Seasonal and Spatial Variability of Primary Production in the Mozambique Channel

Abstract

The surface circulation in the Mozambique Channel changes from the northern part, where the system is under dominance of the monsoons, to the central and southern parts, where mesoscale eddies are more frequent. Despite these differences in the physics between the three regions, satellite-based primary production shows that the whole region is characterized by similar seasonal variability of primary production, in which winter is the most productive season. A coupled physical-biogeochemical model configuration applied for the Mozambique Channel is used to investigate how wind stress and heat fluxes modulate seasonally and spatially the distribution of new and primary production in the region. Higher new production integrated over the euphotic layer depth in winter accounts for about 50% of the total primary production in the Mozambique Channel, indicating the seasonality of primary production is driven by new nutrients upwelled from bellow the euphotic zone. During the other seasons of the year the depth-integrated primary production is low, which is the period when the system depends on remineralization of the organic matter to sustain phytoplankton growth at the subsurface. Stronger wind stress is the dominant surface forcing in the northern part of the Mozambique Channel, which is responsible for vertical advection and entrainment of nitrate from below the euphotic zone that sustain the primary production during winter, while intense negative net heat flux is the dominant forcing in the central/southern parts. However, it is important to note that mesoscale eddies also enhance primary productivity in the region with a focus on the winter period.