Including filter-feeding gelatinous macrozooplankton in a global marine
biogeochemical model: model-data comparison and impact on the ocean
carbon cycle
Corentin Clerc
LMD / IPSL, Ecole normale supérieure / Université PSL, CNRS, Ecole Polytechnique, Sorbonne Université, Paris, France, LMD / IPSL, Ecole normale supérieure / Université PSL, CNRS, Ecole Polytechnique, Sorbonne Université, Paris, France
Corresponding Author:[email protected]
Author ProfileFabio Benedetti
Environmental Physics, Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, 8092, Zürich, Switzerland., Environmental Physics, Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, 8092, Zürich, Switzerland.
Author ProfileAbstract
Filter-feeding gelatinous macrozooplankton (FFGM), namely salps,
pyrosomes and doliolids, are increasingly recognized as an essential
component of the marine ecosystem. Unlike crustacean zooplankton (e.g.,
copepods) that feed on preys that are an order of magnitude smaller,
filter-feeding allows FFGM to have access to a wider range of organisms,
with predator over prey ratios as high as 10$^5$:1. In addition,
most FFGM produce carcasses and/or fecal pellets that sink 10 times
faster than those of copepods. This implies a rapid and efficient export
of organic matter to depth. Even if these organisms represent
$<$5\% of the overall planktonic biomass,
the induced organic matter flux could be substantial. Here we present a
first estimate of the influence of FFGM organisms on the export of
particulate organic matter to the deep ocean based on the marine
biogeochemical model NEMO-PISCES. In this new version of PISCES, two
processes characterize FFGM: the preference for small organisms due to
filter feeding, and the rapid sinking of carcasses and fecal pellets. To
evaluate our modeled FFGM distribution, we compiled FFGM abundance
observations into a monthly biomass climatology using a taxon-specific
conversion. A model-observation comparison supports the model ability to
quantify the global and large-scale patterns of FFGM biomass
distribution, but reveals an urgent need to better understand the
factors triggering the boom-and-bust FFGM dynamics before we can
reproduce the observed spatio-temporal variability of FFGM. FFGM
contribute strongly to carbon export at depth (0.4 Pg C yr$^{-1}$
at 1000 m), particularly in low-productivity region (up to
40\% of organic carbon export at 1000 m) where they
dominate macrozooplankton by a factor of 2. The FFGM-induced export
increases in importance with depth, with a simulated transfer efficiency
close to one.