The Arctic sea ice, in particular the ice pack, acts as an insulator between the atmosphere and the ocean. Leads, commonly found in the Arctic, facilitate ocean-atmosphere flux exchanges. Local observations have captured heat fluxes through some leads one order of magnitude larger than those outside of the leads, leading to the speculation that air-sea exchanges through leads contribute significantly to the Arctic Ocean surface buoyancy forcing. Here, we quantify the magnitude and impact on the ocean surface of the leads using SEDNA, a subkilometer pan-Arctic hindcast. Leads account for 22% of the sea ice cover surface, and within them, there is approximately 25% of the total surface water mass transformation. In other words, the water mass transformation in leads is similar to those underneath the surrounding ice-covered oceans. Thus, the present estimate indicates that leads have a small contribution to Arctic Ocean dynamics, contrary to previous hypotheses.