Chapter 12 Key Concepts

Productivity expresses the rate of production of biological materials, and biomass refers to the amount of biological material present at any one time. Both measures are expressed as a function of ocean area.
A food web is a complex diagram of feeding interactions. A food chain is a linear sequence, often a simplification of a food web that reveals which organisms consume which other organisms in an environment.
Transfer from one trophic level to the next is not complete.
Food chain efficiency can be used to calculate the potential fish production at the top of a food chain.
Food chains can be classified on the basis of oceanographic conditions, which helps determine the number of trophic levels.
Is there a limit to the number of links in a food chain? The total number may be limited by the structure of the food chain, the possible energy that can be transported through many links, or to a possible instability of large food chains.
Strong food web interactions in trophic cascades can result in strong regime shifts that are driven by human and climatic forcing.
The oxygen technique relies on the fact that oxygen is released in proportion to the amount of photosynthesis.
The radiocarbon technique uses the radioactive isotope ¹⁴C as a tracer in uptake of bicarbonate during the process of photosynthesis.
High-accuracy oxygen electrodes can be used to measure primary productivity from measures of oxygen change taken directly in the water in the environment.
The amount of photosynthesis can be estimated by measuring the fluorescence obtained from phytoplankton active photosystem II centers that have been exposed to a sequence of light flashes.
Data collected by instruments on ocean moorings can be used to estimate continuous changes in primary production.
Satellite color scanners can crudely estimate relative standing stocks of phytoplankton, which can in turn be used with ocean surface data and productivity models to estimate changes in primary production.
Continental shelf and open-ocean upwelling areas are among the most productive, owing to winds that move surface water offshore and bring nutrient-rich water from below.
At convergences and fronts, nutrients are concentrated, and primary productivity is high.
Central oceans and gyre centers are nutrient-poor and relatively barren of primary productivity.
Different oceans have different overall levels of primary productivity, which are determined by latitude, ocean basin shape, wind-driven surface currents, and the influence of surrounding continents.
Carbon dioxide increase in the past 200 years from human additions has led the earth to a carbon dioxide level in the atmosphere not seen in at least 400,000 years.
Carbon is transferred downward into the ocean by means of a solubility pump and a biological pump. Fluctuations in these processes may be crucial in affecting global climate.
Ocean transparency measurements suggest that carbon dioxide increase has not had an apparent impact on primary production over the past 70 years, except in the Arctic Ocean. But there is evidence for a more recent decline of production that may have been caused by increased ocean stratification.
Carbon dioxide increase may select for different dominance patterns in nutrient use among phytoplankton species.
Some relief from global climate change might be obtained by stimulating production by iron addition in high-nutrient, low-productivity areas of the ocean, resulting in sinking and carbon sequestration for hundreds or thousands of years in the seabed.
Dimethyl sulfide is a natural by-product of phytoplankton metabolism and may strongly affect regional oceanic climate.
Ocean acidification may cause major reorganizations in the plankton by eliminating some calcifying plankton, especially those that precipitate aragonite.