Sediment radioisotope (234Th) and carbon from sampling conducted at the Compass Station in Bedford Basin, Nova Scotia, Canada from 2021 to 2024
Project
| Contributors | Affiliation | Role |
|---|---|---|
| Healey, Madeline | Dalhousie University | Co-Principal Investigator |
| Kienast, Stephanie S. | Dalhousie University | Co-Principal Investigator |
| Rauch, Shannon | Woods Hole Oceanographic Institution (WHOI BCO-DMO) | BCO-DMO Data Manager |
Abstract
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.
- Imported original file "BB_2021_2024_Sediments.csv" into the BCO-DMO system.
- Renamed fields to comply with BCO-DMO naming conventions.
- Converted date format to YYYY-MM.
- Saved the final file as "988753_v1_bedford_basin_sediment_th_2021-2024.csv".
| Parameter | Description | Units |
| Sampling_Date | Date of sample collection | unitless |
| Latitude | latitude where samples were collected | decimal degrees |
| Longitude | longitude where samples were collected | decimal degrees |
| Layer_Start | Upper boundary (shallower depth) of the sampled layer | centimeters |
| Layer_End | Lower boundary (deeper depth) of the sampled layer | centimeters |
| Mid_Layer | Midpoint depth of the sampled interval | centimeters |
| Raw_234Th | Measured (uncorrected) 234Th activity in the sample | decays per minute per gram (dpm/g) |
| Unc_Raw_234Th | Analytical uncertainty associated with Raw_234Th | decays per minute per gram (dpm/g) |
| Decay_corr_234Th | 234Th activity corrected for radioactive decay between collection and counting | decays per minute per gram (dpm/g) |
| Unc_Decay_corr_234Th | Analytical uncertainty on decay-corrected 234Th | decays per minute per gram (dpm/g) |
| Thxs234 | Excess (unsupported) 234Th activity | decays per minute per gram (dpm/g) |
| Unc_234Thxs | Analytical uncertainty (1?) associated with 234Thxs | decays per minute per gram (dpm/g) |
| Dataset-specific Instrument Name | High-Purity Germanium (HPGe) detectors |
| Generic Instrument Name | Germanium detector |
| Dataset-specific Description | 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 g of sediment |
| Generic Instrument Description | Germanium detectors are semiconductor diodes having a p-i-n structure in which the intrinsic (i) region is sensitive to ionizing radiation, particularly x rays and gamma rays. Under reverse bias, an electric field extends across the intrinsic or depleted region. When photons interact with the material within the depleted volume of a detector, charge carriers (holes and electrons) are produced and are swept by the electric field to the p and n electrodes. This charge, which is in proportion to the energy deposited in the detector by the incoming photon, is converted into a voltage pulse by an integral charge sensitive preamplifier. Germanium detectors are mostly used for gamma spectroscopy in nuclear physics, as well as x-ray spectroscopy. |
| Dataset-specific Instrument Name | KC Denmark - Multicorer |
| Generic Instrument Name | Multi Corer |
| Dataset-specific Description | Equipped with four 60 cm long, 10 cm internal diameter core barrels made of polycarbonate |
| Generic Instrument Description | The Multi Corer is a benthic coring device used to collect multiple, simultaneous, undisturbed sediment/water samples from the seafloor. Multiple coring tubes with varying sampling capacity depending on tube dimensions are mounted in a frame designed to sample the deep ocean seafloor. For more information, see Barnett et al. (1984) in Oceanologica Acta, 7, pp. 399-408. |
Ocean Frontier Institute Seed Fund Grant: Bedford Basin 2019 (Bedford Basin 2019)
In coastal regions, the transport of carbon from surface waters to the seafloor is a key mechanism of carbon burial and it has been suggested that one-fifth of the carbon entering coastal areas off of eastern North America (from the atmosphere and through rivers) is subsequently buried in these coastal areas (Najjar et al., 2018). However, direct measurements coupling carbon fluxes in coastal waters to accumulation in sediment remains a challenge.
Bedford Basin is a well-studied coastal system in Nova Scotia, Canada (Bedford Basin Monitoring Program) that can provide unique insight into carbon cycling in these shallow marine regions. To quantify sinking particulate carbon and benthic-pelagic carbon cycling, and to examine the potential factors influencing coastal carbon budgets, carbon content and radioisotope (i.e., Thorium-234) measurements were collected at the Compass Station in Bedford Basin at four time periods (February to August 2019). Sediment cores and seawater samples were analyzed. Size fractionated filtration was performed to examine differences in 'sinking' (>51 micrometers) and 'suspended' (1-51 micrometers) particulate organic carbon and Thorium-234.
References Cited:
Najjar, R. G., et al. (2018). Carbon Budget of Tidal Wetlands, Estuaries, and Shelf Waters of Eastern North America. In Global Biogeochemical Cycles (Vol. 32, Issue 3, pp. 389–416). American Geophysical Union (AGU). https://doi.org/10.1002/2017gb005790
| Funding Source | Award |
|---|---|
| National Sciences and Engineering Research Council of Canada (NSERC) |
[ table of contents | back to top ]