Tracer measurements in growing sea ice support convective gravity drainage parameterisations

Gravity drainage is the dominant process redistributing solutes in growing sea ice. Modelling gravity drainage is therefore necessary to predict physical and biogeochemical variables in sea ice. We evaluate seven gravity drainage parameterisations, spanning the range of approaches in the literature, using tracer measurements in a sea‐ice growth experiment. Artificial sea ice is grown to around 17 cm thickness in a new experimental facility, the Roland von Glasow air‐sea‐ice chamber. We use NaCl (present in the water initially) and rhodamine (injected into the water after 10 cm of sea‐ice growth) as independent tracers of brine dynamics. We measure vertical profiles of bulk salinity in situ, as well as bulk salinity and rhodamine in discrete samples taken at the end of the experiment. Convective parameterisations that diagnose gravity drainage using Rayleigh numbers outperform a simpler convective parameterisation and diffusive parameterisations when compared to observations. This study is the first to numerically model solutes decoupled from salinity using convective gravity drainage parameterisations. Our results show that 1) convective, Rayleigh number based parameterisations are our most accurate and precise tool for predicting sea‐ice bulk salinity; and 2) these parameterisations can be generalised to brine dynamics parameterisations, and hence can predict the dynamics of any solute in growing sea ice.

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