The shoaling of the Central American Seaway (CAS) around 4.6 Ma (million years ago) is thought to have enhanced the Gulf Stream, strengthening the Atlantic Meridional Overturning Circulation and potentially influencing the evolution of Pliocene climate. Paleoclimate records indicate a buildup of heat and salinity in the Caribbean and changes in the formation of North Atlantic Deep Water (NADW) associated with a major step in the shoaling of the CAS around 4.6 Ma. However, so far, direct evidences supporting an intensification of the Gulf Stream are scarce. Here we report new North Atlantic early Pliocene (5.3–3.9 Ma) records of sea surface temperatures (SSTs) reconstructed using the UK37’ and TEX86 paleotemperature indices. Based on new sediment trap measurements near the study site, we suggest that in this particular region, the two paleothermometers record SSTs during different seasons: spring for UK37’ and summer for TEX86. At 4.6 and 4.2 Ma, our results indicate a substantial increase in SST and salinity during summer but not spring, pointing to a significant intensification of the Gulf Stream and its extension, the North Atlantic Current, after the shoaling of the CAS. The divergence of the UK37’ and TEX86 temperature trends in those intervals suggests that the Gulf Stream intensification contributed to the strong North Atlantic seasonality that is observed today.