Collection, analysis, and age-dating of sediment cores from a salt marsh platform and ponds, Rowley, Massachusetts, 2014-15

Sediment cores were collected in coastal salt marshes in 2014 and 2015. A piston coring system was used, where the PVC core liner (diameter 11 cm, 1-2 m in length) was fitted with a gasketed piston that was placed on the sediment surface. The clear, sharpened core liner was pushed down into the marsh subsurface, while the piston was maintained at the marsh surface via tension on the piston. We visually observed the sediment surface to ensure that the soil column did not compact during collection. Once the core reached the desired depth, the core liner and piston were removed from the marsh with a pulley system. Cores were collected from three general locations on the marsh platform (attribute "Status" = MARSH) and from three separate ponds (attribute "Status" = POND). These locations are given an enumerated "Site_ID". Each core was assigned an enumerated "Core_ID". Note that replicate cores were collected from each marsh site but only one core was collected from each of the three ponds. The process date reflects the last occurrence of the work.

After each collection, the sediment cores were immediately returned to the USGS Woods Hole Coastal and Marine Science Center. They were placed in a refrigerator for 1 to 3 days, then split vertically, sectioned at 1 or 2 cm intervals, frozen, and then freeze dried for 7 days, until sediment weights did not change further. Dry bulk density was determined as the dry weight of a known volume of sample.
Approximately 5 g of dried sediment sample was blended and homogenized prior to sealing in a jar for a minimum of three weeks and then placed on a planar-type gamma counter for 24 to 48 hours to measure 7Be, 137Cs, 210Pb, and 226Ra at 477, 661.6, 46.5 and 352 kiloelectronvolts (KeV) energies respectively (Canberra Inc., USA). The detection limit is specific to an individual sample and is a function of: 1) the detector efficiency at the energy of the peak being measured; 2) the branching ratio (number of decay events observed in each peak), 3) the background activity within the sample. Detector efficiency was determined from EPA standard pitchblende ore in the same geometry as the samples. Activities of 7Be, 137Cs, and 210Pb were decay corrected to time of collection. Suppression of low energy peaks by self-absorption was corrected for according to Cutshall and others, 1983. Peak detection, with respect to background activity, is calculated for each radioisotope in the APTEC software during sample analysis. Generally, measured radioisotope activity greater than or equal to 0.2 (210Pb), 0.1 (226Ra), 0.4 (7Be), and 0.1(137Cs) dpm/g were accepted as above detection limit for this dataset. Values reported are above these limits, while values below are reported as 0. All gamma analyses were ongoing from 2015 and completed in 2017.
Cutshall, N.H., Larsen, I.L., and Olsen, C.R., 1983, Direct analysis of 210 Pb in sediment samples—Self-absorption corrections: Nuclear Instruments and Methods in Physics Research, v. 206, issues 1–2 , p. 309–312, https://doi.org/10.1016/0167-5087(83)91273-5.

Data from gamma analysis was entered into an EXCEL spreadsheet. The Excel spreadsheet was exported as a CSV (UTF-8) file from Excel for Mac version 15.33. The file was further proofed and saved as a .CSV from EXCEL for WINDOWS 10.

Repaired some issues that the ScienceBase turn live process introduced - removed empty elements (geospatial presentation form), in the distribution section added the additional links and access instructions that had been deleted, and changed the digital transfer format name from digital data to something more specific. Added additional cross-references to related datasets.