Neogene evolution of Atlantic thermohaline circulation: Perspective from Walvis Ridge, southeastern Atlantic Ocean

We present new Nd isotope records from Walvis Ridge Ocean Drilling Program ( ODP) sites 1262-1264 ( southeastern Atlantic) spanning the past 24 Ma to investigate the Neogene evolution of Atlantic thermohaline circulation. The new data indicate that deepwater epsilon(Nd)( t) values from ODP Site 1262 decrease from -11.0 at 10.6 Ma to -12.5 by 7.3 Ma. This decrease parallels the Nd isotope trends contained in Fe-Mn crust records from the northwestern Atlantic; however, the shift at ODP Site 1262 ( 4755 m water depth) occurred up to similar to 6 Ma earlier than the corresponding changes in crust records from the Atlantic and earlier than any Atlantic site shallower than 2700 m paleowater depth. Recent interpretations of the rapid decrease in Fe-Mn crust Nd epsilon(Nd)( t) ssvalues invoke changes in weathering inputs to the Labrador Sea region rather than a fundamental change in deepwater convection in the Labrador Sea. However, the new evidence for significant depth stratification of the Nd isotope signal in the southeastern Atlantic between 10.6 and 7.3 Ma suggests that the onset of deepwater convection in the Labrador Sea may have played a role in the deepwater decrease in Nd isotopic composition. Climatic conditions during the middle to late Miocene likely favored an increase in the importance of glacially induced mechanical weathering, while at the same time promoting deep convection in the Labrador Sea.