Accelerating global sea-level rise highlights the need for accurate and efficient ice-sheet dynamics models. Conventional non-Newtonian models based on Glen’s flow law are limited by the strong spatial and temporal variability of ice viscosity. Here, focusing on the Greenland Ice Sheet, we develop a simplified Newtonian framework based on warm-ice rheology and multi-source satellite observations to investigate ice-flow dynamics and cross-scale turbulence. A 1-km-resolution Greenland ice-sheet dataset is constructed, and the scaled Navier-Stokes equations are reduced to a 2D linear equilibrium model balancing horizontal pressure gradients with an effective resistance term that represents basal friction, internal viscosity, and subglacial topography. The model reveals a scale-dependent turbulence regime in Greenland ice flow. The second-order structure function follows a 2/3 scaling over 3~500 km, while the third-order structure function changes sign near 120 km, indicating a transition from a forward cascade at smaller scales to an inverse cascade at larger scales. Three regimes are identified: topography-dominated scales (0.5~10 km), forward-cascade mesoscales (10~50 km), and Coriolis-controlled inverse-cascade large scales (300~1000 km). These results show that ice-sheet flow can be captured by a linear equilibrium model across broad spatial scales, while nonlinear advection and Coriolis effects remain essential for describing temporal evolution and complex dynamics. The framework provides a simple and physically based approach for modeling Greenland and Antarctic ice-sheet flows.