Changes in ocean water mass properties: oscillations or trends?

A new transindian hydrographic section across 32 degrees S reveals that thermocline mode waters have become saltier and colder since 1987. This change almost entirely reverses the observed freshening of mode waters from the 1960s to 1987 that has been interpreted to be the result of anthropogenic climate change on the basis of coupled climate models. Here, we compare five hydrographic sections from 1936, 1965, 1987, 1995, and 2002 to show that upper thermocline waters (10 degrees C to 17 degrees C) changed little from 1936 to 1965, freshened from 1965 to 1987, and since 1987 have become saltier. These results demonstrate substantial oscillations in mode-water properties.