Milne Glacier is a marine-terminating glacier located on the northern coast of Ellesmere Island in the Canadian High Arctic, a region that has experienced extensive ice-mass loss over the last two decades. Milne Glacier flows into Milne Fiord where it transitions from grounded to floating at its grounding line. The glacier rests on a retrograde slope and is therefore potentially vulnerable to marine ice-sheet instability where enhanced basal melt and grounding-line retreat can trigger further deterioration of the glacier. Glacier changes that occur in the ice flexure zone, which spans from the hinge line, the inland limit of tidal flexure, past the grounding line to the landward limit of hydrostatic equilibrium, are critical for glacier dynamics. In this study, we quantify changes in the Milne Glacier grounding-line position from 1966 to 2023 using satellite, airborne, and ground radar observations. Double difference interferometric analysis of Synthetic Aperture Radar (DDInSAR) images acquired between 1992 and 2023 from European Remote Sensing (ERS-1/2) satellites, Sentinel-1 A/B, and RADARSAT Constellation Mission (RCM) was performed to delineate a timeseries of the hinge line. We used these hinge lines to quantify changes in the grounding-line position as their migration rates are directly correlated. RCM-derived results had the highest spatial resolution (10 m) and the best coherence between 4-day repeat acquisitions, which provided the most continuous and detailed hinge-line delineation across the glacier. We also used airborne and ground-based ice penetrating radar (IPR) data collected between 2014 and 2023 to calculate the normalized bed reflection (NBRP) and internal reflection power (NIRP) coefficients to distinguish between basal returns associated with water versus bed and assess signal attenuation within the ice column. Spatial patterns in NBRP and NIRP coefficients allowed us to reliably separate the floating and grounded parts of Milne Glacier. This alternate way of delineating the grounding line was in good agreement with our satellite-based DDInSAR results. Analysis of historical airborne radar surveys in 1966 and 1981 in conjunction with our more recent NBRP/NIRP analysis revealed a ∼3.1 km retreat (or ∼55 m yr−1) of the grounding line along the glacier centerline over the past 57 years. DDInSAR analysis provided additional details on this shift across the Milne Glacier. ERS and RCM images acquired in 3 and 4-day repeat cycles, respectively, revealed variability in hinge-line positions. This information allowed us to estimate the landward and seaward bounds, associated with the short-term hinge-line migration, that were used to quantify the grounding-line retreat over years. The grounding line retreat was highly asymmetric with the grounding-line retreating at over twice the average rate near the western margin (124 m yr−1) than at the center (53 m yr−1) of the glacier between 2011 and 2023. The calculated average retreat rates of grounding line showed a close association with changes in the ocean temperatures and subglacial discharge. Our study demonstrated that satellite-based monitoring of the hinge line at high spatiotemporal resolution is crucial to better assess the grounding line short-term positional variability and reliably quantify its long-term retreat. Airborne and ground-based radar observations can provide additional in-situ information to explain changes in the grounding line that affect glacier dynamics and viability.

中文翻译：

---

1966 年至 2023 年加拿大埃尔斯米尔岛米尔恩冰川的接地线退缩，来自卫星、机载和地面雷达数据


米尔恩冰川是位于加拿大高北极地区埃尔斯米尔岛北部海岸的海洋终止冰川，该地区在过去二十年中经历了广泛的冰团损失。米尔恩冰川流入米尔恩峡湾，在那里它从搁浅过渡到漂浮在其接地线上。冰川位于逆行斜坡上，因此可能容易受到海洋冰盖不稳定的影响，其中增强的基底融化和接地线后退会引发冰川的进一步恶化。冰弯曲区发生的冰川变化，从铰链线、潮汐弯曲的内陆界限，越过接地线到静水平衡的陆地极限，对冰川动力学至关重要。在这项研究中，我们使用卫星、机载和地面雷达观测量化了 1966 年至 2023 年米尔恩冰川接地线位置的变化。对 1992 年至 2023 年间从欧洲遥感 （ERS-1/2） 卫星、Sentinel-1 A/B 和 RADARSAT 星座任务 （RCM） 获取的合成孔径雷达 （DDInSAR） 图像进行双差干涉分析，以描绘铰链线的时间序列。我们使用这些铰链线来量化接地线位置的变化，因为它们的迁移率直接相关。RCM 得出的结果具有最高的空间分辨率 （10 m） 和 4 天重复采集之间的最佳连贯性，从而提供了整个冰川上最连续和最详细的铰链线描绘。 我们还使用了 2014 年至 2023 年间收集的机载和地基穿冰雷达 （IPR） 数据来计算归一化床反射 （NBRP） 和内反射功率 （NIRP） 系数，以区分与水与床相关的基础回波，并评估冰柱内的信号衰减。NBRP 和 NIRP 系数的空间模式使我们能够可靠地区分米尔恩冰川的浮动部分和接地部分。这种描绘接地线的替代方法与我们基于卫星的 DDInSAR 结果非常吻合。对 1966 年和 1981 年历史机载雷达调查的分析与我们最近的 NBRP/NIRP 分析相结合，揭示了在过去 57 年中，沿冰川中心线的接地线后退了约 3.1 公里（或 ∼55 m yr-1）。DDInSAR 分析提供了有关米尔恩冰川这一变化的更多细节。分别在 3 天和 4 天重复周期中获取的 ERS 和 RCM 图像揭示了铰链线位置的变化。这些信息使我们能够估计与短期铰链线迁移相关的向陆地和向海边界，用于量化多年来接地线后退。接地线后退是高度不对称的，2011 年至 2023 年期间，接地线在西缘附近 （124 m yr-1） 的平均后退速度是冰川中心 （53 m yr-1） 的两倍多。计算出的接地线平均后退率与海洋温度变化和冰下排放密切相关。 我们的研究表明，以高时空分辨率对铰链线进行基于卫星的监测对于更好地评估接地线的短期位置变化和可靠地量化其长期后退至关重要。机载和地面雷达观测可以提供额外的原位信息，以解释影响冰川动力学和生存能力的接地线变化。