Journal article
Disentangling upwelling: how light and nutrient supply shape primary producers and stoichiometry in the Humboldt upwelling system
Deep-sea research. Part II, Topical studies in oceanography, Vol.223, pp.1-18
09/2025
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Abstract
The Humboldt upwelling system (HUS) is known for its extraordinary productivity due to wind-driven upwelling of nutrient-rich deep water, resulting in the highest fish catches per unit area worldwide. However, contrary to other Eastern boundary upwelling systems, upwelling intensity is highest in winter, while primary productivity reaches its peak during the summer months. Our current understanding of the counterintuitive relationship between upwelling intensity and productivity is insufficient to predict the consequences of climate change on this ecosystem. To elucidate the drivers of the upwelling-productivity relationship in the HUS, we tested the hypothesis that low light availability limits primary productivity in winter despite strong upwelling intensity supplying plenty of nutrients into the surface layer, while light availability in the shallower mixed layer in summer enables an effective use of the upwelled nutrients. To disentangle the interactive effects of light and nutrients on primary production and carbon cycling, we enclosed natural plankton communities off the coast of Callao (Peru) during a 35-day mesocosm experiment by recreating summer-time high light and winter-time low light conditions under different upwelling intensities (0 %, 15 %, 30 %, 45 % and 60 %). Primary productivity and phytoplankton biomass scaled with both nitrate and light availability. Comparing the same upwelling intensity at different light levels, our data confirmed the hypothesis that light limitation due to deepening of the mixed layer is a key driver for the out-of-phase observations in primary productivity in the Humboldt upwelling system. Under light limiting conditions phytoplankton had low POC:Chla ratios indicating photoacclimation and low POC:PON ratios indicating light limitation of nitrate uptake which leads to increased food quality for grazers in winter. Our study indicates that small seasonal changes in phytoplankton biomass (estimated using Chla) might hide larger changes in primary productivity (carbon uptake), and highlights the importance of combining satellite studies with in situ observations and experimental studies to predict the fate of upwelling systems in a changing ocean. Increased stratification caused by global warming in upwelling systems such as the HUS would lead to less phytoplankton biomass with higher POC:Chla and POC:PON ratios. This phytoplankton community would have lower food quality for grazers and might lead to a decline in the transfer to higher trophic levels, but at the same time might lead to increased CO2 drawdown in an otherwise CO2 emitting ecosystem. Understanding the unique relationship between upwelling intensity and productivity in the HUS contributes to predicting the reaction of this valuable ecosystem for fisheries to the impacts of climate change.
Details
- Title
- Disentangling upwelling: how light and nutrient supply shape primary producers and stoichiometry in the Humboldt upwelling system
- Creators
- Antonia U. Thielecke - GEOMAR Helmholtz Centre for Ocean Research KielMar Fernández-Méndez - GEOMAR Helmholtz Centre for Ocean Research KielJavier Arístegui - Universidad de Las Palmas de Gran CanariaMoritz Baumann - GEOMAR Helmholtz Centre for Ocean Research KielJacqueline Behncke - GEOMAR Helmholtz Centre for Ocean Research KielStella A. Berger - Leibniz Institute of Freshwater Ecology and Inland FisheriesVeit Dausmann - GEOMAR Helmholtz Centre for Ocean Research KielSilvia Georgieva - GEOMAR Helmholtz Centre for Ocean Research KielSilvan U. Goldenberg - GEOMAR Helmholtz Centre for Ocean Research KielGonzalo V. Gomez-Saez - LMUGMichelle Graco - Instituto del Mar del PeruToralf Heene - Leibniz Institute for Baltic Sea Research WarnemündeLeila Richards Kittu - GEOMAR Helmholtz Centre for Ocean Research KielJeffrey W. Krause - Dauphin Island Sea LabAndrea Ludwig - GEOMAR Helmholtz Centre for Ocean Research KielJana Meyer - GEOMAR Helmholtz Centre for Ocean Research KielVolker Mohrholz - Leibniz Institute for Baltic Sea Research WarnemündeJens C. Nejstgaard - Leibniz Institute of Freshwater Ecology and Inland FisheriesJoaquin Ortiz-Cortes - GEOMAR Helmholtz Centre for Ocean Research KielKai G. Schulz - Southern Cross UniversityAlexandra M. Smith - Dauphin Island Sea LabKristian Spilling - Finnish Environment Institute, Helsinki, FinlandMichael Sswat - GEOMAR Helmholtz Centre for Ocean Research KielJan Taucher - GEOMAR Helmholtz Centre for Ocean Research KielMari Vanharanta - Finnish Environment Institute, Helsinki, FinlandPia Varmanen - Finnish Environment Institute, Helsinki, FinlandUlf Riebesell - GEOMAR Helmholtz Centre for Ocean Research Kiel
- Publication Details
- Deep-sea research. Part II, Topical studies in oceanography, Vol.223, pp.1-18
- Publisher
- Elsevier Ltd
- Grant note
- This work was part of project CUSCO, funded by the German Bundesministerium für Bildung und Forschung (BMBF Funding number 03F0813A and 03F0813F for SAB and JCN).
- Identifiers
- 991013372624302368
- Copyright
- © 2025 The Authors.
- Academic Unit
- Faculty of Science and Engineering
- Language
- English
- Resource Type
- Journal article