The Salt of the Earth
Surface-level Salinity Average for 2023
This map grew out of a casual observation on a dive trip to Vancouver Island. Our trip leader mentioned that we needed less weight than usual because the water there was less salty. I had no idea just how much seawater salinity varied around the world, and that curiosity turned into an exploration of its global distribution.
The map shows average surface salinity, derived from monthly raster datasets and averaged over a year. The data was projected to an equal-area projection and classified into tenths, so each color represents roughly 10% of the ocean’s surface area. While this is a global, surface-level view based on remote sensing and not intended for local or operational use, it is well suited for revealing large-scale patterns.
Major ocean surface currents are included to help explain how salinity is transported across vast distances, while major rivers provide context for sudden freshwater inputs and sharp local contrasts. Only features that directly support interpretation are shown or labeled, keeping the focus on the data itself.
Several patterns become immediately legible. Regions with high rainfall, ice melt, or strong river outflow show reduced salinity, while enclosed or evaporation-dominated waters stand out as highly saline. Following major currents from freshwater sources reveals clear, coherent paths across the oceans, reinforcing the idea that salinity is shaped by dynamic, interconnected systems rather than static conditions.
The result is primarily a cartographic curiosity, but one that highlights the complexity of Earth’s ocean systems. It invites viewers to slow down, trace patterns, and develop an intuitive understanding of how freshwater, evaporation, and circulation shape the chemistry of the global ocean.
2024-09-03