Ocean Upwelling: Nutrients, Fisheries and Climate
Upwelling is the upward replacement of surface water that has diverged or moved away, often when alongshore winds and Earth’s rotation transport coastal surface water offshore. The rising water is usually colder and richer in nutrients, supporting phytoplankton and productive food webs. Its ecological effects depend…
Timeline
- 2026-10-12: Current NOAA upwelling, current, fisheries-indicator and climate guidance was rechecked.
- 2026-10-11: Primary and authoritative sources were reviewed for this guide.
Ocean upwelling is the rise of subsurface water toward the surface to replace water that has moved away. Along many coasts, wind blowing parallel to shore exerts stress on the upper ocean. Earth’s rotation turns the net transport of that surface layer to one side of the wind, and when the transport is offshore, deeper water rises near the coast. The opposite arrangement can pile surface water toward shore and produce downwelling. [1][2][3]
The turning comes from the Coriolis effect and friction through the wind-driven layer, often summarized as Ekman transport. In the Northern Hemisphere the net transport is to the right of the wind; in the Southern Hemisphere it is to the left. Whether that means offshore movement depends on coastline orientation and wind direction. Coastal shape, shelf width and existing currents modify the response, so identical wind directions do not produce equal upwelling everywhere. [2][3]
Water arriving from depth is commonly colder, saltier and richer in dissolved nutrients than the surface layer it replaces. Sunlit surface waters may have already lost nitrate, phosphate and other nutrients to biological uptake, while deeper waters accumulate material regenerated as organisms sink and decompose. When upwelling brings nutrients back into the euphotic zone, phytoplankton can grow and provide food for zooplankton, forage fish and larger predators. [1][3]
That pathway helps make eastern-boundary systems such as the California, Humboldt, Canary and Benguela currents exceptionally productive. NOAA notes that coastal upwelling regions occupy a small fraction of ocean area yet support a disproportionate share of fisheries landings. Productivity is not an instant fish forecast, however: harvest also depends on species, age structure, habitat, fishing pressure, management and whether plankton production occurs at the right place and time for young animals. [1][3]
Upwelling can impose costs as well as benefits. Offshore surface transport can carry drifting eggs and larvae away from nursery habitat. Source water may contain little dissolved oxygen or more dissolved carbon dioxide, which can contribute to hypoxia or corrosive conditions when it reaches the shelf. An intense bloom can later consume oxygen as organic matter decomposes. Thus stronger nutrient delivery can change an ecosystem without producing a simple, uniformly positive outcome. [1][3]
Upwelling also occurs away from ordinary coastlines. At the equator, the Coriolis effect turns wind-driven surface water in opposite directions on the two sides, creating divergence that deeper water replaces. Divergence around ocean fronts, eddies and headlands can have a similar result. The general rule is continuity: water rises where surface flow removes or separates water faster than horizontal inflow can replace it. [2][4]
Climate variability changes the winds, stratification and source waters. During many El Niño events, weakened Pacific trade winds suppress equatorial and South American coastal upwelling, warming the eastern tropical Pacific and reducing nutrient supply. Regional responses are more complicated than a single global switch. Long-term warming can strengthen stratification, while future wind changes may enhance or weaken coastal transport differently by season and location. [3][4]
Scientists therefore track more than one signal: alongshore wind stress, offshore transport indices, sea-surface temperature, water-column structure, nutrients, oxygen, chlorophyll and biological observations. A cold coastal patch can support an upwelling interpretation, but clouds, currents and mixing can also change temperature. For fisheries or climate reporting, the strongest claim combines the physical indicators with ecosystem measurements and specifies the region and season instead of treating “upwelling” as a universal cause. [1][2][3][4]
Sources
- NOAA Ocean Exploration — What Is Upwelling?
- NOAA Ocean Exploration — What Causes Ocean Currents?
- NOAA Fisheries — Local Physical Indicators: Coastal Upwelling
- NOAA Climate Prediction Center — El Niño–Southern Oscillation: Advanced