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South Pacific Gyre

October 18, 2023

The Southern Pacific Gyre is part of the Earth's system of rotating ocean currents, bounded by the Equator to the north, Australia to the west, the Antarctic Circumpolar Current to the south, and South America to the east.[1] The center of the South Pacific Gyre is the oceanic pole of inaccessibility, the site on Earth farthest from any continents and productive ocean regions and is regarded as Earth's largest oceanic desert.[2] With an area of 37 million square kilometres it makes up ~10 % of the Earth's ocean surface.[3] The gyre, as with Earth's other four gyres, contains an area with elevated concentrations of pelagic plastics, chemical sludge, and other debris known as the South Pacific garbage patch.[4]

Sediment flux and accumulation Edit

 
The South Pacific Gyre.

Earth's trade winds and Coriolis force cause the ocean currents in South Pacific Ocean to circulate counterclockwise. The currents act to isolate the center of the gyre from nutrient upwelling and few nutrients are transported there by the wind (eolian processes) because there is relatively little land in the Southern Hemisphere to supply dust to the prevailing winds. The low levels of nutrients in the region result in extremely low primary productivity in the ocean surface and subsequently very low flux of organic material settling to the ocean floor as marine snow. The low levels of biogenic and eolian deposition cause sediments to accumulate on the ocean floor very slowly. In the center of the South Pacific Gyre, the sedimentation rate is 0.1 to 1 m (0.3 to 3.3 ft) per million years. The sediment thickness (from basement basalts to the seafloor) ranges from 1 to 70m, with thinner sediments occurring closer to the center of the Gyre. The low flux of particles to the South Pacific Gyre cause the water there to be the clearest seawater in the world.[2]

Subseafloor biosphere Edit

Beneath the seafloor, the marine sediments and surrounding porewaters contain an unusual subseafloor biosphere. Despite extremely low amounts of buried organic material, microbes live throughout the entire sediment column. Average cell abundances and net rates of respiration are a few orders of magnitude lower than in any other subseafloor biosphere previously studied.[2]

The South Pacific Gyre subseafloor community is also unusual because it contains oxygen throughout the entire sediment column. In other subseafloor biospheres, microbial respiration will break down organic material and consume all the oxygen near the seafloor leaving the deeper portions of the sediment column anoxic. However, in the South Pacific Gyre the low levels of organic material, the low rates of respiration, and the thin sediments allow the porewater to be oxygenated throughout the entire sediment column.[5] In July 2020, marine biologists reported that aerobic microorganisms (mainly), in "quasi-suspended animation", were found in organically poor sediments, up to 101.5 million years old, 250 feet below the seafloor of the region and could be the longest-living life forms ever found.[6][7]

Radiolytic H2: a benthic energy source Edit

Benthic microbes in organic-poor sediments in oligotrophic oceanic regions, such as the South Pacific Gyre, are hypothesized to metabolize radiolytic hydrogen (H2) as a primary energy source.[8][2][9]

The oceanic regions within the South Pacific Gyre (SPG), and other subtropical gyres, are characterized by low primary productivity in the surface ocean; i.e. they are oligotrophic. The center of the SPG is the furthest oceanic province from a continent and contains the clearest ocean water on Earth[2] with ≥ 0.14 mg chlorophyll per m3.[2] Carbon exported to the underlying deep ocean sediments via the biological pump is limited in the SPG, resulting in sedimentation rates that are orders of magnitude lower than in productive zones, e.g. continental margins.[2]

Typically, deep-ocean benthic microbial life utilizes the organic carbon exported from surface waters. In oligotrophic regions where sediments are poor in organic material, subsurface benthic life exploits other primary energy sources, such as molecular hydrogen (H2).[10][8][2][9]

Radiolysis of interstitial water Edit

Radioactive decay of naturally occurring uranium (238U and 235U), thorium (232Th), and potassium (40K) in seafloor sediments collectively bombard the interstitial water with α, β, and γ radiation. The irradiation ionizes and breaks apart water molecules, eventually yielding H2. The products of this reaction are aqueous electrons (e−aq), hydrogen radicals (H·), protons (H+), and hydroxyl radicals (OH·).[9] The radicals are highly reactive, therefore short-lived, and recombine to produce hydrogen peroxide (H2O2), and molecular hydrogen (H2).[10]

The amount of radiolytic H2 production in seafloor sediments is dependent on the quantities of radioactive isotopes present, sediment porosity, and grain size. These criteria indicate that certain sediment types, such as abyssal clays and siliceous oozes, may have higher radiolytic H2 production relative to other seafloor strata.[9] Also, radiolytic H2 production has been measured in seawater intrusions into subseafloor basement basalts.[10]

Microbial activity Edit

The microbes best suited to utilize radiolytic H2 are the knallgas bacteria, lithoautotrophes, that obtain energy by oxidizing molecular hydrogen via the knallgas reaction:[11]

              H2 (aq) + 0.5O2 (aq)  H2O (l)[12]

In the surface layer of sediment cores from oligotrophic regions of the SPG, O2 is the primary electron acceptor used in microbial metabolisms. The O2 concentrations decline slightly in surface sediment (initial few decimeters) and are unchanged to depth. Meanwhile, nitrate concentrations slightly increase downward or remain constant in sediment column at approximately the same concentrations as the deep water above the seafloor. Measured negative fluxes of O2 in the surface layer demonstrate that a relatively low abundance of aerobic microbes that are oxidizing the minimally deposited organic matter from the ocean above. Extremely low cell counts corroborate that microbes exist in small quantities in these surface sediments. In contrast, a sediment cores outside of the SPG show rapid elimination of O2 and nitrate at 1 meter below sea floor (mbsf) and 2.5 mbsf, respectively. This is evidence of much higher microbial activity, both aerobic and anaerobic.[9][2]

The production of radiolytic H2 (electron donor) is stoichiometrically balanced with production of 0.5 O2 (electron acceptor), therefore a measurable flux in O2 is not expected in the substrate if both radiolysis of water and knallgas bacteria co-occur.[9][2] So, despite the known occurrence of radiolytic H2 production, molecular hydrogen is below the detectable limit in the SPG cores, leading to the hypothesis that H2 is the primary energy source in low-organic seafloor sediments below the surface layer.[9][2][8]

Water color Edit

Satellite data images show that some areas in the gyre are greener than the surrounding clear blue water, which is frequently interpreted as areas with higher concentrations of living phytoplankton. However, the assumption that greener ocean water always contains more phytoplankton is not always true. Even though the South Pacific Gyre contains these patches of green water, it has very little organism growth. Instead, some studies hypothesize that these green patches are a result of the accumulated waste of marine life. The optical properties of the South Pacific Gyre remain largely unexplored.[13]

Garbage patch Edit

This section is an excerpt from South Pacific garbage patch.[edit]
 
The South Pacific Gyre can be seen in the lack of oceanic currents off the west coast of South America. Map of ocean currents circa 1943
 
This photo demonstrates the dispersal of plastic fragments of various sizes
Visualization of the flow pattern of ocean pollutants
The South Pacific garbage patch is an area of ocean with increased levels of marine debris and plastic particle pollution, within the ocean's pelagic zone. This area is in the South Pacific Gyre, which itself spans from waters east of Australia to the South American continent, as far north as the Equator, and south until reaching the Antarctic Circumpolar Current.[14] The degradation of plastics in the ocean also leads to a rise in the level of toxics in the area.[15] The garbage patch was confirmed in mid-2017, and has been compared to the Great Pacific garbage patch's state in 2007, making the former ten years younger. The South Pacific garbage patch is not visible on satellites, and is not a landmass. Most particles are smaller than a grain of rice.[16] A researcher said: "This cloud of microplastics extends both vertically and horizontally. It's more like smog than a patch".[16]

References Edit

  1. ^ "Anybody home? Little response in Pacific gyre". NBC News. Associated Press. 22 June 2009. Retrieved 3 January 2021.
  2. ^ a b c d e f g h i j k D'Hondt, Steven; et al. (July 2009). "Subseafloor Sediment In South Pacific Gyre One Of Least Inhabited Places On Earth". Proceedings of the National Academy of Sciences of the United States of America. 106 (28): 11651–11656. Bibcode:2009PNAS..10611651D. doi:10.1073/pnas.0811793106. PMC 2702254. PMID 19561304.
  3. ^ Inc, Pelmorex Weather Networks (27 July 2020). "What lives in the Pacific's 'ocean desert'". The Weather Network. Retrieved 31 December 2022. {{cite web}}: |last= has generic name (help)
  4. ^ Montgomery, Hailey (28 July 2017). . Pelmorex Weather Networks. The Weather Network. Archived from the original on 28 November 2020. Retrieved 14 August 2017.
  5. ^ Fischer, J.P., et al. "Oxygen Penetration deep into the sediment of the South Pacific Gyre" Biogeoscience (Aug. 2009): 1467(6).
  6. ^ Wu, Katherine J. (28 July 2020). "These Microbes May Have Survived 100 Million Years Beneath the Seafloor – Rescued from their cold, cramped and nutrient-poor homes, the bacteria awoke in the lab and grew". Retrieved 31 July 2020.
  7. ^ Morono, Yuki; et al. (28 July 2020). "Aerobic microbial life persists in oxic marine sediment as old as 101.5 million years". Nature Communications. 11 (3626): 3626. Bibcode:2020NatCo..11.3626M. doi:10.1038/s41467-020-17330-1. PMC 7387439. PMID 32724059.
  8. ^ a b c Sauvage, J; et al. (2013). "Radiolysis and life in deep subseafloor sediment of the South Pacific Gyre". Goldschmidt 2013 Conference Abstracts: 2140.
  9. ^ a b c d e f g Blair, CC; et al. (2007). "Radiolytic Hydrogen and Microbial Respiration in Subsurface Sediments". Astrobiology. 7 (6): 951–970. Bibcode:2007AsBio...7..951B. doi:10.1089/ast.2007.0150. PMID 18163872.
  10. ^ a b c Dzaugis, ME; et al. (2016). "Radiolytic Hydrogen Production in the Subseafloor Basaltic Aquifer". Frontiers in Microbiology. 7: 76. doi:10.3389/fmicb.2016.00076. PMC 4740390. PMID 26870029.
  11. ^ Singleton P and D Sainsbury (2001). "Hydrogen-oxidizing bacteria (the 'hydrogen bacteria'; knallgas bacteria)". Dictionary of Microbiology and Molecular Biology. 3rd ed.
  12. ^ Amend JP and EL Shock (2001). "Energetics of overall metabolic reactions of thermophilic and hyperthermophilic Archaea and Bacteria". FEMS Microbiology Reviews. 25 (2): 175–243. doi:10.1111/j.1574-6976.2001.tb00576.x. PMID 11250035.
  13. ^ Claustre, Herve; Maritorena, Stephane (2003). "The many shades of ocean blue. (Ocean Science)". Science. 302 (5650): 1514–1515. doi:10.1126/science.1092704. PMID 14645833. S2CID 128518190.
  14. ^ "South Pacific Gyre – Correntes Oceânicas" – via Google Sites.
  15. ^ Barry, Carolyn (20 August 2009). "Plastic Breaks Down in Ocean, After All And Fast". National Geographic Society.
  16. ^ a b Nield, David (25 July 2017). "There's Another Huge Plastic Garbage Patch in The Pacific Ocean". Sciencealert.com. ScienceAlert.

Further reading Edit

October 18, 2023
south, pacific, gyre, southern, pacific, gyre, part, earth, system, rotating, ocean, currents, bounded, equator, north, australia, west, antarctic, circumpolar, current, south, south, america, east, center, oceanic, pole, inaccessibility, site, earth, farthest. The Southern Pacific Gyre is part of the Earth s system of rotating ocean currents bounded by the Equator to the north Australia to the west the Antarctic Circumpolar Current to the south and South America to the east 1 The center of the South Pacific Gyre is the oceanic pole of inaccessibility the site on Earth farthest from any continents and productive ocean regions and is regarded as Earth s largest oceanic desert 2 With an area of 37 million square kilometres it makes up 10 of the Earth s ocean surface 3 The gyre as with Earth s other four gyres contains an area with elevated concentrations of pelagic plastics chemical sludge and other debris known as the South Pacific garbage patch 4 Contents 1 Sediment flux and accumulation 2 Subseafloor biosphere 2 1 Radiolytic H2 a benthic energy source 2 1 1 Radiolysis of interstitial water 2 1 2 Microbial activity 3 Water color 4 Garbage patch 5 References 6 Further readingSediment flux and accumulation Edit nbsp The South Pacific Gyre Earth s trade winds and Coriolis force cause the ocean currents in South Pacific Ocean to circulate counterclockwise The currents act to isolate the center of the gyre from nutrient upwelling and few nutrients are transported there by the wind eolian processes because there is relatively little land in the Southern Hemisphere to supply dust to the prevailing winds The low levels of nutrients in the region result in extremely low primary productivity in the ocean surface and subsequently very low flux of organic material settling to the ocean floor as marine snow The low levels of biogenic and eolian deposition cause sediments to accumulate on the ocean floor very slowly In the center of the South Pacific Gyre the sedimentation rate is 0 1 to 1 m 0 3 to 3 3 ft per million years The sediment thickness from basement basalts to the seafloor ranges from 1 to 70m with thinner sediments occurring closer to the center of the Gyre The low flux of particles to the South Pacific Gyre cause the water there to be the clearest seawater in the world 2 Subseafloor biosphere EditBeneath the seafloor the marine sediments and surrounding porewaters contain an unusual subseafloor biosphere Despite extremely low amounts of buried organic material microbes live throughout the entire sediment column Average cell abundances and net rates of respiration are a few orders of magnitude lower than in any other subseafloor biosphere previously studied 2 The South Pacific Gyre subseafloor community is also unusual because it contains oxygen throughout the entire sediment column In other subseafloor biospheres microbial respiration will break down organic material and consume all the oxygen near the seafloor leaving the deeper portions of the sediment column anoxic However in the South Pacific Gyre the low levels of organic material the low rates of respiration and the thin sediments allow the porewater to be oxygenated throughout the entire sediment column 5 In July 2020 marine biologists reported that aerobic microorganisms mainly in quasi suspended animation were found in organically poor sediments up to 101 5 million years old 250 feet below the seafloor of the region and could be the longest living life forms ever found 6 7 Radiolytic H2 a benthic energy source Edit Benthic microbes in organic poor sediments in oligotrophic oceanic regions such as the South Pacific Gyre are hypothesized to metabolize radiolytic hydrogen H2 as a primary energy source 8 2 9 The oceanic regions within the South Pacific Gyre SPG and other subtropical gyres are characterized by low primary productivity in the surface ocean i e they are oligotrophic The center of the SPG is the furthest oceanic province from a continent and contains the clearest ocean water on Earth 2 with 0 14 mg chlorophyll per m3 2 Carbon exported to the underlying deep ocean sediments via the biological pump is limited in the SPG resulting in sedimentation rates that are orders of magnitude lower than in productive zones e g continental margins 2 Typically deep ocean benthic microbial life utilizes the organic carbon exported from surface waters In oligotrophic regions where sediments are poor in organic material subsurface benthic life exploits other primary energy sources such as molecular hydrogen H2 10 8 2 9 Radiolysis of interstitial water Edit Radioactive decay of naturally occurring uranium 238U and 235U thorium 232Th and potassium 40K in seafloor sediments collectively bombard the interstitial water with a b and g radiation The irradiation ionizes and breaks apart water molecules eventually yielding H2 The products of this reaction are aqueous electrons e aq hydrogen radicals H protons H and hydroxyl radicals OH 9 The radicals are highly reactive therefore short lived and recombine to produce hydrogen peroxide H2O2 and molecular hydrogen H2 10 The amount of radiolytic H2 production in seafloor sediments is dependent on the quantities of radioactive isotopes present sediment porosity and grain size These criteria indicate that certain sediment types such as abyssal clays and siliceous oozes may have higher radiolytic H2 production relative to other seafloor strata 9 Also radiolytic H2 production has been measured in seawater intrusions into subseafloor basement basalts 10 Microbial activity Edit The microbes best suited to utilize radiolytic H2 are the knallgas bacteria lithoautotrophes that obtain energy by oxidizing molecular hydrogen via the knallgas reaction 11 H2 aq 0 5O2 aq H2O l 12 In the surface layer of sediment cores from oligotrophic regions of the SPG O2 is the primary electron acceptor used in microbial metabolisms The O2 concentrations decline slightly in surface sediment initial few decimeters and are unchanged to depth Meanwhile nitrate concentrations slightly increase downward or remain constant in sediment column at approximately the same concentrations as the deep water above the seafloor Measured negative fluxes of O2 in the surface layer demonstrate that a relatively low abundance of aerobic microbes that are oxidizing the minimally deposited organic matter from the ocean above Extremely low cell counts corroborate that microbes exist in small quantities in these surface sediments In contrast a sediment cores outside of the SPG show rapid elimination of O2 and nitrate at 1 meter below sea floor mbsf and 2 5 mbsf respectively This is evidence of much higher microbial activity both aerobic and anaerobic 9 2 The production of radiolytic H2 electron donor is stoichiometrically balanced with production of 0 5 O2 electron acceptor therefore a measurable flux in O2 is not expected in the substrate if both radiolysis of water and knallgas bacteria co occur 9 2 So despite the known occurrence of radiolytic H2 production molecular hydrogen is below the detectable limit in the SPG cores leading to the hypothesis that H2 is the primary energy source in low organic seafloor sediments below the surface layer 9 2 8 Water color EditSatellite data images show that some areas in the gyre are greener than the surrounding clear blue water which is frequently interpreted as areas with higher concentrations of living phytoplankton However the assumption that greener ocean water always contains more phytoplankton is not always true Even though the South Pacific Gyre contains these patches of green water it has very little organism growth Instead some studies hypothesize that these green patches are a result of the accumulated waste of marine life The optical properties of the South Pacific Gyre remain largely unexplored 13 Garbage patch EditThis section is an excerpt from South Pacific garbage patch edit nbsp The South Pacific Gyre can be seen in the lack of oceanic currents off the west coast of South America Map of ocean currents circa 1943 nbsp This photo demonstrates the dispersal of plastic fragments of various sizes source source source source source source source Visualization of the flow pattern of ocean pollutants The South Pacific garbage patch is an area of ocean with increased levels of marine debris and plastic particle pollution within the ocean s pelagic zone This area is in the South Pacific Gyre which itself spans from waters east of Australia to the South American continent as far north as the Equator and south until reaching the Antarctic Circumpolar Current 14 The degradation of plastics in the ocean also leads to a rise in the level of toxics in the area 15 The garbage patch was confirmed in mid 2017 and has been compared to the Great Pacific garbage patch s state in 2007 making the former ten years younger The South Pacific garbage patch is not visible on satellites and is not a landmass Most particles are smaller than a grain of rice 16 A researcher said This cloud of microplastics extends both vertically and horizontally It s more like smog than a patch 16 References Edit Anybody home Little response in Pacific gyre NBC News Associated Press 22 June 2009 Retrieved 3 January 2021 a b c d e f g h i j k D Hondt Steven et al July 2009 Subseafloor Sediment In South Pacific Gyre One Of Least Inhabited Places On Earth Proceedings of the National Academy of Sciences of the United States of America 106 28 11651 11656 Bibcode 2009PNAS 10611651D doi 10 1073 pnas 0811793106 PMC 2702254 PMID 19561304 Inc Pelmorex Weather Networks 27 July 2020 What lives in the Pacific s ocean desert The Weather Network Retrieved 31 December 2022 a href Template Cite web html title Template Cite web cite web a last has generic name help Montgomery Hailey 28 July 2017 South Pacific Ocean Gyre Holds Massive Garbage Patch Pelmorex Weather Networks The Weather Network Archived from the original on 28 November 2020 Retrieved 14 August 2017 Fischer J P et al Oxygen Penetration deep into the sediment of the South Pacific Gyre Biogeoscience Aug 2009 1467 6 Wu Katherine J 28 July 2020 These Microbes May Have Survived 100 Million Years Beneath the Seafloor Rescued from their cold cramped and nutrient poor homes the bacteria awoke in the lab and grew Retrieved 31 July 2020 Morono Yuki et al 28 July 2020 Aerobic microbial life persists in oxic marine sediment as old as 101 5 million years Nature Communications 11 3626 3626 Bibcode 2020NatCo 11 3626M doi 10 1038 s41467 020 17330 1 PMC 7387439 PMID 32724059 a b c Sauvage J et al 2013 Radiolysis and life in deep subseafloor sediment of the South Pacific Gyre Goldschmidt 2013 Conference Abstracts 2140 a b c d e f g Blair CC et al 2007 Radiolytic Hydrogen and Microbial Respiration in Subsurface Sediments Astrobiology 7 6 951 970 Bibcode 2007AsBio 7 951B doi 10 1089 ast 2007 0150 PMID 18163872 a b c Dzaugis ME et al 2016 Radiolytic Hydrogen Production in the Subseafloor Basaltic Aquifer Frontiers in Microbiology 7 76 doi 10 3389 fmicb 2016 00076 PMC 4740390 PMID 26870029 Singleton P and D Sainsbury 2001 Hydrogen oxidizing bacteria the hydrogen bacteria knallgas bacteria Dictionary of Microbiology and Molecular Biology 3rd ed Amend JP and EL Shock 2001 Energetics of overall metabolic reactions of thermophilic and hyperthermophilic Archaea and Bacteria FEMS Microbiology Reviews 25 2 175 243 doi 10 1111 j 1574 6976 2001 tb00576 x PMID 11250035 Claustre Herve Maritorena Stephane 2003 The many shades of ocean blue Ocean Science Science 302 5650 1514 1515 doi 10 1126 science 1092704 PMID 14645833 S2CID 128518190 South Pacific Gyre Correntes Oceanicas via Google Sites Barry Carolyn 20 August 2009 Plastic Breaks Down in Ocean After All And Fast National Geographic Society a b Nield David 25 July 2017 There s Another Huge Plastic Garbage Patch in The Pacific Ocean Sciencealert com ScienceAlert Further reading EditDunning Brian 16 December 2008 Skeptoid 132 The Sargasso Sea and the Pacific Garbage Patch Skeptoid Retrieved from https en wikipedia org w index php title South Pacific Gyre amp oldid 1163138160, wikipedia, wiki, book, books, library,

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