The climate-related diachronous disappearance of Pulleniatina obliquiloculata in late quaternary sediments of the Atlantic and Caribbean

Abstract

The planktonic foraminifera Pulleniatina obliquiloculata (Parker and Jones) undergoes several climatically controlled disappearances and reappearances in the equatorial Atlantic and Caribbean sediments during Late Quaternary time. One such disappearance occurs near the middle of the last glacial (Middle Wisconsin, middle Y zone, O 16 stage 3). The age of this disappearances is time transgressive from approximately 60, 000 yr in the Gulf of Mexico, to 50, 000 yr in the western Caribbean, to 35, 000 yr in the equatorial Atlantic. The time-transgressive transgressive nature of P. obliquiloculata's disappearance from the Atlantic is thought to represent the decreasing “width” of P. obliquiloculata's adaptive zone as surface water salinities progressively increased during the glacial intervals due to expanding continental glaciers. A simple ecologic model predicts that P. obliquiloculata should disappear first from areas of high salinity and is consistent with observations that both modern sea-surface salinity and the age of the P. obliquiloculata biohorizon increase from the equatorial Atlantic to the Gulf of Mexico. The biohorizon, Y P. obliq , is a subdivision of Ericson's Y zone and occurs throughout the western equatorial Atlantic as well as throughout most of the Caribbean and Gulf of Mexico. Here, the horizon is useful for correlating and determining accumulation rates in continental margin sediments where rapid deposition often prevents piston cores from penetrating through the last glacial interval. Along the coast of Africa, in areas of coastal upwelling and the equatorward transport of cold water, the biohorizon does not occur.