Monsoon-Driven Coastal Upwelling Off Zamboanga Peninsula, Philippines

Abstract

Cooler temperatures and elevated chlorophyll a, indicative of upwelling, are observed off the coast of Zamboanga Peninsula, Philippines. This upwelling is driven primarily by offshore Ekman transport as the Northeast Monsoon winds blow parallel along the coast of Zamboanga, with enhancement of positive wind stress curl due to the land’s frictional retarding force. Analysis of sea surface temperature time series reveals interannual variations in upwelling, with weakening during the 2007/2008 La Niña and strengthening during the 2006/2007 El Niño. Upwelling areas are known as productive and biologically rich, and the Zamboanga upwelling supports a thriving sardine fishery in the southern Philippines. Sardine landing data correlate remarkably well with monthly chlorophyll values during 2009–2010. Despite the prevailing notion that La Niña causes strengthening of the monsoon-driven upwelling, long-term fisheries production data for Zamboanga demonstrate a decrease in fish catch due to weaker upwelling during the 1999/2000 and 2007/2008 La Niñas. Interannual variations in upwelling, phytoplankton productivity, and sardine catch suggest that interannual El Niño-Southern Oscillation variations can affect the small Zamboanga Peninsula pelagic fishery.

Keywords

• Philippine Archipelago
• PhilEx
• Zamboanga Peninsula
• northeast monsoon