Record of upwelling based on coral skeletal Ba/Ca in the Bicol Shelf, east Luzon, Philippines

Ba/Ca trends from skeletons of coral Porites sp. located at the opposing sides of the NEC bifurcation, in Bicol and Surigao shelves along the eastern seaboard of the Philippines, are utilized to establish temporal variation in upwelling events off the northeast shelf of Luzon and to define their influencing factors. Ba/Ca with near monthly resolution, 25 years (1981-2006) for the Bicol sample and 12 years (1992-2004) for the Surigao sample, are higher in the former as expected because of upwelling there. Ba/Ca peaks in both sites occur more during the southwest monsoon but peaks that occur during the northeast monsoon typically are higher. For Surigao, several Ba/Ca peaks, especially during La Niña, coincided with high precipitation events. This can be due to the relative proximity of the core site to the coast. In contrast, Ba/Ca highs in Bicol are more frequent during El Nino and this is attributed to shallowing of thermocline. Prior to the early 1990's, the Bicol Ba/Ca ratios show little change. Only two significant peaks are present which coincide with the strong 1986-1987 El Niño event. Since then, the Ba/Ca started to be significantly higher. This elevation is most likely due to the northward shift of the NEC bifurcation by 1990 that persisted for several years. The Ba/Ca peaks remained high from 1998 to 2002 despite the southward shift of the bifurcation. This can be due to long residence time of Ba in seawater.