Marine mollusk shells reveal how prehistoric humans adapted to intense climate change 

Peer-Reviewed Publication


Cantabrian coast (N Iberian Peninsula)

Current global climatic warming is having, and will continue to have, widespread consequences for human history, in the same way that environmental fluctuations had significant consequences for human populations in the past. The so-called ‘8.2 ka event’ has been identified as the largest and most abrupt climatic event of the past 11,700 years, caused by cool meltwater from North American lakes flooding into the North Atlantic and stopping ocean circulation systems. The cooling and drying effects of this event have been documented around the world, including along the Atlantic coast of Europe. Nevertheless, the sweeping impacts of the 8.2 ka (kilo annum i.e., thousand years ago) event on different environments and human societies are often assumed rather than proven. 

The journal Scientific Reports has published a paper led by Asier García Escárzaga, current researcher from the Institute of Environmental Science and Technology (ICTA-UAB) and the Department of Prehistory of the Universitat Autònoma de Barcelona, together with Igor Gutiérrez Zugasti, from the Universidad de Cantabria (UC). The study was coordinated from the Universidad de La Rioja (UR) and the Max Planck Institute (Germany) alongside members of other academic centres (Max Planck Institute, University of Burgos, Universidad Complutense de Madrid and University of Faro).    

The study applies a multidisciplinary toolkit of archaeomalacological studies and stable oxygen isotope analyses to shell remains recovered from the shell midden site of the El Mazo cave (Asturias, N Spain). With a long stratigraphic sequence of 1,500 years, El Mazo is a unique context along the European Atlantic coast, with especially high chronological resolution of each archaeological layer.  

The results obtained by these scientists allowed them to determine that colder seawater temperatures, deduced from stable oxygen isotope values measured on marine shells, led to changes in the availability of different shellfish species. For instance, one of the most commonly consumed species, the warm-adapted species P. lineatus, decreased during the 8.2 ka event, while populations of cold-adapted P. vulgata, another commonly exploited species, increased. Intriguingly, the warm-adapted limpet P. depressa also increased during this cool period, owing to a higher resistance to cold temperatures than other warm-water species. 

Their results also revealed an increase in the intensification of mollusc exploitation by humans, as indicated by a decrease in average mollusc size and evidence for increased harvesting in more dangerous coastal areas. The authors argued that this occurred because of human demographic growth in these Atlantic coastal settings which acted as refugia during this cold event, encouraging populations to move there from further inland. Nevertheless, populations around El Mazo managed to avoid over exploiting their coastal resources, as average mollusc size very rarely decreased below 20mm, the minimum size specified by modern regulations to guarantee long-term species survival. 

“Our results suggest an ongoing application of local marine ecological knowledge by some of the last foragers in western Europe, despite major changes to climate and demography” says Asier García-Escárzaga lead author of the current study.  

The resolution provided by the combination of taxonomic, geochemical and chronological analysis of molluscs from archaeological sites has major implications for other studies seeking to determine the significance of climate change on marine environments, and can provide detailed clues to the magnitude and nature of future climate changes and their impacts on human societies. 


Scientific Reports




Experimental study




Human forager response to abrupt climate change at 8.2 ka on the Atlantic coast of Europe

From EurekAlert!

Here is the Abstract and Introduction

The cooling and drying associated with the so-called ‘8.2 ka event’ have long been hypothesized as having sweeping implications for human societies in the Early Holocene, including some of the last Mesolithic hunter-gatherers in Atlantic Europe. Nevertheless, detailed ‘on-site’ records with which the impacts of broader climate changes on human-relevant environments can be explored have been lacking. Here, we reconstruct sea surface temperatures (SST) from δ18O values measured on subfossil topshells Phorcus lineatus exploited by the Mesolithic human groups that lived at El Mazo cave (N Spain) between 9 and 7.4 ka. Bayesian modelling of 65 radiocarbon dates, in combination with this δ18O data, provide a high-resolution seasonal record of SST, revealing that colder SST during the 8.2 ka event led to changes in the availability of different shellfish species. Intensification in the exploitation of molluscs by humans indicates demographic growth in these Atlantic coastal settings which acted as refugia during this cold event.


Current global climate warming is having, and will continue to have, widespread consequences for humans. Looking to the past, multiple climatic and environmental changes have long been thought to have shaped human evolution and behaviour1,2,3. The Holocene (11.7–0 ka cal BP) is a geological epoch characterized by comparative stable climatic conditions. However, that stability was punctuated by a series of sudden climate changes, particularly during the Early Holocene4. Among these, the ‘8.2 ka event’ has been identified as the largest and most abrupt climatic event of the Holocene5,6. Climate scientists suggest that this ‘event’ was the result of an outburst of glacial meltwater from the Laurentide lakes in North America7. The influx of cold water into the Atlantic Ocean led to a reduction of sea surface salinity and a decline of the Atlantic meridional overturning circulation (AMOC), provoking a reduction in sea surface temperatures (SST) across the North Atlantic8. The cooling effects of this event have been documented in proxies from the Greenland ice cores6 and across Europe5,9,10. Short and sharp periods of colder or drier conditions have also been recorded ~ 8.2 ka throughout the northern11,12,13 and southern hemispheres11,12,14. Nevertheless, while now a well-established climatic phenomenon, the sweeping impacts of the ‘8.2 ka event’ on different environments often remain assumed rather than proven, and local records of marine or terrestrial conditions available at an appropriate resolution often remain lacking. Furthermore, while temperature or rainfall changes associated with the ‘8.2 ka event’ are often well-established, there are few palaeoclimatic proxies available that have enabled insights into the influence of the ‘8.2 ka event’ on the seasonality of climatic conditions in different parts of the world.

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Gregory Woods
April 24, 2022 2:29 am

That is how ‘climate’ is: You have to go along in order to get along….

Reply to  Scissor
April 24, 2022 7:32 am

People with mental illness….

Reply to  DMacKenzie
April 25, 2022 5:22 am

Which describes alarmists.

Nicholas McGinley
Reply to  Scissor
April 24, 2022 1:21 pm

The seven towers of Agamemnon tremble!

The seven towers of agamemnon tremble.JPG
Peta of Newark
April 24, 2022 2:53 am

Just wow, what a coincidence..
I was just surfing/browsing the UK Met Office only yesterday and there was their 10 day forecast.
A several warning of Youngest Dryness sometime around Wednesday lunchtime and even worse, the 97% projection of another Yongler Drysen just after the weekend.

That’s it fo’sure – I’ll be seeing you all down the beach gathering a 500 year supply of mercury laden germ infested sea-bugs to see us thro the upcoming horror.

Biggest problem, should I be wearing a sun-hat and which colour shorts should I bring. sigh
……s’not ezee this climate lark is it

April 24, 2022 2:55 am

There were Ice Ages and Warm Ages. They seem to cycle with various long frequencies. Long before mankind became a factor at all. I suspect mankind’s contribution to Age changes is noise.

April 24, 2022 3:19 am

“ a series of sudden climate changes”

Surely not

G Mawer
Reply to  fretslider
April 24, 2022 2:22 pm

“prehistoric humans adapted to intense climate change ”
Hey if they could—-can’t we??

April 24, 2022 4:12 am

They examined a 1500-year-old midden pile to determine the effects of 8,200-year-old climate changes?? Riiiight!

Reply to  hiskorr
April 24, 2022 4:26 am

No, I think the midden pile had a life of 1,500 years and was in use during the 8.2 ka event.

Reply to  Oldseadog
April 24, 2022 8:25 am

As I suspected, an arbitrary and unspecified fifteen hundred year span is assumed to represent 8,200 years of “sudden climate changes” in the same way that the last forty years represent the next 80. “All things being equal” – which they never are.

Reply to  Oldseadog
April 25, 2022 5:27 am

An alleged fact that ignores where sea level was 8,200 years ago.

Those midden piles are hundreds of feet deep now.

Stephen Skinner
April 24, 2022 4:32 am

One question. How did they study human coastal foraging at 8.2 ka ago because the oceans hadn’t fully risen to where they are now. Here are the sea levels (estimates) for each thousand year back:
7 ka -6m
8 ka -12m
9 ka -27m
10 ka -46m

Pat from kerbob
Reply to  Stephen Skinner
April 24, 2022 7:12 am

I think they lives where the caves were and then had to walk for lunch.

Conversely, they were more honest than Obama and they didn’t buy right by the sea

Richard Page
Reply to  Stephen Skinner
April 24, 2022 8:13 am

The caves are currently between 0.7km and 1.4km from the Cantabrian Sea, but would have been within 5km during the mesolithic.

April 24, 2022 4:50 am

Some archaeologists argue an impact in form of an exploding meteorit that hit some American plains, the east cost and the western Atlantic, followed by an 1.5k year drop in a new iceage.
One of them researching on that time of the past is Andrew Collins, publishing several books about with a lot of references to papers and mythological sources from around the world.

Last edited 1 year ago by Krishna Gans
Reply to  Krishna Gans
April 24, 2022 7:15 am

The problem with the Younger Dryas is that the temperature dropped suddenly by about 10C and then continued to rise for about 1,000 years before equally suddenly rising about 10C and continuing on it’s trajectory.

OK, but meteorites drop the temperature suddenly before steadily climbing back over the next 5-10 years, not 1,000. I can’t think of anything which could cause a sudden rise 1,000 years later. Can you?

Reply to  Disputin
April 24, 2022 7:41 am

Upstream plugging of the Denmark Strait Cataract by ice might do that….It is sort of the jet pump of Atlantic circulation.

Matt Kiro
April 24, 2022 5:14 am

If cooling causes drying, then a slightly warming earth should not cause more droughts.

It always amazes me that researchers keep finding examples of the earth warming and cooling in the past but now they can only blame humans without even looking at anything else.

April 24, 2022 5:15 am

The wrinkles that form on the finger tips increase the ability to grasp slippery objects in water. This adaptation is found in no other ape species.

It could be the lowly mullosk shaped human evolution.

Last edited 1 year ago by ferdberple
Reply to  ferdberple
April 24, 2022 8:38 am

Ah, yes. “human evolution”. “Evolution is the theory that explains why all hirsute primates live in the Arctic.”

April 24, 2022 5:32 am

It may well be that humans developed a bipedal stance as a result of hunting the mullosk.

Walking upright in water is easier than on land and increases the water depth that can be explored using the foot to dig into soft sediment to locate food. Over time, in populations that relied on mullosk as a primary food source this would select for a more upright gait.

Reply to  ferdberple
April 24, 2022 7:24 am

Yes, fair comment, but the vast majority of people did not live by the sea, so unless you are going to postulate all the rest of mankind was wiped out and the world was then repopulated from the seaside dwellers…

Andy Pattullo
April 24, 2022 7:07 am

They have their observations which are interesting. And then they have their interpretations which in many cases are pure conjecture.

Pat from kerbob
April 24, 2022 7:08 am

Cold is bad
Who knew, except all of us of course

April 24, 2022 7:11 am

A lot of assumptions there. Decreasing shell size shows increased harvesting; could it not have been an adaption to cooling, or reduced mollusc population due to cooling, or increased human population rather than more harvesting from the same number of humans, or increased harvesting due to declines in other food sources?

Ditto for the coincidence of the current regulation minimum shell size with the smallest shell size in the middens.

April 24, 2022 7:29 am

Nonsense conclusions to get CC funding for the road trip of a lifetime at taxpayers expense….the assumption that the cave was constantly inhabited is likely incorrect for starters. The assumption that the people leaving shells in the cave were on average diets is also likely incorrect. Possibly it was used as a prison for societal outcasts at times….maybe a religious site at others….maybe storage of supplies at others….teenage party spot at others….nobody really knows….even assuming the shells are from the immediate area is questionable. Sure it’s interesting what the detritus layers show….but assuming a CC relationship is a leap.

Last edited 1 year ago by DMacKenzie
Reply to  DMacKenzie
April 24, 2022 7:50 am

Actually I want to apologize for my opening statement. The researchers likely had intentions of doing decent anthropology and were forced into the CC narrative by those in charge of the purse strings.

H. D. Hoese
April 24, 2022 7:42 am

“Marine molluscs have very specific environmental requirements and are extremely sensitive to climate change, as revealed by previous studies across Atlantic Europe22,23”
One of these citations is for Crisp’s British study on the severe winters of 1962-63. 62 was a severe northern Gulf fish-killing freeze, as also 2021, fish-eating birds still mostly avoiding the mainland. Freezes are difficult to study, statistically and otherwise, requires freedom from other commitments. Oysters are also killed, this species is harvested from Prince Edward Island to southern Mexico. It does require the specificity of seawater.

Climate believer
April 24, 2022 8:26 am


“Current global climatic warming is having, and will continue to have, widespread BENEFICIAL consequences for human history”…

Dave Fair
April 24, 2022 11:37 am

“Our results suggest an ongoing application of local marine ecological knowledge by some of the last foragers in western Europe, despite major changes to climate and demography.” “… can provide detailed clues to the magnitude and nature of future climate changes and their impacts on human societies.”

Yep, prehistoric foragers’ knowledge of local marine ecology will provide guidance for modern societies’ adaptation to climate change. Whatever hauls in the grant money.

Chris Nisbet
April 24, 2022 11:50 am

How does anyone who believes that human-caused CO2 emissions are the driving force behind climate change believe studies like this, when they suggest that there were major changes in climate before we started emitting significant CO2?
Is CO2 the control knob except when it isn’t?

Bill Treuren
April 24, 2022 2:12 pm

The Maori of NZ emigrated in canoes from the warm Pacific to a middle age warm period that was able to sustain their crops.
The temperature fell 2C or so and their warmer pacific crops failed thrusting them into population decline and tribal warfare.
The first victims of global temperature change, this was well researched but more recently airbrushed from the narrative to some idyllic age of harmony where cannibalism was a rare cultural event rather than a portion of their diet.

April 24, 2022 5:27 pm

So, am I not understanding what they’re saying, or was the influence of the Atlantic Meridional Oscillation just “set aside” because it wasn’t/isn’t influenced by Hoomans?

Just askin’. My cat has killed her third mouse and ceremoniously presented it to me, instead of eating it.

That has a bit more meaning to it than whatever it is these researchers are trying to say. The famous snows of Kilimanjaro came into existence approximately 10,000 BP (before present day) and sometime 5200 YBP, the Ootzi the Iceman went on a fully-equipped “dreamwalk” to bargain with The Gods to stop the snow that was killing off his people. So it was cold back then, plenty cold and people were having difficulty with extreme weather events all the way back to the start of the Holocene, or earlier.

Did I miss something in what they reported? Just tryin’ to understand, that’s all, but it’s as though the only places that are referenced in these studies are highly localized and the “events” seem to be extrapolated into a “global something-something” and unfortunately, it just doesn’t seem logical to little old me.

Jeff Norman
April 24, 2022 5:35 pm

The presumptive cause of the 8.2k event was the massive inflow of glacial melt water into the North Atlantic halting the thermohaline cycle for a couple of centuries.

The only problem, is if the heat didn’t flow into the North Atlantic, where else did it go? There are no proxy records for anywhere during this period that got warmer. Places like the South China Sea and Indonesia actually got cooler.

There are a couple of explanations for this.

Either the glacial inflow wasn’t the cause, as some Chinese researchers have suggested.

Or proxy records currently used do not record warmer periods.

Matthew Sykes
April 25, 2022 12:32 am

Current global climatic warming is having, and will continue to have, widespread consequences for human history”

Really? As Leo Kerse, the Scottish comedian said, “Climate change, you mean we can undo the top button on our duffel coat”

And that, is about the extent of the impact of current warming on humanity. We might feel like undoing a button because it isnt so cold.

April 25, 2022 5:20 am

Nevertheless, populations around El Mazo managed to avoid over exploiting their coastal resources, as average mollusc size very rarely decreased below 20mm, the minimum size specified by modern regulations to guarantee long-term species survival.”

More researcher armchair speculation.
Humans, without massive machinery and ocean going ships, barely harvest a narrow coastal strip where they have easy access to mollusks.

Leaving vast areas of mollusks where humans are unable to harvest them. Humans caused zero impact on mollusk fecundity. Mollusk shell size does indicate which seasons humans harvested them.

These researchers apparently believe inland peoples migrated to the coasts so they could eat mollusks. Completely ignoring that humans waste piles of mollusk shells have been identified as seasonal piles.

Not a year round food source.

Perhaps the researchers should investigate the origins of the multitude brassica varieties, a plant that grows best during cool/cold weather?

Ulric Lyons
April 25, 2022 6:52 am

How about looking at human populations instead of snails during the 8.2kyr event. There were widespread expansions of village settlements in the Indus, in Serbia and surrounding regions, and in southern England with wheat growing. The strong cooling in Greenland would be due to a positive NAO/AO regime, giving good summers and milder winters in Europe, and notably faster trade winds giving a La Nina regime.
3450 years later was again a strong cooling in Greenland from around 2750 BC, when city building began worldwide, and another 3450 years later, another strong Greenland cooling accompanied by again very warm conditions in northern Europe in the 700’s AD (Esper 2014). The glacial lake release which is popularly associated with the 8.2kyr event was actually about 150 years earlier.

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