Li, J., A. J. Miller, D. J. Amaya, Q. Wang, P. Li, Y. Gu and P. Bai, 2025:
Vertical structure of chlorophyll-a during Marine Heatwaves in the California Current Ecosystem
Communications Earth & Environment, in press.
Abstract. In the past decades, the California Current Ecosystem (CCE) has experienced intense marine heatwaves (MHWs),
which have induced significant disruptions to local phytoplankton communities. Using 30-year CalCOFI observations,
we identify a previously undocumented vertical structure in chlorophyll-a concentration (CHL) response to MHWs,
characterized by CHL reductions in the surface layer coupled with increases in the subsurface. By integrating
observations and coupled physical-biogeochemical model products, we demonstrate that surface CHL declines are
primarily attributed to suppressed nutrient upwelled to the upper ocean. Although surface irradiance increased
modestly (+3.5%), light availability in the subsurface layer improved substantially (+21.7%) due to reduced
phytoplankton shading at the surface. Concurrent with enhanced lateral nutrient transport, phytoplankton growth
at depth was promoted during MHWs. This study highlights the pivotal role of
subsurface phytoplankton dynamics in shaping the vertical CHL structure and its variability under extreme events.
Reprint (pdf)