Measured Horizontal Temperature Gradients Constrain Heat Transfer Mechanisms in Greenland Ice

Ice in the ablation zone of the Greenland ice sheet is known to contain vertical temperature gradients that arise from conduction at the boundaries, the addition of strain and latent heat, and advective heat transport. A three‐dimensional array of temperature measurements in a grid of boreholes reveals horizontal ice temperature gradients that challenge the present conceptualization of heat transfer. We measure two distinct types of temperature variability in the horizontal direction, one impacting a confined region where ice temperatures span a range of 5°C, and another with temperatures consistently varying by approximately 2°C across the entire 3‐D block. We suggest the first demonstrates the localized and limited nature of latent heat input, and the second demonstrates that vertical heat advection outpaces diffusion. These findings imply that ice flow is highly variable over sub‐ice‐thickness length scales, which in turn generates contrasts in ice temperature that may impact ice deformation and fracturing. Key Points The 3‐D thermal structure of an ~8 × 107 m3 block of ice in the Greenland ice sheet ablation zone was measured with over 300 sensors Unexpected horizontal temperature gradients are present across length scales below one ice thickness and through the full ice column Slow rates of diffusion relative to advective heat transfer can generate a heterogeneous temperature structure similar to what we observe