The δ18O values of planktonic foraminifera increased in the Caribbean by about 0.5% relative to the equatorial East Pacific values between 4.6 and 4.2 Ma as a consequence of the closure of the Central American Gateway (CAG). This increase in δ18O can be interpreted either as an increase in Caribbean sea surface (mixed layer) salinity (SSS) or as a decrease in sea surface temperatures (SST). This problem represents an ideal situation to apply the recently developed paleotemperature proxy δ44/40Ca together with Mg/Ca and δ18O on the planktic foraminifer Globigerinoides sacculifer from ODP Site 999. Although differences in absolute temperature calibration of δ44/40Ca and Mg/Ca exist, the general pattern is similar indicating a SST decrease of about 2-3 °C between 4.4 and 4.3 Ma followed by an increase in the same order of magnitude between 4.3 and 4.0 Ma. Correcting the δ18O record for this temperature change and assuming that changes in global ice volume are negligible, the salinity-induced planktonic δ18O signal decreased by about 0.4% between 4.4 and 4.3 Ma and increased by about 0.9% between 4.3 and 4.0 Ma in the Caribbean. The observed temperature and salinity trends are interpreted to reflect the restricted exchange of surface water between the Caribbean and the Pacific in response to the shoaling of the Panamanian Seaway, possibly accompanied by a southward shift of the Intertropical Convergence Zone (ITCZ) between 4.4 and 4.3 Ma. Differences in Mg/Ca- and δ44/40Ca Ca-derived temperatures can be reconciled by corrections for secular variations of the marine Mg/Ca sw and δ44/40Ca, a salinity effect on the Mg/Ca ratio and a constant temperature offset of ∼2.5 °C between both SST proxy calibrations. © 2004 Elsevier B.V. All rights reserved.