actions to be effective is rapidly closing, said Professor Törnqvist.
The study is published in the journal Science Advances.