Water Antarctic Bottom

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). 

A requirement of the heat balance for a steady-state ocean is that the input of new cold abyssal water (Antarctic Bottom Water and North Atlantic Deep Water) sinking in the high-latitude regions must be balanced by input of... 

Deep water also forms along the margins of Antartica and feeds the Circumpolar Current. The Weddell Sea, because of its very low temperature, is the main source of Antarctic Bottom Water (AABW) which flows northward at the very bottom into the South Atlantic, and then through the Verna Channel in the Rio Grande Rise into the North Atlantic. It ultimately returns southward as part of the NADW. 

Abyssal clays are found in greater abundance on the western side of the Atlantic Ocean than on the eastern side. This is due to bottom topography that restricts the flow of North Atlantic Deep Water and Antarctic Bottom Water to the western side of the basin. The lower temperature of the western waters causes the CCD to be somewhat shaUower than on the east side of the basin as calcite solubility increases with decreasing... 

AABW, Antarctic bottom water The densest water mass in the open ocean. 

North Atlantic Deep Water (NADW), which is formed with an initial 5 C-value between 1.0 and 1.5%c, becomes gradually depleted in C as it travels southward and mixes with Antarctic bottom water, which has an average 8 C-value of 0.3%c (Kroopnick 1985). As this deep water travels to the Pacific Ocean, its C/ C ratio is further reduced by 0.5%o by the continuous flux and oxidation of organic matter in the water column. This is the basis for using 8 C-values as a tracer of paleo-oceanographic changes in deep water circulation (e.g., Curry et al. 1988). 

The density of the water controls the deepwater circulation. If the density of a water body increases, it has a tendency to sink. Subsequently, it will spread out over a horizon of uniform circulatory system is also known as thermohaline circulation. As shown in Figure 5 of the ocean conveyor belt, the densest oceanic waters are formed in Polar Regions due to the relatively low temperatures and the salinity increase that results from ice formation. Antarctic Bottom Water (ABW) is generated in the Weddell Sea and flows northward into the South Atlantic. North Atlantic Deep Water (NADW)... 

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... 

Ledbetter M. T. and Johnson D. A. (1976) Increased transport of Antarctic bottom water in the Verna Channel during the Last Ice Age. Science 194, 837-839. 

Below 1,500 m in the world ocean, the distribution of carbonate ion concentration is remarkably simple (see Broecker and Sutherland, 2000 for summary). For the most part, waters in the Pacific, Indian, and Southern Oceans have concentrations confined to the range 83 8 lamolkg . The exception is the northern Pacific, where the values drop to as low as 60p.molkg In contrast, much of the deep water in the Atlantic has concentrations in the range 112 5 p.mol kg The principal exception is the deepest portion of the western basin where Antarctic bottom water (AABW) intrudes. 

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... 

All proxies of the temporal change in the chemical composition of seawater are complicated by artifacts. Some have been discarded because of difficulties in interpretation and may reappear as they are better rmderstood. Taken together, there are a few results about which we may be relatively confident. It is pretty clear that the chemical tracers and age of North Atlantic Deep Water indicate that it was less prominent in the Atlantic relative to Antarctic Bottom Water during the last glacial period. Cd Ca ratios indicate that the... 

The general abyssal circulation can be summarized rather briefly. Antarctic Bottom Water, the densest of... 

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. 

Most of the deep waters in contact with the abyssal sediments are a mixture of North Atlantic and Antarctic bottom-water masses. They are relatively saline and fairly cold (0.5-1.5°C). Currents at these depths typically are slow and do not impose shear stress of sufficient magnitude to transport sediments (Gardner etal., 1984 Demidova, 1999). 

For water masses deeper than 2000 m, Zahn and Mix (1991) obtained a slope as high as 1.53. This gradient is explained with the formation of sea-ice in the source areas especially for southern component water masses. Since the freezing of polar snrface waters raises the salinity, but does not fractionate oxygen isotopes, southern source deep water masses, like the Antarctic Bottom Water, exhibit relatively low 5 0 values, and so do other water masses, which are derived from the admixtnre of sonth polar water masses (Macken-sen2001). 

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