Influence of melting icebergs on distribution, characteristics and transport of marine particles in an East Greenland fjord

A detailed study of distribution of suspended sediments in an East Greenland fiord with a high iceberg production rate reveals the existence of intermediate nepheloid layers (INLs). Observed INLs extended from the head to the mouth of the fjord at water depths between 100 and 400 m. Particulate organic carbon and nitrogen, chlorophyll a, and nutrient measurements and observation by microscope and energy dispersive X- ray analyses were used to characterize marine particles. Particles in the INLs are composed of glacial flour including >50 mu m quartz and feldspar grains with angular and sharp edges, considered to be released from melting icebergs. In situ photographs show large aggregates (>1 mm) at high concentration (>300 particles per liter) in and below INLs. These aggregates, in comparison with the dispersed particle size distribution, demonstrate that smaller size particles (e.g., clay) settle effectively along with larger single size grains. In Kangerlugssuaq Fjord, the mass transport of marine particles was governed by the subsurface iceberg melting, producing observed INLs, rather than the surface meltwater plume. This suggests that the subsurface water temperature controls release of iceberg debris and the existence of warm subsurface water, as well as the spread of cold and fresh water in the surface layer, needs to be considered to evaluate the occurrence of ice-rafted debris layers, including Heinrich layers. This study provides the field evidence of a modern analogue on ocean conditions that could form iceberg-rafted layers.