confined to continents and islands, and navigation was strictly on the surface until
the 20th century, the ocean has been a realm of considerable mystery. In the last
several decades, the exploration of the sea bottom, sensing by satellites, and
research into connections between sea surfaces and weather over the land half
the globe away has started to correct the deficiencies in our knowledge. Still, some
writers have lamented we know less about the world ocean than the cosmos.
As the most common substance on Earth’s surface, ocean water provides an
immense thermal stability for the planet. Water is the natural substance with the
highest specific heat. This means that water heats and cools much more slowly
than atmosphere or land. The great mass of the ocean represents a tremendous
capacity for heat storage so the presence of the ocean greatly moderates solar heat-
ing of theatmosphereand slows atmospheric cooling. Geographically, ocean
water heats and cools according to patterns of insolation and warm and coldocean
currents. This is evidenced in the observation that seasonaltemperaturediffer-
ences over land are much more extreme than over the ocean. In a scenario of
global warmingthe ocean is a “sink” dissolving and sequestering much of the
carbon dioxide released into the atmosphere; it is unclear as to the capacity of
the ocean in this respect.
The ocean is the most important source of water feeding into the atmospheric
portion of thehydrologic cyclewith some water waiting in the oceanic storage
for thousands and thousands of years. The evaporation from tropical oceans is in
net terms transported from the tropics toward the poles helping to balance the
ongoing global energy imbalance. The latent heat captured by evaporation can
be transported thousands of kilometers and transformed into atmospheric stormi-
ness. Because most globalprecipitationoriginates from oceanic evaporation
and because the ocean is so large, approximately 77 percent of the world’s precipi-
tation falls over oceans.
Geographers and others have subdivided the world ocean into several large parts
commonly called “oceans.” Water exchanges between the oceans to the extent that
the composition of seawater is quite similar over the planet, but some passages are
constricted thus decreasing free circulation by ocean currents. A case in point is
the Bering Strait, which is shallow and has a width of only 80 km thus impeding
circulation between the Arctic Ocean and the Pacific Ocean.
By far the largest ocean is the Pacific Ocean comprising a surface of
167,000,000 sq km, which approximates one-third the surface of the planet and
contains 46 percent of the world ocean’s water. It extends from the Arctic to the
Antarctic, roughly between 90°west longitude and 120°east longitude. The
Atlantic Ocean is the second largest and, like the Pacific, extends from the Arctic
to Antarctica. However, the Atlantic’s longitudinal extent is only about half of the
Pacific’s. The Indian Ocean is a bit smaller than the Atlantic and extends from the
Oceans 247