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37-619: The Weddell Sea, part of the Southern Ocean, is a unique scientific research environment. The outflow of Weddell Sea Bottom Water and Antarctic Bottom Water formed in the Weddell and Ross Seas is a major source of oceanic deep water and changes affecting the formation of these water masses are liable to have an effect on the circulation of deep water globally. The water of the Weddell Sea is about 1400 m deep at its deepest point; it

74-618: 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 . Antarctic bottom water is created is formed in the Weddell and Ross Seas , off the Adélie Coast and by Cape Darnley from surface water cooling in polynyas and below

111-451: 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. 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

148-533: A single season, amounting to about 2,000 km of sea ice. 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 forms overflows down the Antarctic continental slope 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

185-594: A total 97 Sv outflow of AABW. 2 to 5 Sv of this production is newly formed bottom water off the Antarctic coast. The Weddell Sea is characterized by a cyclonic gyre bounded on the south by the Antarctic continent , on the west by the Antarctic Peninsula , on the north by the Scotia Ridge , and extending as far east as 20 to 30°E. The precursor to bottom water formation is derived from

222-430: Is a major contributor to Antarctic Bottom Water (AABW). While WSBW is considered part of AABW, the distinction comes in its potential temperature . The potential temperature of WSBW is -0.7 °C. At this temperature, the potential temperature vs. salinity chart shows a sharp change in slope. The outflow of WSBW is influenced greatly by the Scotia Ridge . The movement of WBSW is listed as 16 Sv which contributes to

259-489: 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. 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. AABW forms the lower branch of the large-scale movement in

296-470: Is due to injection of high-salinity shelf water characteristic of the region. Fahrbach et al. propose that low-salinity bottom water is formed near the Larsen Ice Shelf . McKee et al., conducted a study of the variability of bottom water temperature relative to El Niño-Southern Oscillation (ENSO), Southern Annular Mode (SAM), and Antarctic Dipole (ADP). This study was conducted to discover

333-588: Is exceptionally clear (the Secchi disk visibility reading at 80 metres recorded in the Weddell Sea on 13 October 1986 was the deepest ever, at the theoretical maximum in absolutely pure water). Much of the southern part of the sea is permanent ice, the Filchner-Ronne Ice Shelf , which can be up to 600 m thick. IWSOE research projects have involved a variety of institutions and covered a wide range of disciplines. For example, in 1969 scientists from

370-787: The Agulhas Passage and over the southern margins of the Agulhas Plateau and then into the Mozambique Basin . 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. This shutdown would have dramatic effects on ocean circulation and global weather patterns. Increased intrusion of warm Circumpolar Deep Water coupled with enhanced ice shelf basal melting can impact

407-677: The Romanche Fracture Zone into the eastern Atlantic. 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

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444-534: The Weddell Sea area. 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. 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

481-423: The ice shelf . An important factor enabling the formation of Antarctic bottom water is the cold surface wind blowing off the Antarctic continent. 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

518-838: The Antarctic bottom water enters the eastern Atlantic through the Vema Fracture Zone . 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. South of Africa, Antarctic bottom water flows northwards through the Agulhas Basin and then east through

555-538: The Holocene (last 10,000 years) is not in a steady-state condition; that is, 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

592-651: 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. 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

629-633: The Universities of Bergen (Norway) and Minnesota, Connecticut and California, Los Angeles (USA) , and the US Coast Guard Oceanographic Unit studied the formation of Antarctic Bottom Water, the population density and diversity of the deep sea benthos of the Weddell Sea, the population dynamics of Antarctic seals and sedimentation processes in the Weddell Sea and carried out physical, chemical and photographic oceanographic surveys. Other subjects of IWSOE research include

666-505: The WSBW 14–20 months later. Their research suggests that there needs to be large ENSO and SAM events in order for the anomalies in WSBW temperature can be noticed. These large fluctuations allow for warm and cold pulses in the WSBW. With a strong ENSO event, sea ice is greatly reduced during the summer which exposes more surface water to the wind allowing it sink. This makes the WSBW colder than normal allowing it to inject colder water into much of

703-589: The Weddell Sea currents and the biology of krill , a species of zooplankton abundance in the area. The expeditions were initially led aboard the USCGC Glacier , an icebreaker modified for oceanographic research which in 1968 was the first ship to cross the Weddell Sea from the edge of the ice pack to the continental landmass. At the time, the Glacier was the world's largest icebreaker. Antarctic Bottom Water The Antarctic bottom water ( AABW )

740-531: The Weddell Sea from the southeast. The low-salinity, better ventilated forms of WSDW and WSBW flowing along the outer rim of the Weddell Gyre have the position and depth range that would lead to overflow of the topographic confines of the Weddell Basin, whereas the more saline forms may be forced to recirculate within the Weddell Gyre are carried by the western boundary current of the Weddell Sea into

777-418: The broad continental shelf west of 40°W where brine released during sea-ice formation produces a large reservoir of cold (0 to - 1.8 °C), high salinity (S ≥ 34.62  psu ) shelf water. This water mass then mixes with a modified form of Warm Deep Water near the edge of the continental shelf to form a dense layer of bottom water, which in turn sinks along the continental slope and flows cyclonically around

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814-474: The core of Weddell Sea Bottom Water lies against the southern edge of the Scotia Ridge, suggesting that the circulation and property distributions are strongly influenced by bathymetry . The transport of Weddell Sea Bottom Water out of the Weddell Sea represents the outflow of newly formed bottom water plus entrained bottom water that enters the Weddell Sea from the southeast. Carmack and Foster estimated

851-500: The formation of dense shelf waters. 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. This has been distinctly prevalent in Antarctic bottom waters near West Antarctica , primarily in

888-523: The fresher and warmer waters will reduce bottom and deep-water circulation and increase warm water flows around Antarctica. 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. This would impact more than Antarctica, as AABW plays

925-590: The gyre. The more saline WSBW is derived from the southwestern Weddell Sea, where high salinity shelf water is abundant. The less saline WSBW, like the more ventilated Weddell Sea Deep Water (WSDW), is derived from lower-salinity shelf water at a point farther north along the Antarctic Peninsula. It is important to distinguish between AABW and a subclass of this water mass, WSBW. WSBW is characterized by lower potential temperatures and larger near-bottom temperature gradients, suggesting recent formation in

962-505: The impact WSBW has on the global climate. An 8-year time study of the potential temperature of the Weddell Gyre outflow was analyzed. Interannual variability was discovered in the winters of 1999 and 2002. The anomalies suggest ENSO influence with a 14-20 month lead time with influences from SAM at 14-20 month lead times as well. Warm ENSO events cause the increase of sea ice advection and more coastal polynyas which allows for more dense shelf water availability. These ENSO and SAM changes impact

999-524: The intruding warm CDW water masses from gaining access to the base of ice shelves, 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, the neighboring ice shelves have started to retreat and may be on the brink of collapse. Evidence indicates that Antarctic bottom water production through

1036-424: The melting of ice sheets, rendering the effects of melting Antarctic glaciers on WSBW minimal. Weddell Sea Bottom Water Weddell Sea Bottom Water (WSBW) is a subset of Antarctic Bottom Water (AABW) that is at a temperature of -0.7 °C or colder. It consists of a higher salinity branch and a lower salinity branch. It originates in the Weddell Sea and closely follows the sea floor as it flows out into

1073-506: The northwest corner of the Weddell Gyre. From there, these water masses flow eastward, either within the northern limb of the Weddell Gyre or reaching northward into the Scotia Sea, eventually cooling the lower 2 km of the world ocean as Antarctic Bottom Water. It is proposed that the more saline, lower-oxygen WSBW is derived from shelf water descending into the deep ocean in the southwest Weddell Sea. The higher salinity of this WSBW

1110-448: The northwestern corner of the Weddell Sea. The fraction of newly formed bottom water in the outflowing WSBW ranges from about 12 to 31%, so the flow of newly formed bottom water out of the Weddell Sea is about 2 to 5 Sv. On the other hand, the much larger production rates sometimes proposed are probably estimates of the total transport of bottom water out of the Weddell Sea that include a large fraction of Antarctic Bottom Water entering

1147-407: The production rate of bottom water from the mixing ratio of newly formed bottom water to entrained bottom water. Bottom water formation models based on hydrographic observations suggested that the bottom water formed at the edge of the continental shelf has an initial temperature of -1.4 to -1.2 °C. This range also represents the coldest bottom water observed at the base of the continental slope in

International Weddell Sea Oceanographic Expeditions - Misplaced Pages Continue

1184-522: The region of Adélie Land . Evidence from sediment cores, containing layers of cross-bedded sediments indicating phases of stronger bottom currents, collected on the Mac. Robertson shelf and Adélie Land suggests that they have switched "on" and "off" again as important bottom water production sites over the last several thousand years. The Vema Channel, a deep trough in the Rio Grande Rise of

1221-404: The rest of the world's oceans. It is created mainly due to the high surface winds blowing off the Antarctic continent which helps cool and oxygenate it. It flows at a rate of 2 to 5  Sv and contributes to the overall flow of the AABW. The Weddell Sea plays an important role in the movement of the world's oceans. An important part of the Weddell Sea is Weddell Sea Bottom Water (WSBW). WSBW

1258-426: 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 C). These warm watermasses are cooled by coastal polynyas to form the denser AABW. Coastal polynyas that form AABW help prevent

1295-503: The southwestern and western Weddell Sea. As this bottom water spreads from its region of sinking, it eventually mixes with the warmer and more saline water above to form AABW. Along the Scotia Ridge-Cape Norvegia section, potential temperature values at depths greater than 4,500 m (14,800 ft) range from -0.94 to -0.63 °C, while salinity values range from 34.639 to 34.652  psu . The northern limit of

1332-481: The western and northern perimeter of the Weddell Sea basin. Because large quantities of the high salinity water are observed on the continental shelf even during summer, bottom water may form throughout the year. Weddell Sea Bottom Water exhibits two forms: a low-salinity, better oxygenated component confined to the outer rim of the Weddell Gyre , and a more saline, less oxygenated component observed farther into

1369-420: The world's oceans through thermohaline circulation . AABW forms near the surface in coastal polynyas along the coastline of Antarctica, where high rates of sea ice formation during winter leads to the densification of the surface waters through brine rejection . Since the water mass forms near the surface, it is responsible for the exchange of large quantities of heat and gases with the atmosphere. AABW has

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