There is a converging body of evidence supporting a measurable slowdown of the Atlantic Meridional Overturning Circulation (AMOC) as climate warms and Northern Hemisphere ice sheets inexorably shrink. Within this context, we assess the variability of the AMOC during the Holocene based on a marine sediment core retrieved from the deep northwest Atlantic, which sensitively recorded large-scale deglacial transitions in deep water circulation. While there is a diffuse notion of Holocene variability in Labrador and Nordic Seas overturning, we report a largely invariable deep water circulation for the last 11,000 years, even during the meltwater pulse associated with the 8.2-ka event. Sensitivity tests along with high-resolution 231 Pa/ 230 Th data constrain the duration and the magnitude of possible Holocene AMOC variations. The generally constant baseline during the Holocene suggests attenuated natural variability of the large-scale AMOC on submillennial timescales and calls for compensating effects involving the upstream components of North Atlantic Deep Water.

Neodymium (Nd) isotopes extracted from authigenic sediment phases are increasingly used as a proxy for past variations in water mass provenance. To better constrain the controls of water mass provenance and nonconservative effects on the archived Nd isotope signal, we present a new depth transect of Nd isotope reconstructions from the Blake Bahama Outer

Radiogenic Pb and Nd isotopes are well established tools in palaeoceanographic science tracing ambient climate and continental runoff to the oceans down to sub-millennial timescales. Particularly in case of Pb isotopes, a clear climate dependency of continental isotopic runoff on glacial-interglacial transitions has been observed. Pb isotopes were reported to be released incongruently during initial chemical weathering. This incongruent release implies that Pb isotopic runoff compositions differ from the bulk catchment Pb isotopic signal. Yet only little is known about the processes leading to the incongruent release and the timescales of weathering on the continents. In this study we targeted the adsorbed trace metal signature in sediments from a Swiss high-Alpine lake that have accumulated since the retreat of the large Alpine ice domes during the last deglaciation to investigate initial Pb and Nd isotope weathering processes in a granitic environment. Additionally, selected adsorbed element concentrations and ratios were analysed to complement the isotopic physicochemical weathering information. The integrity of the presented isotope records is supported by further investigation into the lake environment (e.g. oxic/anoxic conditions) and its potential influence on the isotopic record. The Pb isotope records during the early lake phase witnessed high-amplitude isotopic fluctuations linked to the initial chemical weathering of fine glacial substrate. This finding is also supported by the lithology of the core and rapidly decreasing adsorbed Th and U concentrations. Following this early lake phase, the majority of the Holocene traced congruent release of 207 Pb/ 204 Pb and 206 Pb/ 204 Pb and a significant depletion of 208 Pb/ 204 Pb in the adsorbed phase. These findings corroborate earlier suggestions of more effective weathering of uranogenic minerals yet also call for the presence of more weathering-resistant thorogenic minerals in the lake catchment. The latest 2.2 ka of the record are significantly overprinted by anthropogenic Pb deposition coinciding with the rise and fall of the Roman Empire. Finally, our data suggest that Nd isotopes are equally affected by incongruent weathering during the initial deglacial weathering processes, albeit at smaller magnitude than seen for Pb isotopes.

Protactinium-231 is a radionuclide of broad interest in paleoceanography and paleoclimatology. This study describes an improved method for the purification and separation of Pa from marine sediment samples using the new TK400 resin by TrisKem International. The focus lies on the improvement of the separation of the abundant Th from the Pa fraction of the sample, which would reduce the peak tailing fromTh on masses 231 and 233 during ICP-MS measurement. Furthermore, the reusability of TK400 has been tested. For this purpose, the conventional method using Dowex AG1X8 for the separation and purification of Pa has been compared to methods using the TK400 resin. A combination of a Dowex AG1X8 prior to a TK400 column has shown most convincing results. Based on our results we suggest a new efficient procedural method of analyzing Pa from marine sediment samples using TK400. Chemical Pa yields for a Dowex-TK400 combination are highest compared to the Dowex only method. Furthermore, theTh/Pa ratio of the Pa-fractions has been reduced by 1 order of magnitude compared to conventional methods with Dowex AG1X8. Additionally, the reusability of TK400 resin up to nine times has been proven. The usage of TK400 is only limited in the presence of samples with a high matrix load (e.g., Fe). Therefore, matrix from sediment samples needs to be removed (here using Dowex resin) before samples are loaded onto TK400. We also report a series of concentration measurements from standard reference materials (UREM-11, NIST 2702), which have been used for Pa calibration.