CLIMATE AND OCEAN CIRCULATION PATTERNS DURING AND AFTER THE EARLY MAASTRICHIAN COOLING EVENT

An early Maastrichtian increase in benthic oxygen isotope values (δ¹⁸O) in the equatorial Pacific and South Atlantic Oceans indicates a brief (~1-2 million year) cooling event at c. 71.5 Ma. Here, we use neodymium isotopes (ε_Nd) from fish debris (microfossil tooth, scale, and bone fragments) to make inferences about intermediate and deep water formation and circulation patterns across the early Maastrichtian cooling event. Correlated shifts in ε_Nd values at widely spaced sites could indicate a change in the location of bottom water formation, whereas the absence of an ε_Nd shift could indicate cooling in the region of downwelling without requiring a change in circulation patterns. Cooling in many regions appears to correlate with changes in ε_Nd values that are consistent with an increase in Southern Component Water (SCW). Anomalously high ε_Nd values are reported during the early Maastrichtian cooling event at a site 525 on Walvis Ridge, but this excursion does not fit the SCW model. For Site 525, the early Maastrichtian shift was attributed to local volcanism with the correlation to widespread δ¹⁸O and δ¹³C excursions apparently coincidental.

At Site 525 we confirm anomalously high ε_Nd values during the early Maastrichtian cooling event, but also observe a 2-3 ε_Nd unit decrease 30 m above the cooling event. Further, even late Maastrichtian values at Site 525 remain ~2 ε_Nd units above expected SCW values, but typical SCW values are found in late Maastrichtian samples in deeper sites from the northern flank of Walvis Ridge. To test whether the ε_Nd value anomalies recorded on the top of Walvis Ridge are local and to search for a record of Southern Component Water along the bathymetric barrier between the Southern Ocean and the South Atlantic, we are analyzing samples from Site 516 (Rio Grande Rise) as well as increasing sampling density at Site 525, and Site 463 (mid-Pacific Mountains, equatorial Pacific Ocean). In addition we are analyzing spot samples from the North Atlantic Ocean, South Atlantic Ocean, and Caribbean Sea.