Description: The intensity of North Atlantic Deep Water (NADW) production has been one of the most important parameters controlling the global thermohaline ocean circulation system and climate. Here we present a new approach to reconstruct the overall strength of NADW export from the North Atlantic to the Southern Ocean over the past 14 Myr applying the deep water Nd and Pb isotope composition as recorded by ferromanganese crusts and nodules. We present the first long-term Nd and Pb isotope time series for deep Southern Ocean water masses, which are compared with previously published time series for NADW from the NW Atlantic Ocean. These data suggest a continuous and strong export of NADW, or a precursor of it, into the Southern Ocean between 14 and 3 Ma. An increasing difference in Nd and Pb isotope compositions between the NW Atlantic and the Southern Ocean over the past 3 Myr gives evidence for a progressive overall reduction of NADW export since the onset of Northern Hemisphere glaciation (NHG). The Nd isotope data allow us to assess at least semiquantitatively that the amount of this reduction has been in the range between 14 and 37% depending on location.

Description: Two Nd and Pb isotope time series of hydrogenous ferromanganese crusts, one from the Tehuantepec Ridge in the deep eastern equatorial Pacific and the other from Blake Plateau in the shallow northwestern Atlantic, which cover the past 7–8 m.y., show no variations coincident with the final closure of the Panama gateway, estimated as ca. 3.5 Ma. The record of the Atlantic crust located in the present-day Gulf Stream shows a shift in isotope composition from ca. 8 to 5 Ma that is explained by a diminishing supply of Pacific water. It is argued that the major restriction of water-mass exchange through the Panama gateway occurred before 5 Ma and thus cannot serve as a direct cause of the onset of Northern Hemisphere glaciation. The absence of a significant signature in the isotope records from the Pacific crust suggests that the volume of water exchanged with the Atlantic through shallow archipelagic straits of the gateway during the 3–4 m.y. prior to closure was too small to influence the radiogenic isotope composition of Pacific deep water.

Description: New time series of Nd and Pb isotopes were generated from two hydrogenous ferromanganese crusts from the eastern Indian Ocean, which were dated by 10Be / 9Be profiles and Co chronometry. The goal was to gain information on the nature and timing of variations of the deep water radiogenic isotope composition as a function of the evolution of the Indonesian Island Arcs since the Early Miocene, changes in ocean circulation related to the different stages of the closing of the Indonesian seaway for deep and intermediate water mass exchange since the Mid-Miocene, and enhanced Himalayan weathering since the Late Oligocene. A crust from 4119 m water depth in the Wharton Basin adjacent to Sumatra and the Java Trench (DODO 232D) has recorded a small variability in Nd isotope, but pronounced variations in Pb isotope composition over the past 17 Myr. Patterns and absolute values of the Nd and Pb isotope time series closely resemble the record of previously published crust SS663 from the central Indian Ocean, located some 2500 km SW of crust DODO 232D in the northern central Indian Ocean. In accordance with the interpretation derived from crust SS663, the Pb isotope composition of deep water in the Wharton Basin has apparently been mainly controlled by products of Himalayan erosion and weathering and to a lesser extent by the evolution of the Indonesian Island Arcs. The location of a second crust (VA16 13KD-1) from 2100 m water depth on the Scott Plateau off NW Australia is beneath the present day outflow of Pacific-derived surface and thermocline water masses into the eastern Indian Ocean. The pattern of the Pb isotope time series of this crust and the observed changes in Pb isotope mixing relationships, which occurred at ∼ 11.5 and ∼ 3.5 Ma, reflect the combined influence of advection and mixing of water masses through the Indonesian Seaway and weathering of volcanic source rocks within the emerging Indonesian Island Arcs over the past 33 Myr. The Nd isotope time series shows a pattern similar to central and southwest Pacific crusts and is best explained by a mixture between Nd from water masses advected from the Indian and Southern Ocean and Nd released by weathering from the emerging Indonesian Island Arcs.

Description: Ferromanganese crusts from the Atlantic, Indian and Pacific Oceans record the Nd and Pb isotope compositions of the water masses from which they form as hydrogenous precipitates. The10Be/9Be-calibrated time series for crusts are compared to estimates based on Co-contents, from which the equatorial Pacific crusts studied are inferred to have recorded ca. 60 Ma of Pacific deep water history. Time series of ɛNd show that the oceans have maintained a strong provinciality in Nd isotopic composition, determined by terrigenous inputs, over periods of up to 60 Ma. Superimposed on the distinct basin-specific signatures are variations in Nd and Pb isotope time series which have been particularly marked over the last 5 Ma. It is shown that changes in erosional inputs, particularly associated with Himalayan uplift and the northern hemisphere glaciation have influenced Indian and Atlantic Ocean deep water isotopic compositions respectively. There is no evidence so far for an imprint of the final closure of the Panama Isthmus on the Pb and Nd isotopic composition in either Atlantic or Pacific deep water masses.