Acoustic travel time and hydrostatic pressure measurements from Sermilik Fjord, southeastern Greenland, 2011-2016

This project will develop and test a non-traditional method to measure the time-varying heat content and vertical temperature profile in high-latitude seas, shelves, and fjords using pressure-sensor-equipped inverted echo sounders (PIES). PIES, which are installed on the seafloor below the reach of destructive iceberg keels, present a promising and inexpensive way to improve understanding of fjord dynamics and shelf-fjord interactions and will increase long-term monitoring capabilities in high latitudes where remoteness and harsh conditions hamper traditional in situ observation techniques. The use of PIES to characterize variability at high latitudes is a novel repurposing of an existing technology, but rests on the same principle as the traditional blue-water uses for PIES: due to the dependence of sound speed on temperature, the surface-to-bottom round-trip acoustic-travel-time associated with reflections between the PIES and the air-sea interface is an excellent proxy for heat content in the intervening water column. Furthermore, since reflections from seawater-ice interfaces are also detected when ice is present, PIES also provide a means to characterize the ice component in high-latitude systems. The PIs propose to develop these methods with existing PIES data collected in a 1-year test deployment in Sermilik Fjord in eastern Greenland and with observations to be collected in a 2-year deployment of three PIES in the fjord and on the nearby shelf.

本项目将研发并测试一种非传统方法，借助配备压力传感器的反演回声测深仪（pressure-sensor-equipped inverted echo sounders, PIES），对高纬度海域、大陆架及峡湾内随时间变化的热含量与垂直温度剖面开展测量。这类测深仪安装于破坏性冰山龙骨无法触及的海床区域，可为增进对峡湾动力学与陆架-峡湾相互作用的认知提供兼具应用前景与经济性的技术路径，同时提升高纬度地区的长期监测能力——该区域因地理位置偏远、环境条件恶劣，传统原位观测技术的应用常受掣肘。将PIES用于表征高纬度海域的水文变化，是对现有技术的全新再利用，但其核心原理与PIES的传统远洋应用一脉相承：由于声速随温度变化，PIES与海气界面间反射对应的水底往返声传播时间，可作为两者间水柱热含量的优质替代指标。此外，当存在海冰时，PIES还可探测到海水-冰界面的反射信号，因此也可用于表征高纬度海洋系统中的冰体组分。本项目的首席研究员们（Principal Investigators, PIs）计划依托现有数据与后续观测完善上述研究方法：前者为在格陵兰东部塞尔米利克峡湾开展的为期1年的测试部署所收集的PIES数据，后者则是后续将在该峡湾与邻近陆架部署3台PIES、为期2年的观测所获取的资料。