Award: OCE-0927241

The isotopes of neodymium (Nd), one of the rare earth elements, are a versatile tracer in the modern and past oceans. This stems from their distinct geographic distribution on land and their input to the ocean through continental weathering, which imprints the local continental Nd isotope ratio onto seawater. As these waters are transported around the ocean, they largely retain their original isotope signature, allowing the determination of their original source region and their transport pathway through the ocean. Neodymium isotopes have therefore gained much attention in studies concerned with the modern distribution of water masses and land-sourced material in the ocean as well as the circulation of the ocean in the past. Yet, there are major gaps in our knowledge of Nd sources, sinks, and internal cycling in the ocean that impedes absolute estimates of water-mass circulation changes based on the Nd isotope tracer. This shortcoming is partly due to the limited amount of seawater Nd isotope and concentration data, and the restricted spatial extent in the oceans. An ideal test of the processes controlling the Nd isotope distribution in seawater is to compare Nd isotope values with conservative parameters for ocean circulation (e.g., salinity, temperature). In this collaborative project we measured Nd isotopes and concentrations in seawater across the North Atlantic as part of the US GEOTRACES North Atlantic zonal transect. The cruise track intersected major water masses of the Atlantic including waters transported southward from the North Atlantic, and sampled the Saharan dust plume off Mauritania, a potentially large supplier of important elements and Nd to the Atlantic. The results from this study that have an unprecedented spatial and vertical resolution clearly allow the tracing of water masses formed in the North Atlantic along their transport southward along the western margin of the US and the inflow of Mediterranean water through the Strait of Gibraltar. Comparison of the distribution of water masses as determined using hydrographic and nutrient data with the distribution of Nd isotopes shows very high correspondence, confirming the use of Nd isotopes in the North Atlantic as a tracer for the source and transport path of water masses. Saharan dust is visible in the surface ocean both through high Nd concentrations and the characteristic Nd isotope signature of the Saharan desert. The results from this study contribute to the global GEOTRACES effort aimed at characterizing and understanding the distributions, sources, sinks and internal cycling of trace element and isotopes in the ocean. They further add to an improved understanding of biogeochemical cycles in the ocean and reinforce the application of Nd as tracer for present and past changes in ocean circulation and mixing. The data therefore yield eminent results that will be of high interest to a wide range of ocean and climate scientists. Last Modified: 07/16/2014 Submitted by: Katharina Pahnke