Glacial Ice Core Samples Reveal Sustainable Land-Use Practices in the Ancient Incan Empire

In the Eastern Cordillera of Bolivia, pollen grains travel from near and far to become sandwiched in layers of snow in the Andean mountaintops, ultimately becoming trapped as the layers turn to ice. Such is the case on the Illimani Glacier, which towers approximately 2,500 meters over Lake Titicaca. The lake sits at an altitude of 3,800 meters above sea level in what was the heart of the ancient Incan Empire.

University of Bern paleoecologist Sandra Brugger headed a team of researchers from various European universities to investigate the vegetative history of the Andean region. Their findings, published in Quaternary Scientific Reviews, indicate that the Inca used sustainable land use practices and that large scale ecological changes did not occur until 1740, long after the Spanish invasion and fall the Inca. The study is one of the first to reconstruct past ecology using pollen grains pulled from glacial ice.

The goal of Brugger’s study was to determine the resilience potential of the Andean mountain-forest ecosystem to a varying intensity of anthropogenic land-use practices. The researchers constructed a timeline of vegetation from 10,000 BC through to the present day. Of particular interest were the years following 1438, which represented the transition from the rise to the demise of the ancient Inca, which was then followed by the the reign of their Spanish conquerors. The degree to which the indigenous peoples altered their environment is a topic still deeply debated amongst researchers.

The Moray Agricultural Terraces (Source: Flickr/Shawn Harquail)

Much like tree rings, glacial ice accumulates in distinct annual layers; therefore, scientists can date ice core samples by ring counting, analyzing the layer’s isotopic signature, or by finding evidence of volcanic eruptions that have been well-dated throughout history. These methods are extremely accurate. Ice from the uppermost layers, which correspond to the last two-hundred years, can be dated within two to five years, while the ice corresponding to the time period of the Incas can be pinpointed to within two decades of accuracy.

The methods for extracting ice cores are actually quite challenging, Brugger said. An experienced team is required to extract samples from high altitudes because conditions become increasingly treacherous with elevation. Moreover, they must ensure that samples remain frozen throughout the delivery process—in this case, from Bolivia to Switzerland. “If they melt, samples are no good,” said Brugger.

The team of Margit Schwikowski at the Paul Scherrer Institute in Switzerland undertook these dangerous drillings, climbing to an elevation of approximately 6,000 meters above sea level. Additionally, they analyzed the chronology and measured many chemical species in the ice cores. Two core samples from the Illimani Glacier were extracted: one in 1999 and another in 2015.

Ice core drilling in Barrow, Alaska (Source: Flickr/NASA: Kathryn Hansen)

Once in the lab, Brugger applied a series of evaporative and chemical-processing techniques to isolate pollen grains from samples corresponding to specific time periods. Each of the samples held approximately 500 pollen grains. “A good sample took me two to three hours to identify,” she said. A bad sample, she added, could take an entire day. The whole process took about three months.

The trickiest part, according to Brugger, was the patience required to identify the pollen. Not only is the catchment area of Illimani large, but the Amazon basin is also one of the most biodiverse regions on the planet, so many different species of pollen were represented in the samples. Undoubtedly, the identification process was painstaking work that required long days behind a microscope at a lab bench – far from the charm of the Bolivian Glacier.

Sandra Brugger counting pollen with a light microscope (Source: Manu Friederich)

Much of the previous research on Andean vegetation was constructed using pollen grains from lake sediments, noted Brugger, which ultimately captures more of a local signal from vegetation directly surrounding the lake. In what was the heart of the Incan Empire near Lake Titicaca, archaeological records suggest that pre-European cultures were highly advanced, domesticating llamas and alpacas, harvesting a wide variety of crops, and practicing metallurgy. Together, these practices could have brought about significant land-use impacts.

Digging deeper, researchers found that llama dung was an important maize fertilizer for the indigenous Andeans.

The switch to agricultural reliance allowed the Inca to abandon traditional hunting and gathering methods and supported the growth of society. An article recently published in the Journal of Archaeological Science details how oribatid mites that once dined on llama feces have been found in sediment cores from wetlands such as Lake Marcacocha, high in the Andes. As merchants passed through these areas with their llamas and maize yields, they boosted the oribatid mite population of the wetlands. This population boom strongly correlates with the time period dominated by the Inca (1483-1533), and the mites’ eventual decline corresponds to the arrival of the Spanish conquistadors, who wiped out the Inca and replaced their llamas with cows, horses, and sheep.

Interestingly, a study published in Applied Animal Behaviour Science suggests that llamas are not as impactful on the landscape as the Old World animals brought over by the Spanish. While llamas graze evenly among the various plant types, cows and sheep appear to be more scrupulous in their dietary decisions. Llamas do not eat plants down to their roots and have padded feet that are less environmentally destructive than hooves. Additionally, explained Brugger, while the native Puna grasses declined around 1740, the population of nutrient-loving weedy species escalated due most likely to the increase European cattle grazing activity. Therefore, the Incan llama grazed the land in a way that was sustainable to the Andean ecosystem, while their European counterparts decimated the land.

Unlike lakes, glaciers trap pollen on a larger scale, as particles drift in from a catchment area of approximately 200-300 kilometers in each direction. Brugger’s research suggests that, on a large scale, the Incan people did not change the Andean forest composition. It is important to note that local versus regional pollen collection methods do not necessarily contradict one another, said Brugger. Instead, they reveal that pockets of disturbance may have occurred closer to the lake where paths and roads were constructed, but overall, the Incan empire did not leave a significant ecological footprint.

Puna vegetation, typical of the Bolivian altiplano (Source: Flickr/Geoff Gallice)

The team identified vegetation that dates as far back as 10,000 BC, establishing an ecological baseline of plant diversity prior to human intervention in the landscape. The baseline served as the control for which human-induced vegetation change over time could be compared.

Brugger found small signs of maize, quinoa, and amaranth, after AD 1, suggesting that the Incas, as well as the indigenous populations before them, grew agricultural crops. Despite signs of human impact, Puna composition did not deviate from previous centuries.

Likewise, the expansion of Polylepis and Alnus after the year 800 followed a warming climate trend. Although Alnus, commonly know as alder, was favored for agroforestry, its range did not dissipate during the Incan regime. According to the book An Environmental History of Latin America, the Incan emperor himself maintained a sustained population of Alder and inflicted harsh punishments for unauthorized logging. In an area naturally defined by so little trees, the alder’s continued existence suggests strict environmental regulation. Its population soon declined with the arrival of Europeans.

A eucalyptus plantation (Source: Flickr/Hari Priyadi)

According to Brugger’s data, changes in the mountain forest composition didn’t occur until around 1740 (two hundred years after the fall of the Incan Empire), implying a long transitional period before the Spanish were able to establish a stable land-use system. After 1740, the pollen record showed a rapid increase in dry grasses and nutrient-loving, weedy species, typical of pasturelands. Then, around 1950, signs of eucalyptus and pine appear in the pollen record, a result of the Bolivian land reform that promoted timber plantations.

Picture from Illimani sitting above La Paz (Source: Margit Schwikowski)

Brugger is now stationed at the Desert Research Institute in Reno, Nevada, analyzing pollen and charcoal in ice cores from Central Greenland in order to reconstruct the response of sensitive Arctic ecosystems to past climate change. “It was a sensation that the approach actually worked,” said Brugger, “as the site was extremely remote from any plants — and pollen.” The prestudy to the project is published in The Holocene.

Glaciers provide an incredible glimpse into the past because they safeguard microscopic clues that allow researchers to uncover our most ancient secrets. For instance, Brugger’s study suggests that the Incan people, though large in number, were able to form a society that peacefully coexisted with its environment. Modern society has largely degraded the Bolivian ecosystem, but might learn a thing or two by studying ancient Incan methods of sustainable agriculture and agroforestry. Brugger’s research is part of a larger project that examines glacial cores from around the world to explain our past. As the project gains momentum, scientists can begin to unravel other fascinating mysteries trapped within glacial ice.

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The Inca’s sustainable land use practices

From Quaternary Science Reviews:

“The extent of pre-Columbian land use and its legacy on modern ecosystems, plant associations, and species distributions of the Americas is still hotly debated. To address this gap, we present a Holocene palynological record (pollen, spores, microscopic charcoal, SCP analyses) from Illimani glacier with exceptional temporal resolution and chronological control close to the center of Inca activities around Lake Titicaca in Bolivia. Our results suggest that Holocene fire activity was largely climate-driven and pre-Columbian agropastoral and agroforestry practices had moderate (large-scale) impacts on plant communities. Unprecedented human-shaped vegetation emerged after AD 1740 following the establishment of novel colonial land use practices and was reinforced in the modern era after AD 1950 with intensified coal consumption and industrial plantations of Pinus and Eucalyptus. Although agroforestry practices date back to the Incas, the recent vast afforestation with exotic monocultures together with rapid climate warming and associated fire regime changes may provoke unprecedented and possibly irreversible ecological and environmental alterations.”

Read the article here.

Lake Titicaca (Source: Wikimedia Commons)

Trump proposes logging nearby Alaskan glaciers

From the Washington Post:

“Politicians have tussled for years over the fate of the Tongass, a massive stretch of southeastern Alaska replete with old-growth spruce, hemlock and cedar, rivers running with salmon, and dramatic fjords. President Bill Clinton put more than half of it off limits to logging just days before leaving office in 2001, when he barred the construction of roads in 58.5 million acres of undeveloped national forest across the country. President George W. Bush sought to reverse that policy, holding a handful of timber sales in the Tongass before a federal judge reinstated the Clinton rule.

Read the article here.

A view of Mendenhall Glacier, which lies in Tongass National Forest (Source: Wikimedia Commons)

Greenland ice sheet mass balance

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“The Programme for Monitoring of the Greenland Ice Sheet (PROMICE) has measured ice-sheet elevation and thickness via repeat airborne surveys circumscribing the ice sheet at an average elevation of 1708 ± 5 m (Sørensen et al. 2018). We refer to this 5415 km survey as the ‘PROMICE perimeter’ (Fig. 1). Here, we assess ice-sheet mass balance following the input-output approach of Andersen et al. (2015). We estimate ice-sheet output, or the ice discharge across the ice-sheet grounding line, by applying downstream corrections to the ice flux across the PROMICE perimeter.”

Read the article here.

A helicopter takes off from the Greenland Ice Sheet. (Source: Wikimedia Commons)

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Ice-core Evidence of Copper Smelting 2700 Years Ago

The mysterious Moche civilization originated on the northern coast of Peru in 200-800 AD. It was known for its metal work, considered by some to be the most accomplished of any Andean civilization. But were the Moche the first Andean culture to originate copper smelting in South America?

While the Moche left comprehensive archaeological evidence of an early sophisticated use of copper, the onset of copper metallurgy is still debated. Some peat-bog records (records of spongy decomposing vegetation) from southern South America demonstrate that copper smelting occurred earlier, around 2000 BC.

Art craft of Moche culture in Lambayeque, PERÚ (source: Douglas Fernandes / Flickr).
Moche mask from Lambayeque, Peru (source: Douglas Fernandes/Flickr).

The question motivated Anja Eichler et al. to launch a massive study of copper emission history. The details of the findings were subsequently published in a paper in Nature. Eichler, an analytical chemistry scientist at the Paul Scherrer Institute in Switzerland, and her team presented a 6500-year copper emission history for the Andean Altiplano based on glacier ice-core records. This is a new methodology applied to trace copper smelting.

“Copper is often referred to as the ‘backbone of Andean metallurgy – the mother of all Andean metals,’” Eichler explained to GlacierHub. “However, in contrast to the early copper metallurgy in the Middle East and Europe, very little information existed about its onset in the Andes.”

The ice-core they used for their research was drilled at the Illimani Glacier in Bolivia in 1999, nearby sites of the ancient cultures. It provides the first complete history of large-scale copper smelting activities in South America and revealed extensive copper metallurgy. Illimani is the highest mountain in the Cordillera Oriental and the second highest peak in Bolivia.

Location of Illimani (source: Eichler et al.).
Location of Illimani (source: Eichler et al.).

When asked about how she started her research, Eichler told GlacierHub, “I got involved in the project in 2012. At that time, PhD students and a post-doc had already obtained exciting findings and secrets revealed by ice-core records. We started looking at copper and lead as traces from copper and silver mining and smelting in the Andes.”

The results of Eichler et al.’s study suggest that the earliest anthropogenic copper pollution occurred between 700–50 BC, during the central Andean Chiripa and Chavin cultures, around 2700 years ago, meaning that copper was produced extensively much earlier than people originally thought.

The sculpted head represented the Chavín culture, considered one of the oldest "civilizations" in the Americas [BSO explain this--sculpted head of mythological being at Chavin.](source: Boring Lovechild / Flickr).
A sculpted head at  Chavín de Huantar (source: Boring Lovechild/Flickr).
“For the first time, our study provides substantial evidence for extensive copper metallurgy already during these early cultures,” said Eichler.

One of the most challenging parts of the research is that copper can show up in the ice core from natural as well as human sources. Eichler’s team accounted for this by calculating the copper Enrichment Factor, which is applied widely to distinguish the natural and anthropogenic origin of metal. The principle of this methodology is to measure the occurrence of different metals. If copper appeared naturally due to wind erosion, it would be found in association with other metals that co-occur with it naturally.

However, according to Eichler’s findings, there was only copper in central Andean Chiripa and Chavin cultures, without cerium or the other metals that occur with it in natural deposits. Hence, it was anthropogenic. The Chiripa culture existed from 1400 BC to 850 BC along the southern shore of Lake Titicaca in Bolivia,  near Illimani Glacier. Soon after the Chiripa, came the Chavin culture, a prehistoric civilization that developed in the northern Andean highlands of Peru from 900 BC to 200 BC, named for Chavín de Huantar, the principal archaeological site where their artifacts have been found.

Moche copper funeral mask with shell ornaments from Ucupe, Peru (source: University of North Carolina)
Moche copper funeral mask with shell ornaments from Ucupe, Peru (source: University of North Carolina).

Copper objects from these earlier cultures are scanty. The reason why there is no sufficient archaeological evidence of copper usage, according to Eichler, is that very often artifacts were reused by subsequent cultures.

“It is known that metallic objects cast by civilizations were typically scavenged from artifacts of their predecessors,” Eichler explained. “Furthermore, ancient metallurgical sites are difficult to find because of the lack of substantive remains, particularly smelting installations. Prehistoric smelting furnaces tended to be small or smelting was performed on open fires and thus left little permanent remains.”

Mount Illimani from Aimara, meaning "Golden Eagle" (source: Arturo / Flickr).
Mount Illimani, seen across the Bolivian Altiplano (source: Arturo/Flickr).

The two major sources of copper in the atmosphere— and hence in ice cores from glaciers, where the atmosphere deposits copper compounds— are smelting activities and natural mineral dust. The contribution of Eichler and her team has been to distinguish these and document the creativity of early cultures who developed means to smelt copper.