| Deep-water circulation was reconstructed for the late Neogene by comparing carbon isotopic records of benthic formainifera from the North Atlantic (NA), Southern Ocean (SO), and deep Pacific basins. The history of NA intermediate water was studied using delta13C at Ocean Drilling Program (ODP) site 982. Production of Glacial North Atlantic Intermediate Water (GNAIW) was enhanced during glacial periods of the late Pleistocene whereas production of lower North Atlantic Deep Water (NADW) was much reduced. During terminations, production of GNAIW ceased briefly until upper-NADW production resumed under full interglacial conditions. The magnitude of benthic delta13C minima, ice-rafted debris maxima at site 982, and glacial suppression of NADW may be related to the spatial and seasonal extent of sea ice in the Nordic Seas.; The history of deep-water circulation in the Atlantic sector of the SO was examined using a delta13C record from ODP site 1090 in the South Atlantic (SA). At 1.55 Ma, glacial delta13C values in the SA sector of the SO became significantly lower than those in the deep Pacific, establishing a pattern that persisted throughout the late Pleistocene. Lower delta13C values in the SO may have resulted from expansion of sea ice and reduced ventilation of deep-water during glacial periods. Accompanying this change in SO deep-water circulation was enhanced interhemispheric coupling between the NA and SA. Calculation of %NADW using site 1090 indicates glacial reduction of NADW was less than suggested previously.; Carbon isotopic records from sites 982, 1090, and 849 (deep Pacific) were used to estimate inter-ocean delta13C gradients for the last 9 myr. Through the late Neogene, benthic delta13C (and inferred deep-water ventilation) of SO deep-water has decreased as sea ice cover and stratification of Antarctic surface waters increased. This reduced upwelling of deep-water to the surface, limited equilibration of surface water with the atmosphere, and altered deep-water formation. Changes in deep-water ventilation occurred in steps at 6.6, 2.7, and 1.5 Ma that likely represented threshold events resulting from gradual cooling of Antarctic surface waters. Each decrease in ventilation acted as positive feedback to ongoing climate cooling by increasing deep-ocean CO2 content and lowering atmospheric pCO2. |
