Identifying Climate Modes Contributing to Sea Surface Salinity Decadal Variation in the North Pacific Ocean

The North Pacific sea surface salinity (SSS) decadal variation (NPSDV) plays key roles in tracing ocean circulation and hydrological cycle, and its contributing climate modes need to be identified. Three data sets, ORAS4, EN4.2.1, and GODAS, were first evaluated. An autoregressive lag 1 (AR-1) process model, along with spectrum and correlation analysis, was then applied to the most robust SSS data set during 1980-2017. The AR-1 reconstructed SSS anomalies explain up to 77% and 55% of the first two modes, respectively. As expected, the NPSDV arises from the superposition of SSS variations with different dynamical origins, including the reemergence, Eastern Pacific and Central Pacific El Nino-Southern Oscillation (ENSO) (EP-ENSO and CP-ENSO), Aleutian Low (AL), North Pacific Oscillation (NPO), and Kuroshio and Oyashio Extension (KOE) meridional and zonal modes (KOE-M and KOE-Z). Its first mode is 50% EP-ENSO and 32% CP-ENSO, while the second mode is 58% NPO and 54% CP-ENSO. Specifically, stronger persistence in salinity explains most of NPSDV variance. The first mode resembles the EP-ENSO pattern with a positive loading center in the eastern North Pacific, and the second mode resembles the CP-ENSO (and also NPO) pattern with a positive loading center near the dateline, alike the contrasting EP-ENSO and CP-ENSO SSS flavors in the tropics. Besides, a fraction of the first mode notable in the KOE region is controlled by KOE-Z and KOE-M as intrinsic oceanic dynamics. The importance of AL to NPSDV, after removing the indirect impact of ENSO, is insignificant. A general NPSDV evolution was lastly revealed. Plain Language Summary Sea surface salinity decadal variation in the North Pacific Ocean is part of the global ocean-atmosphere climate system which influences the weather over Eurasia and North America. To investigate its cause is important but also complicated because it arises from the superposition of variations related to different climate phenomena, such as the well-known El Nino-Southern Oscillation (ENSO) among others. We managed to identify these climate phenomena and quantify their contribution to the North Pacific salinity variation by performing some effective methods. We also evaluated the robustness of salinity measurements, which are scarce over past decades, and differentiated the role of salinity versus temperature in decadal climate. Key Points The contribution of major climate modes to the North Pacific sea surface salinity decadal variation is quantified The damping of salinity versus temperature is characterized, and the robustness of salinity data sets used for decadal analysis is tested