Abstract: In the research program "Acoustic Monitoring of the Ocean Climate in the Arctic" (AMOC), the objective is to assess the possibility of using acoustic methods to monitor any long term changes in temperature and ice thickness in the Arctic. The main influx/efflux of water (and heat) to the Arctic Ocean is through the Fram-Strait. Thus, monitoring the temperature distribution and water flux in the Fram-Strait is an important issue in this respect. In this presentation we focus on certain aspects of acoustic thermometry using ray tracing. In order to apply acoustic means for monitoring temperature and flux of water masses it is essential that it is possible to identify arrival of individual rays at the receiver location, while the environment undergoes seasonal and shorter time scale variations. The present study is based on ray simulations using environmental data for the period 1950-1990 in terms of decadal means. In addition a detailed map of one passing meso scale eddy was used. The main conclusion is that some rays may be identified most of the time, even during passing eddies.