The vertical distribution of phytoplankton biomass, commonly represented by chlorophyll-a concentration, is a key determinant of ocean biogeochemical cycling and carbon export. The vertical redistribution of phytoplankton by mesoscale eddies remains poorly resolved across eddy life cycles. Here we use continuous autonomous float observations and an XGBoost machine learning model to reconstruct high-resolution chlorophyll profiles, tracking an anticyclonic eddy in the North Pacific from formation to decay. We find that chlorophyll vertical responses differ systematically between eddy intensification and decay phases: the subsurface chlorophyll maximum deepens during intensification but shoals and broadens during decay. These results establish eddy life stage as a primary control on the vertical redistribution of chlorophyll and highlight the synergy of autonomous floats and machine learning for capturing sub-seasonal ecosystem dynamics.