Climate Science and Policy

It is important to understand the complex physical and biological interactions of the climate system for the adaptation to and mitigation of the many consequences of climate change. This study aimed to understand the impacts of Atmospheric Rivers (ARs) on Harmful Algal Bloom (HAB) causing phytoplankton taxa. ARs are ephemeral corridors of the atmosphere carrying massive amounts of water vapor from the tropics to mid latitudes and are strongly correlated with orographic precipitation. ARs are defined and characterized by the vertically Integrated Vapor Transport (IVT), which is the measured amount of water and its movement in the atmospheric column. Abundances of 13 different taxa of phytoplankton associated with HABs at 12 different monitoring stations along the California Coast were obtained from CalHABMAP. IVT magnitudes as well as a chronology of AR occurrences at 0.25° by 0.25° grid cells at each of these 12 locations were obtained from the CW3E, which acquired the information from ECMWF ERA5 Reanalysis data. Here I attempt to answer two questions: 1) When a specific HAB-causing phytoplankton taxon was present, was its abundance correlated with the IVT magnitude the week prior to sampling? 2) When this HAB-causing phytoplankton taxon was present, was its abundance different when an AR occurred during the week prior to sampling versus no AR? To reveal potential relationships between phytoplankton abundance with the IVT magnitude or presence of ARs, I quantified correlations between the phytoplankton abundances and the IVT magnitude or AR occurrence the week before phytoplankton sampling. Some dinoflagellate taxa showed consistent positive correlations in Northern California, while different dinoflagellate taxa showed more consistent negative correlations in Southern California. AR presence consistently was associated with a decrease in the abundance of phytoplankton in most diatom and dinoflagellate taxa. With little latitudinal trend in the sign of the correlation, different taxa were significantly negatively correlated with AR presence in Southern California than in Northern California. Further research should be conducted to understand the mechanisms behind these correlations and dive deeper into the nuances of these relationships. This study was meant to serve as an introduction to understanding the relationships between AR occurrence, IVT magnitude, and HAB-forming phytoplankton taxa, to advise decision making for HAB warning systems and education in the face of a changing climate.