Main producers are small floating autotrophic plants which are less vascular than their terrestrial counterparts. Compared to nutrient-bearing regions, nutrient-deplete regions (e.g., the subtropical gyres) have a larger fraction of chlorophyll below the depth that can be sensed by the satellite (Smith 1981). Therefore, SP in the ocean is small in comparison to NPP. In this case, NEP is also often referred to as "export production" (or "new production" (Dugdale & Goering 1967), as discussed below). In at least some of these polar systems, it appears that light and iron can "co-limit" summertime photosynthesis (Maldonado et al. There are different factors that affect it in different environments. A band of cool, plant-rich waters circles the globe at the Equator, with the strongest signal in the Atlantic Ocean and the open waters of the . A large amount of photosynthesis taking place should mean a large productivity! 1979, Chisholm et al. Run the animation. But