| Summary: | 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 salt 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 at 4.6 Ma. However, so far, direct evidence supporting an intensification of the Gulf Stream is scarce. Here we report new North Atlantic early Pliocene (5.3–3.9 Ma) records of sea surface temperature (SST) reconstructed using the U' 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 SST during different seasons: spring for U' and summer for TEX86. At 4.6 and 4.2 Ma, our results indicate substantial increases 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 U' and TEX86 temperature trends in those intervals suggests that the Gulf Stream intensification contributed to the strong North Atlantic seasonality that is observed today.
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