Dataset: Sediment radioisotope (234Th) and carbon from sampling conducted at the Compass Station in Bedford Basin, Nova Scotia, Canada from 2021 to 2024

Samples were collected at Compass Station in the Bedford Basin, Halifax, Nova Scotia, Canada (44.7 N, -63.6 W) on day-trips aboard Connor's Diving Ltd, vessel EASTCOM in May 2021, January 2022, May 2023, August 2023, and January 2024.

For the measurement of 234Th in the sediment, a KC Denmark Multicorer was deployed at the Compass Station following water column sampling. Sediments were processed either the same day of retrieval or stored at 4 degrees Celsius (°C) for 24 to 48 hours prior to processing. Cores were sliced into 0.5–1 centimeter (cm) thick sections and then dried at 55°C for approximately 24 hours. After this period, they were weighed and returned to the oven and reweighed at regular intervals until a constant weight was achieved. To correct for residual salt content, salt contribution from porewater was estimated from the salinity of the overlying water and subtracted from the measured dry weight. Once dry, sediments were manually homogenized and weighed into a petri dish. Analysis of sedimentary 234Th and 238U activities were carried out by non-destructive gamma counting on High-Purity Germanium (HPGe) detectors (Dartmouth College, USA) with ~ 15 grams (g) of sediment. The raw 234Th activities (at 63.3 kiloelectron volts (keV)) in sediments were decay corrected to time of collection. Unsupported or 'excess' 234Th is 234Th that is not in secular equilibrium with the 238U parent present in the uppermost sediments, presumably because it was supplied by settling particles.