Reconstruction of Caribbean sea surface temperature and salinity fluctuations in response to the pliocene closure of the Central American Gateway and radiative forcing, using δ44/40Ca, δ18O and Mg/Ca ratios

The delta(18)O values of planktonic foraminifera increased in the Caribbean by about 0.5parts per thousand 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 delta(18)O 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 delta(44/40)Ca together with Mg/Ca and delta(18)O on the planktic foraminifer Globigerinoides sacculifer from ODP Site 999. Although differences in absolute temperature calibration of delta(44/40)Ca and Mg/Ca exist, the general pattern is similar indicating a SST decrease of about 2-3 degreesC 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 delta(18)O record for this temperature change and assuming that changes in global ice volume are negligible, the salinity-induced planktonic delta(18)O signal decreased by about 0.4parts per thousand between 4.4 and 4.3 Ma and increased by about 0.9parts per thousand 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 delta(44/40)Ca-derived temperatures can be reconciled by corrections for secular variations of the marine Mg/Ca-sw and delta(44/40)Ca, a salinity effect on the Mg/Ca ratio and a constant temperature offset of similar to2.5 degreesC between both SST proxy calibrations. (C) 2004 Elsevier B.V. All rights reserved.,