Patagonia

Patagonia. A beautiful region of South America, often ignored against the prominence of the Amazon Rainforest. Yet, while perhaps less biologically diverse, a number of abiotic factors have led to the development of a diverse set of features across the region.

The header image, “Cerro Torre and Fitz Roy from Ruta Provincial 23 to El Chaltén” by Miguel Vieira, is licensed under CC BY 2.0

“Andes backyard” by Kevin Rheese is licensed under CC BY 2.0

As with the majority of South America, perhaps the most apparent geological feature is the Andes, a vast mountain range stretching from the top to the very bottom of the continent. This range influences the climate, and hence the environments, which develop in its neighbouring areas. To the east of Patagonia, for example, lies the Patagonian Steppe, an ecoregion covering a vast 487,000km2 featuring predominantely shrub lands, grasslands, rivers and lakes. As a desert, this area sparsely experiences rain due to the inhibition of the westerly flow of moisture from the Pacific leading to the formation of a rain shadow.

In spite of the aridness of the Steppes, it is not in any way void of life. As in the majority of other deserts around the world, a number of well adapted reptiles such as the Patagonian Gecko (geko patagónico), and lizards such as Liolaemus fitzingeri. More than 100 bird species reside on the Steppe, including the Lesser Rhea – a large flightless bird similar to the Ostrich and Emu (possibly having originated from an ancestor common to these groups when the three continents were connected in the supercontinent Gondwana).

“Lesser Rhea” by Federhirn is licensed under CC BY-NC 2.0
“GUANACO” by cuatrok77 is licensed under CC BY-SA 2.0

While deserts are typically viewed as hot places such as the Sahara and Gobi, this is a much colder desert. With winter temperatures of around -2°C, the animals living here have had to evolve various strategies to deal with the extreme conditions. This is shown very well in the Guanaco, a mammal related to the camel. These are the largest herbivores (browsing grasses, shrubs and lichen) in the region, and have thick wool coats which are dark on the top and white on the bottom – the darker colours likely helping to absorb incident heat, while the white inhibits the cooling effect of the ground. Thick eye lashes are present, which help the Guanaco against the dust present (kicked up by west winds blowing during the summer).

From these Guanacos the Llama and the Alpaca have been selectively bred and domesticated for wool, meat and skin. Between 1,000,000 and 2,200,000 are believed to live within the Patagonian Steppe.

West from the Steppe lies the Andes, framed by the thin green strip of the Andean-Patagonian forests. These are the southernmost forests in the world, and have likely been present for the past ~45 million years. The forest covers ~98,000km2, and is one of the largest isolated forests – blocked from the east by the Steppe and to the west by the Pacific, the Andes, the Atacama, and the Chilean Coastal range. Due to this, little mixing has occurred with other forests, and thus it has differed from other forests around the world. For instance, it has large numbers of flowering plants in contrast to the usual dominance of conifers.

The Andes themselves are the longest continental mountain range in the world, at about 9000km long. A simplified story of their formation begins with the end of Triassic, and the end of Pangaea. As Pangaea rifted, the area to the west of the Andes rifted apart from the east. This rifting led to the formation of a back arc basin which later collided with South America. This back arc collision led to the beginning of the formation of the Andes, approximately 30Mya (The actual story is a lot more complicated than this – this is overly simplified).

As a continuation of this formation, there is a subduction zone under the coast of South America, where the Nazca plate is subducting under South American plate. To the south there is a triple junction between the Nazca, South American, and Antarctic plate. The story is further complicated by the fact that the East Pacific Rise (a spreading centre) is subducting beneath South America. As you would expect, this complicated story has led to a lot of active faults along the extent of this west side of South America, which caused the 2010 Chilean Earthquake and the 2007 Peruvian Earthquake. Similarly, it is the hydration of the mantle above this which leads to the formation of magma chambers in the crust below, leading to the formation of volcanoes along this arc, and the formation of geysers such as the El Tatio – one of the highest geyser fields in the world.

Two of the mountains in the Andes are Cerro Chaltén and Mount Hudson. The former is located in the Southern Patagonian Ice Field in Argentina and is named for the HMS Beagle Captain Robert FitzRoy (notably, the ship which took Darwin to South America where he famously developed the theory of evolution!). The latter, technically a volcano, was the site of one of the largest eruptions in the 20th century (It was overshadowed by Mount Pinatubo, however) in 1991. Luckily the area was evacuated and so nobody was killed, unlike an earlier 1971 eruption which while it was weaker (VEI3 instead of 5), caused lahars killing 5 people. This mountainous region also contains one of the worlds only advancing glaciers – Glaciar Perito Moreno. The reason for this is as yet unknown.

“Los Glaciares National Park” by Jorge Láscar is licensed under CC BY 2.0

The Andes themselves, while rather barren (in the higher reaches) are not at all void of life. Guanacos are still present, however the Andes are notable for their birds – with over 400 species present! A notable bird species in South America is the Andean Condor (Vultur gryphus) which is a species of condor with the largest wingspan of any flying bird in South America – a whopping 3.2m! They have the largest wing area of any bird. The Andean Condor is the national animal of Colombia, and is one of the largest birds of prey at 20-25 pounds – though males are larger than females, as these birds show sexual dimorphism. Unfortunately, in 1973 they were added to the endangered animal list as a result of over hunting, being shot by farmers, and their food being poisoned. As the condors are scavengers, they primarily eat carrion – so when this was poisoned (say by farmers) it affected the birds. They inhabit high mountains, low deserts, and alpine in Venezuela, Colombia, Peru, Argentina and Chile, and unlike many other bird species they don’t build nests, preferring instead to lay eggs among borders in order to conceal them from sight.

“Magnificent Andean Condor” by Pedro Szekely is licensed under CC BY-SA 2.0

Further west from the Andes lies both the Atacama desert and the Chilean Coastal Range. While not technically in Patagonia, the Atacama desert is rather interesting as it is the world’s driest non polar desert, due to being entirely closed off by both the Andes and the Pacific Ocean’s Humboldt Current. This dryness leads to salt pans and dry barren rock formations, with cloudless nights (Large numbers of telescopes are present to take advantage of this!) and no light pollution. The temperatures can range from 5C to 40C, likely in part due to the dryness of the atmosphere reducing its ability to buffer the temperature.

The incredible dryness of this area gives itself readily to comparisons with Mars – so much so, that the Atacama Desert is used to explore the suitability of life to survive on Mars, and to test cave detection programs for Mars – such as the Earth-Mars Cave Detection Program. It also makes it a useful place for solar power. The lack of moisture means there are almost always clear skies and so large amounts of sunlight – which is exploited by projects such as the $1.1bn Atacama 1 Concentrated Solar Power Plant (Planta Solar Cerro Dominador).

The Chilean Coastal Range faces onto the Pacific ocean in areas and is as a result of aligned uplifted blocks along the coast, which were separated from the Andes. At the moment this area shows no sign of volcanic activity.

Patagonia is flanked by oceans – the Pacific ocean to the west, the Atlantic to the right, and the Drake Passage in the Southern Ocean to the south. These are inhabited by a range of creatures, such as the Magellanic Penguins (Spheniscus magellanicus) and the Southern Elephant Seals (Mirounga leonina).

“Magellanic Penguin” by Don Faulkner is licensed under CC BY-SA 2.0

Magellanic Penguins are a species of penguin which is only found in South America. Approximately 1,600,000 breeding pairs exist, in loose colonies around areas such as Golfo San Matías, Tierra del Fuego and Puerto Montt. These penguins, like many others (notably excluding Emperor penguins) breed over the summer – which in the southern hemisphere involves breeding in September and laying eggs in October. Typically two eggs will be laid, followed by a 40 day incubation. Incubation is split equally between the mother and father while the other parent goes off to forage for food such as anchovies and sardines.

Changes to the environment around them due to climate change, fishing and oil pollution have greatly affected these penguins. This is shown in how a typical breeding pair would usually produce ~1.5 chicks, yet in the Falklands due to the limited availability of fish only ~0.5 chicks are able to survive through childhood. Other ways that climate change might affect these beautiful creatures is in their site fidelity. As the sea level rises, this may lead to traditional colony areas being flooded, harming the survival of the penguins.

“Southern Elephant Seal on the beach” by Liam Quinn is licensed under CC BY-SA 2.0

Magellanic Penguins are predated upon by Southern Elephant Seals, which live in the cold yet fish rich seas of the sub Antarctic and Antarctic waters. These are the largest type of seals, with males growing up to 4.5m long – though they are sexually dimorphic and females only grow to around 2.8m. While the Penguins are monogamous for life, the elephant seals are somewhat more… promiscuous. Males battle for harems of 40-50 females in often violent fights. These females give birth in late winter (Approximately September), and after an 11 month pregnancy give birth to young who then suckle off of their blubber.

Similar to the penguins, however, the seals have been negatively impacted upon by human activities. During the 19th century these majestic creatures were hunted for their oil and blubber, a process which only ceased when this was outlawed in 1964. Following the banning of this hunting they have rebounded to almost 600,000 individuals with an almost circumpolar distribution.

The complex geology of Patagonia has had massive impacts upon environments and ecosystems which have developed, however human actions look set to seriously harm many of the amazing creatures who live in these areas. Some progress has been made – the regulation (1910, licenses required) and later prohibition (1964) of hunting Southern Elephant Seals, for example. However, more needs to be made if this amazing area is to be preserved.

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Ben

When I was younger I enjoyed reading books and watching shows about science, such as Nick Lane's The Vital Question and Chris Hadfield's Astronaut's Guide to Life on Earth. Since then, I've started a degree in Natural Science at the University of Cambridge where I'm specialising in Earth Science.

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