Understanding airborne fertilization of oceanic ecosystems using MODIS, VIIRS and CALIPSO

A long-standing hypothesis suggests that atmospheric deposition of nutrients to the oceans significantly affects oceanic ecosystems. Validating this hypothesis requires (1) an understanding of the frequency and characteristics of airborne deposition events, both dust and volcanic ash, and (2) a characterization of how ocean ecosystems respond to such events. Today we have the tools necessary to address both requirements. Using a combination of satellite data products and reanalysis data we can quantify the transport and deposition of airborne mineral nutrients into the ocean. In addition, we have new satellite tools for detecting and distinguishing different forms of ocean ecosystem response. We are embarking on an ambitious global study that will identify specific deposition events and then characterize the ocean ecosystem response to these events. The goal is to obtain a sufficient number of events globally to approach the analysis with ensemble statistics. As a pilot study we have focused on specific volcanic eruptions with ash plumes extending over nutrient-limited ocean waters. We use MODIS observations to track the extent of the ash and MERRA reanalysis products to quantify deposition into the water. The pattern of the ash dispersion, both temporally and spatially, is linked to MODIS observations of anomalous phytoplankton chlorophyll concentrations, biomass, physiology, and fluorescence quantum yields. Mixed layer depths did not change during the events, suggesting therefore that the observed ecosystem changes were a consequence of atmospheric deposition rather than physical oceanic processes. The possibility of artifacts in the interpretation of the satellite products is also considered. This preliminary pilot study provides encouragement that we will be able to approach the global analysis successfully with similar tools and methods.