View source for Biology:Blood Falls

{{Short description|Red-colored seep of saltwater flowing from Taylor Glacier in Antarctica}}
[[File:Blood Falls by Peter Rejcek.jpg|thumb|Blood Falls, 2006]]
[[File:Taylorglacier pho 2013 studinger.jpg|thumb|Blood Falls, at the toe of Taylor Glacier,  2013]]
'''Blood Falls''' is an outflow of an [[Chemistry:Iron oxide|iron oxide]]–tainted plume of saltwater, flowing from the tongue of Taylor Glacier onto the ice-covered surface of West Lake Bonney in the Taylor Valley of the McMurdo Dry Valleys in Victoria Land, [[Earth:East Antarctica|East Antarctica]].

Iron-rich hypersaline water sporadically emerges from small fissures in the ice cascades. The saltwater source is a subglacial pool of unknown size overlain by about {{convert|400|m}} of ice several kilometers from its tiny outlet at Blood Falls.

The reddish deposit was found in 1911 by the Australian geologist Thomas Griffith Taylor, who first explored the valley that bears his name.<ref>{{Cite web |url=https://www.sciencedaily.com/releases/2003/11/031105064856.htm |title=Explanation offered for Antarctica's 'Blood Falls' |work=ScienceDaily |agency=Ohio State University |date=November 5, 2003 |access-date=April 18, 2009}}</ref> The Antarctica pioneers first attributed the red color to [[Biology:Red algae|red algae]], but later it was proven to be due to iron oxides.

==Geochemistry==
Poorly soluble [[Chemistry:Hydrous ferric oxides|hydrous ferric oxides]] are deposited at the surface of ice after the [[Chemistry:Ferrous|ferrous ions]] present in the unfrozen saltwater are [[Chemistry:Redox|oxidized]] in contact with atmospheric [[Chemistry:Oxygen|oxygen]]. The more soluble ferrous ions initially are dissolved in old seawater trapped in an ancient pocket remaining from the [[Earth:Southern Ocean|Antarctic Ocean]] when a [[Earth:Fjord|fjord]] was isolated by the glacier in its progression during the Miocene period, some 5&nbsp;million years ago, when the sea level was higher than today.

Unlike most Antarctic glaciers, the Taylor Glacier is not frozen to the [[Earth:Bedrock|bedrock]], probably because of the presence of salts concentrated by the [[Physics:Crystallization|crystallization]] of the ancient [[Earth:Seawater|seawater]] imprisoned below it. Salt cryo-concentration occurred in the deep relict seawater when pure ice crystallized and expelled its dissolved salts as it cooled down because of the [[Physics:Heat transfer|heat exchange]] of the captive liquid seawater with the enormous ice mass of the glacier. As a consequence, the trapped seawater was concentrated in [[Earth:Brine|brine]]s with a [[Earth:Salinity|salinity]] two to three times that of the [[Physics:Vienna Standard Mean Ocean Water|mean ocean water]]. A second mechanism sometimes also explaining the formation of hypersaline brines is the water evaporation of surface lakes directly exposed to the very dry polar atmosphere in the McMurdo Dry Valleys. The analyses of stable isotopes of water allow, in principle, to distinguish between both processes as long as there is no mixing between differently formed brines.<ref>{{Cite journal |title=Isotopic evolution of saline lakes in the low-latitude and polar regions |journal=Aquatic Geochemistry |first=Juske |last=Horita |volume=15 |issue=1–2 |pages=43–69 |date=February 2009 |doi=10.1007/s10498-008-9050-3|s2cid=140535685 |url=https://zenodo.org/record/1232783 }}</ref>

Hypersaline fluid, sampled fortuitously through a crack in the ice, was oxygen-free and rich in [[Chemistry:Sulfate|sulfate]] and ferrous ion. Sulfate is a remnant geochemical signature of marine conditions, while soluble divalent iron was likely liberated under reducing conditions from the subglacial bedrock minerals weathered by microbial activity.

==Microbial ecosystem==
[[Image:blood falls1 f Low Res nsf.gov.jpg|thumb|300px|A schematic cross-section of Blood Falls showing how subglacial microbial communities have survived in cold, darkness, and absence of oxygen for a million years in brine water below Taylor Glacier.]]

Chemical and microbial analyses both indicate that a rare subglacial [[Earth:Ecosystem|ecosystem]] of [[Biology:Autotroph|autotroph]]ic [[Biology:Bacteria|bacteria]] developed that metabolizes sulfate and [[Chemistry:Ferric|ferric]] ions.<ref name=ScienceNOW>{{Cite news |url=https://www.science.org/content/article/ancient-ecosystem-discovered-beneath-antarctic-glacier |title=Ancient Ecosystem Discovered Beneath Antarctic Glacier |work=Science |first=Jackie |last=Grom |date=April 16, 2009 |access-date=April 17, 2009}}</ref><ref>{{Cite journal |title=A Contemporary Microbially Maintained Subglacial Ferrous "Ocean" |journal=Science |first1=Jill A. |last1=Mikucki |first2=Ann |last2=Pearson |first3=David T. |last3=Johnston |first4=Alexandra V. |last4=Turchyn |first5=James |last5=Farquhar |first6=Daniel P. |last6=Schrag |first7=Ariel D. |last7=Anbar |first8=John C. |last8=Priscu |first9=Peter A. |last9=Lee |display-authors=1 |volume=324 |issue=5925 |pages=397–400 |date=April 17, 2009 |doi=10.1126/science.1167350 |pmid=19372431 |bibcode=2009Sci...324..397M|s2cid=44802632 }}</ref> According to [[Biology:Geomicrobiology|geomicrobiologist]] [[Biography:Jill Mikucki|Jill Mikucki]] at the [[Organization:University of Tennessee|University of Tennessee]], water samples from Blood Falls contained at least 17 different types of [[Biology:Microorganism|microbes]], and almost no oxygen.<ref name=ScienceNOW/> An explanation may be that the microbes use sulfate to respire with ferric ions and metabolize the trace levels of [[Chemistry:Organic matter|organic matter]] trapped with them.  Such a metabolic process had never before been observed in nature.<ref name=ScienceNOW/>

A puzzling observation is the coexistence of ferrous and sulfate ions under [[Earth:Anoxic waters|anoxic]] conditions. No [[Chemistry:Sulfide|sulfide]] anions are found in the system. This suggests an intricate and poorly understood interaction between the [[Biology:Sulfur cycle|sulfur]] and the [[Earth:Iron cycle|iron]] biochemical cycles.

In December 2014, scientists and engineers led by Mikucki returned to Taylor Glacier and used a probe called [[Engineering:IceMole|IceMole]], designed by a German collaboration, to melt into the glacier and directly sample the salty water (brine) that feeds Blood Falls.<ref name="AntSun20150304">{{Cite news |url=http://antarcticsun.usap.gov/science/contenthandler.cfm?id=4122 |title=Lifeblood of a Glacier |work=The Antarctic Sun |first=Peter |last=Rejcek |date=March 4, 2015 |access-date=March 4, 2015}}</ref>

Samples were analyzed, and revealed a cold ({{Convert|-7|C|F|abbr=|sp=us}}), iron-rich (3.4&nbsp;mM) subglacial brine (8% [[Chemistry:Sodium chloride|sodium chloride]]). From these samples, scientists isolated and characterized a type of bacteria capable of growing in salty water ([[Biology:Halophile|halophilic]]), that thrives in the cold ([[Biology:Psychrophile|psychrophile]]), and is [[Biology:Heterotroph|heterotroph]]ic, which they assigned to the genus ''[[Biology:Marinobacter|Marinobacter]]''.<ref name="Carter 2016">{{cite journal |title=Induction of cryptic metabolites from a rare Antarctic psychrophile, ''Marinobacter'' sp. |journal=Planta Medica |first1=J. |last1=Carter |first2=M. |last2=Judge |first3=L. |last3=McLean |first4=J. |last4=Mikucki |first5=L. A. |last5=Giddings |display-authors=1 |volume=82 |issue=S 01 |at=P581 |date=December 2016 |issn=0032-0943 |doi=10.1055/s-0036-1596642}}</ref> DNA [[Biology:Bioinformatics|bioinformatic]] analysis indicated the presence of at least four gene clusters involved in secondary metabolism. Two gene clusters are related to the production of [[Chemistry:Aryl|aryl]] [[Chemistry:Polyene|polyene]]s, which function as [[Biology:Antioxidant|antioxidant]]s that protect the bacteria from [[Biology:Reactive oxygen species|reactive oxygen species]].<ref name="Carter 2016"/> Another gene cluster seems to be involved in [[Biology:Terpene|terpene]] biosynthesis, most likely to produce pigments.<ref name="Carter 2016"/>  Other bacteria identified are ''Thiomicrospira'' sp., and ''[[Biology:Desulfocapsa|Desulfocapsa]]'' sp.

==Implications for the Snowball Earth hypothesis==
According to Mikucki ''et al.'' (2009), the now-inaccessible subglacial pool was sealed off {{nowrap|1.5 to 2 million}} years ago and transformed into a kind of "time capsule", isolating the ancient microbial population for a sufficiently long time to evolve independently of other similar marine organisms. It explains how other microorganisms could have survived when the Earth (according to the [[Earth:Snowball Earth|Snowball Earth]] hypothesis) was entirely frozen over.

Ice-covered oceans might have been the only [[Biology:Refugium (population biology)|refugium]] for microbial ecosystems when the Earth apparently was covered by glaciers at tropical latitudes during the [[Earth:Proterozoic|Proterozoic]] [[Earth:Geologic time scale#Terminology|eon]] about {{nowrap|650 to 750 million}} years ago.

==Implications for astrobiology==
This unusual place offers scientists a unique opportunity to study deep subsurface microbial life in extreme conditions without the need to drill deep [[Engineering:Borehole|borehole]]s in the polar [[Earth:Ice cap|ice cap]], with the associated contamination risk of a fragile and still-intact environment.

The study of harsh environments on Earth is useful to understand the range of conditions to which life can adapt and to advance assessment of the possibility of life elsewhere in the solar system, in places such as [[Astronomy:Mars|Mars]] or [[Astronomy:Europa (moon)|Europa]], an ice-covered moon of [[Astronomy:Jupiter|Jupiter]]. Scientists of the [[Organization:NASA Astrobiology Institute|NASA Astrobiology Institute]] speculate that these worlds could contain subglacial liquid water environments favorable to hosting elementary forms of life, which would be better protected at depth from [[Physics:Ultraviolet|ultraviolet]] and [[Astronomy:Cosmic ray|cosmic radiation]] than on the surface.<ref>{{Cite web |url=http://mars.jpl.nasa.gov/programmissions/science/goal1/ |title=Science Goal 1: Determine if Life Ever Arose On Mars |publisher=NASA |series=Mars Exploration Program |access-date=October 17, 2010}}</ref><ref>{{Cite web |url=https://science.nasa.gov/science-news/science-at-nasa/2001/ast05jan_1/ |title=The Case of the Missing Mars Water |publisher=NASA |series=Science@NASA |date=January 5, 2001 |access-date=April 20, 2009}}</ref>

==See also==
* [[Earth:Extremophile|Extremophile]]s (organisms resistant to extreme conditions)
** [[Biology:Psychrophile|Psychrophile]] (bacteria resistant to cold)
* Cryoconcentration of hypersaline [[Earth:Brine|brine]]s
** [[Physics:Eutectic system|Eutectic system]]
** [[Chemistry:Freezing-point depression|Freezing-point depression]]
* [[Astronomy:Life on Mars|Life on Mars]]

==References==
{{reflist}}

==Further reading==
* {{Cite journal |title=Saline Lakes' Response to Global Change |journal=Aquatic Geochemistry |first=Abraham |last=Lerman |volume=15 |issue=1–2 |pages=1–5 |date=February 2009 |doi=10.1007/s10498-008-9058-8|s2cid=129653802 }}
* {{Cite journal |title=The Saline Lakes of the McMurdo Dry Valleys, Antarctica |journal=Aquatic Geochemistry |first1=William J. |last1=Green |first2=W. Berry |last2=Lyons |volume=15 |issue=1–2 |pages=321–348 |date=February 2009 |doi=10.1007/s10498-008-9052-1|s2cid=128898063 }}
* {{Cite news |url=http://content.time.com/time/health/article/0,8599,1892289,00.html |title=An Organism Survives Antarctica, and Maybe Mars |work={{wipe|Time (magazine)}} |first=Jeffrey |last=Kluger |date=April 18, 2009}}
* {{Cite news |url=http://tierneylab.blogs.nytimes.com/2009/04/19/the-dark-secret-at-blood-falls/ |title=The Dark Secret at Blood Falls |work={{wipe|The New York Times}} |first=John |last=Tierney |date=April 19, 2009}}
* {{Cite news |url=https://www.sciencedaily.com/releases/2009/04/090416144512.htm |title=Newly Discovered Iron-breathing Species Have Lived In Cold Isolation For Millions Of Years |work=ScienceDaily |agency=Harvard University |date=April 17, 2009}}
* {{cite journal |title=An englacial hydrologic system of brine within a cold glacier: Blood Falls, McMurdo Dry Valleys, Antarctica |journal=Journal of Glaciology |volume=63 |issue=239 |first1=Jessica A. |last1=Badgeley |first2=Erin C. |last2=Pettit |first3=Christina G. |last3=Carr |first4=Slawek |last4=Tulaczyk |first5=Jill A. |last5=Mikucki |first6=W. Berry |last6=Lyons |display-authors=3 |pages=387–400 |date=24 April 2017 |doi=10.1017/jog.2017.16|bibcode=2017JGlac..63..387B |doi-access=free }}

==External links==
* [https://earthobservatory.nasa.gov/IOTD/view.php?id=35535 Blood Falls, Antarctica's Dry Valleys] by [[Astronomy:NASA Earth Observatory|NASA Earth Observatory]]
* {{YouTube|id=gKtWiFyyOGM|title=Blood Falls - 100 Wonders}} by Atlas Obscura

{{Extremophile}}
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[[Category:Geomicrobiology]]

{{Sourceattribution|Blood Falls}}