The role of zooplankton for carbon export, nutrient recycling and phytoplankton bloom phenology in an ocean biogeochemical model

• Main Author: Karakuş, Onur
• Other Authors: Hauck, Judith, Le Quéré, Corinne
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Universität Bremen 2022
• Subjects: biogeochemical modelling; biogogical carbon pump; zooplankton functional types; 570; 570 Life sciences; biology; ddc:570; Sea ice
• Online Access: https://media.suub.uni-bremen.de/handle/elib/6088; https://doi.org/10.26092/elib/1670; https://nbn-resolving.org/urn:nbn:de:gbv:46-elib60889

Marine zooplankton, i.e., heterotrophic marine plankton, serve as trophic links between primary producers and higher trophic levels, and as recyclers for nutrients and carbon in the pelagic ecosystem. In addition, they play a major role for the carbon export flux due to fecal pellet production and fragmentation of particles. They are distributed all over the ocean and constitute a large variety of organisms. Because of large uncertainties in the estimation of parameters and the forms of equations, zooplankton are often parameterized in strongly simplified forms in ocean biogeochemical models. Nowadays, however, increasing data availability from experiments and observations makes it possible to implement different zooplankton functional types in models. This thesis presents the implementation of new zooplankton functional types into an ocean biogeochemical model. Subsequently, the sensitivity of net primary production, carbon export and nutrients to the implementation of these new zooplankton functional types was analyzed. In my thesis, I use a global setup of the biogeochemical model Regulated Ocean Ecosystem Model (REcoM) coupled with the Finite Element Sea-Ice Ocean Model (FESOM). I implemented an explicit parametrization of micro-, meso-, and polar macrozooplankton based on process rates and biomass observations from the literature, as well as a representation of fast-sinking detritus. This extended version of REcoM was used to analyze the role of zooplankton for carbon export, nutrient recycling, and phytoplankton bloom phenology. In a second step, a new sinking routine that considers the roles of mineral ballasting and seawater viscosity on the particle sinking speed and the effect of oxygen on remineralization rates was added to the model. This set-up was used to assess the role of each factor (ballast minerals, seawater viscosity, and oxygen concentration) for the export and transfer efficiencies of carbon, i.e. the amount of particulate organic carbon that is exported across the euphotic depth and ...