Tulane University
Given the present-day rate of global sea-level rise, remaining marshes in the Mississippi Delta are likely to drown, according to a new Tulane University study.
A key finding of the study, published in Science Advances, is that coastal marshes experience tipping points, where a small increase in the rate of sea-level rise leads to widespread submergence.
The loss of 2,000 square miles (5,000 km2) of wetlands in coastal Louisiana over the past century is well documented, but it has been more challenging to predict the fate of the remaining 6,000 square miles (15,000 km2) of marshland.
The study used hundreds of sediment cores collected since the early 1990s to examine how marshes responded to a range of rates of sea-level rise during the past 8,500 years.
“Previous investigations have suggested that marshes can keep up with rates of sea-level rise as high as half an inch per year (10 mm/yr), but those studies were based on observations over very short time windows, typically a few decades or less,” said Torbjörn Törnqvist, lead author and Vokes Geology Professor in the Tulane Department of Earth and Environmental Sciences.
“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 researchers found that in the Mississippi Delta most marshes drown in a few centuries once the rate of sea-level rise exceeds about one-tenth of an inch per year (3 mm/yr). When the rate exceeds a quarter of an inch per year (7.5 mm/yr), drowning occurs in about half a century.
“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,” Törnqvist said. “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.”
While these findings indicate that the loss of remaining marshes in coastal Louisiana is probably inevitable, there are still meaningful actions that can be taken to prevent the worst possible outcomes. The most important one, Törnqvist said, 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 other one is to implement major river diversions as quickly as possible, so at least small portions of the Mississippi Delta can survive for a longer time. However, the window of opportunity for these actions to be effective is rapidly closing, he said.
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Törnqvist conducted the research with Krista Jankowski and Juan González, who received their PhD degrees at Tulane under his supervision, and Yong-Xiang Li, a former postdoc in his group.
Justin Lawrence of the National Science Foundation, which provided funding for the study, added, “The effects of marsh loss are a serious public concern in coastal regions of the United States and elsewhere, and this study could lead to better management decisions that curtail those effects.”
Additional funding was provided by the National Institute for Climatic Change Research Coastal Center of the U.S. Department of Energy.
Over decades and centuries, a marsh is free to pack up the household and move upstream when the downstream domicile becomes unsuitable. The nature of nature is not static. Who wants to tell them?
Nonsense Heyseuss, those marshes were exactly the same for 4.5 billion years until we came along and started burning fossil fuels. It’s just like the coral that had been happy for 200 million years of perfectly stable climate, now on the brink due to massive fractional degree warming of the ocean, obviously caused exclusively by our CO2 emissions.
I like your take. To generalize a little, are all alarmists marsh dwellers? I don’t really know, but I am forming an opinion ..
You left out the “ocean acidification” charge against mankind. What’s app with that? ;-))
If geology and climatology can tell ua anything, it is that nothing is permanent. Get lost.
Don’t forget cosmetology!
“All is flux.” (Heraclitus) And I agree, Rich Davis, the study of cosmetics will show that change is inevitable, and fashionably so.
Big problem with the delta is all the flood control on the river – no longer deposits silt, building up the delta. Not saying flood control is bad. But like all things it does have consequences both good and bad.
These agenda-driven pseudoscience studies make their lies by telling partial stories. Telling just half-truths in order to deceive a naive public, leaving out important information that alters the conclusion that would otherwise be drawn. It’s all pretty standard fare for the pseudoscience behind the climate scam.
By far the biggest factor is Delta subsidence under consolidation of long-ago deposited silts and clays, and with diversions and channels dredged, the marshes are without a steady resupply of fresh sediments.
As a Tulane engineering graduate, I receive the TULANE magazine. The team headed by Prof. Tornqvist continues to publish alarmist papers claiming the disappearance of the Mississippi delta as a result of climate change. https://issuu.com/tulaneuniversity/docs/tulane_september-2017/8 (page 17).
Two letters of mine refuting this were published in the TULANE magazine. In the first I reminded the professor than 1897 issue of the NATIONAL GEOGRAPHIC vol.8, #12, page 353 https://archive.org/details/nationalgeograph81897nati/page/352/mode/2up contained the observation that: “It is a fact well known to the people living in the delta of the Mississippi that large tracts of land were long ago abandoned in consequence of overflow by Gulf waters due to sinking of the lands.”
This fact has not sunk in over a hundred years later.
https://issuu.com/tulaneuniversity/docs/tulane_december_2015 (page 4)
https://issuu.com/tulaneuniversity/docs/tulane_december-2017 (page 4)
“Has not sunk in yet”
Nice pun, Charlie!
The scary thing, the key finding of this sharticle is that the inch is about to pass a staggering 30mm tipping point.
The world’s land area INCREASED in the last 30 years. Anthropogenic sea level rise since the beginning of time is estimated at 2 inches in a consensus of current literature.
If the delta is “in a state of irreversible collapse” then there is nothing to be done and we can all stop worrying about it. Move on…it’s irreversible.
Meanwhile, adapt any new construction to take this into account.
Jeez, it this really so hard?
To the college educated? Apparently.
Of course, we must always remember that the satellite dataset has the fiddle factor of 0.3mm per year added to “account for changes to ocean basin size”. Adjustments are only allowed in one direction. Why not say we should take off 1mm per year to account for thermal expansion coming out of the LIA, and another 1mm for the changes to glaciers since LIA. The data is no longer what the name of the data says it is. The ACTUAL sea level rather than the ADJUSTED sea level is what is useful to people.
Subsidence, not sea level changes.
These statistical ‘What-If’ pseudo scientists are very busy getting paid to demolish the reputation of science.
The study is nonsense, because it completely disregards the well-known issues with the Mississippi Delta due to the way the river has been managed in recent years. Attributing issues such as subsidence of marshes to climate change and comparing the current situation with conditions from 7000 years ago while disregarding man-made conditions is disingenuous, to be kind.
I will nominate this post for the 2020 Crock of Schist award. It is well known and proved that most of the relative sea level rise in the Miss. delta is because of thermal subsidence, a result of crustal cooling under this passive margin – a tectonic process. Crustal subsidence in the delta is much more rapid than the change in absolute sea level.
As has been documented and analyzed at WUWT numerous times, the world-wide change in the elevation of sea level relative to the earth geoid, called eustatic sea level, is less than +2 MM per year as determined by tide gauges with long-term records.
Something is missing in this report because any geo professor or grad student knows this, or, at least that once was the case.
In addition to sediment diversion, (in upstream dams and at the modern outlet) oil, gas and salt withdrawls have also contributed to subsidence. Straightening channels helps promote tidal scour as well. So the Mississippi delta has multiple strikes against it.
The Mississippi river has spent the Holocene moving across the landscape like a loose firehose, spraying sediment from one place to the next. Where it deposits sediments, the land advances, when the depocenter moves elsewhere, the sediment continues to compact, leading to saltwater intrusion and interdistributary bays.
The rate of sea level rise does have an impact, but it has been minor in the Holocene Mississippi delta. That’s why they can’t see the known highstands in their record.
OMG It’s worse than we thought … again! Drums fingers slowly on table
Based on this article, the study is flawed since it fails to address the loss of land in the Chandeleur Islands. When the mouth of the Mississippi River shifted to the present course, the sediment inflow stopped. The result, the islands began to sink and shrink. The present outlet has had sediment loss due to restricting flood waters to the mouth of the river rather than letting the river banks be flooded over. The Mississippi River mouth should be located near Morgan City. The Corps of Engineering controls the water flow through to the Atchafalaya River. A new delta has now formed in the Atchafalaya Bay. The present river course is kept open because of the river traffic and keeping open the Port of New Orleans. River sediment is important to the life of the coastal marshlands of Louisiana. Cut it off, the natural compaction leads to the land sinking. This is an ongoing process since the Mississippi River was formed.
The Chandeleur Islands were deposited by the Saint Bernard lobe of the Holocene delta. This lobe was active during the 1500 to 3000 BP time range. That is supposedly missing from their record.
Take away the hype and their open-source article tells an interesting story of the last stages of the Holocene transgression, where the basal peats they dated show the transgression of the rising sea followed by delta progradation. The low rate of sea level rise they record is a measure of how much the sediment compensated for modest sea level increases. All of their sediments younger than 6000 years are listed as terrestrial or indeterminant.
With an estimated precision in the +/- 0.5 meter range for ASL it really doesn’t add that much to the debate. Their accuarcy on sea level is biased, since some compaction will take place, regardless of their attempts to minimize. They should have considered the data as two separate sets based on geography, and included sediment density or % water.
Humans come along and put in levies, then wonder why the delta sinks beneath the waves?
“The Mississippi between Cairo and New Orleans was twelve hundred and fifteen miles long one hundred and seventy-six years ago… Its length is only nine hundred and seventy-three miles at present.
Now, if I wanted to be one of those ponderous scientific people, and “let on” to prove what had occurred in the remote past by what had occurred in a given time in the recent past… what an opportunity is here! Geology never had such a chance, nor such exact data to argue from! …
In the space of one hundred and seventy-six years the Lower Mississippi has shortened itself two hundred and forty-two miles. That is an average of a trifle over one mile and a third per year. Therefore, any calm person, who is not blind or idiotic, can see that in the Old Oolitic Silurian Period, just a million years ago next November, the Lower Mississippi River was upwards of one million three hundred thousand miles long, and stuck out over the Gulf of Mexico like a fishing-rod. And by the same token any person can see that seven hundred and forty-two years from now the lower Mississippi will be only a mile and three-quarters long…
There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.”
Mark Twain, Life on the Mississippi
Never mind their dubious conclusion that Mississippi marshes are suddenly more susceptible to a lower rate of sea level rise than earlier studies showed, they apparently can’t tell the difference between sea level rise and land subsidence. Land subsidence in the Mississippi Delta is twice the rate of sea level rise. So the biggest “problem” here, if there is any at all, is land subsidence, not sea level rise. See NOAA tide gauges around the delta here:
https://tidesandcurrents.noaa.gov/sltrends/sltrends.html
Who cares ?
Tropical depression, which is moving to the Gulf of Mexico, will bring downpours in the eastern half of the US.
http://tropic.ssec.wisc.edu/real-time/mtpw2/webAnims/tpw_nrl_colors/natl/mimictpw_natl_latest.gif
Sea level rising same as it has for thousands of years.
Another bunch of twits being paid on taxpayer funding to lie about CO2.
It’s funny that they try to claim they’ve adjusted for sediment compaction and subsidince, when their sea level curve is still typical for subsidince at a rapid depocenter.
This latest study has three radiocarbon dates from the last 500 years. 146 years, 202 years and 342 years. The elevation of “sea level” at these three dates, at those sites, are -280, -300 and -350 mm below sea level ” respectively. Not clear how they estimate .35 – .36 mm/year subsidence rates for these three dates, but just using age and depth of the holocene surface below “sea level”, I calculate almost 2 mm per year for the last date, and 1mm per year for the earliest. The slight increase in subsidence since the little ice age could be real, or could just indicate the lack of sediment at that site, at that time.
A “state of irreversible collapse? NOT. Katrina dumped multiple centimeters of sediment on the city of New Orleans in one event. Sure, dumping water and sediment into the city may not make economic sense, and the city will probably sink beneath sea level and remain dry due to levees and pumps. But elsewhere in south LA, flooding is how the land is built.