Despite the lack of "simultaneously" obtained oceanographic data and acoustic measurements, TAP demonstrates the feasibility of using travel-time measurements to monitor changes in averaged ocean temperature, which was the one of the main objectives of this experiment.
Less attention during TAP was made to extracting information about the sea ice cover. The sea ice has an dampening effect on acoustic waves due to reflection loss and scattering, and Mikhalevsky et al. (1999) conclude, without any sensitivity study, that the attenuation contains information about the sea ice properties. Our results, which will be described in this paper, indicates that this is an overstatement at the low frequency used (20 Hz) in TAP.
The overall aim of AMOC is to develop and design an acoustic system for long-term monitoring of the ocean temperature and ice thickness in the Arctic Ocean, including the Fram Strait, for climate variability studies and global warming detection .
The approach of AMOC is to monitor climate changes and detect and quantify global warming in the Arctic Ocean using gyre scale acoustic long range propagation for basin ocean temperature and ice thickness changes in combination with remote sensing of sea ice from satellites, modelling and data assimilation. AMOC consist of the following tasks:
Task 1: Arctic Ocean data analysis: Compilation and analysis of existing ocean and ice data (temperature, salinity and speed of sound fields, ice thickness, concentration and extent) from the Arctic Ocean for use in climate and acoustic models.
Task 2: Climate and ice modeling: Simulation of present and future ocean temperature, salinity and speed of sound fields, ice thickness, concentration and extent in the Arctic Ocean caused by natural variability and global warming scenarios, as input to acoustic modeling.
Task 3: Acoustic modeling of Arctic basin: Simulation of present and future basin-wide acoustic propagation using natural variability and global warming scenarios (input from climate and ice modeling) to investigate the sensitivity of acoustic methods for global warming detection.
Task 4. Acoustic modeling of the Fram Strait: Simulation of present and future acoustic propagation in the Fram Strait to investigate the sensitivity of acoustic methods for monitoring heat and volume fluxes in an area of strong mesoscale eddy activity.
Task 5: Acoustic monitoring: Design of an optimum acoustic monitoring system for climate change detection in the Arctic Ocean including volume and heat fluxes in the Fram Strait.
METHODOLOGICAL APPROACH
In order to design a monitoring system to detect changes in averaged temperature and ice conditions for the Arctic basin caused by a climate change, a sensitivity study will be carried out in the project. This study applies two main methods: (1) analysis of existing data and (2) use of numerical models for simulations of Arctic ocean climate and acoustic propagation.
Climate change scenarios in the Arctic are simulated by Task 2, from which the most sensitive regions are identified. Based on this acoustic transmission paths will be selected in the Fram Strait and Arctic Basin in areas where the transmission is optimal and where the sensitivity with respect to temperature and current changes is at a maximum. The Fram Strait is the region where almost all heat and mass exchange between the Arctic Ocean and the Atlantic Ocean takes place apart from the Atlantic inflow through the St. Anna trough. A track following 79｡? across the Fram Strait is suggested for monitoring heat and mass flux through the strait by using acoustics.
