Particle Size Specific Magnetic Properties Across the Norwegian-Greenland Seas: Insights Into the Influence of Sediment Source and Texture on Bulk Magnetic Records

We make fundamental observations of the particle size variability of magnetic properties from 71 core tops that span the southern Greenland and Norwegian Seas. These data provide the first detailed regional characterization of how bulk magnetic properties vary with sediment texture, sediment source, and sediment transport. Magnetic susceptibility (MS) and hysteresis parameters were measured on the bulk sediment and the five constituent sediment particle size fractions (clay, fine silt, medium silt, coarse silt, and sand). The median MS value of the medium silt size fraction is 3-5 times higher than that of the sand and clay size fractions and results in a strong sensitivity of bulk MS to sediment texture. Hysteresis properties of the clay size fraction are relatively homogeneous and contrast that silt and sand size fractions which show regional differences across the study area. These coarser fractions are more transport limited and using medium silt hysteresis measurements and low temperature MS behavior we establish three endmembers that effectively explain the variability observed across the region. We model the response of bulk magnetic properties to changes in sediment texture and suggest that variations in sediment source are required to explain the bulk magnetic property variability observed in cores across the southern Greenland and Norwegian Seas. These findings imply that sediment source has a greater influence on driving bulk magnetic property variability across this region than has previously been assumed. Plain Language Summary Sediments from the bottom of the ocean can tell us about past environmental conditions (climate, ocean circulation, ice sheet growth, and retreat) that we cannot obtain by other means. Naturally occurring iron-bearing minerals in the sediment are strongly sensitive to changing environmental conditions and can be rapidly and nondestructively characterized by using a suite of magnetic property measurements. To better understand these records we split bulk sediments recovered from 71 locations across the Norwegian and Greenland Seas into five different grain size ranges and made the same magnetic measurements on each size fraction and the bulk sediment. The silt-size fractions contain several times the amount of magnetic material than the clay- or sand-size fractions resulting in a strong dependence of bulk properties on the presence of clay, silt, and sand. Sediment source also strongly influences silt and bulk magnetic properties and by sampling widely across the study region we present new evidence for source-driven variability that was not previously known. These findings suggest that we need to consider how changes in sediment source and sediment grain size might affect interpretations of bulk sediment magnetic properties. These new insights can provide detailed new information about Earth's past.