A map reconnaissance of the Earth’s landmasses reveals a variety of conditions, including arid deserts, verdant forests and ice sheets. How do we explain this? The answer begins with the distribution of heating by the sun. Since incoming solar radiation is not distributed uniformly around the Earth, a mechanism must exist to transport energy from regions of abundance to regions of deficiency. This is where the oceans come into play. Because of the properties of water, much of the incoming solar energy is absorbed by the ocean before some of it is exchanged to the atmosphere. This receipt and exchange results in ocean currents and winds that are nature’s way of effecting an energy balance around the Earth. The ensuing patterns of the currents and the winds are what determine the placements of the deserts, forests and ice sheets. These same patterns also determine how nutrients are distributed in the oceans and hence where the oceans themselves may have both verdant and desert-like regions. Being that the oceans are the primary recipients of solar energy and that the coupling between the oceans and the atmosphere determines the distribution of life around the Earth, it is fair to say that the ocean circulation is existential, which is why we study it.