Introducing Oceanography

the deep, slow movement of ocean waters, now called the thermohaline circulation.

decrease in salinity with depth is a feature of Atlantic waters and is not observed in the Pacific and Indian Oceans

years in the ocean

is estimated that sodium (Na+) has a residence time of 78 million years and calcium (Ca2+) around 1.1 million

ratio. Examples of shelf seas are the North Sea in Europe or the Yellow Sea in Asia

There is nowhere on the surface of the planet that does not rely on the effects that the oceans have on climate, and even more importantly in driving major water, oxygen, carbon dioxide, nitrogen and other cycles of the elements fundamental to life on Earth.

Temperature and salinity sections through the Atlantic from the Antarctic ice edge to the edge of the Arctic Ocean show how the circulation of the deep ocean can be interpreted from T–S data (Figure 1.9). Starting at the southern end of the section, the coldest water (formed in the Weddell Sea in winter) sinks to the ocean bottom and spreads northward as very cold, relatively salty, Antarctic Bottom Water (ABW). Salt is added to seawater during ice formation, and this helps to increase the density of this water. The surface layers of the ocean around the Antarctic continent formed in summer are cold, but less saline because of melting ice. These stretch northward and sink at the Antarctic convergence (about 50° S) as Antarctic Intermediate Water (AIW). Between these two water masses, North Atlantic Deep Water (NADW) flows southwards. NADW forms in the extreme north Atlantic where cold water sinks to a depth of about 3000 m and travels southwards towards the Antarctic.