Arctic Climate Observations using Underwater Sound (ACOUS)
Peter Mikhalevsky
Science Applications international Corporatuon
In October 1998 a 20 Hz acoustic source was deployed from the Russian icebreaker, Akademic Fedorov in the Franz Victoria Trough between Spitzbergen and Franz Josef Land. At the same time an acoustic receive array was deployed in the Lincoln Sea approximately 1000 kms away. These are the first installations of an acoustic thermometry grid for the Arctic Ocean under the Arctic Climate Observations using Underwater Sound (ACOUS, from the Greek, "akous", meamng "listen!"). The source is autonomous and is desrgned for a three year life. The array is also autonomous and designed for an 18 month life. In the summer of 2000 a cabled acoustic array is planned for installation in the Beaufort Sea. A second acoustic source is also planned for installation in 2000/2001 most likely in the central Arctic.
Since the early 1990's it appears that inflow of warmer Atlantic Water into the Arctic Ocean increased resulting in temperature increases in the Atlantic Layer that are continuing until today. Point measurements from icebreakers in 1991 and 1993 showed temperature increases of several tenths of a degree C over historical climatologies. In 1994 acoustic transmissions were made from a site north of the Svalbard Archipelago across the entire Arctic Ocean to receiver arrays located in the Lincoln Sea and the Beaufort Sea. The travel time measurements revealed an average .4 C increase in the Atlantic Layer. This was the first basin scale measurement of this large scale warming. Since 1994 there have been annual trans-Arctic submarine cruises and one trans-Arctic icebreaker cruise that have also observed these changes.
Coupled atmosphere-ice-ocean modelling and analysis of recent data appear to support a possible decadal scale oscillation in the atmospheric and ocean circulation in the Arctic that may explain the recent warming and portend a return to cooler temperatures. The need for year-round real-time data from the Arctic is evident. Acoustic energy propagates across the entire Arctic basin in 30 minutes. An acoustic network that is beginning under ACOUS could provide real-time, year-round, synoptic Arctic Ocean temperature data on spatial and temporal scales that are simply not possible by submarine, ice breaker or ice camp methods. In addition to using the travel time measurements to obtain ocean temperature, research is underway to use the acoustic attenuation changes to measure changes in average sea ice roughness and thickness, and the use of multiple frequencies to measure the depth of the thermocline and thus the thickness of the upper mixed layer in the Arctic Ocean.
Acoustic Monitoring of Ocean Climate in the Arctic (AMOC)
Ola Johannessen
Nansen Environmental & Remote Sensing Center
The overall objective 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 unique combination of the underwater acoustic remote sensing (AMOC) with satellite remote sensing of the ice cover including modeling and data assimilation, in the predicted sensitive climate region of the Arctic Ocean, is perhaps the key solution to monitor globai climate changes and early detection of global warming.
