OCEAN · MIXED-LAYER DEPTH

Mixed-Layer Depth

How thick the well-stirred surface layer of the ocean is — a live global map of mixed-layer depth in metres, the uniform slab that wind and waves churn at the top of the sea before it meets the calm, stratified deep. Dark where the layer is thin (a few metres, under the warm summer cap); bright where it is deep (hundreds of metres, in the stormy winter North Atlantic and the Southern Ocean). One of the quietly most important numbers in the ocean: it sets how much heat the sea stores and whether nutrients from below ever reach the sunlight where plankton can use them — so it controls where and when the great blooms happen. A genuinely new phenomenon no other layer here shows. Updated daily.