Project: Collaborative Research: Iron Incorporation into Biogenic Silica

NSF Award Abstract:
Ocean research over the last several decades has increasingly shown the great importance of iron chemistry on marine biological processes. In certain areas of the ocean where iron is scarce, it can limit biological growth even though other essential nutrients like nitrogen and phosphorus are abundant. Consequently, to fully understand and quantify biological productivity in the ocean, a complete knowledge of all sources and sinks for iron is essential. The researchers funded for this project have already generated exciting preliminary data that suggest a potentially large, yet, unquantified pathway for iron removal. Diatoms, phytoplankton with shells made of silica, are shown to incorporate traces of iron into their shells, making it unavailable for rapid recycling or use by marine organisms in surface waters. Given the great abundance of diatoms in many parts of the ocean, this could represent a major, unstudied removal mechanism that regulates the concentration of iron in seawater. This research could transform current understanding of how iron is removed from the ocean, and it will impact understanding of both the chemical and biological processes involving iron in seawater. The investigator also plans outreach in K-12 schools by providing educational courses for Earth Science teachers and will support graduate student training in advanced chemical analysis and oceanography.

High-resolution synchrotron-based chemical techniques will allow determination of the concentration and oxidation state of iron bound within diatom frustules. This analytical advance has created the ability for unique evaluation of iron sequestration into biogenic silica as a major pathway for iron removal from the ocean. Samples from the Pacific sector of the Southern Ocean have been collected in a previous CLIVAR field campaign and a subset of these are available for new synchrotron analysis of iron (Fe) with Near Edge X-ray Fluorescence Spectroscopy (Fe-NEXFS) and submicron scale X-ray fluorescence mapping, as well as a variety of other chemical characterizations. With these methods, the project will determine the importance of iron sequestered into biogenic silica as a new and unquantified loss term in the oceanic Fe cycle and examine the changing chemical complexes of iron during vertical transport of silica particles through the water column.