0 1991, by the American Society of Limnology and Oceanography, Inc. Hypotheses to explain high-nutrient conditions in the open sea

• Main Author: John J. Culled
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Antarctic; Pacific; Antarc*; Subarctic
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.535.8736; http://www.soest.hawaii.edu/oceanography/courses/OCN626/2008_OCN 626/cullen_1991.pdf

Oceanic high-nutrient, low-chlorophyll waters are clharacterized principally by the persistence of major nutrients at the sea surface. This condition indicates control of autotrophic production by something other than NO, or P04, but the nature of this control is at present unresolved. The range of hypotheses to explain the high-nutrient condition is illustrated by the grazing hypothesis (specific growth rates of phytoplankton are maximal and environmental stability allows develop-ment of a balanced food web that maintains low standing crops of phytoplankton) and the iron hypothesis (standing crop of plankton is constrained by availability of Fe: if more Fe were available, the standing crop of phytoplankton would increase and NO, would be depleted, despite grazing). The iron hypothesis has been examined experimentally in the subarctic and equatorial Pacific and in Antarctic waters. In each environment, Fe enrichment enhanced the final yield of phyto-plankton biomass after incubations of many days. Interpretation of these experiments is contentious because containment in bottles is unnatural. Nonetheless, recent studies in the laboratory and in the field indicate that Fe and possibly other trace elements exert selective pressures on oceanic phytoplankton and that enrichment of high-nutrient waters with Fe would change the species