North Pacific Deep Water

Particulate Fe does not show an eolian influence in the surface layer and its distribution is more constant with depth. 48% of Fe in the surface water (0-100 m) is in the dissolved form and 55% in deep water (500 -4,000 m). Most of the particulate Fe in the intermediate and deep water is in the form of refractory alumino-silicate minerals of eolian origin. The higher concentration of particulate Fe in North Atlantic deep water (1.2 mnol kg ) than in central North Pacific deep water (0.3 nmol kg ) again reflects the higher input of eolian material into the Atlantic compared to the Pacific Ocean. 

When REE fractionation is discussed, it is common to normalize the data to the values in shale which are thought to be representative of the REEs in the upper continental crust. The shale-normalization not only helps to eliminate the well-known distinctive even-odd variation in natural abundance (the Oddo-Har-kins effect) of REEs but also visualizes, to a first approximation, fractionation relative to the continental source. It should be noted, however, that different shale values in the literature have been employed for normalization, together with the ones of the Post-Archean Australian Sedimentary rocks (PAAS) adopted here (Table 1). Thus, caution must be paid on the choice of the shale values if one ought to interpret small anomalies at the strictly trivalent lanthanides such as Gd and Tb. Alternatively, for detailed arguments concerning fractionation between different water masses in the ocean, it has been recommended that the data are normalized relative to the REE values of a distinctive reference water mass, for example, the North Pacific Deep Water (NPDW, Table 1). The NPDW-normalization eliminates the common features of seawater that appeared in the shale-normalized REE pattern and can single out fractionation relative to the REEs in the dissolved end product in the route of the global ocean circulation. 

Dissolved (<0.04nm) REE in the North Pacific Deep Water at 2500 +100m (after Alibo and Nozaki, 1999). 

Figure 6 Zonal section of A C in the South Pacific collected during the WOCE program. The two minima at 2000-2500 m depth are thought to be the core of southward-flowing North Pacific Deep Water. Northward-flowing Circumpolar Deep Water is identified by the relatively high values in the Kermadec Trench area at the bottom between 140°W and the Date Line.

Deep Water Masses AABW Arvtarctic Bottom Water PDW Pacific Deep Water lODW Indian Ocean Deep Water NADW North Atlantic Deep Water... 

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). 

On the other hand, a nutrient-type trace metal like Zn attains a concentration of dissolved Zn that is approximately five times greater in the old, nutrient-rich deep waters of the North Pacific than they are in the young, nutrient-poor North Atlantic deep waters. Its distribution in both ocean basins is similar to that of silicic acid. The efficiency with which Zn is recycled in the ocean leads to its relatively long oceanic residence time. 

Earlier in Ghapter 5 a map of the G age of DIG in the ocean s deep waters (Fig. 5.17) revealed that the age difference between the northern North Atlantic Deep Water and that in the Northeast Pacific is C.1700 y. This value compares the most recent and most ancient ventilation ages of the deep ocean, whereas the box model compares the mean deep water age of the entire ocean, c. - 160%o (c. 1480 y) with that of the surface ocean, c. - 50%o (400 y) (1480 - 400 = 1080 y). In some ways, the largest task of the two-layer-ocean calculation is determining representative A G values for the mean surface and deep ocean. More complicated models with more reservoirs (see, for... 

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. 

After isolation from the atmosphere a water mass ages, and as it reflects biological cycling its S Cdic decreases and its nutrient content increases (Kroopnick 1985). Values of deep-water mass S Cdic range from 1.2%o in the core of North Atlantic Deep Water, via 0.4%o in Circumpolar Deep Water, to — 1.0%o in northem Pacific Deep Water. 

---