The Blue Machine

In the deep ocean basins, there is generally a stack of three or four major layers which are known to oceanographers as water masses. Each one has a distinct character and history, and these are the biggest components of the ocean engine. Lesson one about the structure of the ocean is that it’s layered, and those layers generally do not mix with each other. The most striking internal boundary in the ocean is defined by temperature, and it’s known as the thermocline. A thermocline is defined as a thin layer of the ocean that undergoes a rapid temperature change with depth, marking the transition between layers which have different temperatures. But when oceanographers refer to ‘the thermocline’, they’re generally talking about the starkest transition of all: the boundary between warm sunlit surface water and the much cooler dark water below. This distinct warm upper layer, known as the ‘mixed layer’, exists over most of the global ocean, and it’s the drivetrain of the planet, connecting the powerhouse of the sun to the ocean engine which runs on that heat energy. The vast ocean basins are filled with much colder water, often untouched by the sun for centuries. In the Pacific Ocean the depth of the thermocline is typically between 60 and 200 metres, and beneath that, the character of the ocean water changes dramatically. This is why NELHA can pump cold water out of the ocean near Hawai‘i, as long as it’s pumping from a depth of 1,000 metres or more, well below the thermocline.