A modeling sensitivity study of the influence of the Atlantic meridional overturning circulation on neodymium isotopic composition at the Last Glacial Maximum

摘要

Using a simple parameterisation that resolves the first order global Ndisotopic composition (hereafter expressed as ε_Nd in anOcean Global Circulation Model, we have tested the impact of differentcirculation scenarios on the ε_Nd in the Atlantic for theLast Glacial Maximum (LGM), relative to a modern control run. Threedifferent LGM freshwater forcing experiments are performed to test forvariability in the ε_Nd oceanic distribution as a functionof ocean circulation. Highly distinct representations of the oceancirculation are generated in the three simulations, which drive significantdifferences in ε_Nd, particularly in deep waters of thewestern part of the basin. However, at the LGM, the Atlantic is moreradiogenic than in the modern control run, particularly in the Labradorbasin and in the Southern Ocean. A fourth experiment shows that changes inNd sources and bathymetry drive a shift in the ε_Ndsignature of the basin that is sufficient to explain the changes in theε_Nd signature of the northern end-member (NADW or GNAIWglacial equivalent) in our LGM simulations. All three of our LGM circulationscenarios show good agreement with the existing intermediate depthε_Nd paleo-data. This study cannot indicate the likelihoodof a given LGM oceanic circulation scenario, even if simulations with aprominent water mass of southern origin provide the most conclusive results.Instead, our modeling results highlight the need for more data from deep andbottom waters from western Atlantic, where the ε_Nd changein the three LGM scenarios is the most important (up to 3 ε_Nd. This would also aid more precise conclusions concerning theevolution of the northern end-member ε_Nd signature, andthus the potential use of ε_Nd as a tracer of past oceaniccirculation.