Answer study question 4 of chapter 14. Organic production at polar latitudes is seasonal, limited by sunlight, of low level in winter and stimulated by a long photoperiod in summer. At temperate latitudes, primary production is seasonal due to changes in solar radiation, and it can also be nutrient limited. Productivity reaches high values in spring and summer at temperate latitudes, but production varies over the year. In the tropics, sunlight is never limiting, but nutrients are.
Productivity is low and changes little during the year.
In the tropics, there is high productivity in upwelling regions only, where water column stability does not prevent nutrient supply to the surface layer. A more detailed explanation is found on pages 378-380 of the textbook.