Defining the northern Nd isotope end member for the reconstruction of the Atlantic Meridional Overturning Circulation during the last glacial cycle

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It is assumed that the CO2 sequestered from the atmosphere during the last glacial cycle was stored away in the deep oceans for thousands of years, yet the water mass structure accommodating such increased carbon storage continues to be debated. Inconsistent results are largely a consequence of the limited data covering the entire glacial cycle. Especially scarce are deep water mass reconstructions for the past 100,000 years with the neodymium (Nd) isotope proxy. As part of the rare earth elements Nd is not affected by biological cycling making the Nd isotopic composition of seawater particularly valuable in helping to disentangle changes in carbon cycling from the deep ocean’s ventilation state. Based on the difference in the Nd isotopic signatures between Northern Sourced Water and Southern Sourced Water a number of studies reported significantly different water mass structures in the Atlantic Ocean in the past. However, recently processes have been identified, which, independent of the water mass provenance, that potentially alter the archived Nd isotope signatures (related to particle dissolution within benthic nepheloid layers) and hence may impede the interpretation as water mass tracer. This is may have significant impact on the paleoceanographic reconstructions, since in the past most studies interpreted Nd isotope records under the assumption of invariable end members. However, currently no Nd isotope record from the North Atlantic, representing the northern end member, exists that spans the entire glacial cycle. The here proposed study will take advantage of the well-established methodology and extensive knowledge about the Nd isotope proxy at Heidelberg University and aims to close this critical data gap by defining a northern Nd isotope end member over the past 100,000 years from a sediment core (IODP U1313) from the subpolar North Atlantic with sufficiently high sedimentation rate and located outside the influence of benthic nepheloid layers or volcanic material.