Catamarca Province Catamarca () is a province of Argentina, located in the northwest of the country. The province had a population of 334,568 as per the , and covers an area of 102,602 km2. Its literacy rate is 95.5%. Neighbouring provinces are (clockwise, fr ...

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

salt flats Salt flats, Salt flat, Salt Flats, or Salt Flat may refer to: Geology *Salt pan (geology), a flat expanse of ground covered with salt and other minerals * Dry lake, an ephemeral lakebed that consists of fine-grained sediments infused with alkali sal ...

evaporation Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. High concentration of the evaporating substance in the surrounding gas significantly slows down evaporation, such as when humidi ...

surface runoff Surface runoff (also known as overland flow) is the flow of water occurring on the ground surface when excess rainwater, stormwater, meltwater, or other sources, can no longer sufficiently rapidly infiltrate in the soil. This can occur when th ...

groundwater Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidate ...

snowmelt In hydrology, snowmelt is surface runoff produced from melting snow. It can also be used to describe the period or season during which such runoff is produced. Water produced by snowmelt is an important part of the annual water cycle in many part ...

microbialite Microbialite is a benthic sedimentary deposit made of carbonate mud (particle diameter < 5 μm) that is formed with the mediation of microbes. The constituent carbonate mud is a type of

carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate g ...

and microorganisms including

diatom A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...

s and various

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

. These structures have a layered internal structure and colours ranging from green to orange-pink to black. They have been compared to

Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...

stromatolith Stromatolites () or stromatoliths () are layered sedimentary formations (microbialite) that are created mainly by photosynthetic microorganisms such as cyanobacteria, sulfate-reducing bacteria, and Pseudomonadota (formerly proteobacteria). The ...

s, which were among the oldest forms of life on Earth.

Regional and local

Laguna Negra lies at an elevation of in the

Tinogasta Department Tinogasta is a western department of Catamarca Province in Argentina. The provincial subdivision has a population of about 22,500 inhabitants in an area of , and its capital city is Tinogasta, which is located around from Buenos Aires B ...

,

Catamarca Province Catamarca () is a province of Argentina, located in the northwest of the country. The province had a population of 334,568 as per the , and covers an area of 102,602 km2. Its literacy rate is 95.5%. Neighbouring provinces are (clockwise, fr ...

of

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

, and near the

San Francisco Pass The San Francisco Pass is a pass over the Andes mountains which connects Argentina and Chile. The highest point of this pass is at AMSL. Location The pass is located at and connects the Argentine province of Catamarca with the Atacama Re ...

between

Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...

and Argentina. The path to

Monte Pissis Monte Pissis is an extinct volcano on the border of La Rioja and Catamarca provinces, Argentina, from the Chilean border. The mountain is the third-highest in the Western Hemisphere, and is located about north of Aconcagua. Monte Pissis is nam ...

passes close to the lake. It covers a surface of and has the rough shape of a rectangle. The average depth of the lake does not exceed . The lake periodically floods its beaches. To the northwest, a salt flat separates the lake from its neighbours to the north and covers over half of the lake basin. A prominent

alluvial fan An alluvial fan is an accumulation of sediments that fans outwards from a concentrated source of sediments, such as a narrow canyon emerging from an escarpment. They are characteristic of mountainous terrain in arid to semiarid climates, but a ...

borders Laguna Negra to the southeast and its northward growth has generated a shallow water area at the southeastern margin of the lake (''Stromatolite Belt''). The waters of the lake are

hypersaline A hypersaline lake is a landlocked body of water that contains significant concentrations of sodium chloride, brines, and other salts, with saline levels surpassing that of ocean water (3.5%, i.e. ). Specific microbial species can thrive in h ...

, their principal salt is

calcium chloride Calcium chloride is an inorganic compound, a salt with the chemical formula . It is a white crystalline solid at room temperature, and it is highly soluble in water. It can be created by neutralising hydrochloric acid with calcium hydroxide. Ca ...

, although they have been described as mesosaline too.

Arsenic Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, but ...

is present at high concentrations. The high salinity prevents the water from freezing except at the margins of Laguna Negra, where salinity is lower due to

inflow Inflow may refer to: * Inflow (hydrology), the water entering a body of water * Inflow (meteorology) Inflow is the flow of a fluid into a large collection of that fluid. Within meteorology, inflow normally refers to the influx of warmth and moi ...

.

Calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

and

aragonite Aragonite is a carbonate mineral, one of the three most common naturally occurring crystal forms of calcium carbonate, (the other forms being the minerals calcite and vaterite). It is formed by biological and physical processes, including prec ...

reach saturation concentration at points where groundwater enters the lake, leading to

carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate g ...

precipitation mainly along the southeastern margin of the lake. Conditions in the lake environments are

alkaline In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a base (chemistry), basic, ionic compound, ionic salt (chemistry), salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as ...

and the consumption of

carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...

by degassing and

photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...

facilitates carbonate precipitation. The lake is fed mainly by

groundwater Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidate ...

and by runoff that enters mainly from the southwestern side. The water mainly originates through annual

snowmelt In hydrology, snowmelt is surface runoff produced from melting snow. It can also be used to describe the period or season during which such runoff is produced. Water produced by snowmelt is an important part of the annual water cycle in many part ...

. Laguna Negra has no surface outflow and is a

closed lake An endorheic lake (also called a sink lake or terminal lake) is a collection of water within an endorheic basin, or sink, with no evident outlet. Endorheic lakes are generally saline as a result of being unable to get rid of solutes left in the l ...

; the lake waters evaporate in the strong wind and at high temperatures, leading to the precipitation of salts such as

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and drywall. ...

,

halite Halite (), commonly known as rock salt, is a type of salt, the mineral (natural) form of sodium chloride ( Na Cl). Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, p ...

and

polyhalite Polyhalite is an evaporite mineral, a hydrated sulfate of potassium, calcium and magnesium with formula: . Polyhalite crystallizes in the triclinic system, although crystals are very rare. The normal habit is massive to fibrous. It is typically co ...

in a sequential manner from carbonates to salts.

Regional context

Laguna Negra is the southernmost of three lakes aligned in north–south direction; the other two are Laguna de la Salina/Laguna Tres Quebradas to the north and Laguna Verde in the middle. They form the Laguna Verde Saline Complex, also known as Laguna Verde Complex or Salar de la Laguna Verde. The Salar de Tres Quebradas salt pan separates Laguna Verde from Laguna Tres Quebradas. Together these two lakes have a water surface of . Smaller lakes exist nearby such as Laguna Azul northeast of Laguna Negra. File:ISS035-E-25019.jpg, alt=Space image of a white plain embedded in mountainous terrain, with a brownish lake to the south. A green lake lies in the middle directly next to the white area, while to the north lies a black lake, Laguna Negra, with Laguna Verde in the middle and Laguna Tres Quebradas/Laguna de la Salina to the north File:ISS035-E-25019 (cropped).jpg, alt=High-elevation photo of a brown lake with a white-brownish plain next to it, Laguna Negra, up is to the north-northwest The lakes lie in the southernmost Puna, a

high plateau In geology and physical geography, a plateau (; ; ), also called a high plain or a tableland, is an area of a highland consisting of flat terrain that is raised sharply above the surrounding area on at least one side. Often one or more sides ha ...

at an elevation of where a dry climate and

Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...

uplift generated the Laguna Verde Saline Complex when block faulting generated separated drainage basins separated by north–south trending mountain ranges. The terrain consists mainly of volcanic rocks such as

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

and

andesite Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predomi ...

; some summits exceed elevation above sea level such as the high Cerro Pissis.

Evaporite An evaporite () is a water-soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as ocea ...

s,

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class of s ...

and

silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension with water. Silt usually has a floury feel when ...

cover the terrain around the lake.

Climate, vegetation and fauna

The climate at Laguna Negra is cold,

arid A region is arid when it severely lacks available water, to the extent of hindering or preventing the growth and development of plant and animal life. Regions with arid climates tend to lack vegetation and are called xeric or desertic. Most ar ...

with strong winds. Temperature is highly variable, ranging between in summer and between in winter. Annual precipitation is less than and falls mainly as

snow Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water throughout ...

. Evidence from other lakes in the region suggests that the environment was wetter than today between about 15,000–14,000 and 13,500–11,300 years before becoming dry during the middle

Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togethe ...

. After about 4,000 years BP precipitation has increased again. Presently, the climate is dominated by the

South Pacific High The South Pacific High is a semi-permanent subtropical anticyclone located in the southeast Pacific Ocean. The area of high atmospheric pressure and the presence of the Humboldt Current in the underlying ocean make the west coast of Peru and no ...

anticyclone An anticyclone is a weather phenomenon defined as a large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere as viewed from abov ...

which draws dry air into the region. During summer, an

Atlantic The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe an ...

anticyclone conversely transports moister and warmer air to the area, resulting in the formation of

convective Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convect ...

clouds and precipitation. Climatic conditions together with high

UV radiation Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...

limit the complexity of life at Laguna Negra, in particular of nonmicrobial life. In this sector of the Andes,

peatland A mire, peatland, or quagmire is a wetland area dominated by living peat-forming plants. Mires arise because of incomplete decomposition of organic matter, usually litter from vegetation, due to water-logging and subsequent anoxia. All types ...

s are the key ecosystems, with the dominant plant species being '' Distichia muscoides'', '' Oxychloe andina'' and ''

Plantago rigida ''Plantago rigida'', colloquially known as "Colchón de agua" (water mattress), is a species of flowering plant in the plantain family found in the high-altitude páramo biome of South America. Distribution Bolivia, Colombia, Ecuador, Peru, Ven ...

'' as well as

graminoid In botany and ecology, graminoid refers to a herbaceous plant with a grass-like morphology, i.e. elongated culms with long, blade-like leaves. They are contrasted to forbs, herbaceous plants without grass-like features. The plants most ofte ...

s and

grass Poaceae () or Gramineae () is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in lawns an ...

es.

Mite Mites are small arachnids (eight-legged arthropods). Mites span two large orders of arachnids, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari, but genetic analysis does not show clear evid ...

s are their most important fauna.

Salt marsh A salt marsh or saltmarsh, also known as a coastal salt marsh or a tidal marsh, is a coastal ecosystem in the upper coastal intertidal zone between land and open saltwater or brackish water that is regularly flooded by the tides. It is dominated ...

grasses of the genus ''

Spartina ''Spartina'' is a taxon of plants in the grass family, frequently found in coastal salt marshes. Its species are commonly known as cordgrass or cord-grass, and are native to the coasts of the Atlantic Ocean in western and southern Europe, north ...

'' grow at the southern end of the lake, and

copepod Copepods (; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (inhabiting sea waters), some are benthos, benthic (living on the ocean floor) ...

s have been observed in ponds; both are linked to areas with lower salinity.

Carbonates and microbial mats

Both

microbial mat A microbial mat is a multi-layered sheet of microorganisms, mainly bacteria and archaea, or bacteria alone. Microbial mats grow at interfaces between different types of material, mostly on submerged or moist surfaces, but a few survive in deserts. ...

s and

microbialites Microbialite is a benthic sedimentary deposit made of carbonate mud (particle diameter < 5 μm) that is formed with the mediation of microbes. The constituent carbonate mud is a type of

carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate g ...

s where new water enters Laguna Negra. At the southern end of the lake,

travertine Travertine ( ) is a form of terrestrial limestone deposited around mineral springs, especially hot springs. It often has a fibrous or concentric appearance and exists in white, tan, cream-colored, and even rusty varieties. It is formed by a pro ...

crusts are found; they might form at sites of groundwater entry. Active

tufa Tufa is a variety of limestone formed when carbonate minerals precipitate out of water in unheated rivers or lakes. Geothermally heated hot springs sometimes produce similar (but less porous) carbonate deposits, which are known as travertine. ...

formation has been observed, making Laguna Negra one of only two lakes in the region where it takes place. White incrustations are formed by evaporation, when

salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantitie ...

precipitates. Laguna Tres Quebradas north of Laguna Negra also features microbialites, which cover an area of in the

river delta A river delta is a landform shaped like a triangle, created by deposition (geology), deposition of sediment that is carried by a river and enters slower-moving or stagnant water. This occurs where a river enters an ocean, sea, estuary, lake, res ...

of the Salado River. In the ''Stromatolite Belt'', a large area at the southeastern part of the lake where water depths do not exceed , they form laminar crusts, oncoids and

stromatolite Stromatolites () or stromatoliths () are layered sedimentary formations (microbialite) that are created mainly by photosynthetic microorganisms such as cyanobacteria, sulfate-reducing bacteria, and Pseudomonadota (formerly proteobacteria). The ...

s that are accompanied by microbial mats. These microbialites are found mainly in the northeastern Stromatolite Belt, while its central and western portions feature abiotic carbonate precipitation. A subdivision in a plant-grown sector, a non-mineralized sector and a carbonate precipitation sector is possible. Oncoids make up the bulk of the Stromatolite Belt. They can have smooth forms and ridged, pillar- or shrub-like protrusions and reach dimensions of over . They can be buried in mud, submerged or partially emerged, and sometimes covered with

halite Halite (), commonly known as rock salt, is a type of salt, the mineral (natural) form of sodium chloride ( Na Cl). Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, p ...

. Colours range from green-yellow over orange to snow white, and the structures have the appearance of rocks strewn onto and emerging from the shallow lake. The oncoids have a concentrically layered internal structure, with the various layers often having different colours; the colour variations relate to compositional differences. The microscopic texture has been described as sparry, "micritic" and "botryoidal". Other growth forms are laminar crusts and column-shaped or flat stromatoliths. Microbial mats have colours ranging from back over pinkish-orange to greenish, and their structure ranges from pustular to stratified. Most are associated with oncoids. Greenish mats occur next to groundwater springs and often are found floating on bubbles, and black mats are found on partially exposed carbonates. The black mats are formed mainly by filamentous

cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...

of the '' Rivularia'' family. Layered microbial mats, where different layers have different colours, are found within deep ponds. So-called "diatom blooms" are linked to white carbonate precipitates that form bright spots on the coloured mats. The colours of the microbial constructs are due to

carotenoid Carotenoids (), also called tetraterpenoids, are yellow, orange, and red organic compound, organic pigments that are produced by plants and algae, as well as several bacteria, and Fungus, fungi. Carotenoids give the characteristic color to pumpki ...

and

scytonemin Scytonemin is a secondary metabolite and an Extracellular matrix, extracellular matrix (sheath) Biological pigment, pigment synthesized by many strains of cyanobacteria, including ''Nostoc'', ''Scytonema'', Calothrix crustacea, ''Calothrix'', ''Lyn ...

pigments, which serve to protect the microorganisms from

UV radiation Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...

.

Radiometric dating Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares t ...

of the carbonate structures is difficult owing to the scarcity of datable material, but uranium-thorium dating performed on one oncolite indicates that it began to develop in the Late Holocene. Observations indicate that the growth of the oncoliths is still ongoing.

Biology and scientific importance

There are both

autotrophic An autotroph or primary producer is an organism that produces complex organic compounds (such as carbohydrates, fats, and proteins) using carbon from simple substances such as carbon dioxide,Morris, J. et al. (2019). "Biology: How Life Works", ...

and

heterotrophic A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...

microorganisms in Laguna Negra. Autotrophs include

cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...

, as well as

green sulfur bacteria The green sulfur bacteria are a phylum of obligately anaerobic photoautotrophic bacteria that metabolize sulfur. Green sulfur bacteria are nonmotile (except ''Chloroherpeton thalassium'', which may glide) and capable of anoxygenic photosynthesi ...

and

purple sulfur bacteria The purple sulfur bacteria (PSB) are part of a group of Pseudomonadota capable of photosynthesis, collectively referred to as purple bacteria. They are anaerobic or microaerophilic, and are often found in stratified water environments including ...

which conduct

anoxygenic photosynthesis Bacterial anoxygenic photosynthesis differs from the better known oxygenic photosynthesis in plants by the reductant used (e.g. hydrogen sulfide instead of water) and the byproduct generated (e.g. elemental sulfur instead of molecular oxygen). Ba ...

;

sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...

deposits form during the process. Heterotrophic organisms include

polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with wa ...

degrading and

sulfate-reducing bacteria Sulfate-reducing microorganisms (SRM) or sulfate-reducing prokaryotes (SRP) are a group composed of sulfate-reducing bacteria (SRB) and sulfate-reducing archaea (SRA), both of which can perform anaerobic respiration utilizing sulfate () as termina ...

. There is a layering in metabolic activity, with regular photosynthesis at the surface, anoxygenic photosynthesis in intermediary layers and sulfate reduction at depth. Many microorganisms are

extremophile An extremophile (from Latin ' meaning "extreme" and Greek ' () meaning "love") is an organism that is able to live (or in some cases thrive) in extreme environments, i.e. environments that make survival challenging such as due to extreme temper ...

s and tolerate high salinity and intense

UV radiation Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...

. Precipitation of carbonates is often associated with life and may be induced by the latter for various reasons, although at Laguna Negra it can also occur independently from biological activity. Subtle environmental variations and changes influence the life in the lake and the structure of the microbial mats. The microbial mats are found in the less saline sector of Laguna Negra, implying that reduced salt stress favours their development.

Stromatolites Stromatolites () or stromatoliths () are layered sedimentary formations (microbialite) that are created mainly by photosynthetic microorganisms such as cyanobacteria, sulfate-reducing bacteria, and Pseudomonadota (formerly proteobacteria). The ...

have been found elsewhere in the Puna, at

Socompa Socompa is a large stratovolcano at the border of Argentina and Chile with an elevation of metres. Part of the Chilean and Argentine Andean Volcanic Belt (AVB), it is part of the Central Volcanic Zone, one of the various segments of the AVB. Th ...

and

Tolar Grande Tolar Grande is a village and rural municipality in Salta Province in northwestern Argentina. Climate The climate is typical of the puna area and more precisely of the very dry Puna de Atacama, with very little rainfall, moderate-temperature ...

. They are considered to be among the oldest forms of life on Earth and a key indicator in the search for

extraterrestrial life Extraterrestrial life, colloquially referred to as alien life, is life that may occur outside Earth and which did not originate on Earth. No extraterrestrial life has yet been conclusively detected, although efforts are underway. Such life might ...

. The forms found at Laguna Negra resemble these of ancient

Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...

stromatolites more than these of recent

Proterozoic The Proterozoic () is a geological eon spanning the time interval from 2500 to 538.8million years ago. It is the most recent part of the Precambrian "supereon". It is also the longest eon of the Earth's geologic time scale, and it is subdivided ...

stromatolites, and the conditions encountered at the lake may resemble these of

Early Earth The early Earth is loosely defined as Earth in its first one billion years, or gigayear (Ga, 109y). The “early Earth” encompasses approximately the first gigayear in the evolution of our planet, from its initial formation in the young Solar Sy ...

and Early Mars and could thus be used as an analogue to interpret deposits on Mars. Analyses of

isotope fractionation Isotope fractionation describes fractionation processes that affect the relative abundance of isotopes, phenomena which are taken advantage of in isotope geochemistry and other fields. Normally, the focus is on stable isotopes of the same element. ...

processes at Laguna Negra also demonstrate that oxygen and carbon isotope variations are not necessarily proof of biological activity.

Microbes

Cyanobacteria and diatoms form aggregates together and with other microorganisms. The aggregates in turn are embedded in

exopolysaccharide Extracellular polymeric substances (EPSs) are natural polymers of high molecular weight secreted by microorganisms into their environment. EPSs establish the functional and structural integrity of biofilms, and are considered the fundamental comp ...

capsules where carbonates precipitate. Living diatoms are often found at the margin of aggregates while their interiors feature " entombed" diatoms. The bacterial species '' Rivularia halophila'' was discovered at Laguna Negra; it is the first ''Rivularia'' species known from hypersaline inland waters. Another species identified and named means "cold/freezing lake/pond" in

Quechua Quechua may refer to: *Quechua people, several indigenous ethnic groups in South America, especially in Peru *Quechuan languages, a Native South American language family spoken primarily in the Andes, derived from a common ancestral language **So ...

and refers to the cold environment of Laguna Negra. there is '' Exiguobacterium chiriqhucha'', although that species was originally discovered elsewhere.

Regional and local

Regional context

Climate, vegetation and fauna

Carbonates and microbial mats

Biology and scientific importance

Microbes

Notes

References

Sources

External links