Galapagos Cold Pool
The Galapagos Cold Pool (GCP) is a persistent region of anomalously cool sea surface temperatures located west and south of the Galapagos Archipelago. SSTs in the cold pool can be 3-6 C cooler than the surrounding tropical Pacific waters, reaching as low as 18 C during the Garua season.
Formation
The cold pool forms through the interaction of the Pacific Equatorial Undercurrent (EUC) with the submarine topography of the Galapagos platform. As the EUC flows eastward at Thermocline depth, it encounters the volcanic edifices of the western islands (Isabela and Fernandina). The topographic obstruction forces the cold, nutrient-rich thermocline water upward to the surface.
Additional upwelling is driven by:
- Wind-driven Ekman divergence along the equator
- Topographic acceleration around the islands
- The Humboldt Current bringing cool water from the southeast
Climatic effects
The GCP is the primary driver of the regional climate asymmetry in the Galapagos:
-
Atmospheric stabilization: The cold SSTs cool the overlying air, creating a shallow, stable marine boundary layer capped by a persistent temperature inversion. This suppresses deep convection and favors stratocumulus cloud formation — the hallmark of the Garua season.
-
Precipitation patterns: The cold pool creates a spatial contrast in Precipitation across the archipelago. The western islands (closer to the cold pool) are drier, while the southeastern islands receive more convective rainfall due to relatively warmer waters.
-
Cloud frequency: Satellite observations show that cloud frequency is highest over the western islands, consistent with persistent low-level stratocumulus formation driven by the cold pool (Zander et al., 2023, Atmosphere).
ENSO response
The GCP responds strongly to ENSO variability:
- During El Nino, the weakening of the EUC reduces topographic upwelling. The cold pool warms or disappears entirely, the inversion breaks down, and convective Precipitation replaces Garua conditions.
- During La Nina, enhanced upwelling intensifies the cold pool, strengthening the inversion and garua.
Schneider et al. (2025, Geophys. Res. Lett.) showed that local SST variability in the GCP region directly modulates heavy rainfall occurrence in the archipelago, highlighting the cold pool as a key mediator between oceanic forcing and island-scale Precipitation.
See also: Pacific Equatorial Undercurrent, Garua, El Nino-Southern Oscillation, Sea surface temperature, Thermocline