Marginal ice zones are composed of individual sea ice floes, whose breakage and melt influence its dynamical behavior. These processes are not well represented by global or regional climate models due to the continuum approximations and uncertainties regarding forcing, data resolution and parameterizations used for sea ice. Here, we use a Discrete Element Model (DEM) coupled to a slab thermodynamic ocean to investigate how breakage and melt processes impact the decay of summer sea ice. The DEM is calibrated using MODIS satellite imagery and reanalysis data within the Arctic Ocean's Baffin Bay during June–July 2018. The sensitivity of the sea ice decay is evaluated by varying the solar heating, the ice/ocean heat exchange parameter, and a prescribed floe breakage rate. For the parameter regime that best fits observations, the ratio of mass loss of resolved floes (diameter (Formula presented.) 2 km) due to breakage versus melt is 0.47, and oceanic versus solar melt is 0.46. The rate at which resolved floes lose mass is most sensitive to the breakage rate, as compared to the solar and oceanic melt parameters. The number decay of the largest floes (D (Formula presented.) 21 km) is controlled by breakage, whereas the decay of smaller floes (D = 2–21 km) depends strongly on lateral and basal melt. Inferences from this exploration of the parameter space may help motivate more accurate parameterizations of the floe size distribution evolution in climate models.