Changes in deep and intermediate water properties in the western North Atlantic during marine isotope stages 11–12: evidence from ODP Leg 172

Abstract

The interval of time represented by marine isotope stages 11 and 12 (∼360–470 ka) contains what may be the most extreme glacial and interglacial climate conditions of the Late Pleistocene. It has been suggested that sea level rose by ∼160 m at the termination of glacial stage 12. This is 30% greater than the sea level rise that followed the most recent glacial maximum. There have been few detailed studies of the unique conditions that existed during the stage 11–12 time period because of the lack of high-quality core material. This problem has been addressed by the collection of high deposition rate cores from sediment drifts in the western North Atlantic during Ocean Drilling Project Leg 172. Benthic foraminiferal δ 13C data from cores collected between ∼4600 and 1800 m were used to reconstruct bathymetric gradients in deep and intermediate water properties for selected time slices during this glacial–interglacial cycle. During glacial stage 12, the deep western North Atlantic was filled by a water mass that was more nutrient-enriched than modern Antarctic Bottom Water. Above 2000 m, a more nutrient-depleted water mass existed during this glacial stage. Such an intermediate water mass has been described for more recent glacial periods and presumably forms in a more proximate region of the North Atlantic. Interglacial stage 11 water mass properties closely resemble those of the present-day western North Atlantic. A nutrient-depleted water mass (δ 13C of 0.75–1.0‰), similar to modern North Atlantic Deep Water existed between 3500 and 2000 m. This was underlain by a water mass with lower δ 13C values (<0.75‰) that probably was derived from a southern source. Using Leg 172 data, along with previously published results from the Atlantic and Pacific oceans, we estimate a mean global δ 13C change of 0.95‰ from stage 12 to stage 11. This is twice the whole ocean δ 13C change reported for the transition from the last glacial maximum to the Holocene.