It has long been realised that the geographical and depth distribution of trace elements, both radioactive and stable, hold clues to the understanding of several important physicochemical

and bio-chemical processes. Studies of trace elements, however, involve a contamination-free collection of large volumes of sea water from different depths in the ocean. Whereas the neutron activation technique is suitable for some elements, it is not applicable in others where it becomes necessary to extract the trace elements in large amounts to study them for their isotopic composition or radioactivity. We discuss in this paper our experiments towards in situ extraction of trace elements from few hundreds of tons of sea water. The techniques employed and their results are discussed for waters upto 3500 meters depth in the ocean. Though one of the techniques seems potential for contamination free extraction of any desired element, most of the results described here involve elements that can be efficiently adsorbed on to ferric-hydroxide dispersed in a matrix form. The implications of the results of the analyses of isotopes of uranium, thorium, radium, lead, silicon and beryllium are briefly described to show the scope of such studies