Stable carbon and oxygen isotope ratios of foraminifera from DSDP Site 94-606

Stable-isotope analysis of two species of benthic foraminifers (Planulina wuellerstorfi and Globocassidulina subglobosa) and one planktonic species (Globigerina bulloides) from DSDP Site 606 reveals the evolution of late Pliocene climate change. No 'stepwise' increase is evident in the delta18O record at 3.2 Ma, but events of 18O-enrichment of increasing magnitude occurred at 3.1, 2.7, 2.6, and 2.4 Ma. The two youngest events are correlated with events indicating glaciation at northeast Atlantic DSDP Hole 552A (Shackleton et al., 1984, doi:10.1038/307620a0). The oldest delta18O spike, centered within the Mammoth Paleomagnetic Event, is the most prominent feature of results for the interval between 3 and 4 Ma. This isotope event is interpreted as evidence of 2°C bottom-water cooling combined with minor glaciation.Carbon-isotope results for P. wuellerstorfi indicate that Site 606 has been under the influence of North Atlantic Deep Water for most of the interval from 2 to 4 Ma. A significant change in 'vital effect' on G. subglobosa at 2.4 Ma is evident in the delta13C record. Specimens dating from that time become smaller and less abundant than older specimens, and have delta13C values lowered by as much as lâ. This effect could introduce a significant artifact into data sets where various species are 'corrected' to P. wuellerstorfi.