Field Investigation of the Lateral Melting Rate of Ice Layers

Under global warming, lateral melting plays an increasingly important role in heat exchange between ice and water. However, field-based observations of its depth-dependent behavior remain limited, hindering the development of reliable parameterizations. To address this, we performed continuous in situ measurements of lateral melting at Lake Hanzhang. Lateral melting rates at depths of 10, 20, 30, and 35 cm during the melt period were measured and analyzed. Total lateral melt amounts over the observation period were 64 mm at 10 cm, 84 mm at 20 cm, 148 mm at 30 cm, and 176 mm at 35 cm, revealing a pronounced depth-dependent gradient. This gradient was accompanied by distinct vertical differences in ice temperature, with the upper layer responding more closely to air temperature and the lower layer to water temperature. With rising air temperatures from −12 °C to above-zero and water temperatures from 2 °C to 4 °C, the lateral melting rate increased from <0.25 mm·h−1 to >2 mm·h−1. A parameterization scheme linking the ice–water temperature difference to the lateral melting rate was developed for different air temperature regimes. Notably, observed lateral melting under sub-freezing air temperatures provides a reference for non-summer conditions. In addition, lateral melting accelerates ice thinning and open-water formation, which enhance heat absorption and ice transparency, thereby increasing water temperature and photosynthetically active radiation beneath the ice. These changes may promote primary productivity, supporting a potential linkage between lateral melting and the under-ice habitat environment. Collectively, the results offer a more realistic basis for parameterizing lateral melting in ice thermodynamic models.