In their paper published in Proceedings of the National Academy of Sciences, the group outlines their study, which included extracting core samples ... pulling sediment samples from each.

The samples and measurements are used for help reconstruct past climate and environmental conditions. X-radiograph of glacial marine sediments in West Greenland sediment core JR175-VC24, showing ...

Such samples contain organic matter that can be analyzed to learn about a region's past climate. The new study was based on data from a sediment core extracted from the bottom of Sikuiui Lake in ...