Iron regulation of ocean ecosystem
Project Managers: Steve Fitzwater, Ken Johnson
Lead Scientist: Ken Johnson
As in the past several years, the goals of this project are to extend our understanding of the role that iron plays in regulating ecosystem structure and the impact of iron on biogeochemical cycles and climate. This is the final year of a three-year project.
On a cruise with R/V Western Flyer, about 800 kilometers southwest of Monterey Bay, we will investigate the role that vertical migration of phytoplankton may play as a mechanism for iron acquisition. Observations throughout the Pacific, indicate that the depth to which iron is depleted near the surface (the ferricline) extends a greater distance below the surface than does the depth to which nitrate is depleted (the nitracline). Large diatoms, such as Rhizosolenia, migrate vertically below the euphotic zone to acquire nitrate, which places the nitracline below the euphotic zone. The observation that the ferricline occurs below the nitracline suggests the hypothesis that iron is also acquired at depth by vertically migrating phytoplankton. If so, this would represent a major, unrecognized source for iron to the phytoplankton community. Since aggregates of Rhizosolenia are visible in video from ROV Tiburon, we can accurately test the hypothesis, conducting targeted sampling at depths below the nitratcline (~150 meters) and ferricline (~180 meters).
A cooperative effort with several other research groups at MBARI will assess the phytoplankton physiological status at depths across the ferrricline and nitracline.
In 2005, we will continue the Monterey Bay time series of iron measurements.
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