Timing and magnitude of spring bloom and effects of physical environments over the Grand Banks of Newfoundland

Abstract

AbstractSpring bloom is a dominant feature of seasonal phytoplankton cycles in the northwest Atlantic continental shelf. In this study, we investigate temporal and spatial variations of spring‐bloom timing and intensity over the Grand Banks of Newfoundland, using satellite ocean color data and other oceanographic measurements from January 1998 to December 2009. The spring bloom has strong interannual and meridional changes in its timing and intensities. Physical oceanographic conditions including the sea surface temperature (SST), wind speed, and mixed layer depth (MLD) also show evident interannual variations. The spring boom starts first in the southern Bank in February–March and often in the central and northern Bank in April, respectively. An early initiation of spring blooms is generally associated with high SST, weak winds, and shallow MLD at the beginning stage of the spring blooms, and tends to result in stronger intensities. However, the photosynthesis available radiance does not seem to affect the bloom initiation in the southern area or the bloom intensity over the entire Banks. In the southern area, higher SST does not lead to larger bloom magnitude. Our analysis shows that the effect of the SST in the northern area is primarily through the earlier ice melting. It also indicates that Sverdrup's critical depth criteria are suitable for conditions over the Grand Banks. The present study points to the significant sub‐bank‐scale differences in the timing and magnitude of the spring bloom attributable to underlying physical environments, important for the integrated management of the Grand Banks ecosystem.