Water Antarctic Intermediate

Conventional T-S diagrams for specific locations in the individual oceans are shown in Fig. 10-4. The inflections in the curves reflect the inputs of water from different sources. The linear regions represent mixing intervals between these core sources. For example, in the Atlantic Ocean the curves reflect input from Antarctic Bottom Water (AABW), North Atlantic Deep Water (NADW), Antarctic Intermediate Water (AIW), Mediterranean Water (MW), and Warm Surface Water (WSW). 

Diverse processes can form intermediate waters within the water column. In the southern South Atlantic, the NADW overrides the denser ABW. Antarctic Intermediate Water results from water sinking along the Antarctic Convergence ( 50°S). Relatively warm, saline... 

Figure 13.2 Section of (A) nitrate versus depth and (B) nitrate versus potential density (sigma theta) using combined data from the 2003 (North Atlantic) and 2005 (South Atlantic) occupations of the A16 line. North Atlantic DeepWater (NADW), Antarctic Bottom Water (A ABW) and Antarctic Intermediate Water (AAIW) are indicated. Units pmol kg. ...

Nitrate-rich signatures of Antarctic Bottom Water (AABW) and Antarctic Intermediate Water (AAIW) extend northward, reflecting the high surface concentrations where these water masses are formed. These water masses are also evident in the zonal structure of the North and South Atlantic, and nitrate-rich (>30 iM) AAIW is evident in the South Atlantic (Fig. 13.3) at mid-depth, along with a hint of AABW with elevated nitrate concentrations in the deep western part of the basin. There is... 

Figure 13-9 Schematic views of (A) meridional and vertical transport of nitrate in the upper Atlantic basin and (B) associated horizontal transport pathways. Nitrate-rich Circumpolar Deep Water (CDW) upwells in the Southern Hemisphere and the residual mean flow transports some of this upwelled water across the polar front into the regions of intermediate and mode water formation. Nitrate-rich Sub-Antarctic Mode Water (SAMW) and Antarctic Intermediate Water move northward in the thermocline, ultimately outcropping in the subpolar North Atlantic. Ekman transfer provides a source of nitrate to the subtropical gyre along with lateral and vertical eddy transport processes.

Within the polar oceans involved in deep water formation, certain regions are more important than others. The Antarctic Zone, the most polar region in the Southern Ocean, is involved in the formation of both deep and intermediate-depth waters, making this region important to the atmosphere/ocean CO2 balance. The quantitative effect of the Subantarctic Zone on atmospheric CO2 is less certain, depending on the degree to which the nutrient status of the Subantarctic surface influences the preformed nutrient concentration of newly formed subsurface water (Antarctic Intermediate Water and Subantarctic mode water), but its significance is probably much less than that of the Antarctic. 

AABW, Antarctic Bottom Water NADW, North Atlantic Deep Water MW, Mediterranean Water AAIW, Antarctic Intermediate Water T and S characteristics from Picard and Emery (1982) How rates are in Sverdrups (10 m s ). 

A useful apphcation of preformed nutrient concentrations is that they are intrinsic to different water masses and sometimes can be used as conservative tracers. For example, the main sources of deep water in the Pacific Ocean are North Atlantic Deep Water (NADW), Antarctic Intermediate Water (AAIW) and Antarctic Bottom Water (AABW), all of which are at least partly homogenized in the Antarctic Circumpolar Water (AACW). It is not possible to determine how much of each of these sources contributes to Pacific deep water by using end member mixing of the conservative properties temperature and salinity because salinities of the end members are not sufficiently different. Since concentrations of DIP are well above detection limits in... 

As the Antarctic Bottom Water flows north, it gradually mixes with the southward flowing North Atlantic Deep Water, which lies immediately above. As the North Atlantic Deep Water flows to the south, it incorporates not only the Antarctic Bottom Water but also the Mediterranean Water and the Antarctic Intermediate Water which lie above. The North Atlantic Deep Water is eventually entrained into the Antarctic Circumpolar Current and flows unimpeded into the Indian and Pacific Oceans. 

Fig. 3.2 (a) Simplified, schematic representation of oceanic deep water circulation (after Broecker 1997). (b) Water masses in theAtlantic (after Stowe 1979). AABW =Antarctic Bottom Water AAIW =Antarctic Intermediate Water AIW = Atlantic Intermediate Water med = Mediterranean Water NADW = North Atlantic DeepWater. 

The collection of water samples obtained from 05°01 S 32°34 W based on the temperature and salinity data represent sample collections from sub-tropical water, Antarctic intermediate water. North Atlantic deep and bottom water and Antarctic bottom water all the major types of sub-surface water present at this location (13). The lowest strontium/ chlorinity ratio value was found at 4387 meters in the Antarctic bottom... 

The two stations located approximately on the equator also contain the same water masses as the southern station. Unfortunately, the distribution of samples was not suflBcient to have a complete collection of representative samples. Only one depth of the Antarctic intermediate water was sampled and the Antarctic bottom water was not sampled at all at these stations and a comparison between Antarctic bottom water at these stations and that at the southern station, unfortunately is not possible. The data that are available, nevertheless, show that at 00°08 N 32°32 W, the observed variation is much larger than at corresponding depths in the southern station at 05°01 S 32°34 W and generally indicates a lower value for the ratio in the upper 75 meters. There is no agreement observed between the two profiles at a depth of about 300 meters, a depth where an increasing oxygen concentration with depth occurs. However, the value of the ratio for the northerly flowing Antarctic intermediate water at 450 meters is comparable with that at the southerly... 

Antarctic Intermediate Water (AAIW), and Antarctic Bottom Water (AABW). Note that 8Nd is -13.5 in NADW, and °Be/ Be is c. 0.5 x 10. In the southern circumpolar water is -9, and Be/ Be is 1 X 10. °Be/ Be, and in particular 8Nd mimic the shape of salinity. Incorporation of these tracers into the sediment at a given location potentially provides information on the distribution and mixing of water masses at this location back through time. 

Observation that pathways of the most recently ventilated Antarctic Intermediate Waters are into the eastern South Indian Ocean, while at that level there appears to be flow of older waters from the South Pacific into the western Indian Ocean. 

With the introduction of the rosette sampler and the echo sounder, choosing the depth at which a sample is to be taken is a simple exercise in chart reading. Samples can be taken at any specified depth or in any specified water mass. Using much less sophisticated equipment on a cruise in the South Pacific [167], we were able to take water samples in the Antarctic Intermediate Water from 63 °S almost to the Equator, in order to demonstrate a horizontal continuity and vertical discontinuity in organic particulate content associated with a particular water mass. 

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