Molybdenum Biogeochemistry in the Open Ocean

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

ABSTRACT OCE-0096453 In this study, researchers at the Woods Hole Oceanographic Institution will conduct a careful study of the marine chemistry of molybdenum (Mo) in the open ocean. Mo is currently believed to behave as a conservative element in the open ocean and therefore to have a relatively uninteresting chemistry in this environment. However, it is well established that Mo is an important micro-nutrient that is required in nitrate reductase and in the most common form of nitrogenase, enzymes which are required for organisms to utilize nitrate and to fix nitrogen (N), respectively. The PIs expect that sufficiently precise analyses of Mo in suspended particulate matter (SPM), and in filtered seawater will reveal variations that are potentially related to biological utilization of Mo. The specific objectives of this proposal are: (1) to establish whether or not non-conservative distributions of Mo in the eastern Pacific result from biological utilization of Mo; and (2) to determine whether or not enrichments of Mo in SPM result from biological utilization of Mo in association with denitrification and/or N-fixation. Accomplishing these objectives is necessary in order to evaluate the potential of Mo enrichments as tracers of these important components of the marine nitrogen cycle. In addition, this work could contribute to a better understanding the biological demand for iron (Fe) in the ocean because biological utilization of Mo and Fe are coupled. To accomplish the objectives stated above the investigators will: (1) determine the vertical distribution of Mo in filtered and unfiltered seawater samples from several sites in the eastern Pacific that represent contrasting regimes of denitrification and Mn oxide redox cycling, (2) complete a suite laboratory culture experiments designed to test our hypothesis that cellular Mo concentration covary with levels of Mo-containing enzyme activity and (3) collect and analyze SPM from regions that support active denitrification and N-fixation in order to establish the relative proportions of Mo associated with lithogenic debris, Mn oxides and biogenic material. Upon completing the proposed work the investigators expect to be able to make a first order assessment of the potential of analyses of dissolved and/or particulate Mo in seawater as tracers of denitrification, N-fixation or Fe-utilization. In addition, they hope to gain insight into the patterns of biological utilization of a non-limiting micronutrient.