Xue, Tianfei , Frenger, Ivy , Oschlies, Andreas , Stock, Charles A., Koeve, Wolfgang , John, Jasmin G. and Prowe, A. E. Friederike (2022) Mixed Layer Depth Promotes Trophic Amplification on a Seasonal Scale. Geophysical Research Letters, 49 (12). Art.Nr. e2022GL098720. DOI 10.1029/2022GL098720.

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Abstract

The Humboldt Upwelling System is of global interest due to its importance to fisheries, though the origin of its high productivity remains elusive. In regional physical-biogeochemical model simulations, the seasonal amplitude of mesozooplankton net production exceeds that of phytoplankton, indicating “seasonal trophic amplification.” An analytical approach identifies amplification to be driven by a seasonally varying trophic transfer efficiency due to mixed layer variations. The latter alters the vertical distribution of phytoplankton and thus the zooplankton and phytoplankton encounters, with lower encounters occurring in a deeper mixed layer where phytoplankton are diluted. In global model simulations, mixed layer depth appears to affect trophic transfer similarly in other productive regions. Our results highlight the importance of mixed layer depth for trophodynamics on a seasonal scale with potential significant implications, given mixed layer depth changes projected under climate change.

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