# Ekman transport Wind blowing over the ocean does not push the water the way it is pointing. Friction drags the surface layer, [[Coriolis_force|Coriolis]] deflection turns each deeper layer a little further, and the net movement of the whole wind-driven layer ends up at right angles to the wind — to the right in the northern hemisphere, left in the southern. Fridtjof Nansen noticed drifting ice doing this on an Arctic expedition before anyone could explain it. ## Microsim — p5.js Sidecar: `Ekman_transport.p5.js` · route leaf: `microsim/p5js/Ekman_transport__20260910T0400Z`. Built to the Betterfire Standard v0 (single `ARTICLE` constant, HUD title and Wikitube URL, control hints, parameter readout and equation). | Control | Does | |---------|------| | `wind dir slider` | direction the wind blows | | `wind speed slider` | stress on the surface | | `[h]` | switch hemisphere | *What to watch:* Turn the wind and watch the spiral twist with it — but the net transport arrow stays stubbornly 90° off, which is the whole point. ## The spiral, and why the net is 90° Each thin layer is dragged by the one above through [[Viscosity]] and deflected by rotation, so current direction rotates steadily with depth while speed decays — the Ekman spiral. Integrate the whole spiral and the transport comes out perpendicular to the wind stress regardless of the details, which is what makes the result useful: you do not need to resolve the spiral to predict where the water goes. Real oceans rarely show a textbook spiral because [[Turbulence]] and [[Thermocline|stratification]] blur it, but the depth-integrated transport holds up well. ## What it drives Because transport is perpendicular to wind, a wind blowing *along* a coast moves water *away* from it, and [[Upwelling]] pulls cold nutrient-rich water up to replace it — the mechanism behind the world's most productive [[Ecosystem|fisheries]]. Where wind patterns make Ekman transport converge, [[Water]] piles up and sinks, setting the pressure field that [[Geostrophic_current|geostrophic currents]] then flow along. The curl of the wind stress — a [[Vorticity]] source — pumps the interior, which is how the surface wind reaches the deep [[Ocean_current|circulation]]. **Reads with:** *Introduction to Physical Oceanography (Robert H. Stewart, 2008)* — [OTL record](https://open.umn.edu/opentextbooks/textbooks/introduction-to-physical-oceanography) · [download](https://github.com/introocean/introocean-en/releases/tag/v20200229) · CC BY-NC-SA. Section 7 of the [[PORTAL_Thury_Hydrodynamics_Apex_Spine|Apex Spine]] book shelf. **On the spine:** [[Coriolis_force]] · [[Geostrophic_current]] · [[Upwelling]] · [[Ocean_current]] · [[WT!Thury_Hydrodynamics_Compendium]]. ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Ekman_transport) : [Wikitube](https://en.wikitube.io/wiki/Ekman_transport) ## Previous hub tags Hubs: `Life_Physics`, `Systems`. Portals: [[PORTAL_Thury_Hydrodynamics_Apex_Spine]], [[PORTAL_WT!Thury_Hydrodynamics_Compendium]], [[PORTAL_Physics]]. --- *Book-section wave · 2026-09-10 · article + p5 microsim shipped together.*