El Niño shifts nutrient and productivity patterns in the Pacific

Satellites show a turnaround in the Pacific

In the summer of 2026, satellites recorded unusual distributions of chlorophyll at the surface of the Pacific Ocean. In classic high‑productivity zones values fell markedly, while sporadic increases appeared elsewhere. The pattern matches typical signals of a developing El Niño event, in which temperature and circulation conditions shift on a broad scale.

Why chlorophyll matters

Surface chlorophyll is an established proxy for phytoplankton biomass — the base of marine food chains. Space‑borne, area‑wide datasets complement local measurements: they reveal where nutrient‑rich water is upwelling and where primary production is stalling. Limits remain: satellites mainly detect the very top layer of the ocean and do not provide information on species composition or production depth. Nevertheless, they allow rapid detection of large‑scale changes.

Reduced upwelling, fewer nutrients

Typical for El Niño is a warming of the central and eastern equatorial Pacific. Warmer, lighter surface water weakens the upwelling of cold, nutrient‑rich deep water. Surface waters then lack nutrients — accordingly, chlorophyll values decline along the South American coast and in equatorial waters. Ecosystems that rely on a steady nutrient supply are affected.

Regional exceptions

Productivity does not fall everywhere to the same degree. Locally, altered currents, eddies or changed precipitation patterns — with consequences for river inputs — can produce short‑term increases. Often different plankton groups come to dominate: smaller cells fare better under warm, nutrient‑poor conditions but transfer less energy to higher trophic levels. That can lead to lower food availability for fish and marine mammals despite a higher biomass at the base.

Impacts on fisheries and fauna

Commercial fish stocks respond sensitively to fluctuations in primary production, especially when they are spatially tied to productive coastal zones. Declining catches are known from past El Niño years; similar patterns are emerging for 2026. Seabirds, seals and whales often react early: lacking prey, breeding success and juvenile survival decline.

Heat, oxygen and biogeochemical cascades

Warming reduces oxygen solubility and weakens vertical mixing. In already low‑oxygen areas deficits can worsen, further restricting habitats. At the same time plankton composition changes and thereby the pathways by which carbon is exported to depth — with implications for the role of the oceans as a carbon sink.

Long‑term context

El Niño events are part of natural climate variability. An overall warmer ocean, however, shifts baseline conditions, increases the likelihood of extreme marine heat events and can influence the frequency or intensity of El Niño. Ecosystems thus lose buffering capacity and may recover more slowly from disturbances.

Data basis and monitoring

Satellite‑based chlorophyll indicators provide comparable, near‑real‑time monitoring across large areas. To constrain causes and assess consequences for biodiversity and stocks, complementary measurements from profiles, buoys and research vessels are necessary.

Outlook

The observed shifts in chlorophyll suggest a reorganization of the Pacific's food base. In the short term, regional catch declines and increased stress on top consumers are likely. How strong and how long the effects will be depends on the duration and intensity of the El Niño event and on the pre‑existing condition of the ecosystems. Adaptive fisheries management, protection of critical habitats and continuous monitoring can help limit ecological and economic damage.