High Fraction of Glacial Meltwater Along Two Separate Isopycnals Observed in Summer 2020 Near and Off the Pine Island and Thwaites Ice Shelves, West Antarctica

Abstract The spatial distribution and dynamics of glacial meltwater (MW) influence ocean circulation off and basal melt rate below Antarctic ice shelves. While previous studies described the MW distribution in Pine Island Bay off Pine Island Ice Shelf (PIIS), quantitative constraints on the spatial heterogeneity of the spread of MW associated with lateral mixing remain unknown. In this study, the distribution and spreading mechanisms of MW were investigated based on in situ observations using conductivity‐temperature‐depth and lowered acoustic Doppler current profiler measurements at 68 stations off PIIS and Thwaites Ice Shelf in summer 2020 (January–February). The composite tracer method was used to calculate the MW fraction using the properties of Winter Water, modified Circumpolar Deep Water, and MW. The results showed that the high‐MW fractions were primarily distributed along two separate isopycnals (27.38 σ θ and 27.48 σ θ ) near PIIS and along a deep isopycnal (27.48 σ θ ) near TIS. Exponentially fitted line of MW fractions along the deeper (27.48 σ θ ) isopycnal showed a much larger curvature and steeper slope near TIS than near PIIS. Based on the 1‐dimensional advection–diffusion model, the results indicated stronger mixing off PIIS than TIS along 27.48 σ θ , and stronger mixing along 27.48 σ θ than 27.38 σ θ off PIIS. This study suggests that along‐isopycnal MW mixing varies between ice shelves and between MW‐rich isopycnals, improving our understanding of MW distribution and spreading patterns and the implications of these patterns for regional circulation.