Abstract
Sea surface salinity patterns have intensified between the mid-20th century and present day, with saline areas becoming saltier and fresher areas fresher. This change has been linked to a human-induced strengthening of the global hydrological cycle as global mean surface temperatures rose. Here we analyse salinity observations from the round-the-world voyages of HMS Challenger and SMS Gazelle in the 1870s, early in the industrial era, to reconstruct surface salinity changes since that decade. We find that the amplification of the salinity change pattern between the 1870s and the 1950s was at a rate that was 54 ± 10% lower than the post-1950s rate. The acceleration in salinity pattern amplification over almost 150 years implies that the hydrological cycle would have similarly accelerated over this period.
Highlights
Sea surface salinity patterns have intensified between the mid-20th century and present day, with saline areas becoming saltier and fresher areas fresher
We noted that the regional patterns of change between the 1950s and 2008 reported by[7] showed saline areas becoming more saline and the fresh areas fresher, an amplification believed to be indicative of strengthening of the global hydrological cycle since the mid-20th century and summarised in[7,8]
In order to reveal whether the patterns of change between the 1870s and the 1950s might have been similar to those since the 1950s we identified regional groups of Challenger and Gazelle stations, the positions of which lay in distinct areas of post-1950s freshening or salinification revealed by the EN4 5 m fields representing the salinity difference from the decadal averages, 1950 to 1959 and 2010 to 2019
Summary
Sea surface salinity patterns have intensified between the mid-20th century and present day, with saline areas becoming saltier and fresher areas fresher. This change has been linked to a human-induced strengthening of the global hydrological cycle as global mean surface temperatures rose. We analyse salinity observations from the round-the-world voyages of HMS Challenger and SMS Gazelle in the 1870s, early in the industrial era, to reconstruct surface salinity changes since that decade. We focus the analysis on three periods, the 1870s and the decades centred on 1954 and 2014 This allows comparisons with other analyses describing salinity change between the latter two periods[6,7,8,9]. We repeated the analysis using the newer Cheng et al.[9] data set, which relies on CMIP511 output
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