Adjusted depth scale and age determinations for IODP Site 347-M0063

Laminated, organic-rich silts and clays with high dissolved gas content characterize sediments at IODP Site M0063 in the Landsort Deep, which at 459 m is the deepest basin in the Baltic Sea. Cores recovered from Hole M0063A experienced significant expansion as gas was released during the recovery process, resulting in high sediment loss. Therefore during operations at the subsequent four holes, penetration was reduced to 2 m per 3.3 m coring run, permitting expansion into 1.3 m of initially empty liner. Fully filled liners were recovered from Holes B through E, indicating that the length of each recovered interval exceeded the penetrated distance by a factor of >1.5. We note a typical logarithmic trend in the down-core gamma density profiles, with anomalously low density values within the upper ~1 m of each core. We interpret that expansion primarily occurred in this upper interval, which is also visible in the core images, and suggest that a simple linear correction is inappropriate. This is supported by Anisotropy of Magnetic Susceptibility data that indicate vertical stretching in the upper ~1.5 m of expanded cores. Based on the mean gamma density profiles of cores from Holes M0063C and D, we obtain an expansion function that is used to adjust the depth of each core to conform to its known penetration. The variance in these profiles allows for quantification of uncertainty in the adjusted depth scale. Together with a number of bulk 14C dates, we explore how the presence of multiple carbon source pathways leads to poorly constrained variations in radiocarbon reservoir age, which significantly affects age and sedimentation rate calculations.