Resumen del producto

Stable oxygen isotopes of Globigerinoides ruber s.l. and Globigerina bulloides have been widely used to infer thevariability of the water column hydrographic structure over various time scales. However, the reliability of thisgeochemical tool requires a regional analysis since the inferred calcification depth and temperature of planktonicforaminifera depend on local environmental conditions. In the present study, d18O values of G. ruber s.l andG. bulloides collected from 21 surface sediment samples were used to infer their calcification depth in thesouthwestern margin of the Baja California peninsula. The d18O values of G. ruber s.l. represented oceanographicconditions from warm tropical water masses (summer-autumn), while G. bulloides represented upwelling conditionsand cold-water masses (winter-spring). Estimated calcification depths ranged from 0 to 30 m for bothspecies. The isotopic difference between them (1.2‰ in this study and 1.1‰ in the Guaymas basin sediment trap)suggests a sea temperature difference of ~5 ?C, which is very similar to the difference inferred from the Mg/Caratio for both species 3 to 14 ka. This suggests that G. ruber s.l. and G. bulloides have calcified over the same depthinterval but under contrasting seasonal oceanographic conditions i.e. upwelling (winter-spring) and stratificationof the water column (summer-autumn).

Palabras clave: Planktonic foraminifera; Upwelling; stable oxygen isotopes; Northeast Pacific; transitional zone

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