The deep ocean is almost the same temperature everywhere on Earth — about 2°C
Below approximately 1,000 metres, the ocean is cold, dark, and nearly uniform worldwide. Deep ocean water temperature is typically 2–4°C regardless of whether you're in the tropics or the poles. This is because the cold, dense water at the poles sinks and flows along the ocean floor in a global circulation pattern (the thermohaline circulation), carrying cold water throughout the world's deep ocean basins. The tropical surface might be 30°C, but 3km directly below it, the water is just 2°C — a thermal cliff invisible from above.
We think of tropical oceans as warm and polar oceans as cold. Finding that the deep ocean is a uniform cold temperature everywhere — that a single global circulation makes the depths of a tropical sea the same temperature as the Arctic — makes the ocean feel like a more unified, interconnected system.
“The deep ocean (below 1km) is almost exactly 2°C everywhere on Earth — tropical deep water and polar deep water are nearly the same temperature. A global circulation keeps the depths uniformly cold. 🌊 #OddlyHuman”