Description: Summary Cruise MSM96 sailed to assess small-and large-scale geochemical and seafloor substrate heterogeneity across the NE Atlantic basin. Weemployed a hierarchical surveying strategy at three spatial scales: local, regional, and basin,to investigatetrace metaland Rare Earth Element and Yttrium concentrationsand patterns. At each of the survey sitesPorcupine Abyssal Plain and Iberian Abyssal Plain, we sampledcovering three data resolution scales: centimeter (TV-MUC), meter (OFOS), and kilometer scale (MBES). Our objective was to quantify the impact of topography on the geochemistry within and between regions and to establish the link –across resolution scales –between geochemistry, imagery,and bathymetrytofacilitate spatial extrapolation of seafloor geochemical dataand substrate characteristics to kilometer-scale.We studied three topography types: valleys, plains,and hills. Theirlocation was objectively chosen bya geomorphons terrain classification.By studying heterogeneity on the local and regional scales, we focused on topographic heterogeneity because spatial heterogeneity with respect to particle and organic matter flux from the sea surface can be expected to be minimal.As a basis, solid-phase and pore-watersamples were taken for on-shore lab analyses of porosity, major elements,total organic carbon, nitrate, anddissolved Mn and Fe.This basic data helps to assess REY controls in the solid phase and pore water. All geochemical parameters together will be used to assess local-to basin-scale heterogeneity and how it is linked to topography.In the future, this should be extended to also incorporate, e.g., oceanography, minerology, microbiology, and eventually link all these parameters across scales.