Climate change caused mangrove collapse in Oman

Study points to sudden decrease of precipitation as cause

UNIVERSITY OF BONN

Research News

IMAGE
IMAGE: 6,000 YEARS AGO, MANGROVES WERE WIDESPREAD IN OMAN. TODAY, ONLY ONE PARTICULARLY ROBUST MANGROVE SPECIES REMAINS THERE, AND THIS IS FOUND IN JUST A FEW LOCATIONS. view more CREDIT: © VALESKA DECKER/UNIVERSITY OF BONN

Most of the mangrove forests on the coasts of Oman disappeared about 6,000 years ago. Until now, the reason for this was not entirely clear. A current study of the University of Bonn (Germany) now sheds light on this: It indicates that the collapse of coastal ecosystems was caused by climatic changes. In contrast, falling sea level or overuse by humans are not likely to be the reasons. The speed of the mangrove extinction was dramatic: Many of the stocks were irreversibly lost within a few decades. The results are published in the journal Quaternary Research.

Mangroves are trees that occupy a very special ecological niche: They grow in the so-called tidal range, meaning coastal areas that are under water at high tide and dry at low tide. Mangroves like a warm climate; most species do not tolerate sea surface temperatures below 24 °C (75°F). They are tolerant to salt, but only up to a tolerance limit that varies from species to species. “This is why we find them nowadays mostly in regions where enough rain falls to reduce salinization of the soil,” explains Valeska Decker of the Institute for Geosciences at the University of Bonn, the lead author of the study.

Fossil finds prove that there used to be many mangrove lagoons on the coast of Oman. However, some 6,000 years ago these suddenly largely vanished – the reasons for this were previously disputed. Over the past few years, Decker traveled several times to the easternmost country of the Arabian Peninsula to pursue this question for her doctoral thesis. With the support of her doctoral supervisor Prof. Gösta Hoffmann, she compiled numerous geochemical, sedimentological and archaeological findings into an overall picture. “From our point of view, everything suggests that the collapse of these ecosystems has climatic reasons,” she says.Low pressure trough shifted to the south

Along the equator there is a low pressure trough, the Intertropical Convergence Zone, which is situated a little further north or south depending on the season. The Indian summer monsoon, for example, is linked to this zone. It is believed that about 10,000 years ago this zone was much further north than today, which meant the monsoon affected large parts of the Arabian Peninsula. Just over 6,000 years ago this low-pressure trough then shifted to the south, but the reason for this and how fast is still not completely clear.

“That this was the case has been well documented for several years,” explains Decker. “Our results now indicate that this climate change had two effects: On the one hand, it caused salinization of the soil, which put the mangroves under extreme stress. On the other hand, the vegetation cover in the affected areas decreased in general due to the greater drought.” This increased erosion: The wind carried large amounts of the barren soil into the lagoons. These silted up and successively dried up. The whole thing happened surprisingly fast: “The ecosystems probably disappeared within a few decades,” stresses Decker. According to previous studies, the environmental changes were gradual. The mangrove ecosystems struggled till a certain threshold was reached and then collapsed within decades. Nowadays, the only mangroves in Oman are those of a particularly robust species and are found only in a few places.

She was able to exclude other possible causes for the disappearance of the mangroves in her study. For example, the researchers found no evidence of a drop in sea level 6,000 years ago that could have triggered the mangrove extinction. “Archaeological findings also speak against a man-made ecological catastrophe,” she says. “It is true that there were humans living in the coastal regions who used the mangroves as firewood. However, they were nomads who did not build permanent settlements. This meant that their need for wood was relatively low – low enough to rule out overuse as a cause.”

Decker and her colleagues now want to further investigate how much the annual precipitation changed and what impact this had on the region. To this end, the researchers plan to study the pollen that has persisted in the lagoon sediment for thousands of years. They want to find out how the vegetation changed as a result of the drought. The results could also be relevant for us: In many regions of the world, the climate is changing at a dramatic pace. Germany has also suffered increasingly from long droughts in recent years. Foresters are therefore already planning to plant more drought-resistant species in this country; this is a consequence of climate change that may leave long-term marks in the history of vegetation.

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Publication: Valeska Decker, Michaela Falkenroth, Susanne Lindauer, Jessica Landgraf, Zahra al-Lawati, Huda al-Rahbi, Sven Oliver Franz and Gösta Hoffmann: Holocene mangrove ecosystems changes along the coastline of Oman; Quaternary Research; DOI: 10.1017/qua.2020.96

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dodgy geezer
January 5, 2021 10:06 pm

The usual problem with early Egyptian SUVs, I suppose.

Reply to  dodgy geezer
January 5, 2021 10:28 pm

Or Camel flatulence perhaps???

Patrick MJD
Reply to  tomwys
January 5, 2021 11:35 pm

Australia exports camels to the ME.

DonM
Reply to  Patrick MJD
January 6, 2021 9:19 am

… and look at how arid Australia is … there’s your smoking gun right there … camels.

tty
Reply to  Patrick MJD
January 6, 2021 1:58 pm

Not to Oman, they export camels to Saudi Arabia.

Robertvd
Reply to  dodgy geezer
January 6, 2021 2:50 am

When the Sahara Was Green

Robertvd
Reply to  dodgy geezer
January 6, 2021 3:01 am

In the early 1990s, Dr. Schoch stunned the world with his revolutionary research that recast the date of the Great Sphinx of Egypt to a period thousands of years earlier than its standard attribution. In demonstrating that the leonine monument has been heavily eroded by water despite the fact that its location on the edge of the Sahara has endured hyper-arid climactic conditions for the past 5,000 years, Dr. Schoch revealed to the world that mankind’s history is greater and older than previously believed.

https://www.robertschoch.com/about.html

Scissor
Reply to  dodgy geezer
January 6, 2021 5:56 am

Pyramid scheme.

Kpar
Reply to  dodgy geezer
January 6, 2021 7:05 am

Beat me to it.

ATheoK
Reply to  dodgy geezer
January 6, 2021 1:41 pm

Ships of the desert; SODs.

January 5, 2021 10:15 pm

Whatever happens anywhere, at any time, it is always found that Global Warming /Climate Change has been responsible for it. No other cause can ever be found and is therefore excluded from any investigation. This situation applies equally to the past, the present and the future and must not be questioned under penalty of law.

Jim Clarke
Reply to  nicholas tesdorf
January 5, 2021 11:09 pm

When all you have is a hammer, Every problem looks like a nail.

MarkW
Reply to  nicholas tesdorf
January 6, 2021 6:19 am

They are talking about an event that happened 6000 years ago. Please read the article before jerking your knee.

Mike
Reply to  MarkW
January 6, 2021 6:23 pm

Please understand the post before replying to it.

John VC
Reply to  nicholas tesdorf
January 6, 2021 7:04 am

That they admit to climate change happening 6000 years ago is rather significant IMO

CRISP
January 5, 2021 10:21 pm

Archeological records indicate a significant drop-off in the amount of farmland under cultivation in the Fertile Crescent after 5000 BC compared with that from 9500BC-5000BC. No-one is sure why but I suspected it was due to climate change i.e. the end of the Holocene Climatic Optimum, which was warmer and wetter, ushering in colder and drier conditions. This appears to confirm this, except that humans felt it before the mangroves.

Stephen Skinner
Reply to  CRISP
January 6, 2021 4:44 am

The Sahara ceased being green around the same time as well as the abandonment of neolithic sites in northern europe.

PCman999
Reply to  CRISP
January 6, 2021 5:25 am

I wonder if the end of the Holocene Optimum spurred the creation of civilization, in that it caused people to get together to create irrigation systems.

Greg K
Reply to  PCman999
January 9, 2021 5:20 pm

In north Africa they gathered around water [ie the Nile] then created irrigation schemes.

[fix your cached email address speling-mod]

Dennis G Sandberg
January 5, 2021 10:56 pm

OMG, blaming “drought” instead of global warming. Is this a first ever in the past 20 years?

Jean Parisot
January 5, 2021 10:59 pm

They didnt mention CO2 and got published!

Tom in Florida
Reply to  Jean Parisot
January 6, 2021 5:42 am

But they did say this:
“The results could also be relevant for us: In many regions of the world, the climate is changing at a dramatic pace”
Implying we are doing it. So close enough for climate work.

Waza
January 5, 2021 11:34 pm

There will always be winners and losers.
The same natural climate change that reduced the mangroves in Oman probably created the Great Barrier Reef in Australia

wazz
Reply to  Waza
January 6, 2021 2:31 am

The GBR has been around for a lot longer than the Holocene

Stephen Skinner
Reply to  wazz
January 6, 2021 4:41 am

GBR is only 8,000 years old in it’s current location. It’s difficult for corals to survive when they are 300ft above sea level.

Waza
Reply to  wazz
January 6, 2021 4:46 am

Waza
My understanding is as per Stephen.
The reef in its current form started growing about 9500 years ago with most of the growth around 7500 years ago. The reef as we know it today is mostly only about 5500 years old.

Peta of Newark
January 5, 2021 11:54 pm

She’s got the lot..
Confirmation Bias
Magical Thinking
and not the very least, a truly unshakeable belief that humans are the sweetest gentlest butter-wouldn’t-melt little critters that ever drew breath

Just look where Oman is, right slap bang between what’s now the Sahara and what the Fertile Crescent became. it didn’t stand a chance.

Valerie, honey-bun sweetness, the ancestors of that sweet adorable thing you see in the mirror cut, slashed, burned and grazed that entire region all the way from Dakar in the west to Nur-Sultan in the east.

Your ‘climate‘ timing is immaculate with that of the supposed creation of the Sahara itself
They created that huge expanse of desert and ‘climate’ hit the rocks because of that
Just as the Aborigine did to Autralia 25 to 30 thousand years prior

Research this dear Val.
Find out what ‘romance’ is all about
The actual practical nitty-gritty of same, not the low lights, music and flowers.

You’ll find that even if The Girls didn’t actually fire the gun, they certainly prepared/loaded it for the boys that they might do the ‘dangerous bit’
Hey, maybe some boys have worked that out – why so few babies are now being made and why there are so many single lonely girls age 40 and above.

But no. Those things are because, as so many around here know to their personal & financial cost, ageing white males are Planet Wrecking Monsters
Add Buck-Passing to that list at the top.

Just one more little reason why Western Society/Civilisation is currently in its death throes.

Nice try tho hun

MarkW
Reply to  Peta of Newark
January 6, 2021 6:22 am

The saying that “butter wouldn’t melt in their mouths” is an insult, not a compliment.

January 6, 2021 12:47 am

Thank you. I will add that to my long list of weird climate impact studies much of which has come from reading wuwt.

observa
January 6, 2021 1:09 am

And in more chaotic climate news sudden stratospheric warming may bring the Beast from the East down on all your heads-
Scientists Warn of an ‘Imminent’ Stratospheric Warming Event Around The North Pole (msn.com)
or kill your mangroves unless your SUV goes into lockdown.

Joel O’Bryan
January 6, 2021 3:02 am

The ITCZ shift I thought was established as a likely consequence of the Malinkovitch cycles and where the planet is today versus 8Kya. more specially a reduction in NH daily average insolation that peaked 8Kya and has fallen since, causing the ITCZ to return it a more southerly latitude.

i also note that definition of “climate change” conveniently changes like a chameleon for rent seekers.

Crispin Pemberton-Pigott
Reply to  Joel O’Bryan
January 6, 2021 5:11 am

No one has mentioned yet the very clear evidence in the UK of a steep drop in temperature at the same time, with nascent agriculture stopping suddenly for several centuries. The tree species changed swiftly and the climate cooled.

This is consistent with a change in the latitude of the ITCZ. It also stopped raining in the Sahara at the same time.

Further, the water pumped from southern Libya in Ghadaffi’s big irrigation schemes was “5000 years old”. Environmentalists were decrying the exploitation of the resource because obviously it doesn’t rain now, so the water is not being used sustainably.

Well, how can it be? It stopped raining there and unless the world warms appreciably the ITCZ will not move north again. I’m not convinced humans can affect the weather enough to cause a change that large, when obviously there are natural forces preventing it.

One idea is that the Earth was hit by a high velocity meteor at a high latitude. This would induce a wobble that could have shifted the position of the Pole about half a degree. The interesting side effect of that is a significant change in sea level at 45 degrees but not at the equator or poles. The evidence for this is in ancient sea shores of Eastern Ireland and eastern Australia. Fairbridge investigated the latter noting that sea level was 2 m higher at the time.

There was a similar smaller incident in 1650 BC approx, also possibility a meteor strike with an attendant cooling cloud. Maybe the sudden cooling of 535 AD is a pointer – it was caused by a large volcanic eruption.

Rainer C. Ment
January 6, 2021 4:51 am

It should be “Womangrove in Owoman” …

Reply to  Rainer C. Ment
January 6, 2021 11:55 am

No, that’s actually not very PC.

Can’t you see…’woman’ has the dreadful word ‘man’ in it. ‘Man’ must henceforth be replaced by ‘person’. Oh, wait a minute…actually ”person has that awful sexist term ‘son’ in it. We need to shorten it to the gender neutral ‘per’. Then everyone’s happy, so the title actually becomes not your : ‘Womangrove in Owoman’ but ‘Pergrove in Oper”.

Simple isn’t it.

Philip
January 6, 2021 5:13 am

Archaeological findings also speak against a man-made ecological catastrophe,” she says. “It is true that there were humans living in the coastal regions who used the mangroves as firewood. However, they were nomads who did not build permanent settlements. This meant that their need for wood was relatively low – low enough to rule out overuse as a cause.”

As thrilled as I am that in this case man isn’t the culprit. I really don’t see how being nomadic means, “that their need for wood was very low.”
Wood, I’d bet, was the primary fuel resource 6000 yrs ago. These nomads probably cut a fair bit as they passed through, taking advantage of this resource. Even to carrying much of it off for future use. And it could be green wood at the time of cutting. Frequent cutting could have introduced an invasive grass say. Not that I want to leave behind any ammunition to start blaming man. It’s just that IMO the language used to explain so much of climate science presumes too much. Very little in this world were change is concerned is all of one thing. If you ask me, in the name of science, climate is a pigeonhole that is having a lot of square pegs driven into it.

There is nothing permanent except change. -Heraclitus

gringojay
Reply to  Philip
January 6, 2021 12:18 pm

Concievably those nomads had livestock. If so, then an appreciable amount of their fire substrate would have been dry dung; which is easier to collect than going among mangroves for fuel risking a twisted ankle.

Philip
Reply to  gringojay
January 6, 2021 3:46 pm

All the more reason to take advantage of a wood source as they passed through the area.

tty
Reply to  Philip
January 6, 2021 2:01 pm

Invasive grass??? Let me guess, you have never seen a mangrove forest.

Philip
Reply to  tty
January 6, 2021 3:41 pm

I have. And sea grasses too.

tty
Reply to  Philip
January 7, 2021 5:45 am

For your information sea grasses aren’t grasses.

Philip
Reply to  tty
January 7, 2021 9:16 am

Really!
You’re a rather pedantic little fellow, aren’t you.

Turtle grass
Manatee grass
Shoal grass
Paddle grass
Star grass
Widgeon grass

A few names of some of the more common sea grasses.

tty
Reply to  Philip
January 10, 2021 3:31 pm

Not one of those plants is a grass.

MarkW
January 6, 2021 6:16 am

The drying up of the Sahara was happening at about the same time.

Harri Luuppala
January 6, 2021 2:03 pm

When I read some articles about Oman after this blog, I got confused!

In Oman they planted trees 4000y ago (Rem. in the Epic of Gilgamesh its hero ~500 years earlier deared cut down trees somewhere in Iran or Libanon! Perhaps owner of the forest told him that ”How dare you?!”

For me all this hints that they had lack of wood in the region and they did what we Finns do today – e.g. planted trees in Oman!

”Archaeological evidence has suggested an industrial presence around Aybut Al Auwal dating to around 100,000 years ago. Oman is also the location of one of the world’s earliest inhabited cities at Al Wattih, which dates back 10,000 years.” RAF museum

”Many livestock owners take their animals to mangrove areas to graze and harvest mangrove leaves to use them as fodder * ” Esri

Archaeological studies made at Qurm Nature Reserve (QNR) indicated the existence of mangrove plants in this area over 4000 yrs ago. The results of these studies clearly prove that Omani people used mangrove trees for many purposes such as building houses and huts and for fuel* ” Esri

tty
Reply to  Harri Luuppala
January 6, 2021 2:48 pm

Most of Oman is much too dry for trees, but there is still a fair amount of scrubby monsoon forest in the Dhofar mountains, incidentally the only place in the world where the incense tree grows.

Wadi Darbat in the monsoon season:

https://www.google.com/maps/@17.0749302,54.435215,3a,75y,274.94h,128.29t/data=!3m8!1e1!3m6!1sAF1QipM3lk4YBHeusCGW0rX6qJ183CS-5L_JTRzTgbfS!2e10!3e11!6shttps:%2F%2Flh5.googleusercontent.com%2Fp%2FAF1QipM3lk4YBHeusCGW0rX6qJ183CS-5L_JTRzTgbfS%3Dw203-h100-k-no-pi-15.467833-ya152.13728-ro-9.409871-fo100!7i5376!8i2688

Not quite the way one usually visualizes Arabia.

ATheoK
January 6, 2021 2:19 pm

More jumps to conclusions…

“late Holocene sea-level highstand in the Persian Gulf. Mid-Holocene transgression of the Gulf surpassed today’s sea level by 7100–6890 cal yr BP, attaining a highstand of > 1 m above current sea level shortly after 5290–4570 cal yr BP”

A higher sea level 6K years ago.

“The extreme salinity and temperature fluctuations of the Persian Gulf waters have created unique marine and coastal ecosystems”

Salinity has increased greatly since “She says.Low{sic} pressure trough shifted to the south”.

Valeska herself states,

They are tolerant to salt, but only up to a tolerance limit that varies from species to species. “This is why we find them nowadays mostly in regions where enough rain falls to reduce salinization of the soil,”

Persian Gulf salinity appears to not be a consideration in Valeska’s conclusions. Except where she claims it’s Climate Change what done it;

“That this was the case has been well documented for several years,” explains Decker. “Our results now indicate that this climate change had two effects: On the one hand, it caused salinization of the soil,”

I would like to know, explicitly, how Climate Change causes “salinization”. I suspect she is referring to weather.

Valeska fails to mention that the prevailing winds

“This increased erosion: The wind carried large amounts of the barren soil into the lagoons. These silted up and successively dried up. “

Prevailing winds in that area are from the East and North heading West and South; easterlies.
Where did all of the alleged barren soil come from? India? Afghanistan?comment image

Last edited 6 months ago by ATheoK
tty
Reply to  ATheoK
January 6, 2021 2:39 pm

“salinization” in this context is a weasel word. It doesn’t have its normal meaning. Mangroves only grow in areas where there is groundwater seepage of fresh water into the sea, so of course with less rain, there will be less seepage and fewer suitable sites.

And I am a bit skeptical about the silting by wind. Khawrs are typically silted up by longshore movement of sand by the sea, as you can see in this overhead view of eight Khawrs just east of Salalah in southern Oman:

https://www.google.com/maps/@17.032828,54.2313095,6066m/data=!3m1!1e3

tty
January 6, 2021 2:24 pm

That mangroves decreased due to increased aridity in mid-Holocene is certainly quite possible and even likely. They only grow in areas where there is an appreciable groundwater seepage into the sea. However they greatly exaggerate the rarity of mangrove in Oman today.

There are quite a few “Khawr” all along the coast, particularly in Dhofar of course, where the monsoon still comes in over the mountains every year, but there are occasional “Khawrs” even as far north as the UAE coast.

Here is a view of Khawr Kalba which is right on the border between Oman and UAE:

https://www.google.com/maps/@25.0158427,56.3599471,3a,60y,246.95h,92.06t/data=!3m6!1e1!3m4!1sf93eM_ejEdHp_3Jfglf-Fg!2e0!7i13312!8i6656

Pat from kerbob
January 6, 2021 7:04 pm

As the earth cooled from the Holocene optimum, the mangroves took it in the neck.

Colder is always worse

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