Real iceberg underwater12/5/2023 Acoustic measurements are not hampered by conditions such as fog, cloud coverage, precipitation, or humidity. Low cost hydrophones are easily deployed, and acoustic data can be gathered continuously for several months or longer with a high sampling rate and low maintenance. But acoustic oceanography may offer some advantages for the study of interactions between land-based ice and the ocean. The researchers note other methods, such as satellite imagery, are effective ways to study large-scale, relatively slow changes in glaciers. “We demonstrated that glacier mass loss from iceberg calving can be measured safely by analyzing the underwater noise generated as icebergs impact the sea surface,” said Glowacki. This model can be used to measure ice loss due to calving from the underwater sound recordings of icebergs impacting the ocean, said the researchers. This finding led the researchers to derive a mathematical formula that calculates the mass of the ice block from the noise it makes. After retrieving the underwater microphones, the researchers analyzed the acoustic data and compared it with photographs from all 169 events, finding a strong relationship between the size of the iceberg breaking off from the glacier and the intensity of the resulting underwater sound. Based on these images, the researchers estimated iceberg volumes and drop heights from 169 calving events. Three time-lapse cameras placed near the glacier simultaneously photographed each calving event. “What we are actually recording is a sound cacophony, a mixture of noise made by all the chunks of ice floating around and the noise made by the glacier itself,” said Glowacki, a postdoctoral scholar at Scripps and lead author of the study. Melting glacier ice is described as “more treble,” said Deane, noting that it sounds like popping or "bacon frying” if you're close to it and more like “hissing static” if it's far away. The hydrophones also recorded the sounds of air bubbles bursting from the glacier ice as it melted. “An iceberg breaking off an ice cliff and falling into the water typically sounds like a cracking, rumbling splash,” said Deane, a research oceanographer at Scripps and study co-author. Over the course of a month and a half, the hydrophones captured the sounds made by icebergs falling into the ocean. The recorders were placed by divers on the ocean floor more than 900 meters (3,000 feet) from the glacier cliff. In an effort to address these challenges, the Scripps team deployed in summer 2016 two underwater microphones (hydrophones) near the Hansbreen glacier in Hornsund fjord, Svalbard, an archipelago in the Arctic north of Norway. This is due to the remote locations of many glaciers, as well as the dangerous conditions that prevent researchers from making direct measurements at unstable ice cliffs. As the planet warms, calving is expected to increase, but accurate estimates of ice loss at the ice-ocean boundary are difficult to obtain, say researchers. Iceberg calving, a process during which ice breaks off from the edges of a glacier, contributes greatly to sea-level rise. In a new study, Scripps polar scientists Oskar Glowacki and Grant Deane describe a new method to measure glacier mass loss from iceberg calving by analyzing underwater acoustic recordings of icebergs as they fall into the ocean and make a splash. Researchers at Scripps Institution of Oceanography at the University of California San Diego are eavesdropping on an Arctic glacier in the name of science.
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