Assessment and Constraint of Mesozooplankton in CMIP6 Earth System Models

Abstract

Although zooplankton play a substantial role in the biological carbon pump and serve as a crucial link between primary producers and higher trophic level consumers, the skillful representation of zooplankton is not often a focus of ocean biogeochemical models. Systematic evaluations of zooplankton in models could improve their representation, but so far, ocean biogeochemical skill assessment of Earth system model (ESM) ensembles have not included zooplankton. Here we use a recently developed global, observationally based map of mesozooplankton biomass to assess the skill of mesozooplankton in six CMIP6 ESMs. We also employ a biome‐based assessment of the ability of these models to reproduce the observed relationship between mesozooplankton biomass and surface chlorophyll. The combined analysis found that most models were able to reasonably simulate the large regional variations in mesozooplankton biomass at the global scale. Additionally, three of the ESMs simulated a mesozooplankton‐chlorophyll relationship within the observational bounds, which we used as an emergent constraint on future mesozooplankton projections. We highlight where differences in model structure and parameters may give rise to varied mesozooplankton distributions under historic and future conditions, and the resultant wide ensemble spread in projected changes in mesozooplankton biomass. Despite differences, the strength of the mesozooplankton‐chlorophyll relationships across all models was related to the projected changes in mesozooplankton biomass globally and in regional biomes. These results suggest that improved observations of mesozooplankton and their relationship to chlorophyll will better constrain projections of climate change impacts on these important animals.

Impacts of Climate Change on the Ascension Island Marine Protected Area and Its Ecosystem Services

“…Only one CMIP6 model in Petrik et al. (2022), CanESM5, projected a rise in global zooplankton biomass under the SSP5‐8.5 scenario. In that study, CanESM5 underestimated the historic zooplankton biomass by an order of magnitude but also projected a significant rise in zooplankton food sources (via surface chlorophyll concentration) over the same period.…”

Trophic amplification: A model intercomparison of climate driven changes in marine food webs

“…Taken together, these processes generally cause a warming-induced decrease in biomass. For example, in FEISTY, basal metabolism increases faster than ingestion with temperature increases, so warming reduces the scope for growth, leading to a decrease in biomass [ 51 ]. In BOATS, warming influences the representative size of primary producers and sets the scope for growth of fish communities [ 48 ], warming causes an increase of the growth, reproduction and mortality rates leading at food web scale to a decrease in biomass [ 19 , 37 ].…”

The Global Distribution of Grazing Dynamics Estimated From Inverse Modeling

“…All relevant WOMBAT output and documentation for these experiments can be found in (Rohr, 2024). Remote sensing data sets can be found at (O'Malley, 2015). CMIP6 model output can be found at (Earth System Grid Federation, 2022).…”

“…However, zooplankton grazing pressure may be the largest source of uncertainty in modern marine biogeochemical (BGC) models (Rohr et al., 2023). This likely contributes to persisting uncertainty in IPCC projections of net primary production (NPP) (Tagliabue et al., 2021), carbon export (Henson et al., 2022), zooplankton biomass (Petrik et al., 2022) and fisheries catch (Tittensor et al., 2021).…”