Journal Article

Direct Measurement of Glacier Ice Melt: Boundary Layer Details Are Critical for Submarine Melt Prediction at Near‐Vertical Ice Faces

Weiss, Kaelan J., Osman, Noah, Cohen, Nadia F., Jackson, Rebecca H., Wengrove, Meagan E., Zhao, Ken X., Pettit, Erin C., Nash, Jonathan D., Sutherland, David A., Nahorniak, Jasmine S.

2025

Overview

Parameterization of submarine melting represents a large source of uncertainty in modeling ice sheet response to climate change. Here we present in situ observations of melt at near‐vertical ice faces using a novel instrument platform mounted rigidly to icebergs. We investigate boundary layer dynamics controlling melt across 31 measurement periods that span a range of momentum and thermal forcing (1–12 cm/s flows and 3–10 K). While melt generally scales with velocity and temperature, we find substantially enhanced melt linked with unsteady forcing. Several implementations of the three‐equation melt parameterization show melt can be predicted within a factor of 2 if the model is evaluated with peak near‐boundary velocities and flows are quasi‐steady. However, if flows are unsteady or the model is evaluated with low‐resolution velocities, melt is underpredicted by 2–75×.$75\\times .$We conclude that understanding the detailed character of near‐boundary flows is critical for submarine melt predictions. Plain Language Summary Glaciers are outlets for the world's ice to flow and melt into the ocean as fresh water. Despite the importance of understanding how glaciers melt and where that water goes, our knowledge of the environment where the glacier meets the ocean is limited due to the challenges of working under actively calving ice cliffs. To address this gap, we developed a remotely deployed instrument that measures melt rate and ocean speed and temperature along near‐vertical, underwater ice faces. In this study, we present results from the initial set of deployments at the sides of icebergs in southeast Alaska. We find that the flows along icebergs can vary rapidly, and that this may enhance melt rates. Furthermore, this enhanced melt rate is not captured by the standard melt models, resulting in a significant underprediction of melt. Therefore, accurate melt rate predictions at glaciers and icebergs require a realistic representation of both ocean characteristics and enhanced melt rate due to rapidly varying flows. Key Points Ice‐ocean boundary layer forcing varies on short timescales; flow unsteadiness appears to enhance melt rate Observed flows violate steady shear assumptions of ice‐ocean models, which underpredict observed melt by a factor of 2–75 Melt models exhibit increased skill when evaluated with instantaneous, highly‐resolved boundary layer conditions

• Publisher: John Wiley & Sons, Inc
• Subject: boundary layer / Boundary layer dynamics / Boundary layers / Climate change / Glaciation / Glacier ice / Glacier measurements / Glacier melting / Glaciers / Ice melting / Ice sheets / Icebergs / ice‐ocean interactions / Instrument platforms / melt rate parameterization / observations / Parameterization / submarine melt