Processed results from of surface carbon and nitrogen analysis of the sediment grab samples recovered as part of the Long Island Sound mapping project Phase II.

Sediment grab samples have been taken in summer of 2017 and 2018 using a modified van Veen grab sampler. A sub-sample of the top two centimeter was taken and stored in a jar. Dried and homogenized splits of the samples were sent to the Cornell Isotope Laboratory (COIL) to be analyzed for carbon and nitrogen concentrations as well as stable isotopic compositions. Total carbon (TC), total nitrogen (TN), and δ15N were determined on an aliquot of untreated, dried homogenized sediments. In order to accurately determine total organic carbon (TOC) and δ13C, removal of carbonate is necessary. This was achieved through sequential treatments of the sediments with dilute hydrochloric acid until no bubbling was observed. The acidified sediments were then rinsed in deionized water and re-dried. In the Cornell Lab the samples were analyzed using a NC2500 elemental analyzer interfaced with a Thermo Delta V isotope ratio mass spectrometer (IRMS). ArcGIS Pro empirical kriging has been used to interpolate values for organic carbon, total carbon, nitrogen, d13C and d15N isotope content onto a 50 m raster. The interpolated raster has been clipped to fit the extent of the phase 2 survey area. The final raster data are in GeoTiff format with UTM 18 N projection.

Time period of content: 2017-08-01 to 2022-11-16

Attribute accuracy: The attribute accuracy varies by element and is measured as +/- 1 standard variation

Completeness: The dataset is mostly complete. A few samples had too little material to perform regular and acid-treated samples.

Positional accuracy: Locations are based on DGPS using the ship GPS antenna for most cores resulting +/- 5 m accuracy.

Attributes:

Sample_ID: Text describing the Name of the grab sample, a combination of survey ID and grab sample number.

Short_name: Text describing just the grab number, but without the survey ID

Latitude: Latitude of grab sample station

Longitude: Longitude of grab sample station

Weight_mg: weight of split sub-sample used for analysis in mg

N2_amp: measured nitrogen value in machine units

N_pct: derived percent of nitrogen in sample

d15N: delta 15N nitrogen isotope ratio in sample

CO2_amp: measured carbondioxid value in machine units

C_pct: derived percent of total carbon in sample

d13C: delta 13N isotope ratio in sample

CO2_amp_acid: measured carbondioxid value in machine units of acid-treated sample

C_acid_pct: derived percent of total organic carbon in acid-treated sample

d13C_acid: delta 13N isotope ratio in acid-treated sample

TIC_pct: derived inorganic carbon