Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Related Publications
• Parameters
• Instruments
• Project Information
• Funding

Sampling and analytical procedures: 

Sediment cores were collected with the piston corer and immediately cut at 2-6 cm intervals and transferred to Teflon large mouth bottles. Care was taken to minimize settling of cores or loss of pore water prior to sectioning. A portion of approximately 15 grams was taken from each bottle and was charged with 150 ml of 18 Mohm water and stirred to form a slurry. The slurry was sonicated for 5 min. The pH of the slurry was adjusted to 8-9 by the dropwise addition of concentrated NH4OH. Following the pH adjustment, 1.0 ml of KMnO4 solution (3.0 g l-1) and 1.0 ml of MnCl2 solution (8.0 g MnCl2 4H2O l-1) was added to form a suspension of MnO2. The slurry was then filtered onto a 142 mm GF/F filter. The sample was loaded into a modified recirculation chamber (after Cai et al. 2012) for counting of 220Rn and 219Rn on the RaDeCC system.  Samples were taken back to the laboratory for immediate counting to minimize error in the ratio. Samples were re-measured in the same RaDeCC system after two days and 45 days to differentiate between supported and excess 224Ra and 223Ra.

To estimate porosity, after the sample was collected and split into representative slabs, a portion of the homogenized slab (typically 15 grams) was dried to constant mass using an oven at 60℃. Mass measurements were taken until constant mass was achieved.  

Problem Report:
Noted in the data file, there were four samples that had anomalous counts. These counts were excluded from the data set and results recalculated. Both the original data calculation and the recalculation have been included in the data set. The recalculated samples are denoted with CORR at the end of the sample name and commented on. 

Location: 
Folly Island and Marsh, South Carolina, 32.68 N, 79.95 W
Daniel Island creek/marsh, South Carolina 32.89 N, 79.9 W

Data from the RaDeCC were in text files. The relevant numbers from the raw data are transferred to Excel spreadsheets where calculations (including decay, coincidence counts, error) are performed to obtain final results.

Excel version: Microsoft® Excel® for Microsoft 365 MSO (Version 2111 Build 16.0.14701.20254) 64-bit   

BCO-DMO Data Manager Processing Notes:
* Data from source file DATASET_Cores.docx Sheet1 were imported into the BCO-DMO data system and combined into one data table.   
* Parameters (column names) renamed to comply with BCO-DMO naming conventions. See https://www.bco-dmo.org/page/bco-dmo-data-processing-conventions
* Date_Time_UTC column converted to ISO 8601 format yyyy-mm-ddTHH:MMZ 
* latitude and longitude rounded to 5 decimal places.
* longitude made negative (West is negative in decimal degree format)
* commas in comments replaced with semicolon for additional csv format support.
* Values "Nd" and "nd" in source file classified as missing data identifiers. Missing data values (Blank/Null) values in this dataset are displayed according to the format of data you access. For example, in csv files it will be blank values. In Matlab .mat files it will be NaN values. When viewing data online at BCO-DMO, the missing value will be shown as "nd" meaning "no data."   See https://www.bco-dmo.org/page/bco-dmo-data-processing-conventions

NSF Award Abstract:
Tidal marshes are critical junctions between marine and terrestrial chemical processes. The chemical and physical processes that tidal marsh sediments undergo determine the nature of the transformation and accumulation of particulate organic carbon (POC) at the marine to terrestrial interface. Physical transport of pore water through marsh sediments greatly influences the availability of carbon and nutrients that can undergo transformative reactions at the marine to terrestrial interface. Past studies have shown that there is a discrepancy between predicted rates of pore water flow and calculated estimates from tracer studies. Because this flow is crucial to the chemistry of sediment at the terrestrial to marine interface, which is the first junction of the chemical species exported to the ocean, it is important to explain the discrepancy between expected rates of flow and observed rates. This study will use a known tracer method based on natural isotopic ratios (224Radon/228Thorium) and will develop a new method (223Radon/ 227Actinium) to evaluate the export of POC due to pore water flow in tidal marsh sediments, which will have much broader impacts to the overall marine carbon budget. Results from this work will also be integrated into workshops that will educate students and teachers from outside of oceanography about oceanographic carbon and climate research. Presentations will also be developed in collaboration with the South Carolina State Museum as part of the Science Café series. Additionally, one graduate student and one undergraduate student will be supported by this funding.

Predicted advection rates of pore water in very fine-grained tidal marsh sediments have been shown to significantly differ from rates calculated using tracer studies. Because tidal marshes are a crucial chemical link at the marine terrestrial interface, and advection has a significant impact on the availability of chemical species to undergo diagenetic reactions at this interface, it is of significant importance to evaluate this discrepancy. Export of particulate organic carbon (POC) and dissolved organic carbon (DIC), in particular, are of interest, due to the impact on microbial communities within sediments. This research aims to validate the method of 224Ra/228Th disequilibrium to calculate pore water exchange rates. Previous studies using this method have provided evidence for more rapid pore water exchange than would generally be expected in such fine-grained sediments, which are less permeable than coarser grained sediment. Additionally, this research will attempt to develop the disequilibrium method for 223Ra/227Ac. The researchers will evaluate the impact of advection rates on the export of chemical species in salt marshes.