TY  - JOUR
A1  - Karakuş, Onur
A1  - Völker, Christoph
A1  - Iversen, Morten
A1  - Hagen, Wilhelm
A1  - Hauck, Judith
T1  - The Role of Zooplankton Grazing and Nutrient Recycling for Global Ocean Biogeochemistry and Phytoplankton Phenology
Y1  - 2022-10-25
VL  - 127
IS  - 10
JF  - Journal of Geophysical Research: Biogeosciences
DO  - 10.1029/2022JG006798
PB  - 
N2  - Zooplankton plays a notable role in ocean biogeochemical cycles. However, it is often simulated as one generic group and top closure term in ocean biogeochemical models. This study presents the description of three zooplankton functional types (zPFTs, micro‐, meso‐ and macrozooplankton) in the ocean biogeochemical model FESOM‐REcoM. In the presented model, microzooplankton is a fast‐growing herbivore group, mesozooplankton is another major consumer of phytoplankton, and macrozooplankton is a slow‐growing group with a low temperature optimum. Meso‐ and macrozooplankton produce fast‐sinking fecal pellets. With three zPFTs, the annual mean zooplankton biomass increases threefold to 210 Tg C. The new food web structure leads to a 25% increase in net primary production and a 10% decrease in export production globally. Consequently, the export ratio decreases from 17% to 12% in the model. The description of three zPFTs reduces model mismatches with observed dissolved inorganic nitrogen and chlorophyll concentrations in the South Pacific and the Arctic Ocean, respectively. Representation of three zPFTs also strongly affects phytoplankton phenology: Fast nutrient recycling by zooplankton sustains higher chlorophyll concentrations in summer and autumn. Additional zooplankton grazing delays the start of the phytoplankton bloom by 3 weeks and controls the magnitude of the bloom peak in the Southern Ocean. As a result, the system switches from a light‐controlled Sverdrup system to a dilution‐controlled Behrenfeld system. Overall, the results suggest that representation of multiple zPFTs is important to capture underlying processes that may shape the response of ecosystems and ecosystem services to on‐going and future environmental change in model projections.
N2  - Plain Language Summary: Zooplankton plays an important role in the ocean food web and biogeochemical cycles. However, it is often represented in very simple forms in mathematical models that are, for example, used to investigate how marine primary productivity will react to climate change. To understand how these models would change when more complicated formulations for zooplankton are used, we present here a new version of the model with three (instead of only one) zooplankton groups. We find that this more complicated representation leads to higher zooplankton biomass, which is closer to observations, and this stimulates growth of phytoplankton since zooplankton also returns nutrients into the system. In addition, zooplankton grazing controls the seasonal cycle of phytoplankton, as we show for one example in the Southern Ocean.
N2  - Key Points: Nutrient recycling by zooplankton stimulates net primary production in the biogeochemical model REcoM‐2. Modeling zooplankton functional types (zPFTs) leads to a switch from a light‐controlled Sverdrup system to a dilution‐controlled Behrenfeld system. Implementing multiple zPFTs improves the modeled zooplankton biomass and zooplankton‐mediated biogeochemical fluxes.
UR  - http://resolver.sub.uni-goettingen.de/purl?gldocs-11858/11588
ER  -