NOAA/WDS Paleoclimatology - Global Ocean Neodymium Isotope Data during the Campanian-Maastrichtian

Models for changing patterns of ocean circulation during the last 10 million years of the Cretaceous (late Campanian–Maastrichtian) have suggested increased downwelling occurred in the Southern Ocean and/or the North Atlantic as well as alternating between northern and southern high-latitude Pacific source regions across the interval. Existing data do not allow simple confirmation or rejection of any of the proposed models, and this uncertainty compromises investigations of the relationship between ocean circulation and climate. Here we use neodymium isotopes (eNd) preserved in fossilized fish debris to examine changes in Pacific circulation by comparing trends from the late Campanian through the Maastrichtian to patterns during a well-documented early Maastrichtian cooling pulse (EMCP). Pacific eNd data have similar values in late Campanian and late Maastrichtian samples but show a small negative eNd excursion that closely correlates with the EMCP. These observations argue against export of southern component waters into the Pacific and, combined with new modeling results of subsurface water mass age, suggest the southwestern Pacific to have been the dominant source region for Pacific intermediate and deep waters throughout the late Campanian–Maastrichtian. We propose that changes in eNd values during the EMCP are related to an increased rate of overturning rather than a shift in the source of Pacific bottom waters.