Flow Over Abrupt Topography: The Application of Patterns in Nutrient and Productivity in Reflecting Physical Processes.

摘要

This project was part of an interdisciplinary study designed to investigate all aspects of seamount oceanography on the local and mesoscale level. The seamount selected for study was Fieberling Guyot a deep topographical feature that rises to within 430m from the surface, located at 32 deg 25'N, 127 deg 47'W, just over 1000 km west of San Diego. In addition the biological components of the program chose to study, for comparison, two more shallow near-shore features, Northeast Bank and Sixtymile Bank, that were visited on cruises out to Fieberling Guyot. During the 3 field years (cruises in September 1989, 1990 and 1991) we made near-surface (ie. the euphotic zone to approximately 100m depth) measurements of nutrients (nitrate, nitrite, ammonium, silicate and phosphate) an new, regenerated and total productivity of the phytoplankton. The nutrient measurements using nanomolar analysis made it possible to clearly delineate the nitracline to be closely positioned near the chlorophyll maximum at about 110m. The productivity measurements made using stable isotopes (13C labelled bicarbonate and 15N labelled nitrate and ammonium) showed ammonium uptake to exceed nitrate uptake with rates typical of oligotrophic waters (i.e. % new prodn. of 9%). There was interannular variability with higher nutrients and productivity in 1991. The shallow Banks showed more nutrients and productivity as apparently, topographically induced physical events there advect sufficient nutrients into the photic zone for a phytoplankton response, unlike at Fieberling, Topography, Seamount, Nutrients, Phytoplankton productivity.