Comparing 60-year, 30-year, and 10-year trends in global ocean salinity - does water cycle intensification dominate the signal?

Multiple studies have shown that long-term salinity trends are indicative of an amplification of the global hydrological cycle, with salty regions of the ocean becoming saltier, and fresh regions of the ocean becoming fresher. However, are these long-term salinity trends consistent over the entire period, or are they dominated by medium and short-term salinity variability? In this study we present salinity trends for 60-year (1951-2014), 30-year (1955-1984, 1985-2014), and 10-year (2005-2014) time periods. The 60-year and 30-year trends are computed from pentadal (5-year average) salinity anomaly fields and the 10-year trends are computed from monthly salinity anomaly fields which are all derived from in situ data within the World Ocean Database (WOD). First, the zonal average, depth-varying trends for each major ocean basin and time period are analyzed and compared. Next, the 0-10 meter salinity trends are analyzed and compared. The results of this study indicate that in many regions, the long-term trends are not consistent through the entire 60-year period and are dominated by medium-term (30-year) trends. In some regions, most notably the North Atlantic, strong trends during the first 30 years were completely reversed during the latter 30 years. In other regions, such as the western (sub) tropical Pacific, freshening trends during the first 30 years were greater than the freshening trends seen over the last 30 years. The inconsistency of these trends and their possible implications are discussed. Additional results show that short-term trends over the past decade are dominated by natural climate variability (e.g., ENSO, PDO, IOD, etc.) and only a small percentage of the short-term salinity trends over the global ocean are directly related to trends in evaporation and precipitation.