Antarctic krill vertical migrations modulate seasonal carbon export

Vertical migrations by marine organisms contribute to carbon export by
consumption of surface phytoplankton followed by defecation in the deep
ocean. However, biogeochemical models lack observational data, leading to
an oversimplified representation of carbon cycling by migrating organisms.
Using a numerical model informed by one year of acoustic observations in
the East Antarctic, we estimated Antarctic krill (Euphausia superba)
contributions to particulate organic carbon flux. We estimated the total
particulate organic carbon (POC) flux from krill faecal pellets to be 9.68
mg C m-2 d-1. A maximum of 25% of krill migrated to depths over 200 m with
a strong seasonality component, transporting less than 10% of the total
krill POC flux (1.28 mg C m-2 d-1). Models that include vertical migration
risk overestimating carbon export if this seasonality is not captured and
accurate estimates are essential to inform climate policy and mitigation
strategies.