In recent years, there has been a significant sea ice retreat in the Pacific sector of the Arctic. One possible cause is the increase in ocean heat flux amplified by the ice-albedo feedback. This paper looks at vertical ocean heat transport from waters of Pacific origin and solar heat into the mixed layer and their impact on the sea ice mass balance in the Community Earth System Model - Large Ensemble (CESM-LE). To this end, we focus on two specific periods with observational hydrographic data from the Arctic Ice Dynamics Joint Experiment (1975-76) and Ice-Tethered Profiler (2004-2018). A comparison between simulated and observed salinity and potential temperature profiles highlights two key model biases in all ensemble members: an absence of Pacific Waters in the water column and a deepening of the winter mixed layer in opposition to observations that show a reduction in depth of the mixed layer and a stronger increase in stratification. Results from a one-dimensional vertical heat budget show that remnant solar heat trapped beneath the halocline is mostly ventilated to the surface by mixing before the following melt season, while vertical advection associated with Ekman pumping, even in early fall when the winds are strong and the pack-ice weak, only has a small effect on the vertical heat transport. Furthermore, we estimate from the 1D heat budget a reduction of 1.4 m winter ice growth over three years (the residence time of ice in the Beaufort Gyre) associated with the missing Pacific Waters.