Stable isotope data for Globigerina bulloides and Cibicidoides pachyderma, benthic foraminiferal census counts and relative abundance of the elevated epibenthos group at Site U1391
Description
Previous modeling has shown that Mediterranean Outflow Water (MOW) variability may affect the formation of North Atlantic Deep Water, which may stabilize or destabilize the thermohaline circulation, and hence trigger climate change. Therefore, understanding the MOW dynamics throughout the geological history is of great significance to decode past and predict future climate changes. Site U1391 (37°21.532’ N, 9°24.656’ W; 1085 m water depth) is situated in the northeastern Atlantic Ocean off the southwestern Iberian margin, and in the distal area of the lower Mediterranean Outflow Water (MOW) core. Foraminiferal stable oxygen and carbon isotopes and benthic foraminiferal records from the 415-m-long composite section at Site U1391 were analyzed to decipher the MOW variability over the last 1.3 myr. Planktonic and benthic foraminiferal oxygen isotope data (δ18O of Globigerina bulloides and Cibicidoides pachyderma) were used to establish the chronostratigraphic framework. This section encompasses the time interval from marine isotope stage (MIS) 1 to MIS 40 (0-1.3 Ma). C. pachyderma δ13C can be used as a tracer for reconstructing the ventilation of past deep-water masses. The benthic δ13C maxima often corresponded to precession maxima and the benthic δ13C minima to precession minima, revealing that the bottom water ventilation off the Portugal increased at precession maxima and decreased at precession minima. Elevated epifaunal species are directly related to the presence of the MOW and can be used as a proxy for MOW reconstruction during the Pleistocene. The variations in the relative abundance of the elevated epibenthos group suggested that the MOW intensity had ~100-kyr, ~41-kyr and ~20-kyr cycles during the last 1.3 myr. The precession forcing was the predominant driver of the~20-kyr cyclic variation in the MOW intensity. The ~41-kyr cyclic variation in the pre- and post-MPT MOW dynamics was strongly controlled by the Earth’s obliquity, and the variation during the MPT was controlled by precession. The variation in the abundance of the elevated epibenthos group was dominated by the ~41-kyr cycle prior to the MPT and had a significant ~100-kyr cycle after the MPT, which suggested there was a MPT-related shift in the MOW dynamics.