Department of Earth System Science, University of California, Irvine, CA 92617.
Department of Earth System Science, University of California, Irvine, CA 92617;
Proc Natl Acad Sci U S A. 2021 Jan 12;118(2). doi: 10.1073/pnas.2015483118.
Zachariae Isstrøm (ZI) and Nioghalvfjerdsfjorden (79N) are marine-terminating glaciers in northeast Greenland that hold an ice volume equivalent to a 1.1-m global sea level rise. ZI lost its floating ice shelf, sped up, retreated at 650 m/y, and experienced a 5-gigaton/y mass loss. Glacier 79N has been more stable despite its exposure to the same climate forcing. We analyze the impact of ocean thermal forcing on the glaciers. A three-dimensional inversion of airborne gravity data reveals an 800-m-deep, broad channel that allows subsurface, warm, Atlantic Intermediate Water (AIW) (+1.[Formula: see text]C) to reach the front of ZI via two sills at 350-m depth. Subsurface ocean temperature in that channel has warmed by 1.3[Formula: see text]C since 1979. Using an ocean model, we calculate a rate of ice removal at the grounding line by the ocean that increased from 108 m/y to 185 m/y in 1979-2019. Observed ice thinning caused a retreat of its flotation line to increase from 105 m/y to 217 m/y, for a combined grounding line retreat of 13 km in 41 y that matches independent observations within 14%. In contrast, the limited access of AIW to 79N via a narrower passage yields lower grounded ice removal (53 m/y to 99 m/y) and thinning-induced retreat (27 m/y to 50 m/y) for a combined retreat of 4.4 km, also within 12% of observations. Ocean-induced removal of ice at the grounding line, modulated by bathymetric barriers, is therefore a main driver of ice sheet retreat, but it is not incorporated in most ice sheet models.
扎卡里亚斯·伊斯斯特罗姆（ZI）和尼加霍夫尔法耶尔冰川（79N）是格陵兰东北部的海洋终止冰川，拥有相当于全球海平面上升 1.1 米的冰量。ZI 失去了其浮动冰架，加速，以 650 米/年的速度后退，并经历了 50 亿吨/年的质量损失。尽管受到相同的气候强迫作用，冰川 79N 一直更加稳定。我们分析了海洋热力强迫对冰川的影响。航空重力数据的三维反演揭示了一个 800 米深的宽阔通道，允许表面下温暖的大西洋中层水（AIW）（+1.[Formula: see text]C）通过两个在 350 米深度的浅滩到达 ZI 的前缘。自 1979 年以来，该通道中的海底温度升高了 1.3[Formula: see text]C。使用海洋模型，我们计算出 1979 年至 2019 年期间，海洋通过海底线移除的冰的速度从 108 米/年增加到 185 米/年。观测到的冰变薄导致其漂浮线的后退速度从 105 米/年增加到 217 米/年，在 41 年内总后退 13 公里，与独立观测值相差 14%。相比之下，AIW 通过更窄的通道进入 79N 的有限通道导致较低的基岩冰移除（53 米/年至 99 米/年）和变薄诱导的后退（27 米/年至 50 米/年），总后退 4.4 公里，也在观测值的 12%以内。因此，受海底地形障碍调制的海底线处的海洋引起的冰移除是冰盖后退的主要驱动因素，但大多数冰盖模型并未将其纳入。
