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The Antarctic bottom water (AABW) is a type of water mass in the Southern Ocean surrounding Antarctica with temperatures ranging from −0.8 to 2 °C (35 °F) and absolute salinities from 34.6 to 35.0 g/kg.^[1] As the densest water mass of the oceans, AABW is found to occupy the depth range below 4000 m of all ocean basins that have a connection to the Southern Ocean at that level.^[2]

AABW is the densest bottom water, forming the lower branch of the large-scale movement in the world's oceans through thermohaline circulation.

AABW forms near the surface in coastal polynyas along the coastline of Antarctica^[3], where high rates of sea ice formation during winter leads to the densification of the surface waters through brine rejection^[4]. Since the water mass forms near the surface, it is responsible for the exchange of large quantities of heat with the atmosphere^[5]. AABW has a high oxygen content relative to the rest of the oceans' deep waters but this depletes over time. This water sinks at four distinct regions around the margins of the continent and forms the AABW; this process leads to ventilation of the deep ocean, or abyssal ventilation.^[6]

Formation and circulation

Antarctic bottom water is created in part due to the major overturning of ocean water.

Antarctic bottom water is formed in the Weddell and Ross Seas, off the Adélie Coast and by Cape Darnley from surface water cooling in polynyas and below the ice shelf.^[7] A unique feature of Antarctic bottom water is the cold surface wind blowing off the Antarctic continent.^[8] The surface winds advect sea ice away from the coast, creating polynyas which opens up the water surface to a cold atmosphere during winter, which further helps form more sea ice. Antarctic coastal polynyas form as much as 10% of the overall Southern Ocean sea ice during a single season^[9], amounting to about 2,000 km³ volume of sea ice^[10]. Surface water is enriched in salt from sea ice formation and cooled due to being exposed to a cold atmosphere during winter which increases the density of this water mass. Due to its increased density, it flows down the Antarctic continental margin and continues north along the bottom. It is the densest water in the open ocean, and underlies other bottom and intermediate waters throughout most of the southern hemisphere. The Weddell Sea Bottom Water is the densest component of the Antarctic bottom water.

A major source water for the formation of AABW is the warm offshore watermass known as the Circumpolar Deep Water (CDW; salinity > 35 g/kg and potential temperature > 0^oC)^[11]. These warm watermasses are cooled by coastal polynyas to form the denser AABW^[12]. Coastal polynyas that form AABW help prevent the intruding warm CDW water masses from gaining access to the base of ice shelves^[13], hence acting to protect ice shelves from enhanced basal melting due to oceanic warming. In areas like the Amundsen Sea, where coastal polynya activity has diminished to the point where dense water formation is hindered^[14], the neighboring ice shelves have started to retreat and may be on the brink of collapse^[15].

Evidence indicates that Antarctic bottom water production through the Holocene (last 10,000 years) is not in a steady-state condition;^[16] that is to say that bottom water production sites shift along the Antarctic margin over decade to century timescales as conditions for the existence of polynyas change. For example, the calving of the Mertz Glacier, which occurred on 12–13 February 2010, dramatically changed the environment for producing bottom water, reducing export by up to 23% in the region of Adelie Land.^[17] Evidence from sediment cores, containing layers of cross-bedded sediments indicating phases of stronger bottom currents, collected on the Mac.Robertson shelf ^[18] and Adélie Land^[19] suggests that they have switched "on" and "off" again as important bottom water production sites over the last several thousand years.

Antarctic bottom water flow in the Equatorial Atlantic

Atlantic Ocean

The Vema Channel, a deep trough in the Rio Grande Rise of the South Atlantic at 31°18′S 39°24′W / 31.3°S 39.4°W / -31.3; -39.4, is an important conduit for Antarctic Bottom Water and Weddell Sea Bottom Water migrating north.^[20] Upon reaching the equator, about one-third of the northward flowing Antarctic bottom water enters the Guiana Basin, mainly through the southern half of the Equatorial Channel at 35°W. The other part recirculates and some of it flows through the Romanche Fracture Zone into the eastern Atlantic.^[21]

In the Guiana Basin, west of 40°W, the sloping topography and the strong, eastward flowing deep western boundary current might prevent the Antarctic bottom water from flowing west: thus it has to turn north at the eastern slope of the Ceará Rise. At 44°W, north of the Ceará Rise, Antarctic bottom water flows west in the interior of the basin. A large fraction of the Antarctic bottom water enters the eastern Atlantic through the Vema Fracture Zone.^[21]

Indian Ocean

In the Indian Ocean the Crozet-Kerguelen Gap allows Antarctic bottom water to move toward the equator. This northward movement amounts to 2.5 Sv. It takes the Antarctic Bottom Water 23 years to reach the Crozet-Kerguelen Gap.^[22] South of Africa, Antarctic bottom water flow northwards through the Agulhas Basin and then east through the Agulhas Passage and over the southern margins of the Agulhas Plateau from where it is transported to into the Mozambique Basin.^[23]

Climate change

Climate change and the subsequent melting of the Southern ice sheet have slowed the formation of AABW, and this slowdown is likely to continue. A complete shutdown of AABW formation is possible as soon as 2050.^[24] This shutdown would have dramatic effects on ocean circulation and global weather patterns.^{[citation needed]}

Potential for AABW Disruption

Due to the cold temperatures and high density of AABW, changes coming from increased surface water temperatures and increased ice melt can impact how the water flows.^[25] For surface water to become deep water, it must be very cold and saline. Much of the deep-water formation comes from brine rejection where the water deposited is extremely saline and cold, making it extremely dense. The increased ice melt that occurred starting in the early 2000s has created a period of fresher water between 2011-2015 within the bottom water.^[26] This has been distinctly prevalent in Antarctic bottom waters near West Antarctica primarily in the Weddell Sea area.^[26]

While the freshening of the AABW has corrected itself over the past few years with a decrease in ice melt, the potential for more ice melt in the future still poses a threat.^[26] With the potential increase in ice melt at extreme enough levels, it can have a serious impact on the ability for deep sea water to be formed. While this would create a slowdown referenced above, it may also create additional warming. Increased stratification coming from the fresher and warmer waters will reduce bottom and deep-water circulation and increase warm water flows around Antarctica.^[25] The sustained warmer surface waters would only increase the level of ice melt, stratification, and the slowdown of the AABW circulation and formation. Additionally, without the presence of those colder waters producing brine rejection which deposits to the AABW, there may eventually be no formation of bottom water around Antarctica anymore.^[25] This would impact more than Antarctica as AABW plays a major role in bottom water formation and deep-sea circulation which deposits oxygen to the deep sea and is a major carbon sink. Without these connections, the deep sea will become drastically changed with the potential for collapse in entire deep-sea communities.^[25]

Some studies indicate that WSBW formation in the Weddell Sea is dominantly driven by wind-driven sea ice changes, however, and that increased sea ice formation overcompensates for the melting of ice sheets, rendering the effects of melting Antarctic glaciers on WSBW minimal.^[27]

References

^ Schmidt, Christina; Morrison, Adele K.; England, Matthew H. (17 June 2023). "Wind– and Sea-Ice–Driven Interannual Variability of Antarctic Bottom Water Formation". Journal of Geophysical Research: Oceans. 128 (6). doi:10.1029/2023JC019774. S2CID 259468175.
^ "AMS Glossary of Meteorology, Antarctic Bottom Water". American Meteorological Society. Retrieved 29 June 2023.
^ Portela, Esther; Rintoul, Stephen R.; Herraiz‐Borreguero, Laura; Roquet, Fabien; Bestley, Sophie; van Wijk, Esmee; Tamura, Takeshi; McMahon, Clive R.; Guinet, Christophe; Harcourt, Robert; Hindell, Mark A. (2022-12). "Controls on Dense Shelf Water Formation in Four East Antarctic Polynyas". Journal of Geophysical Research: Oceans. 127 (12). doi:10.1029/2022JC018804. ISSN 2169-9275. {{cite journal}}: Check date values in: |date= (help)
^ Ohshima, Kay I.; Fukamachi, Yasushi; Williams, Guy D.; Nihashi, Sohey; Roquet, Fabien; Kitade, Yujiro; Tamura, Takeshi; Hirano, Daisuke; Herraiz-Borreguero, Laura; Field, Iain; Hindell, Mark; Aoki, Shigeru; Wakatsuchi, Masaaki (2013-03). "Antarctic Bottom Water production by intense sea-ice formation in the Cape Darnley polynya". Nature Geoscience. 6 (3): 235–240. doi:10.1038/ngeo1738. ISSN 1752-0908. {{cite journal}}: Check date values in: |date= (help)
^ Renfrew, Ian A.; King, John C.; Markus, Thorsten (2002-06). "Coastal polynyas in the southern Weddell Sea: Variability of the surface energy budget". Journal of Geophysical Research: Oceans. 107 (C6). doi:10.1029/2000JC000720. ISSN 0148-0227. {{cite journal}}: Check date values in: |date= (help)
^ Gunn, Kathryn L.; Rintoul, Stephen R.; England, Matthew H.; Bowen, Melissa M. (June 2023). "Recent reduced abyssal overturning and ventilation in the Australian Antarctic Basin". Nature Climate Change. 13 (6): 537–544. doi:10.1038/s41558-023-01667-8.
^ Talley, Lynne (1999). "Some aspects of ocean heat transport by the shallow, intermediate and deep overturning circulations". Mechanisms of Global Climate Change at Millennial Time Scales. Geophysical Monograph Series. Vol. 112. pp. 1–22. Bibcode:1999GMS...112....1T. doi:10.1029/GM112p0001. ISBN 0-87590-095-X.
^ Massom, R.; Michael, K.; Harris, P.T.; Potter, M.J. (1998). "The distribution and formative processes of latent heat polynyas in East Antarctica". Annals of Glaciology. 27: 420–426. Bibcode:1998AnGla..27..420M. doi:10.3189/1998aog27-1-420-426.
^ Tamura, Takeshi; Ohshima, Kay I.; Nihashi, Sohey (2008-04). "Mapping of sea ice production for Antarctic coastal polynyas". Geophysical Research Letters. 35 (7). doi:10.1029/2007GL032903. ISSN 0094-8276. {{cite journal}}: Check date values in: |date= (help)
^ Tamura, Takeshi; Ohshima, Kay I.; Fraser, Alexander D.; Williams, Guy D. (2016-05). "Sea ice production variability in Antarctic coastal polynyas". Journal of Geophysical Research: Oceans. 121 (5): 2967–2979. doi:10.1002/2015JC011537. ISSN 2169-9275. {{cite journal}}: Check date values in: |date= (help)
^ Morrison, A. K.; Hogg, A. McC.; England, M. H.; Spence, P. (2020-05). "Warm Circumpolar Deep Water transport toward Antarctica driven by local dense water export in canyons". Science Advances. 6 (18). doi:10.1126/sciadv.aav2516. ISSN 2375-2548. PMC 7195130. PMID 32494658. {{cite journal}}: Check date values in: |date= (help)CS1 maint: PMC format (link)
^ Williams, G. D.; Herraiz-Borreguero, L.; Roquet, F.; Tamura, T.; Ohshima, K. I.; Fukamachi, Y.; Fraser, A. D.; Gao, L.; Chen, H.; McMahon, C. R.; Harcourt, R.; Hindell, M. (2016-08-23). "The suppression of Antarctic bottom water formation by melting ice shelves in Prydz Bay". Nature Communications. 7 (1): 12577. doi:10.1038/ncomms12577. ISSN 2041-1723.
^ Narayanan, Aditya; Gille, Sarah T.; Mazloff, Matthew R.; du Plessis, Marcel D.; Murali, K.; Roquet, Fabien (2023-06). "Zonal Distribution of Circumpolar Deep Water Transformation Rates and Its Relation to Heat Content on Antarctic Shelves". Journal of Geophysical Research: Oceans. 128 (6). doi:10.1029/2022JC019310. ISSN 2169-9275. {{cite journal}}: Check date values in: |date= (help)
^ Moorman, Ruth; Thompson, Andrew F.; Wilson, Earle A. (2023-08-28). "Coastal Polynyas Enable Transitions Between High and Low West Antarctic Ice Shelf Melt Rates". Geophysical Research Letters. 50 (16). doi:10.1029/2023GL104724. ISSN 0094-8276.
^ Naughten, Kaitlin A.; Holland, Paul R.; De Rydt, Jan (2023-11). "Unavoidable future increase in West Antarctic ice-shelf melting over the twenty-first century". Nature Climate Change. 13 (11): 1222–1228. doi:10.1038/s41558-023-01818-x. ISSN 1758-6798. {{cite journal}}: Check date values in: |date= (help)
^ Broecker, W. S.; Peacock, S. L.; Walker, S.; Weiss, R.; Fahrbach, E.; Schroeder, M.; Mikolajewicz, U.; Heinze, C.; Key, R.; Peng, T.-H.; Rubin, S. (1998). "How much deep water is formed in the Southern Ocean?". Journal of Geophysical Research: Oceans. 103 (C8): 15833–15843. Bibcode:1998JGR...10315833B. doi:10.1029/98JC00248.
^ Kusahara, Kazuya; Hasumi, Hiroyasu; Williams, Guy D. (2011). "Impact of the Mertz Glacier Tongue calving on dense water formation and export". Nature Communications. 2 (1): 159. Bibcode:2011NatCo...2..159K. doi:10.1038/ncomms1156. PMID 21245840.
^ Harris, P.T. (2000). "Ripple cross-laminated sediments on the East Antarctic shelf: evidence for episodic bottom water production during the Holocene?". Marine Geology. 170 (3–4): 317–330. Bibcode:2000MGeol.170..317H. doi:10.1016/s0025-3227(00)00096-7.
^ Harris, P.T.; Brancolini, G.; Armand, L.; Busetti, M.; Beaman, R.J.; Giorgetti, G.; Prestie, M.; Trincardi, F. (2001). "Continental shelf drift deposit indicates non-steady state Antarctic bottom water production in the Holocene". Marine Geology. 179 (1–2): 1–8. Bibcode:2001MGeol.179....1H. doi:10.1016/s0025-3227(01)00183-9.
^ "AMS Glossary, Vema Channel". American Meteorological Society. Retrieved 2012-02-20.^{[permanent dead link]}
^ ^a ^b Rhein, Monika; Stramma, Lothar; Krahmann, Gerd (1998). "The spreading of Antarctic bottom water in the tropical Atlantic" (PDF). Deep-Sea Research Part I. 45 (4–5): 507–527. Bibcode:1998DSRI...45..507R. CiteSeerX 10.1.1.571.6529. doi:10.1016/S0967-0637(97)00030-7. Retrieved 2012-02-14.
^ Haine, T. W. N.; Watson, A. J.; Liddicoat, M. I.; Dickson, R. R. (1998). "The flow of Antarctic bottom water to the southwest Indian Ocean estimated using CFCs". Journal of Geophysical Research. 103 (C12): 27637–27653. Bibcode:1998JGR...10327637H. doi:10.1029/98JC02476.
^ Uenzelmann-Neben, G.; Huhn, K. (2009). "Sedimentary deposits on the southern South African continental margin: Slumping versus non-deposition or erosion by oceanic currents?" (PDF). Marine Geology. 266 (1–4): 65–79. Bibcode:2009MGeol.266...65U. doi:10.1016/j.margeo.2009.07.011. Retrieved 1 April 2015.
^ Hansen, James; Sato, Makiko; Hearty, Paul; Ruedy, Reto; Kelley, Maxwell; Masson-Delmotte, Valerie; Russell, Gary; Tselioudis, George; Cao, Junji (2016-03-22). "Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming could be dangerous". Atmospheric Chemistry and Physics. 16 (6): 3761–3812. arXiv:1602.01393. Bibcode:2016ACP....16.3761H. doi:10.5194/acp-16-3761-2016. ISSN 1680-7324. S2CID 9410444.
^ ^a ^b ^c ^d Silvano, A., Rintoul, S. R., Peña-Molino, B., Hobbs, W. R., van Wijk, E., Aoki, S., ... & Williams, G. D. (2018). Freshening by glacial meltwater enhances the melting of ice shelves and reduces the formation of Antarctic Bottom Water. Science advances, 4(4), eaap9467.
^ ^a ^b ^c Aoki, S., Yamazaki, K., Hirano, D., Katsumata, K., Shimada, K., Kitade, Y., ... & Murase, H. (2020). Reversal of freshening trend of Antarctic Bottom Water in the Australian-Antarctic Basin during 2010s. Scientific reports, 10(1), 1-7.
^ Zhou, Shenjie; Meijers, Andrew J. S.; Meredith, Michael P.; Abrahamsen, E. Povl; Holland, Paul R.; Silvano, Alessandro; Sallée, Jean-Baptiste; Østerhus, Svein (12 June 2023). "Slowdown of Antarctic Bottom Water export driven by climatic wind and sea-ice changes". Nature Climate Change. 13 (7): 701–709. doi:10.1038/s41558-023-01695-4. ISSN 1758-6798.

Glossary of Physical Oceanography
Steele, John H., Steve A. Thorpe and Karl K. Turekian, editors, Ocean Currents: A derivative of the Encyclopedia of Ocean Sciences, Academic Press, 1st ed., 2010 ISBN 978-0-08-096486-7
Seabrooke, James M.; Hufford, Gary L.; Elder, Robert B. (1971). "Formation of Antarctic Bottom Water in the Weddell Sea". Journal of Geophysical Research. 76 (9): 2164–2178. Bibcode:1971JGR....76.2164S. doi:10.1029/jc076i009p02164.
Fahrbach, E.; Rohardt, G.; Scheele, N.; Schroder, M.; Strass, V.; Wisotzki, A. (1995). "Formation and discharge of deep and bottom water in the northwestern Weddell Sea". Journal of Marine Research. 53 (4): 515–538. doi:10.1357/0022240953213089.

[Schmidt-1] Schmidt, Christina; Morrison, Adele K.; England, Matthew H. (17 June 2023). "Wind– and Sea-Ice–Driven Interannual Variability of Antarctic Bottom Water Formation". Journal of Geophysical Research: Oceans. 128 (6). doi:10.1029/2023JC019774. S2CID 259468175.

[2] "AMS Glossary of Meteorology, Antarctic Bottom Water". American Meteorological Society. Retrieved 29 June 2023.

[3] Portela, Esther; Rintoul, Stephen R.; Herraiz‐Borreguero, Laura; Roquet, Fabien; Bestley, Sophie; van Wijk, Esmee; Tamura, Takeshi; McMahon, Clive R.; Guinet, Christophe; Harcourt, Robert; Hindell, Mark A. (2022-12). "Controls on Dense Shelf Water Formation in Four East Antarctic Polynyas". Journal of Geophysical Research: Oceans. 127 (12). doi:10.1029/2022JC018804. ISSN 2169-9275. {{cite journal}}: Check date values in: |date= (help)

[4] Ohshima, Kay I.; Fukamachi, Yasushi; Williams, Guy D.; Nihashi, Sohey; Roquet, Fabien; Kitade, Yujiro; Tamura, Takeshi; Hirano, Daisuke; Herraiz-Borreguero, Laura; Field, Iain; Hindell, Mark; Aoki, Shigeru; Wakatsuchi, Masaaki (2013-03). "Antarctic Bottom Water production by intense sea-ice formation in the Cape Darnley polynya". Nature Geoscience. 6 (3): 235–240. doi:10.1038/ngeo1738. ISSN 1752-0908. {{cite journal}}: Check date values in: |date= (help)

[5] Renfrew, Ian A.; King, John C.; Markus, Thorsten (2002-06). "Coastal polynyas in the southern Weddell Sea: Variability of the surface energy budget". Journal of Geophysical Research: Oceans. 107 (C6). doi:10.1029/2000JC000720. ISSN 0148-0227. {{cite journal}}: Check date values in: |date= (help)

[Gunn-6] Gunn, Kathryn L.; Rintoul, Stephen R.; England, Matthew H.; Bowen, Melissa M. (June 2023). "Recent reduced abyssal overturning and ventilation in the Australian Antarctic Basin". Nature Climate Change. 13 (6): 537–544. doi:10.1038/s41558-023-01667-8.

[7] Talley, Lynne (1999). "Some aspects of ocean heat transport by the shallow, intermediate and deep overturning circulations". Mechanisms of Global Climate Change at Millennial Time Scales. Geophysical Monograph Series. Vol. 112. pp. 1–22. Bibcode:1999GMS...112....1T. doi:10.1029/GM112p0001. ISBN 0-87590-095-X.

[8] Massom, R.; Michael, K.; Harris, P.T.; Potter, M.J. (1998). "The distribution and formative processes of latent heat polynyas in East Antarctica". Annals of Glaciology. 27: 420–426. Bibcode:1998AnGla..27..420M. doi:10.3189/1998aog27-1-420-426.

[9] Tamura, Takeshi; Ohshima, Kay I.; Nihashi, Sohey (2008-04). "Mapping of sea ice production for Antarctic coastal polynyas". Geophysical Research Letters. 35 (7). doi:10.1029/2007GL032903. ISSN 0094-8276. {{cite journal}}: Check date values in: |date= (help)

[10] Tamura, Takeshi; Ohshima, Kay I.; Fraser, Alexander D.; Williams, Guy D. (2016-05). "Sea ice production variability in Antarctic coastal polynyas". Journal of Geophysical Research: Oceans. 121 (5): 2967–2979. doi:10.1002/2015JC011537. ISSN 2169-9275. {{cite journal}}: Check date values in: |date= (help)

[11] Morrison, A. K.; Hogg, A. McC.; England, M. H.; Spence, P. (2020-05). "Warm Circumpolar Deep Water transport toward Antarctica driven by local dense water export in canyons". Science Advances. 6 (18). doi:10.1126/sciadv.aav2516. ISSN 2375-2548. PMC 7195130. PMID 32494658. {{cite journal}}: Check date values in: |date= (help)CS1 maint: PMC format (link)

[12] Williams, G. D.; Herraiz-Borreguero, L.; Roquet, F.; Tamura, T.; Ohshima, K. I.; Fukamachi, Y.; Fraser, A. D.; Gao, L.; Chen, H.; McMahon, C. R.; Harcourt, R.; Hindell, M. (2016-08-23). "The suppression of Antarctic bottom water formation by melting ice shelves in Prydz Bay". Nature Communications. 7 (1): 12577. doi:10.1038/ncomms12577. ISSN 2041-1723.

[13] Narayanan, Aditya; Gille, Sarah T.; Mazloff, Matthew R.; du Plessis, Marcel D.; Murali, K.; Roquet, Fabien (2023-06). "Zonal Distribution of Circumpolar Deep Water Transformation Rates and Its Relation to Heat Content on Antarctic Shelves". Journal of Geophysical Research: Oceans. 128 (6). doi:10.1029/2022JC019310. ISSN 2169-9275. {{cite journal}}: Check date values in: |date= (help)

[14] Moorman, Ruth; Thompson, Andrew F.; Wilson, Earle A. (2023-08-28). "Coastal Polynyas Enable Transitions Between High and Low West Antarctic Ice Shelf Melt Rates". Geophysical Research Letters. 50 (16). doi:10.1029/2023GL104724. ISSN 0094-8276.

[15] Naughten, Kaitlin A.; Holland, Paul R.; De Rydt, Jan (2023-11). "Unavoidable future increase in West Antarctic ice-shelf melting over the twenty-first century". Nature Climate Change. 13 (11): 1222–1228. doi:10.1038/s41558-023-01818-x. ISSN 1758-6798. {{cite journal}}: Check date values in: |date= (help)

[16] Broecker, W. S.; Peacock, S. L.; Walker, S.; Weiss, R.; Fahrbach, E.; Schroeder, M.; Mikolajewicz, U.; Heinze, C.; Key, R.; Peng, T.-H.; Rubin, S. (1998). "How much deep water is formed in the Southern Ocean?". Journal of Geophysical Research: Oceans. 103 (C8): 15833–15843. Bibcode:1998JGR...10315833B. doi:10.1029/98JC00248.

[17] Kusahara, Kazuya; Hasumi, Hiroyasu; Williams, Guy D. (2011). "Impact of the Mertz Glacier Tongue calving on dense water formation and export". Nature Communications. 2 (1): 159. Bibcode:2011NatCo...2..159K. doi:10.1038/ncomms1156. PMID 21245840.

[18] Harris, P.T. (2000). "Ripple cross-laminated sediments on the East Antarctic shelf: evidence for episodic bottom water production during the Holocene?". Marine Geology. 170 (3–4): 317–330. Bibcode:2000MGeol.170..317H. doi:10.1016/s0025-3227(00)00096-7.

[19] Harris, P.T.; Brancolini, G.; Armand, L.; Busetti, M.; Beaman, R.J.; Giorgetti, G.; Prestie, M.; Trincardi, F. (2001). "Continental shelf drift deposit indicates non-steady state Antarctic bottom water production in the Holocene". Marine Geology. 179 (1–2): 1–8. Bibcode:2001MGeol.179....1H. doi:10.1016/s0025-3227(01)00183-9.

[20] "AMS Glossary, Vema Channel". American Meteorological Society. Retrieved 2012-02-20.^{[permanent dead link]}

[monika-21] Rhein, Monika; Stramma, Lothar; Krahmann, Gerd (1998). "The spreading of Antarctic bottom water in the tropical Atlantic" (PDF). Deep-Sea Research Part I. 45 (4–5): 507–527. Bibcode:1998DSRI...45..507R. CiteSeerX 10.1.1.571.6529. doi:10.1016/S0967-0637(97)00030-7. Retrieved 2012-02-14.

[22] Haine, T. W. N.; Watson, A. J.; Liddicoat, M. I.; Dickson, R. R. (1998). "The flow of Antarctic bottom water to the southwest Indian Ocean estimated using CFCs". Journal of Geophysical Research. 103 (C12): 27637–27653. Bibcode:1998JGR...10327637H. doi:10.1029/98JC02476.

[23] Uenzelmann-Neben, G.; Huhn, K. (2009). "Sedimentary deposits on the southern South African continental margin: Slumping versus non-deposition or erosion by oceanic currents?" (PDF). Marine Geology. 266 (1–4): 65–79. Bibcode:2009MGeol.266...65U. doi:10.1016/j.margeo.2009.07.011. Retrieved 1 April 2015.

[24] Hansen, James; Sato, Makiko; Hearty, Paul; Ruedy, Reto; Kelley, Maxwell; Masson-Delmotte, Valerie; Russell, Gary; Tselioudis, George; Cao, Junji (2016-03-22). "Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming could be dangerous". Atmospheric Chemistry and Physics. 16 (6): 3761–3812. arXiv:1602.01393. Bibcode:2016ACP....16.3761H. doi:10.5194/acp-16-3761-2016. ISSN 1680-7324. S2CID 9410444.

[Silvano-25] Silvano, A., Rintoul, S. R., Peña-Molino, B., Hobbs, W. R., van Wijk, E., Aoki, S., ... & Williams, G. D. (2018). Freshening by glacial meltwater enhances the melting of ice shelves and reduces the formation of Antarctic Bottom Water. Science advances, 4(4), eaap9467.

[Aoki-26] Aoki, S., Yamazaki, K., Hirano, D., Katsumata, K., Shimada, K., Kitade, Y., ... & Murase, H. (2020). Reversal of freshening trend of Antarctic Bottom Water in the Australian-Antarctic Basin during 2010s. Scientific reports, 10(1), 1-7.

[27] Zhou, Shenjie; Meijers, Andrew J. S.; Meredith, Michael P.; Abrahamsen, E. Povl; Holland, Paul R.; Silvano, Alessandro; Sallée, Jean-Baptiste; Østerhus, Svein (12 June 2023). "Slowdown of Antarctic Bottom Water export driven by climatic wind and sea-ice changes". Nature Climate Change. 13 (7): 701–709. doi:10.1038/s41558-023-01695-4. ISSN 1758-6798.

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 The '''Antarctic bottom water''' ('''AABW''') is a type of [[water mass]] in the [[Southern Ocean]] surrounding [[Antarctica]] with temperatures ranging from −0.8 to 2&nbsp;°C (35&nbsp;°F) and absolute [[Salinity#Definitions|salinities]] from 34.6 to 35.0 g/kg.<ref name=Schmidt>{{cite journal|last1=Schmidt|first1=Christina|last2=Morrison|first2=Adele K.|last3=England |first3=Matthew H.|date=17 June 2023|title=Wind– and Sea-Ice–Driven Interannual Variability of Antarctic Bottom Water Formation|url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2023JC019774|journal=Journal of Geophysical Research: Oceans|volume=128|issue=6|doi=10.1029/2023JC019774|s2cid=259468175 |doi-access=free}}</ref> As the densest water mass of the oceans, AABW is found to occupy the depth range below 4000&nbsp;m of all ocean basins that have a connection to the Southern Ocean at that level.<ref>{{Cite web|title=AMS Glossary of Meteorology, Antarctic Bottom Water|url=https://glossary.ametsoc.org/wiki/Antarctic_bottom_water|publisher=American Meteorological Society|access-date=29 June 2023}}</ref>
-The major significance of Antarctic bottom water is that it is the coldest bottom water, giving it a significant influence on large-scale movement in the world's oceans through [[thermohaline circulation]].
+AABW is the densest bottom water, forming the lower branch of the large-scale movement in the world's oceans through [[thermohaline circulation]].
-Initially, AABW has a high oxygen content relative to the rest of the oceans' deep waters but this depletes over time. This early oxygen abundance comes from the precursor water mass of the AABW, which is cold, relatively salty and oxygen-rich dense shelf water (DSW) formed above Antarctica’s [[continental shelf]] by wintertime cooling and [[brine rejection]]. This water sinks at four distinct regions around the margins of the continent and forms the AABW; this process leads to ventilation of the deep ocean, or ''abyssal ventilation''.<ref name=Gunn>{{cite journal |last1=Gunn|first1=Kathryn L.|last2=Rintoul|first2=Stephen R.|last3=England|first3=Matthew H.|last4=Bowen|first4=Melissa M.|date=June 2023|title=Recent reduced abyssal overturning and ventilation in the Australian Antarctic Basin|journal=Nature Climate Change|volume=13|issue=6 |pages=537–544|doi=10.1038/s41558-023-01667-8|doi-access=free}}</ref>
+AABW forms near the surface in coastal polynyas along the coastline of Antarctica<ref>{{Cite journal |last=Portela |first=Esther |last2=Rintoul |first2=Stephen R. |last3=Herraiz‐Borreguero |first3=Laura |last4=Roquet |first4=Fabien |last5=Bestley |first5=Sophie |last6=van Wijk |first6=Esmee |last7=Tamura |first7=Takeshi |last8=McMahon |first8=Clive R. |last9=Guinet |first9=Christophe |last10=Harcourt |first10=Robert |last11=Hindell |first11=Mark A. |date=2022-12 |title=Controls on Dense Shelf Water Formation in Four East Antarctic Polynyas |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022JC018804 |journal=Journal of Geophysical Research: Oceans |language=en |volume=127 |issue=12 |doi=10.1029/2022JC018804 |issn=2169-9275}}</ref>, where high rates of sea ice formation during winter leads to the densification of the surface waters through [[brine rejection]]<ref>{{Cite journal |last=Ohshima |first=Kay I. |last2=Fukamachi |first2=Yasushi |last3=Williams |first3=Guy D. |last4=Nihashi |first4=Sohey |last5=Roquet |first5=Fabien |last6=Kitade |first6=Yujiro |last7=Tamura |first7=Takeshi |last8=Hirano |first8=Daisuke |last9=Herraiz-Borreguero |first9=Laura |last10=Field |first10=Iain |last11=Hindell |first11=Mark |last12=Aoki |first12=Shigeru |last13=Wakatsuchi |first13=Masaaki |date=2013-03 |title=Antarctic Bottom Water production by intense sea-ice formation in the Cape Darnley polynya |url=https://www.nature.com/articles/ngeo1738 |journal=Nature Geoscience |language=en |volume=6 |issue=3 |pages=235–240 |doi=10.1038/ngeo1738 |issn=1752-0908}}</ref>. Since the water mass forms near the surface, it is responsible for the exchange of large quantities of heat with the atmosphere<ref>{{Cite journal |last=Renfrew |first=Ian A. |last2=King |first2=John C. |last3=Markus |first3=Thorsten |date=2002-06 |title=Coastal polynyas in the southern Weddell Sea: Variability of the surface energy budget |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2000JC000720 |journal=Journal of Geophysical Research: Oceans |language=en |volume=107 |issue=C6 |doi=10.1029/2000JC000720 |issn=0148-0227}}</ref>. AABW has a high oxygen content relative to the rest of the oceans' deep waters but this depletes over time. This water sinks at four distinct regions around the margins of the continent and forms the AABW; this process leads to ventilation of the deep ocean, or ''abyssal ventilation''.<ref name=Gunn>{{cite journal |last1=Gunn|first1=Kathryn L.|last2=Rintoul|first2=Stephen R.|last3=England|first3=Matthew H.|last4=Bowen|first4=Melissa M.|date=June 2023|title=Recent reduced abyssal overturning and ventilation in the Australian Antarctic Basin|journal=Nature Climate Change|volume=13|issue=6 |pages=537–544|doi=10.1038/s41558-023-01667-8|doi-access=free}}</ref>
 ==Formation and circulation==
 Antarctic bottom water is created in part due to the major overturning of ocean water.
-Antarctic bottom water is formed in the [[Weddell Sea|Weddell]] and [[Ross Sea]]s, off the [[Adélie Coast]] and by [[Cape Darnley (Mac. Robertson Land)|Cape Darnley]] from surface water cooling in [[polynya]]s and below the [[ice shelf]].<ref>{{cite book|last=Talley|first=Lynne|title=Mechanisms of Global Climate Change at Millennial Time Scales|chapter=Some aspects of ocean heat transport by the shallow, intermediate and deep overturning circulations|series=Geophysical Monograph Series|year=1999|volume=112|pages=1–22|doi=10.1029/GM112p0001|bibcode=1999GMS...112....1T|isbn=0-87590-095-X}}</ref> A unique feature of Antarctic bottom water is the cold surface wind blowing off the Antarctic continent.<ref>{{cite journal | last1 = Massom | first1 = R. | last2 = Michael | first2 = K. | last3 = Harris | first3 = P.T. | last4 = Potter | first4 = M.J. | year = 1998 | title = The distribution and formative processes of latent heat polynyas in East Antarctica | journal = Annals of Glaciology | volume = 27 | pages = 420–426 | doi = 10.3189/1998aog27-1-420-426 | bibcode = 1998AnGla..27..420M | doi-access = free }}</ref> The surface wind creates the polynyas which opens up the water surface to more wind. This Antarctic wind is stronger during the winter months and thus the Antarctic bottom water formation is more pronounced during the Antarctic winter season. Surface water is enriched in salt from sea ice formation. Due to its increased density, it flows down the Antarctic [[continental margin]] and continues north along the bottom. It is the densest water in the free ocean, and underlies other bottom and intermediate waters throughout most of the southern hemisphere.  The [[Weddell Sea Bottom Water]] is the densest component of the Antarctic bottom water.
+Antarctic bottom water is formed in the [[Weddell Sea|Weddell]] and [[Ross Sea]]s, off the [[Adélie Coast]] and by [[Cape Darnley (Mac. Robertson Land)|Cape Darnley]] from surface water cooling in [[polynya]]s and below the [[ice shelf]].<ref>{{cite book|last=Talley|first=Lynne|title=Mechanisms of Global Climate Change at Millennial Time Scales|chapter=Some aspects of ocean heat transport by the shallow, intermediate and deep overturning circulations|series=Geophysical Monograph Series|year=1999|volume=112|pages=1–22|doi=10.1029/GM112p0001|bibcode=1999GMS...112....1T|isbn=0-87590-095-X}}</ref> A unique feature of Antarctic bottom water is the cold surface wind blowing off the Antarctic continent.<ref>{{cite journal | last1 = Massom | first1 = R. | last2 = Michael | first2 = K. | last3 = Harris | first3 = P.T. | last4 = Potter | first4 = M.J. | year = 1998 | title = The distribution and formative processes of latent heat polynyas in East Antarctica | journal = Annals of Glaciology | volume = 27 | pages = 420–426 | doi = 10.3189/1998aog27-1-420-426 | bibcode = 1998AnGla..27..420M | doi-access = free }}</ref> The surface winds advect sea ice away from the coast, creating polynyas which opens up the water surface to a cold atmosphere during winter, which further helps form more sea ice. Antarctic coastal polynyas form as much as 10% of the overall Southern Ocean sea ice during a single season<ref>{{Cite journal |last=Tamura |first=Takeshi |last2=Ohshima |first2=Kay I. |last3=Nihashi |first3=Sohey |date=2008-04 |title=Mapping of sea ice production for Antarctic coastal polynyas |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2007GL032903 |journal=Geophysical Research Letters |language=en |volume=35 |issue=7 |doi=10.1029/2007GL032903 |issn=0094-8276}}</ref>, amounting to about 2,000&nbsp;km<sup>3</sup> volume of sea ice<ref>{{Cite journal |last=Tamura |first=Takeshi |last2=Ohshima |first2=Kay I. |last3=Fraser |first3=Alexander D. |last4=Williams |first4=Guy D. |date=2016-05 |title=Sea ice production variability in Antarctic coastal polynyas |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1002/2015JC011537 |journal=Journal of Geophysical Research: Oceans |language=en |volume=121 |issue=5 |pages=2967–2979 |doi=10.1002/2015JC011537 |issn=2169-9275}}</ref>. Surface water is enriched in salt from sea ice formation and cooled due to being exposed to a cold atmosphere during winter which increases the density of this water mass. Due to its increased density, it flows down the Antarctic [[continental margin]] and continues north along the bottom. It is the densest water in the open ocean, and underlies other bottom and intermediate waters throughout most of the southern hemisphere.  The [[Weddell Sea Bottom Water]] is the densest component of the Antarctic bottom water.
+A major source water for the formation of AABW is the warm offshore watermass known as the Circumpolar Deep Water (CDW; salinity > 35&amp;nbsp;g/kg and potential temperature > 0<sup>o</sup>C)<ref>{{Cite journal |last=Morrison |first=A. K. |last2=Hogg |first2=A. McC. |last3=England |first3=M. H. |last4=Spence |first4=P. |date=2020-05 |title=Warm Circumpolar Deep Water transport toward Antarctica driven by local dense water export in canyons |url=https://www.science.org/doi/10.1126/sciadv.aav2516 |journal=Science Advances |language=en |volume=6 |issue=18 |doi=10.1126/sciadv.aav2516 |issn=2375-2548 |pmc=PMC7195130 |pmid=32494658}}</ref>. These warm watermasses are cooled by coastal polynyas to form the denser AABW<ref>{{Cite journal |last=Williams |first=G. D. |last2=Herraiz-Borreguero |first2=L. |last3=Roquet |first3=F. |last4=Tamura |first4=T. |last5=Ohshima |first5=K. I. |last6=Fukamachi |first6=Y. |last7=Fraser |first7=A. D. |last8=Gao |first8=L. |last9=Chen |first9=H. |last10=McMahon |first10=C. R. |last11=Harcourt |first11=R. |last12=Hindell |first12=M. |date=2016-08-23 |title=The suppression of Antarctic bottom water formation by melting ice shelves in Prydz Bay |url=https://www.nature.com/articles/ncomms12577 |journal=Nature Communications |language=en |volume=7 |issue=1 |pages=12577 |doi=10.1038/ncomms12577 |issn=2041-1723}}</ref>. Coastal polynyas that form AABW help prevent the intruding warm CDW water masses from gaining access to the base of ice shelves<ref>{{Cite journal |last=Narayanan |first=Aditya |last2=Gille |first2=Sarah T. |last3=Mazloff |first3=Matthew R. |last4=du Plessis |first4=Marcel D. |last5=Murali |first5=K. |last6=Roquet |first6=Fabien |date=2023-06 |title=Zonal Distribution of Circumpolar Deep Water Transformation Rates and Its Relation to Heat Content on Antarctic Shelves |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022JC019310 |journal=Journal of Geophysical Research: Oceans |language=en |volume=128 |issue=6 |doi=10.1029/2022JC019310 |issn=2169-9275}}</ref>, hence acting to protect ice shelves from enhanced basal melting due to oceanic warming. In areas like the Amundsen Sea, where coastal polynya activity has diminished to the point where dense water formation is hindered<ref>{{Cite journal |last=Moorman |first=Ruth |last2=Thompson |first2=Andrew F. |last3=Wilson |first3=Earle A. |date=2023-08-28 |title=Coastal Polynyas Enable Transitions Between High and Low West Antarctic Ice Shelf Melt Rates |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2023GL104724 |journal=Geophysical Research Letters |language=en |volume=50 |issue=16 |doi=10.1029/2023GL104724 |issn=0094-8276}}</ref>, the neighboring ice shelves have started to retreat and may be on the brink of collapse<ref>{{Cite journal |last=Naughten |first=Kaitlin A. |last2=Holland |first2=Paul R. |last3=De Rydt |first3=Jan |date=2023-11 |title=Unavoidable future increase in West Antarctic ice-shelf melting over the twenty-first century |url=https://www.nature.com/articles/s41558-023-01818-x |journal=Nature Climate Change |language=en |volume=13 |issue=11 |pages=1222–1228 |doi=10.1038/s41558-023-01818-x |issn=1758-6798}}</ref>.
 Evidence indicates that Antarctic bottom water production through the Holocene (last 10,000&nbsp;years) is not in a steady-state condition;<ref>{{Cite journal |doi = 10.1029/98JC00248|title = How much deep water is formed in the Southern Ocean?|year = 1998|last1 = Broecker|first1 = W. S.|last2 = Peacock|first2 = S. L.|last3 = Walker|first3 = S.|last4 = Weiss|first4 = R.|last5 = Fahrbach|first5 = E.|last6 = Schroeder|first6 = M.|last7 = Mikolajewicz|first7 = U.|last8 = Heinze|first8 = C.|last9 = Key|first9 = R.|last10 = Peng|first10 = T.-H.|last11 = Rubin|first11 = S.|journal = Journal of Geophysical Research: Oceans|volume = 103|issue = C8|pages = 15833–15843|bibcode = 1998JGR...10315833B|doi-access = free}}</ref> that is to say that bottom water production sites shift along the Antarctic margin over decade to century timescales as conditions for the existence of [[polynya]]s change.  For example, the calving of the Mertz Glacier, which occurred on 12–13 February 2010, dramatically changed the environment for producing bottom water, reducing export by up to 23% in the region of Adelie Land.<ref>{{Cite journal |doi = 10.1038/ncomms1156|title = Impact of the Mertz Glacier Tongue calving on dense water formation and export|year = 2011|last1 = Kusahara|first1 = Kazuya|last2 = Hasumi|first2 = Hiroyasu|last3 = Williams|first3 = Guy D.|journal = Nature Communications|volume = 2|issue = 1|page = 159|pmid = 21245840|bibcode = 2011NatCo...2..159K|doi-access = free}}</ref>  Evidence from sediment cores, containing layers of cross-bedded sediments indicating phases of stronger bottom currents, collected on the Mac.Robertson shelf <ref>{{cite journal | last1 = Harris | first1 = P.T. | year = 2000 | title = Ripple cross-laminated sediments on the East Antarctic shelf: evidence for episodic bottom water production during the Holocene? | journal = Marine Geology | volume = 170 | issue = 3–4| pages = 317–330 | doi = 10.1016/s0025-3227(00)00096-7 | bibcode = 2000MGeol.170..317H }}</ref> and [[Adélie Land]]<ref>{{cite journal | last1 = Harris | first1 = P.T. | last2 = Brancolini | first2 = G. | last3 = Armand | first3 = L. | last4 = Busetti | first4 = M. | last5 = Beaman | first5 = R.J. | last6 = Giorgetti | first6 = G. | last7 = Prestie | first7 = M. | last8 = Trincardi | first8 = F. | year = 2001 | title = Continental shelf drift deposit indicates non-steady state Antarctic bottom water production in the Holocene | journal = Marine Geology | volume = 179 | issue = 1–2| pages = 1–8 | doi = 10.1016/s0025-3227(01)00183-9 | bibcode = 2001MGeol.179....1H }}</ref> suggests that they have switched "on" and "off" again as important bottom water production sites over the last several thousand years.