In the oceans, a nearly constant biomass of organisms is found in equal log- intervals of body-size. This large-scale regularity is referred to as the size spectrum. In this new modelling study, we find that parameters of the size spectrum correlate strongly with the export and export efficiency of particles into the deep ocean. These parameters performed better than other commonly used export predictors such as temperature or primary production.
The magnitude and efficiency of particulate carbon export from the ocean surface depends not only on net primary production (NPP) but also on how carbon is consumed, respired, and repackaged by organisms. We contend that several of these processes can be captured by the size spectrum of the plankton community. However, most global models have relatively simple food-web structures that are unable to generate plankton size-spectra. Moreover, the life-cycles of multicellular zooplankton are typically not resolved, restricting the ability of models to represent time-lags that are known to impact carbon export and its efficiency (pe-ratio). Here, we use a global mechanistic size-spectrum model of the marine plankton community to investigate how particulate export and pe-ratio relate to the community size spectrum, community composition, and time-lags between predators and prey. The model generates emergent food-webs with associated size distributions for organisms and detrital particles. To resolve time-lags between phytoplankton and zooplankton, we implement the life-cycle of multicellular zooplankton (here represented by copepods). We find that carbon export correlates best with copepod biomass and trophic level, whereas the pe-ratio correlates best with the exponent of the size spectrum and sea surface temperature (SST). Community metrics performed better than NPP or SST for both deep export and pe-ratio. Time-lags between phytoplankton and copepods did not strongly affect export or pe-ratio. We conclude by discussing how can we reconcile size-spectrum theory with field sampling.
Link to the paper: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021GB007275
Serra‐Pompei, C., Ward, B. A., Pinti, J., Visser, A. W., Kiørboe, T., & Andersen, K. H. (2022). Linking plankton size spectra and community composition to carbon export and its efficiency. Global Biogeochemical Cycles, e2021GB007275.