Work

New Representation of Sea Ice Salt Dynamics in NEMO‐SI 3 v5: Evaluation and Impacts

Year: 2026

Type: article

Abstract: Although many large‐scale sea ice models now represent salt dynamics, few studies have evaluated them, and uncertainty remains regarding key parameterization choices. Here, we conduct global 1° ocean–ice simulations with NEMO‐SI 3 v5, forced by climatological atmospheric data, tuned to the salinity–thickness relationship, and evaluated against more than 1,400 ice cores. Simulations investigate (a) the treatment of vertical ice salinity variations (diagnostic vs. prognostic), (b) gravity drainage physics (brine fraction‐based vs. Rayleigh number‐based), and (c) key parameter values. On average, ice salinity is simulated within 0.1 g/kg (Arctic) and 0.7 g/kg (Antarctic) of observations, capturing large‐scale features including the Arctic–Antarctic contrast, seasonality, vertical profile, and the salinity–thickness relationship. Using a high value for the new ice liquid fraction parameter is critical for simulating high salinity in the thin ice range. Vertically‐resolved salt dynamics generally outperform the diagnostic approach, consistently across hemispheres, seasons, depth and thickness. Brine fraction‐based and Rayleigh number‐based parameterizations of gravity drainage produce different salinity fields, both through direct effects and interactions with melt ponds. However, limited observational constraints on measurement biases prevent firm conclusions on which approach performs best. Uncertainties in ice salinity are generally larger in the Antarctic than in the Arctic. While salt dynamics strongly affect sea ice mass and salt budget terms, they affect sea ice volume moderately, and have little effect on ocean salinity due to compensating effects.

Source: Journal of Advances in Modeling Earth Systems

DOI: 10.1029/2025ms005487

Authors: Elise Ortega, Martin Vancoppenolle, Clément Rousset, Eva Lemaire