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Geosciences Column: How climate change put a damper on the Maya civilisation

Geosciences Column: How climate change put a damper on the Maya civilisation

More than 4,000 years ago, when the Great Pyramid of Giza and Stonehenge were being built, the Maya civilisation emerged in Central America. The indigenous group prospered for thousands of years until its fall in the 13th century (potentially due to severe drought). However, thousands of years before this collapse, severely soggy conditions lasting for many centuries likely inhibited the civilisation’s development, according to a recent study published in EGU’s open access journal Climate of the Past.

During their most productive era, often referred to as the Classic period (300-800 CE), Maya communities had established a complex civilisation, with a network of highly populated cities, large-scale infrastructure, a thriving agricultural system and an advanced understanding in mathematics and astronomy. However, in their early days, dating back to at least 2600 BCE, the Maya people were largely mobile hunter-gatherers, hunting, fishing and foraging across the lowlands.

Around 1000 BCE, some Maya communities had started to transition away from their nomadic lifestyles, and instead were moving towards establishing more sedentary societies, building small villages and relying more heavily on cultivating crops for their sustenance. However, experts suggest that agricultural practices didn’t gain momentum until 400 BCE, raising the question as to why Maya development was delayed for so many centuries.

By analysing two new palaeo-precipitation records, Kees Nooren, lead author of the study and a researcher at Utrecht University in the Netherlands, and his colleagues were able to gain insight into the environmental conditions during this pivotal time, and the impact that climate change could have had on the Maya society.

To determine the regional climate conditions during this period of time, the authors examined a beach ridge plain in the Mexican state of Tabasco, off the Gulf of Mexico, which contains a long-term record of ridge elevation changes for much of the late Holocene. Since precipitation has a large influence on the elevation of this beach ridge, this record is a good indicator of how much rainfall and flooding may have occurred during Maya settlement.

A large part of the central Maya lowlands (outlined with a black dashed line) is drained by the Usumacinta (Us.) River (a). During the Pre-Classic period this river was the main supplier of sand contributing to the formation of the extensive beach ridge plain at the Gulf of Mexico coast (b). Periods of low rainfall result in low river discharges and are associated with relatively elevated beach ridges. Taken from Nooren, K et al., 2018

Additionally, the researchers also assessed core samples taken from Lake Tuspan, a shallow body of water in northern Guatemala that is situated within the Central Maya Lowlands. Because the lake receives its water almost exclusively from a small section of the region (770 square kilometres), its sediment layers provide a good record of rainfall on a very local scale.

The image on p. 74 of the Dresden Codex depicts a torrential downpour probably associated with a destructive flood (Thompson, 1972). Taken from Nooren, K et al., 2018

The research team’s analysis suggested that, starting around 1000-850 BCE, the region shifted from a relatively dry climate, to a wetter environment. Such conditions would have made a farming in this region more difficult and less appealing compared to foraging and hunting. The researchers suggest that this change in climate could be one of the reasons why Maya agricultural development was at a standstill for such a long time.

The researchers also propose that this long-term climate trend could have been brought on by a shift of the Intertropical Convergence Zone (ITCZ), a region near the equator where northeast and southeast winds intermingle and where most of the Earth’s rain makes landfall. The position of this zone can move naturally in response to Earth’s changes in insolation, and a northerly shift of the ITCZ could help account for some of the morphological changes the authors observed in the precipitation records.

After more than 450 years of excessive rainfall and large floods, the records then suggest that the region experienced drier conditions once again. By this time period, the Maya populations began to rapidly intensify their farming efforts and develop major cities, further suggesting that the wet conditions may have helped delay such efforts.

This is not the first time the Nooren and his colleagues have found evidence of major environmental influence on the Maya civilisation. For example, earlier research led by Nooren suggests that, in the 6th century, the El Chichón volcano in southern Mexico released massive amounts of sulfur into the stratosphere, triggering global climate change that likely contributed to a ‘dark age’ in Maya history for several decades. During this time, often referred to as the “Maya Hiatus,’ Maya societies experienced stagnation, increased warfare and political unrest. The research results were presented at the 2016 General Assembly and later published in Geology.

The results of these studies highlight how changes in our climate have greatly influenced communities and at times even shaped the course of societal history, both for better and for worse.

By Olivia Trani, EGU Communications Officer

References

Ebert, C. et al.: Regional response to drought during the formation and decline of Preclassic Maya societies. Quaternary Science Reviews 173:211-235, 2017

Nooren, K., Hoek, W. Z., Dermody, B. J., Galop, D., Metcalfe, S., Islebe, G., and Middelkoop, H.: Climate impact on the development of Pre-Classic Maya civilization. Clim. Past, 14, 1253-1273, 2018

Nooren, K.: Holocene evolution of the Tabasco delta – Mexico : impact of climate, volcanism and humans. Utrecht University Repository (Dissertation). 2017

Nooren, K. et al.: Explosive eruption of El Chichón volcano (Mexico) disrupted 6th century Maya civilization and contributed to global cooling, Geology, 45, 175-178, 2016

Press conference: Volcanoes, climate changes and droughts: civilisational resilience and collapse. European Geosciences Union General Assembly 2016

Caltech Climate Dynamics Group, Why does the ITCZ shift and how? 2016

Put it in a nutshell – or in this case a 21 ft container

In his final post from the Floating University, Jens Weiser shares what it’s like to be part of an oceanographic research cruise and sums up some of the best experiences he’s had on board…

I started this series asking whether anyone of you had ever thought about joining a research cruise. Now that this cruise is coming to an end, I can only strongly advise everyone who might have responded to that by shaking their head to think at least twice. The experiences I have had, the people I have met, and the things I have seen and learned cannot be valued high enough. The overall scientific outcome cannot be assessed yet, since we still have a lot of work ahead of us: far from all the samples have been counted, datasets have yet to be processed and there are still sediment cores to be opened. The practical work we’ve carried out during the cruise is not only interesting but also opens your eyes towards why datasets are rarely perfect and gapless, why a samples from certain depths can be missing or why a core is not as long as you might want it to be. And of course, it has shown what a remarkable amount of work is needed to get these raw data in the first place.

From a more personal point of view the new insights are just as valuable. Meeting people from another place is almost always a rewarding experience, but having a common (scientific) starting point for sharing your thoughts gives you a whole lot of other ideas and ways to think about whatever nut there is to crack.

But of course we did not only talk and discuss research, but spent the last days on board disassembling our gear and packing our lab equipment back into the boxes and containers we unloaded them from before we set off. The containers will be send back to Germany and arrive there in approximately 6 weeks, when the whole game of unloading and unpacking will start over again. Yet this time we can also unpack bits and pieces of two of the most interesting regions in the world: the Agulhas region and the Namibian upwelling system, both of which are fascinating from a biological, oceanographical and geoscientific points of view. Seeing them with your own eyes, as I and the other students aboard the FS Meteor have been able to do, is probably one of the most valuable experiences to take home from the cruise, helping to get a hold of the gigantic puzzle we are all trying to put together.

A jumping humpback whale – just one of the great sights we encountered on this cruise (Credits: Volker Mohrholz)

A jumping humpback whale – just one of the great sights we encountered on this cruise (Credits: Volker Mohrholz)

By Jens Weiser, University of Bremen 

Catch up on previous posts in the series here:

A dangerous fish in the lab and a Vibrocorer on the move – who said research was monotonous?

Earlier this month Jens Weiser set off aboard a research vessel fondly known as the Floating University to find out more about the oceans off southern Africa. After several weeks at sea, Weiser has some exciting findings to report back from FS Meteor as he and 14 other young scientists explore the region’s biology and geology…

A certain routine has developed over the last week here on board. The teams worked well together, so that we were able to collect a lot of samples and data. During 4 transects from deep water conditions in the open ocean onto the shallow shelf we collected various plankton samples and measured a number of seawater properties. Off Mossel Bay we also retrieved four more sediment cores. But all this data is, of course, useless if not processed properly. So we spent a lot time in the labs, trying to bring some order into this big chunk of raw information.

For the biologists this meant seeing several days through the oculars of their microscopes.  Approximately 200 samples had to be counted for their plankton content. And since different fish larvae and copepods tend to look very much alike when you first look at them, this was a pretty time consuming process! However, the effort paid off and we could see a nice change in the plankton composition from the northern sample stations to the ones further south. Generally speaking the samples taken off Durban displayed a high fish egg content, which were rarely found further south. Also the fish larvae show a distinct variability: they get less abundant but increase in size as we move further south. So we were able to track the development of the plankton assemblages along the Agulhas current.

Safety first! The nets recovered quite a number of peculiar organisms, so better be safe than sorry.

Safety first! The nets recovered quite a number of peculiar organisms, so better be safe than sorry (click for larger). (Credit: Jens Weiser)

The oceanographers spent a lot of time at their laptops, processing the CTD data. The plots don’t only look nice, but also show an interesting link between the dissolved oxygen content and the distribution of chlorophyll in the water column. The oxygen gets depleted wherever there is high primary production (indicated by high chlorophyll content) because plankton use it to take up organic matter in a process known as remineralisation.

CTD data mirroring the linkage between linkage between oxygen content and phytoplankton abundance as indicated by the chlorophyll. (Credit: Jens Weiser)

CTD data mirroring the linkage between linkage between oxygen content and phytoplankton abundance as indicated by the chlorophyll (click for larger). (Credit: Jens Weiser)

The geological lab work consisted of opening the cores, making visual core descriptions, preparing smear slides and measuring the colour reflectance. Splitting and describing the cores resulted in a lot of smiling faces, since we did eventually hit the lagoonal muds we missed last week and recovered a lot of other interesting features that probably indicate strong storm events as well as sliding or slumping of material down the slopes of the seafloor topography. On a much smaller scale, the smear slides showed a nice mineralogical link to granites that are found in the hinterland. We could also confirm that the lagoonal deposits are abundant in microfossils, which we will be able to use for paleoenvironmental reconstructions later on!

Opening the cores: some say it’s just dirt, others call it Earth history stuck in a barrel. (Credit: Jens Weiser)

Opening the cores: some say it’s just dirt, others call it Earth history stuck in a barrel. (Credit: Jens Weiser)

Smiling faces were certainly encountered following a few tense moments where we nearly lostour equipment. At the last coring station the wire holding the Vibrocorer snapped, leaving the admittedly not cheap instrument on the seafloor. However, it was still connected to the ship via the electrical cable, so all hope was not lost. We cleared the stage for the ship’s crew and let them work their magic. Lowering a big hook down to the device along the cable, they were indeed able to hook onto the Vibrocorer and lift it back on the ship. So this cruise featured the (probably) first and only successful retrieval of a lost Vibrocorer. Nobody really knows what went wrong or why the wire snapped, but the joy of recovering it soon made the search for reasons obsolete.

To top it all, dinner was a delicious barbecue on deck, live music and sunset over sea included. Sometimes things seem to a have way of working out!

Yesterdays sunset as seen from the top deck, looks just like somebody wanted to reimburse us for the drama of the afternoon… (Credit: Jens Weiser)

Yesterdays sunset as seen from the top deck, looks just like somebody wanted to reimburse us for the drama of the afternoon… (Credit: Jens Weiser)

By Jens Weiser, University of Bremen

Catch up on previous posts in the series here (setting out for the sea) and here (the hunt for plankton and lagoonal muds). 

Seawater, fish larvae and sediments – a snapshot of an ecosystem off South Africa

Earlier this month Jens Weiser set out from southern Africa to find out more about the region’s biology and geology. Back aboard FS Meteor, he’s searching for layers of lagoonal muds to see what the climate was like here in the late Quaternary…

After quite a lot of transit, we arrived at our first big station off Durban on Wednesday afternoon. On our way here we used the time to introduce ourselves and our work to the rest of the group. Every participant had prepared a short talk about a recently finished project or his/her home institution. Since we all come from different parts of the world (South Africa, Germany, Kenya, Madagascar, Mauritius and Spain) and are involved in very different projects, these sessions were a nice opportunity to think outside the box for a while. I had for example never heard a talk on the ecology of fish larvae before, so meant that I could look at the environment from another perspective, rather than my usual geological approach.

We started our fieldwork with a CTD (Conductivity, Temperature, Density)-cast, as we will on every major stop from now on. The device is lowered down to a specific depth, constantly measuring the physical properties of the water. These will give a good insight into the architecture of the water mass and should correlate with the biological data too.

The biological work included plankton nets, multi nets and a ring trawl. The nets are used to retrieve plankton in various sizes and from varying depths, since the opening of the multi net can be opened and closed independently. As it is towed vertically back to the ship, different levels of the water column can be sampled. The ring trawl is towed while the vessel is moving and recovers plankton from the surface. During analysis, the biologist on board will focus on the fish larvae and copepods. As we are following the Agulhas Current to the South, changes in their age and abundance will give insight into the ecology of these organisms in this hydrologically dynamic region.

The multi net is lowered to a desired depth. On its way back to the surface it recovers plankton samples from varying intervals of the water column. (Credit: Jens Weiser)

The multi net is lowered to a desired depth. On its way back to the surface it recovers plankton samples from varying intervals of the water column. (Credit: Jens Weiser)

The weather was far from perfect the entire night, but when we wanted to start the geological work just before sunrise the strong rain and winds of up to 8 on the Beaufort Scale made things really uncomfortable. Since the selected sites looked promising on the PARASOUND (sub-seafloor, high-resolution imaging) instrument, we wanted to try it anyway. Promising, in this case, means: a thin layer of coarse, sandy sediments overlying lagoonal muds – what we were searching for. The first device we tried was the gravity corer, which uses only a heavy weight to force the drill pipe into the sediment. This did not return a satisfying core though, even when we changed the position. So we switched to the Vibrocorer, which uses a vibrating engine and is more suitable for coarse-grained sediments. This worked much better and throughout the day we were able to recover three cores of that were 5 metres long. Unfortunately none of them reached the lagoonal sediments, which are the more useful paleoenvironmental archive. A more detailed investigation in the next few days will reveal whether we can use the sand and shell debris we have recovered anyway. Some of the biologist are interested in them as well – it’s a good thing we are on such a multidisciplinary cruise.

The Vibrocorer is prepared on deck. It is the lowered to the seafloor, where it can recover cores from coarse-grained sediments. (Credit: Jens Weiser)

The Vibrocorer is prepared on deck. It is the lowered to the seafloor, where it can recover cores from coarse-grained sediments. (Credit: Jens Weiser)

By Jens Weiser, University of Bremen

Catch up on findings from the research cruise here.