North Atlantic lead concentrations

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. 

Table 2 Distributions of concentrations of dissolved cadmium, mercury, and lead (pmoll ) in rivers, estuaries, the English Channel and the North Atlantic...

Figure 2 Changes in concentration of atmospheric lead at Bermuda and dissolved surface oceanic lead near Bermuda from the mid-1970s to the mid-1990s. (Data reproduced with permission from Wu J and Boyle EA (1997) Lead in the western North Atlantic Ocean Completed response to leaded gasoline phaseout. Geochimica et Cosmochimica Acta 61 3279-3283 and from Huang S, Arimoto R and Rahn KA (1996) Changes in atmospheric lead and other pollution elements at Bermuda. Journal of Geophysical Research 101 21 033-21 040.)...

The O2 content of the surface waters is lower at mid-latitudes because of higher temperatures, which lead to lower gas solubility. As shown in Figure 10.1a, the ther-mocline is characterized by a concentration minimum that increases in intensity from the Atlantic to the North Pacific. Note that the O2 minimum is less pronounced in the vertical profile from 45°S as compared to 9°N in the Atlantic Ocean because of close proximity to the site of AABW formation. Mid-water phosphate and nitrate maxima... 

Decreasing concentrations of Pb in surface waters of the Atlantic Ocean have been documented by observations from 1979 until the present (Figure 3). The decreasing concentration of Pb in the upper layers of the ocean is also observed (Figure 4), with a slower response in the deeper waters that are replaced on decadal timescales. These decreases are seen in other parts of the Atlantic and North Pacific as well. This evidence amply demonstrates that the phasing out of leaded gasoline in the USA has been closely followed by decreases of the Pb concentration of the ocean on the appropriate timescale. 

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