Iceberg Grounding Enhances the Release of Freshwater on the Antarctic Continental Shelf

The importance of Antarctic iceberg meltwater for the Southern Ocean has been a strong incentive to include Lagrangian icebergs in ocean and climate models. However, the modeled iceberg thickness has previously been constrained to 250 m, which appears to be underestimated given the frequent observations of icebergs grounded on substantially deeper bathymetric ridges. In this study, we define the initial iceberg thickness based on the thickness of the ice shelf from which they calve and rationalize the way to define the iceberg size classes. Ocean–sea-ice–iceberg simulations reveal that more than half of the iceberg melting is discharged over the Antarctic continental shelf, reaching an average of 631 Gt yr-1 when the interaction of icebergs with bathymetry is neglected, and 802 Gt yr-1 when a simple grounding scheme is implemented. Such additional freshwater injected over the continental shelf prone to sea ice production has important consequences for the ocean properties around Antarctica. It enhances ocean stratification, inhibits deep convection and isolates dense deep waters from the colder and fresher surface layers. This isolation allows the deep waters to warm and become saltier, thereby intensifying subsequent ice-shelf melting. Moreover, the simulated distribution of grounded icebergs blocks drifting sea ice, promoting the formation of thick sea ice and polynyas when the fast ice parameterization is included. This work emphasizes the need for further research into the physical representation of iceberg grounding and iceberg–sea-ice interaction.

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