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The discharge of icebergs into the polar oceans is expected to increase over the coming century, which raises the importance of accurate representations of icebergs in global climate models (GCMs) used for future projections. Here we analyze the prospects for interactive icebergs in GCMs by forcing an iceberg drift and decay model with circulation and temperature fields from (i) state-of-the-art GCM output and (ii) an observational state estimate. The spread of meltwater is found to be smaller for the GCM than for the observational state estimate, despite a substantial high wind bias in the GCM-a bias that is similar to most current GCMs. We argue that this large-scale reduction in the spread of meltwater occurs primarily due to localized differences in ocean currents, which may be related to the coarseness of the horizontal resolution in the GCM. The high wind bias in the GCM is shown to have relatively little impact on the meltwater distribution, despite Arctic iceberg drift typically being dominated by the wind forcing. We find that this is due to compensating effects between faster drift under stronger winds and larger wind-driven wave erosion. These results may have implications for future changes in the Atlantic meridional overturning circulation simulated with iceberg-enabled GCMs.

Plain Language Summary Recent reductions in the volume of the polar ice sheets highlight the importance of the question how ice sheet meltwater impacts the large-scale ocean circulation and global climate. For example, it has been argued that increased meltwater from Greenland will slow down the Atlantic meridional overturning circulation (AMOC) in the coming decades. The likelihood of this scenario depends on where the meltwater is released at the ocean surface. Icebergs, which carry up to half of this meltwater, play a crucial role in transporting meltwater equatorward in the North Atlantic. Our results suggest that climate models that include icebergs will underestimate this equatorward transport of meltwater, with potentially far-reaching implications for the AMOC.