Antarctic Intermediate Water (AAIW) is a cold, relatively low salinity water mass found mostly at intermediate depths in the Southern Ocean . The AAIW is formed at the ocean surface in the Antarctic Convergence zone or more commonly called the Antarctic Polar Front zone. This convergence zone is normally located between 50°S and 60°S, hence this is where almost all of the AAIW is formed.
23-568: The AAIW is a unique water mass in that it is a sinking water mass with a moderately low salinity, unlike most sinking water masses which have a relatively high salinity. This salinity minimum, unique to the AAIW, can be recognized throughout the Southern Ocean at depths ranging from 700 to 1200 meters. Typical temperature values for the AAIW are 3-7°C, and a salinity of 34.2-34.4 psu upon initial formation. Due to vertical mixing at intermediate depths in
46-421: A T-S diagram. In the diagram pictured at the top, it categorises a water mass by the temperature and salinity of the water and is represented by a single point. However, water masses are not constant. Throughout time climates can change, seasons can drag out, or there could be less rainfall meaning that the water masses might change in temperature or salinity. To have a complete water mass classification, it requires
69-519: Is a water mass found between the top cold, relatively fresh polar water and the bottom deep water in the Arctic domain (bounded by the polar and arctic fronts ). AIW is formed in small quantities compared to other water masses, and has limited influence outside of the Arctic domain. Two types of AIW are found, which are lower AIW and upper AIW separately. Lower AIW is the water mass with temperature and salinity maximum found at 250~400m deep, right above
92-543: Is a strong current north of the Antarctic Coastal Current, called the Antarctic Circumpolar Current (ACC) created by the strong westerlies in this region which flows clockwise around Antarctica. Again, Ekman transport will push this water to the left of the surface motion, meaning away from Antarctica. Because water just offshore of Antarctica is being pushed away and into Antarctica, it leads to
115-461: Is also identified by its non-conservative flow tracers such as silicate, nitrate, oxygen, and phosphate. Water masses are generally distinguished not only by their respective tracers but also by their location in the Worlds' oceans. Water masses are also distinguished by their vertical position so that there are surface water masses, intermediate water masses and deep water masses. Common water masses in
138-503: Is cold and quite salty. For many years the aforementioned formation of AAIW was thought to be the only formation process. Recent studies have found that there exists some evidence that some Subantarctic mode water is able to penetrate through the Subantarctic front (frontal region separating the Polar frontal zone from the Subantarctic zone) and become the dominant source of AAIW, rather than
161-522: Is colder than 0 °C with salinity in the range 34.4-34.7. Amount of AIW varies with different seasons. For example, the upper AIW in Iceland sea increased from about 10% of the total volume in fall to over 21% in winter. In the same time, both ASW and lower AIW show significant summer-to-winter decreases, which might contribute to the new upper AIW. Similar process can also be found in Greenland sea, but with
184-490: Is formed and modified in the north part of Arctic domain. As AIW moves from north to south along the Greenland continental slope, its temperature and salinity, on the whole, decrease southwards due to mixing with surface cold water. The lower AIW is produced by the cooling and sinking of Atlantic Water (AW), which is traditionally defined with salinity greater than 35, and by the Polar Intermediate Water (PIW) that
207-427: Is how far it extends northward. The salinity minima associated with the AAIW can be seen in intermediate waters (~1000m) as far north as 20°N, with trace amounts as far as 60°N. It is by far the largest spreading intermediate water of all the ocean intermediate water masses. It continues northward until it encounters other intermediate water masses (e.g. AIW ). The movement of the AAIW is predominantly northward due to
230-532: The polar easterlies where winds blow from the east to the west. This creates a counter-clockwise surface current near the coast of Antarctica, called the Antarctic Coastal Current. Ekman transport causes the water to push towards the left of the surface motion in the Southern Hemisphere. Thus, this westward directed coastal current in Antarctica will push the water towards Antarctica. At the same time there
253-457: The AASW. Because of the difficulty of getting observations in this very treacherous area, this research on Subantarctic mode water mixing theory is still being worked out, but a lot of evidence exists for its inclusion in the formation of AAIW. It is important to note that the biggest source of AAIW formation is just southwest of the southern tip of South America. The interesting characteristic of AAIW
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#1732852659404276-582: The Antarctic Convergence Zone/Antarctic Polar Front because of the sharp gradients in both temperature and salinity (esp. temperature) between the Antarctic waters and the Subantarctic waters. It is also a region of strong vertical mixing. It is important to note that this convergence zone does not occur simply because the Subantarctic water is flowing southward and the AASW is flowing northward, but due to Ekman convergence. Once
299-519: The Antarctic Divergence region. Here, upwelling of North Atlantic Deep Water (NADW) takes place. NADW is cold and quite saline. Once the NADW is upwelled to the surface some of it diverges towards Antarctica, gets colder, and sinks back down as Antarctic Bottom Water . The NADW water also diverges away from Antarctica when it is upwelled. This diverged water moves northward (equatorward), and at
322-669: The Ekman volume transport mostly directed in that way. When the AAIW is initially formed, the ACC is able to transport the AAIW into all ocean basins because the ACC flows clockwise around Antarctica with no land based boundaries. Water mass An oceanographic water mass is an identifiable body of water with a common formation history which has physical properties distinct from surrounding water. Properties include temperature , salinity , chemical - isotopic ratios, and other physical quantities which are conservative flow tracers . Water mass
345-473: The Southern Ocean, the salinity slowly rises as it moves northward. Typical density of AAIW water is between 1026.82 kg/m and 1027.43 kg/m. The thickness of the AAIW ranges greatly between where it forms and its most northern extent. The formation of AAIW can be explained very simply through the Ekman transport process and the divergence and convergence of water masses. The winds over Antarctica are called
368-596: The atmosphere, thereby increasing the temperature slightly. When this water reaches between 50°S and 60°S it encounters the Antarctic Convergence zone. At this point the Subantarctic waters, which are characterized as being much warmer than the Antarctic waters, are just north of the Antarctic Polar Front and the Antarctic waters are just south of the Antarctic Polar Front. This region is referred to as
391-497: The deep water, with temperature for lower AIW ranges from 0 to 3 °C and salinity greater than 34.9. Upper AIW is defined to be a denser layer on top of the lower AIW, between surface cold water and the lower AIW, including water masses with temperature maximum to minimum. It is characterized by temperatures less than 2 °C in the salinity ranges from 34.7 to 34.9. The upper AIW is usually found at 75~150m, overlain by Arctic Surface Water (ASW). However, it could be found at
414-400: The ice less dense than the water which is why glaciers float. This also in turn causes the salinity of the water to decrease. The salinity of the water makes water freeze at lower temperatures than freshwater. Freshwater freezes at the standard 0 °C (32 °F), while saltwater freezes at an average of -2 °C (28.4 °F). The best method of classifying a water mass is through using
437-473: The northward propagating Antarctic Surface Water reaches the Antarctic Convergence zone it begins to sink because it is more dense than the Subantarctic water to its north, but less dense than the Antarctic water to its south. This water is then referred to as AAIW. The sinking AAIW becomes sandwiched between the Subantarctic water (above) which is much warmer, but more saline and the NADW (below) which
460-438: The same time persistent precipitation (location is near the polar lows ~60°S) along with an influx of melt water decreases the salinity of the original NADW. Because the salinity of the NADW has changed by so much and it has essentially lost all its unique characteristics to be NADW, this northward propagating surface water is now called Antarctic Surface Water (AASW). Also, the AASW movement northward has gained some heat from
483-483: The sea surface in winter. There are overlaps in density for upper and lower AIW according to their definitions. It is possible that water mass falling within the definition of upper AIW is below the defined lower AIW. For example, in Norwegian Sea , one intermediate layer of salinity slightly less than 34.9 was found below the water mass with temperature and salinity maximum. It is generally accepted that AIW
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#1732852659404506-439: The water type of the source and the standard deviations of the temperature and salinity. It can take many years to establish the standard deviations of the water mass and requires constant surveillance. Once all of the necessary measures are completed, the data will now determine what the current density of the water is and help further classify the water mass. Arctic Intermediate Water The Arctic Intermediate Water (AIW)
529-415: The world ocean are: Although there are many types of water masses, they all share characteristics. Water Masses are formed from regions of water having different temperatures. When ice is being formed in a cold climate like Antarctica, the cold temperatures separate the molecular bonds of the water causing it to become less dense. However, because water increases its volume by about 9% when frozen, this makes
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