Biogeochemical and Physical Processes Regulating the Benthic Flux and Speciation of Iron from Non-Upwelling Continental Margins

Iron is an important nutrient for phytoplankton in the ocean. Dust from the continents is the primary source of most of the iron delivered to the ocean. However, this iron is not soluble in the surface ocean, and most settles to the bottom rather than being used by phytoplankton.

This project investigates whether sediments could be an important source of iron to the ocean. The team of scientists will quantify biogeochemical and physical processes that influence the flux of iron from sediments to the water column on continental margins. They will measure fluxes of iron at the seafloor along the western North Atlantic Ocean and in the western Mediterranean Sea.

Shipboard analyses of different forms of iron will complement the benthic flux studies. This research will re-examine whether the iron coming from sediments is primarily in organic forms versus inorganic (mineral) forms. Most previous studies have been conducted in the eastern parts of the oceans, where deep waters are transported to the surface.

In addition, the exact composition of dissolved iron diffusing out of the sediment has often not been determined. The project will provide training for two Ph.D. students from underrepresented minority groups who will gain experience in science and engineering. A capstone course for undergraduate students will be offered that creates opportunities for students to learn and engage in oceanographic field work.

The researchers will participate in meaningful outreach to spark the interest of K-12 students in chemical oceanographic research through hands-on experiments and online lesson plans. This information will be shared with K-12 teachers for use in the classroom.

This study will use in situ benthic flux measurements, in situ physical measurements, and iron speciation analyses supported by reactive transport model calculations to: (1) investigate the role of the organic carbon input flux to the sediment on the release of iron from the sediment; (2) identify the bottom water transport processes that may affect the benthic flux of dissolved iron; and (3) extrapolate the findings of the proposed study to the global ocean using data generated during the proposed study, including data from the cruise of opportunity in France, and data from other published studies. This study will characterize the role of sediments in the supply of nutrient to surface waters.

The proposed research will also help identifying how the transport of bottom waters affects the exchange of chemicals at the sediment-water interface. Results from this study will provide new data that can be incorporated in ocean circulation models to predict the effect of climate change on ocean productivity, atmospheric CO2 consumption, sediment carbon transformation, and the expansion of oxygen minimum zones.

This project includes training for two Ph.D. students from traditionally underrepresented minorities, several undergraduates from Science and Engineering, and guest students during the cruises. The Ph.D. students will be recruited via the new Ocean Science and Engineering program at Georgia Tech that provides training in both engineering and science.

Additional ship time is requested to expose senior undergraduates from an Environmental Field Methods capstone course to oceanographic research. The PI and his group will also continue outreach activities by exposing K-12 students who visit Georgia Tech to chemical oceanography research via presentations and hands-on experiments. A web site with lesson plans and podcasts will be provided to K-12 teachers via the Center for Education Integrating Science, Mathematics, and Computing.

The science team will also interact with students during the cruises via satellite communication and social media.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.