Award: OCE-0926981

Neodymium (Nd) isotopes are a powerful tool used to reconstruct patterns of ocean circulation in the past. Circulation of water masses in the ocean redistribute heat, nutrients, and carbon dioxide around the globe on time scales on the same magnitude of human civilization. The importance of ocean circulation to global climate cannot be overstated, particularly the air-sea exchange and deep water production occurring in the North Atlantic. These processes exert a powerful control on heat released to the atmosphere in the North Atlantic, influencing Europe and having global consequences for climate. In this project we measured the Nd isotopic composition of seawater samples collected as part of the US GEOTRACES North Atlantic section, which intersected water masses produced in the North Atlantic by the processes above. In addition samples collected on a southward transect from the Iberian Peninsula captured Mediterranean overflow water, as well as seawater under the influence of the Saharan dust plume. These measurements have provided crucial constraints on the cycling of Nd in the oceans which in turn allow more accurate interpretation of Nd isotope records of past ocean circulation. This study has greatly increased the volume of Nd isotope measurements from the North Atlantic (Fig 1). In this study we have constrained the flow of Labrador Seawater from its source in the Labrador Sea and constrain the proportion of this distinct water mass across the Atlantic. Moreover, the concentrations of Nd underneath the Saharan dust plume show surface maxima that decrease with distance from the margin. A subsurface minimum in concentrations suggests scavenging of Nd from the water column. These variations are associated with subtle changes in the isotopic composition of Nd, though deep water Nd isotopes are consistent with water mass mixing. One of the key outcomes of this study is an understanding of particle-seawater interactions and how it affects the Nd isotope distribution. The large input of particles along the transect underneath the Saharan dust plume show strong Nd dissolved concentration gradients. These gradients are being interpreted with particulate Nd concentration and isotope data. Last Modified: 02/11/2014 Submitted by: Howard Scher