If you have entered the national park, Torres del Paine, from the East side, you probably saw the beautiful green lagoon with an incredible view of the towers. This lagoon is called Amarga, and it has an interesting coloration that often becomes more intense green on windy days. This lagoon is located inside the property of Estancia Laguna Amarga and has given its name to both the estancia and the whole area. This is a popular spot for landscape photography, but also for wildlife photography because the Chilean flamingo is often observed here, due to its salty water. Being salty is the reason of its name "amarga", which means bitter in Spanish.

Why is the lagoon salty

Pure water, that we usually drink, has a pH level of 7. The pH level of Amarga Lagoon is around 9, which can be compared to the same pH level as the bicarbonate of soda. For most animals, and humans, that would be too salty to drink.

The reason for its very salty water is that the lake has a so-called "closed system". In lake ecology, a closed system refers to a body of water, in this case, a lagoon, that has little or no exchange of water sources, for example from a river, another lake, or the ocean. This system only has an inflow of water. The water from Amarga Lagoon comes from the groundwater, rain, and snow, but there is no drainage of that water.

If the system was open, the water would continue towards another river, or the ocean, carrying the minerals with it. The lack of drainage only allows the water to evaporate. When water evaporates, it cannot carry the minerals it contains in its liquid state, and this automatically causes a more saline environment.

Fossil formations at the shore

You might be wondering what the rocky formations at the shore are. Such closed systems, that Amarga Lagoon has, support the growth of microorganisms that could not survive in normal drained systems with a neutral pH. This microorganism is called cyanobacteria, also known as blue-green algae. This organism lives in shallow water, where they will stick to rocks or the seafloor, and create layers of sediments around themselves. Over time, these layers will build up and harden, forming rocky structures, known as stromatolites. Stromatolites are not only considered to be fossils, they are some of the oldest fossils on Earth.

First life on Earth

Stromatolites are important because they are some of the oldest evidence of life on Earth. They also played a key role in creating Earth's atmosphere, as the cyanobacteria living in stromatolites were some of the first organisms to produce oxygen through photosynthesis. Some of the oldest evidence of the stromatolites are found in Shark Bay, Western Australia, dating back to more than 3.5 million years. In the case of the Amarga Lagoon, the formations are not that old since the formation of the lagoon goes back approximately 7,000 to 14,000 years with the retreat of the glaciers.

Flamingos and salty lakes

The Chilean flamingos are often seen on the shores of Amarga Lagoon all year round. So how come these high pH level lakes and lagoons are so attractive to flamingos? Flamingos prefer alkaline water, which is water with a high pH level above 7.0. This is because the type of food that flamingos eat requires a specific pH level in their digestive system to be properly broken down and absorbed. Flamingos feed on tiny crustaceans, such as shrimp and algae, that contain pigments called carotenoids. These pigments give the flamingos their distinctive pink coloration. However, carotenoids are difficult to digest, and the flamingo's digestive system requires a high pH level to break them down properly. This is why the flamingos prefer salty lakes because it helps them to digest their food.

Amarga Lagoon being a natural laboratory

As mentioned, these curious fossil formations around the lagoon are very interesting to understand how the first life on Earth started, and the Amarga Lagoon is, therefore, a natural laboratory for scientists. Right now, as of 2023, there is a group of researchers and graduate students from the Universidad del Desarrollo y Universidad Andrés Bello in Chile, and the Universidade Federal do Paraná in Brazil, carrying out studies in different lagoons of the Magallanes region. The purpose of the studies is to understand the dynamics of these geological and microbiological systems as a key to understanding the rock-forming processes and the origin of microorganisms in the past.

We hope that later on, we will have more information about these fascinating formations, and their important to understand life on Earth.

Photo credit: Cristina Harboe