ND ISOTOPIC EVIDENCE FOR NORTHERN COMPONENT WATER FORMATION IN THE NORTH ATLANTIC AT THE END OF THE CRETACEOUS GREENHOUSE CLIMATE

A shift in ε_Nd(t) values from -16 to -11 measured in fish debris collected from four sites in the western tropical Atlantic provides the most direct evidence yet for a change during the Maastrichtian in North Atlantic circulation at intermediate water depths. The Maastrichtian Age (70.6 – 65.5 Ma) was a time of general cooling during the transition into a relatively temperate interval sandwiched between the hot greenhouse climates of the Late Cretaceous and early Eocene. Discussion of the causes of paleontological and paleoclimatic evolution within the Maastrichtian has long focused on intermediate and deep water circulation, but the timing and pattern of circulation changes remain controversial. We interpret the ε_Nd shift as evidence that a warm, saline water mass sourced in the tropical Atlantic was replaced by a cooler water mass sourced in the North Atlantic. The ε_Nd shift begins before 69 Ma at the deepest site studied (ODP Site 1258) but not until ~66 Ma at the shallowest site (ODP Site 1260). The shift is associated with regional (North Atlantic) warming during a time of cooling elsewhere at the end of the Cretaceous greenhouse. The inferred changes in circulation match predictions of a proposed heat piracy model for explaining anomalous North Atlantic warming during the Maastrichtian. It also suggests the Late Cretaceous hot greenhouse ocean had a different circulation pattern than did the ocean during relatively temperate late Maastrichtian and Paleocene times.