| Summary: | Autonomous buoys were deployed in 2011 in the central Arctic: An Ice-Tethered Profiler (ITP) and Ice Mass Balance (IMB) buoys were deployed in the Makarov basin; a Polar Ocean Profiling System (POPS) and Ice Thickness (Ice-T) buoy were deployed on the Eurasian Basin. The two different sites were approximately 70km apart. We compare the two different drifting stations to investigate spatial variability associated with heat fluxes near the ice base and spatial water property variability within the surface mixed layer. Our case study follows Vivier et al. (2016) who found the early basal melt onset at the Eurasian Basin site. Focusing on the basal melt onset, we ask the following questions: (1) Do spatial variations in the upper ocean drive the different timing of the basal melt onset? (2) How is the basal melt onset timing affected by these spatial variations? We found spatial differences in upper water properties and melt onset during the spring-summer transition. The freshening of surface water at the Eurasian Basin site happens about 20 days earlier than the Makarov Basin site. We identified low ice speed is associated with warming and freshening near the surface, suggesting accumulation of absorbed solar radiation heat near the ice is mixed deeper after quiescent periods. Subsequent mixing affects the vertical heat flux between the water above and below. During surface layer freshening, variability in lead opening and ice motion controls the spatial variability in the mixed layer as well as the basal melt associated with heat flux from the upper ocean to the bottom of the sea ice. At non-quiescent times, in spring, heat flux is related to deeper stratification.
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