Tungsten isotopes are the ideal tracers of core-mantle chemical interaction. Given that W is moderately siderophile, it preferentially partitioned into the Earth's core during its segregation, leaving the mantle depleted in this element. In contrast, Hf is lithophile, and its short-lived radioactive isotope 182 Hf decayed entirely to 182 W in the mantle after metal-silicate segregation. Therefore, the 182 W isotopic composition of the Earth's mantle and its core are expected to differ by about 200 ppm. Here, we report new high precision W isotope data for mantle-derived rock samples from the Paleoarchean Pilbara Craton, and the Réunion Island and the Kerguelen Archipelago hotspots. Together with other available data, they reveal a temporal shift in the 182 W isotopic composition of the mantle that is best explained by core-mantle chemical interaction. Core-mantle exchange might be facilitated by diffusive isotope exchange at the core-mantle boundary, or the exsolution of W-rich, Si-Mg-Fe oxides from the core into the mantle. Tungsten-182 isotope compositions of mantle-derived magmas are similar from 4.3 to 2.7 Ga and decrease afterwards. This change could be related to the onset of the crystallisation of the inner core or to the initiation of post-Archean deep slab subduction that more efficiently mixed the mantle.

No abstract

<p><strong>The Atlantic Meridional Overturning Circulation (AMOC) and the production rate of the North Atlantic Deep Water (NADW) are major components of the North Atlantic climate-system, with important hemispheric climatic influences. The post-glacial history of the AMOC, as reconstructed from Nd-isotopes (ε</strong><strong>Nd) in biogenic minerals and sediments</strong><strong>, demonstrates its sensitivity to freshwater fluxes, </strong><strong>leading to concerns about its near-future response to the ongoing accelerated Greenland/Arctic ice melting</strong><strong>. Whereas the early Holocene inception of the deep NADW components originating from the Nordic Seas has been well documented from such ε</strong><strong>Nd-data, information on the status of its western, shallower and most sensitive component, the Labrador Sea Water (LSW), is still missing. New ε</strong><strong>Nd-measurements in corals from the Labrador Slope provide the means to fill this gap. These data demonstrate that convection in the Labrador Sea was fully implemented by ca. 4 ka BP only, i.e., well after the final demise of the Laurentide ice-sheet. The time- and space-transgressive pattern of the full AMOC inception implies more complex driving mechanisms than meltwater fluxes only. </strong><strong>Whereas the late Holocene neo-glacial cooling trend could have played here a minor role, the penetration and strengthening of the Irminger Current into the Labrador Sea has likely been the driving force. </strong></p>

No abstract

No abstract