Chlorophyll shifts associated with the North Equatorial Current bifurcation latitude in Lamon Bay and off eastern Luzon, Philippines

The circulation pattern within Lamon Bay off the eastern coast of Luzon as observed during two oceanographic cruises conducted May of 2011 and 2012 features a northward flowing current, the nascent Kuroshio, bracketed by an anticyclonic gyre to its northeast and a cyclonic gyre to its southwest. The flow pattern is evident in the surface chlorophyll distribution (both from in situ and satellite observations) as well as within the upper thermocline. Difference in chlorophyll distributions between the two years are evident particularly at the depth of the Deep Chlorophyll Maximum (DCM). We hypothesize that the change is associated with a change in source waters which in turn is linked to the shift in the bifurcation latitude of the North Equatorial Current. The more northerly NEC bifurcation latitude (during the 2011 cruise) results in more subtropical water from the Kuroshio recirculation while a more southerly bifurcation latitude (during the 2012 cruise) injects in more tropical NEC waters into Lamon Bay. Mean chlorophyll profiles showed higher concentrations during May-June of 2011 (LB01) when the bifurcation latitude was at 13-14°N than during April-May of 2012 (LB02) when the bifurcation latitude was observed at 10-11°N. Further, a stronger gradient between offshore and shelf chlorophyll was seen during LB02 while a generally high chlorophyll both at offshore and shelf was seen during LB01. EOF analysis of MODIS chlorophyll data from 2003-2013 showed that the primary mode of variability was associated with longer term variability of the NEC bifurcation latitude.