A section of14C activities of sea water between 9°s and 66°s in the South-West Pacific Ocean

Abstract

Since late 1956 ¹⁴C activities of 16 surface and 22 subsurface samples of sea water have been determined. The distribution of these activities in a section extending from 9° S to 66° S through the South West Pacific Ocean is described and compared with ideas of the nature and movements of water masses inferred from conventional oceanographic data. It is confirmed that upwelling of Deep Water occurs in a divergence region near 64° S and that sinking occurs near the Antarctic Convergence at 61° S. The upwelling water at the divergence has a low ¹⁴C activity and water sinking at the convergence does so while the ¹⁴C content is still far removed from equilibrium with that in the atmosphere. The activity of this sinking water is about 6% to 14% lower than that of water sinking near Greenland, so that great care must be taken in interpreting the activity of a sample as the time spent since leaving the surface, unless there is only one possible source of sinking water. However, if the distribution of ¹⁴C activity is sufficiently well known, the maximum possible time or the least possible time since sinking may be estimated in certain circumstances. Other features of the distribution allow interpretations that are tentative only, owing to the small number of observations within the section and the lack of data to the east and west, particularly in regions from which water masses move into the section. In most cases there is agreement with possible interpretations of the salinity and temperature distributions suggested by previous authors. It is suggested that the use of the ¹⁴C activity as an indicator characteristic may provide. information in a very powerful manner in certain cases where the temperature and salinity characteristics vary only slightly, because of the requirement that density surfaces must usually be almost horizontal. In such cases nearby water masses near the same level may have widely different activities since, even though they originate from similar sources, they may have done so at greatly dissimilar times and have followed different paths. The activities in the Intermediate and Deep Waters north of New Zealand display this feature.