The marine biogeochemistry of dissolved and colloidal iron
Name
869215443-MIT.pdf
Description
Full printable version
Size
32.82 MB
Format
Adobe PDF
Checksum (MD5)
b90fc4b1eb6fb1feaf055f8dbac2b750
Author(s)
Fitzsimmons, Jessica Nicole
Advisor(s)
Edward A. Boyle.
Date Issued
2013
Publisher
Massachusetts Institute of Technology
Abstract
Iron is a redox active trace metal micronutrient essential for primary production and nitrogen acquisition in the open ocean. Dissolved iron (dFe) has extremely low concentrations in marine waters that can drive phytoplankton to Fe limitation, effectively linking the Fe and carbon cycles. Understanding the marine biogeochemical cycling and composition of dFe was the focus of this thesis, with an emphasis on the role of the size partitioning of dFe (<0.2 jm) into soluble (sFe<0.02 jm) and colloidal (0.02ptmI nmol/kg) concentrations coincident with the oxygen minimum zone were determined to be caused by remineralization of a high Fe:C organic material (vertical flux), instead of a laterally advected low oxygen-high dFe plume from the African margin. In the South Pacific Ocean, dFe maxima near 2000m were determined by comparison with dissolved manganese and 3He to be caused by hydrothermal venting. The location of these stations hundreds to thousands of kilometers from the nearest vents confirms the "leaky vent" hypothesis that enough dFe escapes precipitation at the vent site to contribute significantly to abyssal dFe inventories. The size partitioning of dFe was also investigated in order to trace the role of dFe composition on its cycling. First, the two most commonly utilized methods of sFe filtration were compared: cross flow filtration (CFF) and Anopore filtration. Both were found to be robust sFe collection methods, and sFe filtrate through CFF (10 kDa) was found to be only 74±21% of the sFe through Anopore (0.02pjm) filters at 28 locations, a function of both pore size differences and the natural variability in distribution of 1 OkDa- 0.02 [m colloids. In the North Atlantic, a colloidal-dominated partitioning was observed in the surface ocean underlying the North African dust plume, in and downstream of the TAG hydrothermal system, and along the western Atlantic margin. However, cFe was depleted or absent at the deep chlorophyll maximum. A summary model of dFe size partitioning in the North Atlantic open ocean is presented in conclusion, hypothesizing that a constant dFe exchange between soluble and colloidal pools modulates the constant partitioning of nearly 50% dFe into the colloidal phase throughout the subsurface North Atlantic Ocean, while sFe and cFe cycle independently in the upper ocean.
Description
Thesis (Ph. D.)--Joint Program in Chemical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2013.
Cataloged from PDF version of thesis.
Includes bibliographical references.
Subjects
Joint Program in Chemical Oceanography.
Earth, Atmospheric, and Planetary Sciences.
Woods Hole Oceanographic Institution.
MIT Department
Joint Program in Chemical Oceanography
Woods Hole Oceanographic Institution
Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences
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