Award: OCE-1751805

Upwelling zones are some of the most biologically productive and diverse regions in the worlds oceans. In relation to the California Current System (CCS), currents driven by equatorward winds and Ekman transport result in surface waters to be transported offshore and replaced by cold, nutrient rich deep waters that seed extensive phytoplankton blooms. The succession of the phytoplankton community during these upwelling events is influenced by many physical and biological components like underwater currents, seed population dynamics, and physiological and molecular shifts. The mechanisms behind how these biotic and abiotic factors intertwine in the course of the upwelling plume remains largely uncharacterized, and such complexity directly influences the local food web as well as carbon export and sequestration in these dynamic regions. Our study aimed to address the following objectives: 1) to determine how phytoplankton respond to the different Upwelling Conveyor Belt Cycle (UCBC) stages at the molecular and physiological levels, 2) to assess which seed populations (i.e., surface versus subsurface) contribute most to phytoplankton blooms during an upwelling event, 3) to determine how phytoplankton elemental composition is altered throughout UCBC stages and; 4) to examine how iron limitation affects the phytoplankton responses to UCBC conditions. By incorporating nutrient amendment incubation experiments, laboratory culture simulated upwelling experiments, through combined physiological and gene expression approaches we identified how phytoplankton groups respond differently to upwelling and how changes in ocean conditions associated with climate change may influence this response. In particular, diatoms were found to be well-adapted to UCBC  through frontloading nitrogen acquisition genes and pathways, a process by which provides them with an advantage for acquiring growth-limiting nutrients once brought to the euphotic zone.  Mixotrophy may also provide an advantage to phytoplankton within upwelling regions where iron bioavailability may become limiting.  Ultimately, understanding how these phytoplankton change through the course of an upwelling event is pivotal to assessing their importance to ocean rate processes, trophic systems, and carbon cycling.

As a part of this project, one post-doctoral fellow and five graduate students were fully or partially supported (3 MSc. and 2 PhD) and six undergraduate students were trained.  Educational activities as part of this project include development of a virtual cruise and lesson plans for middle school students, integration of practical training sessions to an upper-level undergraduate course and participation in numerous public outreach events and educational conferences. Numerous scientific papers related to this project have been published with several others in final stages of preparation.

Last Modified: 08/12/2025
Modified by: Adrian Marchetti