NSF Award
2421626
Biological production in ocean surface waters is an important part of the global carbon cycle. In some areas, particularly high latitudes, the availability of iron – an important but scarce nutrient element – can limit the amount of production. It is important to understand sources of iron to the ocean in these regions. This project will focus on the role that ocean sediments play in supplying iron to the surface waters of the Labrador Sea, between Canada and Greenland. The team will collect sediments and sediment pore waters to identify and quantify iron sources from the sediments to overlying ocean waters. They will use numerical models of ocean circulation to study the possible transport pathways of this iron to surface waters where phytoplankton can use it. The project will support graduate and undergraduate students. The team will focus on effective mentoring with the goal of supporting young scientists who identify with groups historically marginalized in oceanography. This will be achieved through two linked approaches: 1) practical and inclusive training of two students who have never been to sea before, and 2) supporting a polar science mentoring network by funding an undergraduate coordinator for the Polar Impact Mentoring Initiative (PIMI).<br/><br/>This project investigates benthic iron fluxes in the Labrador Sea, an important region of deep-water formation where the efficiency of the biological carbon pump may be influenced by iron availability. Glacial meltwater from the Greenland Ice Sheet provides iron to this region, but glacial iron is estimated to sustain less than half of the annual productivity, restricted to late summer blooms during peak meltwater discharge. Thus, additional iron sources from the sediments are likely important. The proposed research tests the hypothesis that continental shelf sediments provide iron (through reductive and nonreductive release) that can be transported in shelf currents to the surface water and the interior Labrador Sea. In conjunction with a previously-funded research expedition, pore water and solid sediments from multicore subcores will be sampled for iron speciation and isotopes, and unique, two-dimensional iron sensors will be deployed on deck along with a suite of other sensors (oxygen, pH, temperature). The 2-D iron sensors generate high-resolution iron(II) concentration profiles for accurate estimation of diffusive fluxes across the sediment-water interface. These datasets will reveal the biogeochemical conditions in the surface sediments and the magnitude and speciation of the resulting iron flux. Finally, the team will investigate possible transport routes from the continental shelf sediments to the euphotic zone in the Labrador Sea using a model of circulation in the region. These tracer experiments will reveal the potential physical fate of benthic iron in the system and test the feasibility of benthic iron fertilizing the surface ocean in the region.<br/><br/>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.
