The biogeochemical cycles of silicon, nitrogen, phosphorus, and iron involve substantial transfer of materials from the continents to the oceans through atmospheric transport of natural and anthropogenic aerosols. To date, these important land-ocean links and their influence on ocean ecosystems and biogeochemical cycling have only been studied for individual elements. In this study, investigators from the University of California at Irvine will couple models of atmospheric chemistry and aerosol transport to a global ocean biogeochemical model. They will simulate the atmospheric deposition and dissolution in the oceans of the nutrients silicate, nitrate, ammonium, phosphate, and iron, and the crustal tracer aluminum. These key nutrients regulate phytoplankton growth rates, community structure, and primary production in the oceans and hence are intimately linked with carbon cycling and air-sea CO2 exchange. The ocean model includes key phytoplankton functional groups and explicit treatment of the biogeochemical cycling of C, O, N, P, Si, and Fe. Mineralogy of both natural and anthropogenic aerosols will vary by source region and particle size, and the nutrient solubility upon deposition will vary dependent on aerosol heterogeneous chemistry, chemical weathering and aging during transport, and whether the deposition is wet or dry. The scientists will produce and disseminate global maps of deposition to the oceans for each of these nutrients. In addition, they will estimate the impact of each nutrient on phytoplankton community structure, spatio-temporal patterns of nutrient limitation, carbon export from surface waters, and air-sea CO2 flux at regional to global scales. Their studies will be among the first to estimate the ocean sensitivity to these patterns globally and to quantify their roles in driving the ocean carbon cycle in a coupled Earth System model framework.
In terms of broader impacts, a better understanding of the links between the biogeochemical cycling of Si, Fe, N, P, and C will improve our understanding of how the Earth system works today and enhance our ability to predict future climate change under different emission and nutrient loading scenarios. The model tools developed and the results will be valuable to a wide array of public and private entities interested in the effects of nutrient loading (from atmospheric sources) on water quality, and for those interested in secondary production, fisheries and marine resource management, and ocean ecosystem dynamics. In addition to the scientific merit, two graduate students will be trained in the latest modeling techniques.
