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Seasonal photoacclimation in the North Pacific Transition Zone
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  • Gregory L Britten,
  • Christine Padalino,
  • Gaël Forget,
  • Michael J. Follows
Gregory L Britten
Massachusetts Institute of Technology, Massachusetts Institute of Technology

Corresponding Author:[email protected]

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Christine Padalino
Massachusetts Institute of Technology, Massachusetts Institute of Technology
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Gaël Forget
Massachusetts Institute of Technology, Massachusetts Institute of Technology
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Michael J. Follows
MIT, MIT
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Abstract

The Transition Zone Chlorophyll Front (TZCF) is a dynamic region of elevated chlorophyll concentrations in the Northeast Pacific that migrates from a southern winter (February) extent of approximately 30 deg. N to a northern summer (August) extent of approximately 40 deg. N. The transition zone has been highlighted as important habitat for marine animals and fisheries. We re-examine the physical and biological drivers of seasonal TZCF variability using a variety of remote sensing, reanalysis, and in situ datasets. Satellite-based remote sensing estimates of chlorophyll and carbon concentrations suggest the seasonal TZCF migration primarily reflects a seasonal increase in the chlorophyll to carbon ratio, rather than changes in carbon biomass. Chlorophyll to carbon ratios increase due to photoacclimation to low light availability and elevated nutrient supply in the transition zone winter. Seasonal mixed-layer-averaged light availability is positively correlated with carbon and negatively correlated with chlorophyll. Analysis of climatological nitrate profiles show that chlorophyll to carbon ratios are further enhanced by wintertime nitrate entrainment. These empirical results are consistent with physiological data and models describing elevated chlorophyll to carbon ratios in low light, nutrient-replete environments, demonstrating the need to incorporate phytoplankton ecophysiology into biogeochemical interpretations of remote-sensing observations.