The Oceans 23140 °40 °40 ° 80 ° 120 ° 160 ° 160 ° 120 ° 80 ° 40 ° 0 °0 °AleutianFig. 6.28Global oceanic deep-water circulation. Major flow routes are marked by stippled ornament. Deep
mixing in the North Pacific is prevented by the topography of the seabed around the Aleutian Arc. Modified
from Stommel (1958), with permission from Elsevier Science.
dissolved CO 2 concentrations, since oxygen has been used to oxidize greater
amounts of organic matter to CO 2. Overall, the supply of dissolved oxygen to
seawater is adequate to oxidize the sinking organic matter and, apart from a few
unusual areas in the oceans, oxygen concentrations in the bottom waters are ade-
quate to support animal life. The higher dissolved CO 2 concentration in the
Pacific results in a shallower calcite compensation depth (CCD) in the Pacific,
relative to the Atlantic Ocean (Section 6.4.4).
The slower regeneration of silicon compared with nitrogen and phosphorus
(Section 6.5.4) means that relatively more silicon is regenerated in deep waters,
producing steeper interocean concentration gradients (Table 6.9 & Fig. 6.20).
Similarly, other elements with nutrient-like behaviour, such as zinc and cadmium,
have higher concentrations in the North Pacific compared with other oceans. By
contrast, scavenged elements have concentrations that are lower in the deep waters
of the Pacific compared with the North Atlantic, because of the longer time
available for their removal by adsorption on to sinking particulate matter
(Table 6.9).
This pattern of global oceanic circulation has probably existed since the end
of the last glaciation, 11 000 years ago. Before this, the circulation pattern is
thought to have been different, due to changes in glacial climatic regime and
changes in polar ice volume. It is unclear whether changes in ocean circulation
provoked climatic change at this time or vice versa. Despite the uncertainty, it is
clear that ocean circulation and global climate are intimately linked.