Millennial Climate Effects on a Lake Ecosystem in Southern Chile

With climate change, people are eager to understand environmental changes over the last few millennia. Unfortunately, regions in the Southern hemisphere are not as well understood as those in the Northern hemisphere, where more data sources are found. This information can be useful in estimating future environmental changes.

A recent study published in the journal The Holocene, scientists examine the millennial changes in the environmental conditions in the Lake Pastahué ecosystem of Chiloé Island, located in southern Chile. Two particular climate events within this period are compared: the Medieval Climate Anomaly (MCA), which was a period of warming from 800 and 1300, and the Little Ice Age (LIA), when temperatures dropped between 1300 and 1850. Scientists investigated signals of climate change in history through analyzing sediment samples from the lake. They also examined historical records to help reconstruct past environmental conditions.

Houses on stilts line the edge of Chiloé Island (Source: Backpackerin/Pixabay)

Biological indicators (pollen and midges) and sedimentological indicators (organic matter and magnetic susceptibility) provided information on the past ecology. Tiny pollen particles that slowly settle into the earth signify historic plant and forest compositions. Midges, popular for fly-fishing, were used as indicators of the trophic changes in lake. Sedimentological indicators allowed researchers to establish a chronological timeline of the core sample, and provided useful information on soil quality.

Researchers found that the highest percentage of pollen was observed during the MCA period. The particles came from trees typically found in the temperate Valdivian forests, suggesting warm conditions. An absence of aquatic plant species, along with an increase in plant species suggests decreased precipitation and increased temperature. Midges adapted to warm conditions were found in this sample, as well as species adapted to semi-terrestrial ecosystems. This suggests the lake was impacted by surrounding terrestrial ecosystem, or a lower water level. These findings were then compared to historical records from 1100-1350, where similar conditions were also observed in Central Chile.

For the LIA period, records show that the climate in central Chile was cooler and more humid beginning in 1350. Pollen results match those of cold events from the Northern Hemisphere. Pollen from trees and shrubs found typically in the North Patagonian forest were recovered, reflecting cold and humid conditions. Aquatic species are much more abundant in this sample, suggesting a larger lake basin. The vegetation structure was also noted to evidence a more humid environment than the earlier period.

Patagonia stretches around 260,000 square miles across South America, consisting of glaciers, steppes, and forests. (Source: Max Pixel)

Historical records of San Rafael Glacier give us a glimpse into the past environment of the region. On a journey from Chiloé to San Rafael Glacier in 1766, a priest described ice floating along the coast up to the glacier. At a later period, Captain Enrique Simpson, a military officer and Admiral of the Chilean Navy, referenced the dimensions of the glacier during his explorations of Chilean archipelagoes in 1875. He reveled at the size of the glacier, describing it as more than a thousand meters high and extending many miles from north to south. According to the article, an explorer at a later period, Hans Steffen in 1910, shared similar findings. “Studying the location and the current dimensions of this huge glacier, we found almost no difference with description given by Captain Simpson on his voyages,” said Steffen.

GlacierHub spoke with Michael Kaplan, a glaciologist who studies climate history in South America. Kaplan considered it novel that the researchers used many techniques and examined historical records in the article. He found it useful to include the historical records of the extensiveness of glaciers, especially considering the state of glaciers in South America today. This reference helps show how climate changes have impacted glaciers and influenced retreat over the course of the millenium. Kaplan also felt that researchers have effectively represented environmental changes in this region during the MCA and LIA. “They show that these events had some manifestation in southern South America, and that’s a really important finding of the paper,” he added.

San Rafael is a major outlet glacier of the Northern Patagonia Ice Field in southern Chile. (Source: Mujer Chilena/Flickr)

Scientists from the study have also observed a growing reduction in tree pollen for the last century. They found that most midge species have diminished. The absence of species related to high nutrient levels suggests that the nutrient conditions at the lake were lower than previous periods. Conditions at this time were warmer and drier than the LIA, and this supports tree ring data which presents the previous 100 years as some of the driest in recent centuries. These environmental changes can be expected to intensify if the climate continues to experience dry conditions.

Marcos Mendoza, an anthropologist who studies environment in Latin America, commented on the relevance of this information for climate projections. Mendoza also told us that these types of studies can be useful in understanding how tree and plant species might respond to future climatological changes. “As indigenous communities, scientists, land managers, and others begin to anticipate how changing temperatures and precipitation patterns will affect the Latin American region of Patagonia, studies like Castro et al. provide windows onto past environmental and climatological conditions,” he said.

This study is useful in understanding the sensitivity of environmental systems to changes in climate. Although historical require careful digging through sources, they can be useful in filling in the gaps in our understanding of past environmental conditions. Reconstructing past conditions can help assess potential changes as well, which may impact people and their environments.

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