Heat Content and Temperature of the Ocean

Abstract

The global ocean is a vast body of water covering approximately two thirds of Earth’s surface and having an average depth around 4,000 m. Temperatures in the ocean can range from a balmy 30°C in the surface layers of the tropics to an icy cold −2°C in polar regions and at abyssal depths. Apart from the strong spatial variability, water temperatures at a place also change on all time scales, from hours to decades. Variability in surface water temperatures affects air-sea heat exchange and is an important factor determining the nature and strength of ocean–atmosphere coupling. Changes in ocean temperatures imply expansion or contraction of the water column and can thus have a major impact on sea level. And given the large heat capacity of seawater compared to that of air and the large mass of the oceans compared to that of the atmosphere, relatively small fluctuations in oceanic temperatures imply substantial changes in heat content, which are essential for properly accounting for the planet’s energy balance. As such, taking the temperature of the oceans and determining changes in its heat content is an essential diagnostic of the state of Earth’s climate and the overall health of our planet.