Chapter_8_Primary_Production - Chapter 8: Primary...

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1 Primary production refers to the formation of organic material through the process of photosynthesis . The vast majority of primary production in the ocean is carried out by chlorophyll containing single-celled organisms referred to collectively as phytoplankton . One of the central goals of biological oceanography is to understand the processes that lead to spatial and temporal variability in the abundance of marine organisms well enough to make predictions of future change. Since primary production forms the base of marine food webs, it is logical to begin the process of understanding ecosystem variability by looking at factors that influence primary production. It is also important to recognize that the process of photosynthesis, both in the ocean and on land, results in the conversion of carbon dioxide gas into particulate organic carbon. Because primary production in the global ocean is very large, its role in the global carbon cycle cannot be ignored. For this reason, oceanic primary production is an essential parameter in modern climate models that are designed to predict future global warming scenarios. In future chapters we will examine the ocean’s role in climate change and a large part of that examination will build directly upon the material presented in this chapter. The chapter begins by examining how variations in light intensity and plant nutrient concentration affect the magnitude of primary production. Observed regional patterns of variability in primary production over the global-ocean will then be explained in terms of how regional physical oceanographic conditions, such as vertical mixing and upwelling, impact light intensity and nutrient availability in the ocean and, thereby, affect the level of primary production. The chapter will end with a brief look at current and future research issues being addressed by oceanographers. Chapter 8: Primary Production in the Ocean Chapter Outline Environmental Factors that Influence Net Primary Production Spatial and Temporal Variability in Primary Production Magnitude of Global Ocean Net Primary Production Frontiers in Primary Production Research
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2 Environmental Factors that Influence Primary Production Learning Objectives 1. Recognize that net primary production results in the uptake of CO 2 (gas) and the formation of particulate organic matter in phytoplankton cells 2. Recognize that light intensity is highest at the surface of the ocean and decreases exponentially with depth and that, consequently, mixing phytoplankton to great depth reduces the daily light exposure received by phytoplankton 3. Recognize that the average cell diameter of the phytoplankton assemblage decreases when going from high to low nutrient conditions 4. Recognize that primary production can be limited by low availability of any one of the following: nitrogen, phosphorous, silicon or iron and that the particular nutrient that limits primary production can change by region and season. 5.
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Chapter_8_Primary_Production - Chapter 8: Primary...

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