Smearing of gravity core profiles in soft sediments

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Abstract
Gravity coring of soft sediments can result in smearing of sediment between adjacent vertical sections in a core. We have quantified this artifact in a laboratory experiment with soft, highly porous gyttja using radiotracers to label the surface of the sediments. After coring, extrusion, and sectioning, the radiotracers were measured down to 5 cm in inner core sections and to 10 cm in outer core sections. We have estimated the impact of smearing on the interpretation of concentration‐depth profiles, and gradients calculated from smeared profiles can be less than those occurring in situ in the sediments. This effect seems most pronounced near the mud— water interface. We have simulated radionuclide profiles in sediments from Chernobyl fallout (e.g. 134Cs) and natural emissions (e.g. 210Pb) to examine this problem. Concentration gradients of these radionuclides and of other contaminants used to establish geochronologies can be altered significantly depending on sediment type. A tracer layered on the surface of the sediments can be used to quantitate smearing effects, and corrections can then be made to concentration‐depth profiles.

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