Ocean subsurface salinity changes yield an anthropogenic climate change signal

Ocean salinity is a vital indicator of the global hydrological cycle and its spatial gradients are likely amplified by global warming as a result of intensification of the hydrologic cycle. Sea surface salinity suggests a hydrological cycle intensification of 5~8% per Kelvin of global surface warming, however, the atmospheric evidence suggests much smaller rate of 1~3%, constrained by surface energy budget. This mismatch might lie in part through the differences between the surface and total salinity. The solution lies in part through the differences between the surface and total salinity. Therefore, vertically-integrated ocean salinity changes should be more representative of persistent climate trends. Here we provide a new reconstruction of ocean subsurface (0-2000m) 3-Dimentional salinity back through the mid 20^th century (1960). The new reconstruction is based on a new method previously tested and exploited for temperatures (Cheng et al. 2017), and further rigorously tested and verified for salinity in our study. Based on the new reconstruction, we provide evidence that an anthropogenic signal (“human fingerprint”) in the ocean subsurface salinity has emerged from the background noise of natural variability. This fingerprint includes a robust pattern of intensification of mean salinity change for the upper 2000m since 1960. This pattern of intensified salinity changes is quantified by a new global metric, that will be shown in this presentation. CMIP5 models and some reanalysis products will also be used and validated. This presentation provides a new insight into the link between ocean subsurface salinity and water cycle.