Variations of the tropical Atlantic and Pacific SSS minimum zones and their relations to the ITCZ and SPCZ rain bands (1979-2009)

Abstract

This study focuses on the time‐space variability of the low Sea Surface Salinity (SSS) waters extending zonally within 2°N–12°N in the Atlantic and Pacific and within 6°S–16°S in the western third of the Pacific. The analysis is based on a combination of in situ SSS observations collected in the last three decades from voluntary observing ships, TAO/TRITON and PIRATA moorings, Argo floats, and (few) CTD profiles. The mean latitudes of the Atlantic and Pacific low SSS waters appear 1°–3° further poleward than the Evaporation minus Precipitation (E‐P) minima linked to the Inter Tropical Convergence Zones (ITCZ) and South Pacific Convergence Zone (SPCZ). At the seasonal time scale, the E‐P minima migrate poleward in summer hemispheres, leading the migration of the SSS minima by 2–3 months in the Atlantic ITCZ, Pacific SPCZ, and in the eastern part of the Pacific ITCZ. On the other hand, the seasonal displacements of E‐P and SSS minima are in antiphase in the central and western parts of the Pacific ITCZ. At the interannual time scale, the E‐P and SSS minima migrate poleward during La Nina events in the Pacific and during the positive phase of the Atlantic Meridional Dipole (AMD) in the Atlantic (and vice versa during El Nino and the negative phase of the AMD). We further document long‐term (1979–2009) meridional migrations of the E‐P and SSS minima, especially in the SPCZ region, and discuss whether or not they are consistent with documented SST and wind stress trends.

Delayed and Quasi‐Synchronous Response of Tropical Atlantic Surface Salinity to Rainfall

“…Journal of Geophysical Research: Oceans due to the Ekman advection (e.g., Tchilibou et al, 2015;Yu, 2015). Spatial patterns of the temporal regression of anomalous SSS with principal components of the two leading PmE modes (Figure 1c) are consistent for the two profile analyses (Figures 5a, 5e and 5b, 5f).…”

“…In contrast to the Amazon plume SSS, the open ocean SSS variability is resolved well by either of profile analyses (Figure ). Its patterns describe deviations from the time mean SSS, which has a well‐known local minimum in the ITCZ latitude band but is slightly displaced northward with respect to the PmE maximum latitude due to the Ekman advection (e.g., Tchilibou et al, ; Yu, ). Spatial patterns of the temporal regression of anomalous SSS with principal components of the two leading PmE modes (Figure c) are consistent for the two profile analyses (Figures a, e and b, f).…”

The contrast between Atlantic and Pacific surface water fluxes

“…The subtropical gyres occupy regions of high SSS and e − p with the highest open ocean SSS found in the North Atlantic subtropical gyre (D'Addezio and Bingham, 2014). Salinity minima are found slightly to the north of the ITCZ (e − p minima) in both the Atlantic and Pacific due to northwards Ekman transport of salt (Tchilibou et al, 2015). The salinity minimum caused by the South Pacific Convergence Zone (SPCZ) is also offset from the e − p minimum due to Ekman transport.…”

SPCZ zonal events and downstream influence on surface ocean conditions in the Indonesian Throughflow region

“…Easterly Pacific trade winds play an important role in driving the main westward flowing upper ocean currents that bifurcate into the western boundary currents upon approaching the far western Pacific [ Hu et al , ]. In the South Pacific, a key atmospheric feature that is related to trade wind strength and location is the position of the SPCZ [ Kiladis et al , ; Vincent et al , ; Cai et al , ; Tchilibou et al , ]. The SPCZ is a persistent rainfall band extending southeast from the WPWP, where it is merged with the ITCZ, into the subtropical South Pacific.…”