Quantifying iceberg calving fluxes with underwater noise
Quantifying iceberg calving fluxes with underwater noise
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DOI：
10.5194/tc-14-1025-2020
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发表时间：
2020-03-17
期刊：
影响因子：
5.2
通讯作者：
Deane, Grant B.
中科院分区：
文献类型：
--
作者：
Glowacki, Oskar;Deane, Grant B.
准确估计崩解通量对于了解小规模冰川动力学和量化海洋终止冰川对海平面上升 (SLR) 和极地淡水预算的贡献至关重要。在这里，我们研究了声学海洋学的应用，利用冰山与水撞击的水下声音来测量崩解通量。延时摄影和被动声学相结合，用于确定斯瓦尔巴群岛汉斯布林的空中崩解事件所产生的 169 座冰山的质量和撞击噪声之间的关系。该分析包括影响观测到的噪声的三个主要因素：(1) 温盐结构的时间依赖性，(2) 沿波导的海洋深度的变化，以及 (3) 来自冰川终点的冲击噪声的反射。冰山下落的（对数转换）动能与根据这三个因素校正的相应测量声能之间存在 0.76 的相关性。应用变量误差线性回归来估计这种关系的系数。对于幂律的乘法因子和指数，未变换变量的能量转换系数分别为 8 x 10(-7) 和 0.92。这个简单的模型可用于测量 Hansbreen 的固体冰排放。估计的不确定性是观察到的产犊事件数量的函数；对于 40 次和 135 次产犊事件，预计 8 个区块的不确定性将分别降至 20% 和 10%。如果可以确定不同产犊方式对接收到的噪声频谱的影响，则可以降低这些误差。
Accurate estimates of calving fluxes are essential in understanding small-scale glacier dynamics and quantifying the contribution of marine-terminating glaciers to both eustatic sea-level rise (SLR) and the freshwater budget of polar regions. Here we investigate the application of acoustical oceanography to measure calving flux using the underwater sounds of iceberg-water impact. A combination of time-lapse photography and passive acoustics is used to determine the relationship between the mass and impact noise of 169 icebergs generated by subaerial calving events from Hansbreen, Svalbard. The analysis includes three major factors affecting the observed noise: (1) time dependency of the thermohaline structure, (2) variability in the ocean depth along the waveguide and (3) reflection of impact noise from the glacier terminus. A correlation of 0.76 is found between the (log-transformed) kinetic energy of the falling iceberg and the corresponding measured acoustic energy corrected for these three factors. An error-in-variables linear regression is applied to estimate the coefficients of this relationship. Energy conversion coefficients for non-transformed variables are 8 x 10(-7) and 0.92, respectively, for the multiplication factor and exponent of the power law. This simple model can be used to measure solid ice discharge from Hansbreen. Uncertainty in the estimate is a function of the number of calving events observed; 50% uncertainty is expected for eight blocks dropping to 20% and 10 %, respectively, for 40 and 135 calving events. It may be possible to lower these errors if the influence of different calving styles on the received noise spectra can be determined.