Chlorophyll Bloom Dynamics and Associations with Mesoscale and Submesoscale Features in the North Pacific Subtropical Gyre

Abstract

Large summer chlorophyll blooms spanning hundreds of square kilometers andpersisting for weeks-months, are consistently observed in satellite records of the Northeast Pacific Subtropical Gyre (NPSG), at an approximate latitude of ~30°N. These blooms occur at a near annual rate, and uniquely within the late summer months of JuneOctober. Understanding the potential impacts and biophysical drivers of these chlorophyll anomalies is both ecologically and climatologically important. These large-scale blooms can export carbon from the upper ocean to the deep ocean and fuel the productive fisheries found in the ecologically important transition zone between the North Pacific Subtropical Gyre and the subpolar gyre. The purpose of this project is to characterize chlorophyll blooms in the NE Pacific Gyre, as well as describe their association with submesoscale and mesoscale features to identify potential physical drivers. First, an analysis of the merged satellite CHL product is done to characterize the magnitude, frequency, and geographic location of chlorophyll blooms in the NPSG. Then the sea level anomaly (SLA) and finite sized Lyapunov exponents (FSLE) were used to identify sub-mesoscale and mesoscale features i.e. fronts, anti-cyclonic eddies, and cyclonic eddies. Through this process, we provide a quantitative characterization of chlorophyll anomalies in the NPSG. Further analyses present a case-study time-series of the 2018 bloom in order to better understand the timeresolved change in phytoplankton biomass and how it relates to physical drivers of biomass growth and accumulation. To achieve this, a generalized additive model (GAM) is used to determine the effects of SLA and SSTA on the CHL anomaly signal of the 2018 plankton bloom.