A study of marine ambient acoustic noise in relation to marine life in Antarctic waters during austral summer of 18 th Indian Expedition to Antarctica (1998-99)

Abstract

The exploration of the Antarctic Ocean (Southern Ocean) receives much attention by Oceanographers of various disciplines, because the ocean supports all the animal life and has the tremendous influence on meteorology and bio-geo-physical problems. Any climatic ocean changes are, of course, of course, of interest in their own right. The thermal and dynamical structure of some coupled atmosphere / ocean models undergo drastic changes, such as virtual cessation of the thermohaline circulation preventing the ventilation of the deeper layers. This could have profound impact on marine life. Towards this. It is utmost to make measurements of ocean temperature over large transects. XBT fall rate variation in waters of extreme temperature and the resulting depth error has been addressed using controlled XBT-CTD data sets collected from this cruise in the southern Ocean. Mean depth errors deduced from the data sets collected in this cruise and also other data sets available are significantly different from those reported earlier for tropical and sub-tropical regions. The comprehensive study of Hanawa et. al 1995. (making use of controlled XBT-CTD data), mostly from tropical and sub-tropical waters, showed that the manufacturer's equation underestimates the probe's fall rate. This is manifested by the mean negative depth error reported from this region. Observed as well as the analytical results suggest that the probe has a decelerating tendency due to viscosity effect in this high latitude waters and the existing correction scheme is not appropriate for the XBT data from regions of such extreme low temperature