Atlantic Ocean Circulation during the Latest Cretaceous and Early Paleogene: Progressive Deep Water Exchange

Monday, 15 December 2014
Sietske Josefien Batenburg1, Silke Voigt1, Oliver Friedrich2 and Martin Frank3, (1)Goethe University Frankfurt, Institut für Geowissenschaften, Frankfurt, Germany, (2)University Heidelberg, Institut für Geowissenschaften, Heidelberg, Germany, (3)GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany
The Atlantic deep ocean circulation in the Latest Cretaceous (75-66 Ma) was dominated by regional processes, as indicated by the presence of distinct deep water masses. Due to the opening of the Atlantic Ocean, its different sub-basins became progressively connected and a global mode of ocean circulation commenced in the early Paleogene, ~60 Ma. To understand the evolution of deep water formation and exchange, Nd-isotope data and δ13C stratigraphies are generated for a range of sites in the North and South Atlantic. These permit to identify different intermediate and deep-water masses, to recognize their potential source regions and to determine the exact timing of deep water connection.

The carbonate-rich pelagic sediments of Site U1403 near Newfoundland can be astronomically tuned and correlated to the global δ13C framework.

Relatively negative seawater εNd(t) signatures in the 67-62 Ma interval at Site U1403 of ~-10 are distinct from those recorded further south in the North Atlantic. Possible explanations could include elevated non-radiogenic weathering inputs from the North American craton.

In the latest Maastrichtian, the Site U1403 εNd(t) record displays a short-term positive excursion before the K/Pg boundary (67-66 Ma) followed by a sudden drop to unradiogenic values at the boundary. Changes in ocean circulation might be related to climatic changes in the pre-extinction interval and the impact itself.

The εNd(t) records at Sites 1267 and 525 at Walvis Ridge show that an early Maastrichtian excursion to highly radiogenic values reflects a brief interval at 72-70 Ma, related to a period of increased hot-spot volcanism. Concomitant measurements of εNd(t) values in three different archives, fish teeth, ferromanganese coatings of bulk sediments and of foraminifera, provide a test for the partial influence of detrital particles on the isotopic composition of coatings.

The first data of Sites U1403, 1267 and 525 indicate the occurrence of a common deep-water neodymium isotope signature (εNd(t) -8) in the North and South Atlantic since 60 Ma. At this time, the sub-basins of the deep Atlantic became fully connected. A deep-water mass with a common εNd(t) signature, likely originating in the high southern latitudes, prevailed over a broad range of water depths, indicating vigorous deep ocean circulation.