Semi-automated quantification of Ice Rafted Debris in sediment archives with Computed Tomography.

Ice rafted debris (IRD) in marine sedimentary sequences provide critical information about the evolution of ice sheets. These include enigmatic phases of ice sheet instability like Heinrich events, Dansgaard-Oeschger cycles or Bond events. Higher sampling resolution and greater spatial coverage in IRD records can help gain a better understanding of paleoaclimate, and help predict the future behavior of ice sheets. However, creating high-resolution IRD-records from marine sediment cores is a manual time- and labor-intensive laboratory procedure. By allowing for rapid and non-destructive quantification of micrometer (µm) scale particles, Computed Tomography (CT) holds the potential to increase both resolution and the pace of analysis. We demonstrate the potential of this approach with results from both experimental results and application on conventionally analyzed records. By using basic image processing tools on CT-imagery of phantom-boxes (replicating marine sediment cores with IRD) we counted sand-particles (>150 µm) of different mineralogies ranging from 25-2000 particles/g. The CT-results proved to match the manual counts with a r² of up to 0.99 and a P-value of 0.00. Further, when applying the method on segments of natural marine sediment cores with published IRD-records, we were able to reconstruct the same trends as continuous counts with a 5 times higher spatial resolution. In addition, this non-destructive method gave further information on the impact of bioturbation, grainsize distribution and the sedimentary structure of IRD-deposits. In conclusion, this work can help the field to gain an even better understanding of the behavior of ice sheets by optimizing the efficiency and spatial resolution of IRD-records, while at the same time gaining a better understanding on the processes affecting the IRD-deposits.