| Five hydrographic surveys and moored time series from 2005--2007 document changes of the surface-layer properties within the Galapagos Archipelago. The annual cycle includes changes of the sea surface temperature (SST), which cools in the Gansa season (June--November) and warms in the wet season (December--May). Sea surface salinity (SSS) freshens in the wet season from local rainfall as the Inter-tropical Convergence Zone (ITCZ) nears and in the late Gatha from influxes of the North Equatorial Countercurrent (NECC). The SSS is high west of Isabela where the EUC collides/upwells, when advected from the Cold Tongue westward by the South Equatorial Current (SEC) into the archipelago, and late in the wet season as the Equatorial Undercurrent (EUC) strengthens.;Tropical instability waves (TIW) appeared in 2005 during late summer (boreal) when the El Nino Southern Oscillation (ENSO) index was cool. The T1W cause the currents and the equatorial front (EF) to meridionally oscillate in the eastern equatorial Pacific. At 0°, 95°W, the SST changes concurrently with changes of the thermocline depth (20°C isotherm). Upwelling of ∼5.0 m day-1 is estimated during a succession of ∼15-day period TIW in the archipelago, dropping temperatures ∼7°C within a week. Concentrations of chlorophyll increased across the archipelago by 25--40% (25%) above its 2004--2006 (1998--2007) mean coincident to the upwelling. A larger surface chlorophyll increase within the archipelago as compared to 95° and 110°W implicates that upwelling within the island platform is iron-enriched.;Interannual changes related to ENSO create anomalies within the archipelago's annual signal. Downwelling Kelvin waves promoting the 2006/07 El Nino and an upwelling Kelvin wave promoting the 2007/08 La Nina cause large surface anomalies. The deepening of the thermocline by 10 and 25 m during the ENSO-warm surveys warms the SST by >2°C. The SSS and water-mass classification remain relatively unchanged in the archipelago. Chlorophyll concentrations decline >0.2 mg m-3, a >15% drop from the respective 1998--2007 monthly mean. |
