Changes in the characteristics of 26.00 Sigma-t water off Port Hacking (1943-1968)

Abstract

Bottom waters at a 50 m station off Port Hacking (34º05'S., 151°13'E.) with a sigma-t of 26.00, have in general increased in salinity, decreased in oxygen, and increased in phosphate and nitrate in the 25 year period 1943-1967.

In seeking an explanation of this trend, changes in upper 25 m column water temperatures, slope water characteristics and surface temperatures, and salinity characteristics off east Australia during this same period have been discovered. The year 1943 at the beginning of this 25-year trend had an exceptionally cold and dry winter. Cause and effect relationships are difficult to prove but an explanation based upon transport variations of the East Australian Current, with minimum transport in the early 1940's and maximum in the late 1950's, is favoured.