How do scientists use ice-rafted debris to learn about ancient icebergs and ocean conditions?

Scientists use ice-rafted debris (IRD)—sediment such as pebbles, cobbles, and boulders transported by icebergs or sea ice—as a key indicator to map the distribution of ancient icebergs and cold surface waters during past geologic periods.1

By analyzing seabed-sediment cores, researchers can identify the presence of IRD at specific depths, which corresponds to different time intervals in the past. The composition of the rock found within this debris allows scientists to trace the material back to its source region, providing insight into the paths and extent of ancient icebergs. Furthermore, the presence of IRD in these cores serves as evidence that icebergs or sea ice were present at a specific location during a given time. This method has been instrumental in mapping glacial conditions across the North Atlantic, North Pacific, and Southern oceans. Additionally, the appearance of IRD in ocean-sediment cores has been used to date the development of continental ice sheets, such as those in North America approximately 2.5 million years ago.12