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Small isotopic differences in the atomic abundance of neodymium-142 (142Nd) in silicate rocks represent the time-averaged effect of decay of formerly live samarium-146 (146Sm) and provide constraints on the timescales and mechanisms by which planetary mantles first differentiated. This chronology, however, assumes that the composition of the total planet is identical to that of primitive undifferentiated meteorites called chondrites. The difference in the 142Nd/144Nd ratio between chondrites and terrestrial samples may therefore indicate very early isolation (<30 Myr from the formation of the Solar System) of the upper mantle or a slightly non-chondritic bulk Earth composition. Here we present high-precision 142Nd data for 16 martian meteorites and show that Mars also has a non-chondritic composition. Meteorites belonging to the shergottite subgroup define a planetary isochron yielding an age of differentiation of 40 ± 18 Myr for the martian mantle. This isochron does not pass through the chondritic reference value (100 × ε142Nd = -21 ± 3; 147Sm/144Nd = 0.1966). The Earth, Moon and Mars all seem to have accreted in a portion of the inner Solar System with ∼5 per cent higher Sm/Nd ratios than material accreted in the asteroid belt. Such chemical heterogeneities may have arisen from sorting of nebular solids or from impact erosion of crustal reservoirs in planetary precursors. The 143Nd composition of the primitive mantle so defined by 142Nd is strikingly similar to the putative endmember component ‘FOZO’ characterized by high 3He/4He ratios. [ABSTRACT FROM AUTHOR]

The deep-ocean circulation is responsible for a significant component of global heat transport. In the present mode of circulation, deep waters form in the North Atlantic and Southern oceans where surface water becomes sufficiently cold and dense to sink. Polar temperatures during the warmest climatic interval of the Cenozoic era (~ 65 to 40 million years (Myr) ago) were significantly warmer than today, and this may have been a consequence of enhanced oceanic heat transport. However, understanding the relationship between deep-ocean circulation and ancient climate is complicated by differences in oceanic gateways, which affect where deep waters form and how they circulate. Here I report records of neodymium isotopes from two cores in the Pacific Ocean that indicate a shift in deep-water production from the Southern Ocean to the North Pacific ~65 Myr ago. The source of deep waters reverted back to the Southern Ocean 40 Myr ago. The relative timing of changes in the neodymium and oxygen isotope records indicates that changes in Cenozoic deep-water circulation patterns were the consequence, not the cause, of extreme Cenozoic warmth. [ABSTRACT FROM AUTHOR]

Reports on the reduced North Atlantic Deep Water flux to the glacial Southern Ocean. How the global circulation of the oceans and the atmosphere transports heat around the Earth; Data for past circulation taken from sediment cores in the South Atlantic Ocean that has yielded conflicting interpretations of ocean circulation in glacial times; Neodymium isotope ratios from the dispersed Fe-Mn oxide component of two southeast Atlantic sediment cores; Increase in biological productivity.

Presents measurements of the neodymium and strontium isotope compositions of a suite of abyssal peridotite clinopyroxenes. Relationship of abyssal peridotite clinopyroxenes and mid-ocean-ridge basalts; Leaching profiles for samples selected; Apparent link between isotopic composition and degrees of partial melting in some basalts.

Compares published hafnium (Hf)-neodymium (Nd) isotope data on supracrustals from Isua, Greenland, with similar data on lunar rocks and the SNC (martian) meteorites. Evidence that the geochemical signature of the Archaean mantle was partly inherited from the initial differentiation of the Earth; Remnants from an early layering in the modern deep mantle.