The impact of an improved ice sheet freshwater flux representation on ocean heat storage
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Freshwater fluxes from the Greenland and Antarctic ice sheet might impact ocean circulation and thereby the distribution of heat in a warming climate. Despite their potential relevance, they are often not well represented in state-of-the-art climate models. Here, we incorporate a best estimate of freshwater runoff from both ice sheets into long-term (1850-2200) climate simulations by the Community Earth System Model (CESM), for both a strong (RCP8.5) and mild (RCP2.6) warming scenario. We analyze the differences with control simulations, focusing on the Atlantic meridional overturning circulation (AMOC), ocean heat uptake and global mean surface air temperature (GMST). Although the direct effects of the CO2 forcing in the climate scenarios are dominant, the incorporation of realistic ice sheet freshwater fluxes has a significant impact on the heat uptake and distribution in the ocean. Antarctic Bottom Water formation is significantly affected, causing a vertical redistribution of heat during the historical period that leads to warmer deep waters and negative GMST anomalies that are on the order of 0.2 K. In the 21st century, the initially colder surface waters enhance high latitude surface heat fluxes from the atmosphere into the ocean, resulting in a global ocean heat uptake anomaly of 60 ZJ by 2100. The AMOC shows an additional reduction of ~1 Sv during the 21st century, mainly effecting the heat content of the Arctic basin.