This chapter will consider biogeochemical cycling in the coastal zone. This is defined as that area of estuarine and coastal, relatively shallow water where there is strong benthic-pelagic linkage and exchange between the water column and the underlying sediment. In deeper water this connection becomes increasingly tenuous as the exchange between the euphotic zone and the benthic layer declines. Longhurst et al. (1995) recognized the coastal boundary domain, divided into 22 provinces, as often bounded by a shelf-break front, and included coastal upwelling regions. The coastal zone generally exhibits high rates of primary production compared with the open ocean (Table 1), and there is the greatest impact from inputs from the land to the coastal sea through estuaries. Estuaries and coastal seas are highly heterotrophic systems which are net exporters of CO2 to the atmosphere due to the mineralization and recycling of both autochthonous and allochthonous organic matter (Borges, 2005).
PHYSICO-CHEMICAL DIFFERENCES BETWEEN LATITUDINAL REGIONS
The physical-biological interactions that influence marine phytoplankton production have been reviewed by Daly & Smith (1993). Because of the spherical shape of the Earth, more solar energy falls per unit area of surface in equatorial regions than at the poles (Fig. 1a), and the incidence of light at the equator is vertical to the surface, but oblique at the poles. Furthermore, the distance radiation travels through the atmosphere is longer at the poles, thus reducing the irradiation incident at the poles compared with equatorial regions.