Dataset DOI: 10.5061/dryad.zpc866tp0

Description of the data and file structure

The 2016 and 2018 cores were collected using a "spade and shovel" method, whereas MAC S1 – 4 were collected using a Wardenaar-type titanium corer. The peat cores were sliced at 5 mm or 1 cm intervals throughout their depth, and subsequently subsampled for various analyses including: 1) paleontological data: testate amoebae, plant macrofossils, and charcoal; 2) geochemistry: ICP-MS, HAWK pyrolysis, PAH, and Hg; 3) age dating: radiocarbon (14C) and 210Pb dates.

These datasets provide insight into hydrological and environmental changes observed in the Mackenzie River Basin throughout the late Holocene.

Files and variables

LIST OF CORES:

• 16PS1
• 16PS2
• 18-GTA-292
• 18-GTA-79
• MAC S1
• MAC S2
• MAC S3
• MAC S4

LIST OF DATASETS:

RADIOCARBON DATING:

• This is a dating technique used to determine the ages of organic materials (<50,000 years old) by measuring the amount of radioactive isotope, Carbon-14 (¹⁴C), that remains.
• C-number: internal numbering system in the Geological Survey of Canada.
• Sample ID: sample identification, including core name and depth
• Plant macrofossils: the type of plant macrofossil that was picked for radiocarbon dating. Plant material for non-aquatic mosses are typically picked for radiocarbon dating where possible. In cases where this was not possible, "bulk" (undifferentiated) material was submitted.
• 14C yrs BP: raw, uncalibrated radiocarbon date "before present", defined as 1950 CE.
• 14C Age σ (sigma): statistical uncertainty or error margin of the radiocarbon date determination.
• Fraction modern, F14C: standardized measurement comparing 14C concentration in a sample to a reference standard.
• F14C σ (sigma): laboratory error margin for the fraction modern.
• mg Graphite: mass of the final graphite target, measured in milligrams.
• AD/BC: acronyms for Anno Domini/Before Christ, calendar year designations used to express the final, calibrated age of the sample. It is synonymous with BCE/CE (Before Common Era/Common Era).
• Depth: depth from the surface of the core, denoted in millimeters or centimeters as indicated in the column heading.
• Notes: additional comments that provides further context to the result in question. “Greater than modern” are results that are more modern than 1950, which is the “zero” date upon which radiocarbon dates are fixed, and therefore cannot be determined. A small size sample also calls into question the accuracy of the radiocarbon date and should be taken into account.
• Null values are empty cells from either the radiocarbon dates being “greater than modern” (see above comment), or were not provided in the analysis (e.g., the laboratory only generated ¹⁴C yrs BP dates and not AD/BC dates).

DATA FILES:

• 16PS1_14C_plantmacros.csv
• 16PS2_14C_plantmacros.csv
• 18GTA292_14C_plantmacros.csv
• 18GTA79_14C_plantmacros.csv
• MACS1_14C_plantmacros.csv
• MACS2_14C_plantmacros.csv
• MACS3_14C_plantmacros.csv
• MACS4_14C_plantmacros.csv

PB-210 DATING

• This is a dating technique for recent material (~150 years) that utilizes a suite of radionuclides for measuring. These radionuclides are included in the report: ¹³⁷Cs (Cesium-137), ²¹⁰Pb (Lead-210), ²²⁶Ra (Radium-226), ²⁴¹Am (Americium-241).
• ¹³⁷Cs is an artificial, man-made radioactive isotope of cesium, which acts as an independent chronological marker of ~1963 when it was introduced globally by atmospheric nuclear weapons testing.
• ²¹⁰Pb is a naturally occurring radioactive form of lead that has a half-life ~22.3 years, and it part of the decay chain of Uranium-238. It is the main isotope used for the dating process. There are two sources of ²¹⁰Pb: supported and unsupported (fallout from atmosphere). The ²¹⁰Pb dating method measures the unsupported ²¹⁰Pb.
• ²²⁶Ra is also a naturally occurring radioactive isotope with a half-life ~1600 years, which decays to 220Ra and eventually to ²¹⁰Pb. It is used to determine the amount of supported ²¹⁰Pb, which is the baseline in sediment.
• ²⁴¹Am is another artificial radionuclide that is produced as a byproduct of plutonium decay, introduced during nuclear weapons testing. It is a secondary time marker to ¹³⁷Cs.
• Density (g/cm³): density of the sample, measured in grams per cubic centimeter.
• Sample ID: name of the sample. Note that some samples were replicated multiple times (denoted by the suffix “Rep” in the sample name).
• Depth (cm): depth measured in centimetres.
• Weight (g): weight measured in grams.
• Count duration (s): time duration measured in seconds.
• Activity (Bq/kg): the concentration of the radioactive isotope in the sample, measured in Becquerels per kilogram of dry mass. One Bq is equal to one radioactive disintegration per second.
• Total uncertainty (Bq/kg): the margin of error associated with activity measurement
• Total relative uncertainty (%): the total uncertainty expressed as a percentage of the measured activity, indicating precision
• Important note: none of the values for ²¹⁰Pb dating reached background

DATA FILES:

• MACS1_210Pb.csv
• MACS2_210Pb.csv
• MACS3_210Pb.csv
• MACS4_210Pb.csv

HAWK PROGRAMMED PYROLYSIS

• This is a technique typically used in petroleum geology and geochemistry to evaluate the source rock potential of sedimentary formations. It works by placing a small sample in an inert atmosphere and then allowing the temperature to rise. As the temperature increases, the sample will release volatile hydrocarbons first, followed by thermal cracking of organic matter (kerogen). The sample is then oxidized in a second oven. The compounds are measured by a flame ionization detector and infrared cells and are displayed as pulses/peaks.
• GSC Sample ID: this is the internal curation number that the Geological Survey of Canada uses to store samples
• Sample Name: the name of the sample
• Depth (m): the sample depth measured in metres
• Analysis Date: date of the analysis
• Time: time of the analysis
• Sample weight: weight of the sample in milligrams
• TOC (%): Total Organic Carbon, defined as the total weight percentage of organic carbon in the dry sample, calculated as the sum of the S1 and S2 peaks and the residual carbon burned during oxidation.
• Tmax (°C): the oven temperature at which the S2 peak reaches maximum intensity. It indicates thermal maturity of the sample.
• HI (Hydrogen Index): calculated as (S2/TOC) * 100, a measurement of the hydrogen content relative to organic carbon.
• OI (Oxygen Index): calculated as (S3CO2/TOC) * 100, a measurement of the oxygen content relative ro organic carbon.
• S1 (mg HC/g rock): the amount of free, unbonded hydrocarbons that volatize at temperatures >300°C.
• S2 (mg HC/g rock): the amount of hydrocarbons generated by thermal cracking of solid organic matter (kerogen) when temperature ranges between 300 - 650 °C.
• S3CO2 (mg CO₂ g/rock): the amount of carbon dioxide released from organic mattter during pyrolysis (>400 °C).
• S3CO (mg CO/g rock): the amount of carbon monoxide released from organic matter during pyrolysis.
• S3' (mg CO₂/g rock): the amount of carbon dioxide released during pyrolysis at higher temperatures, associated with early thermal decomposition of specific labile carbonate minerals.
• S3'CO (mg CO/g rock): amount of carbon monoxide released at higher temperatures during pyrolysis.
• S4CO2 (mg CO₂/g rock): amoung of carbon dioxide generated during the oxidation stage when residual carbon is burned off.
• S4CO (mg CO/g rock): the amount of carbon monoxide generated during the oxidation stage.
• S5 (mg CO₂/g rock): the amount of carbon dioxide derived from complete thermal decomposition of carbonates during the highest temperature during the oxidation stage.
• CC (%): Carbonate Carbon, the weight percentage of carbon bound strictly to carbonates, derived primarily from the S5 peak.
• CaCO₃ (%): weight percentage of equivalent calcium carbonate in the sampe, back-calculated directly from the CC% value.
• GOC (PC) %: Generative Organic Carbon (Pyrolyzable Carbon), the fraction of TOC that has the capacity of generating hydrocarbons.
• NGOC (RC) %: Non-Generative Organic Carbon (Residual Carbon), the inert fraction of TOC that cannot generate hydrocarbons.
• AI (Adsorption Index): this tracks how much generated hydrocarbon is retained by the matrix.
• PI (Production Index): calculated as S1/(S1+S2), it characterized the ratio of free hydrocarbons to total potential hydrocarbons.
• OSI (Oil Saturation Index): calculated as (S1/TOC) * 100, it can indicate whether the potential moveable oil exceeds natural adsoprtion capacity of shale.
• Method: indicates the type of pyrolysis run on the samples

DATA FILES:

• 16PS1_HAWK.csv
• 16PS2_HAWK.csv
• 18GTA292_HAWK.csv
• 18GTA79_HAWK.csv
• MACS1_HAWK.csv
• MACS2_HAWK.csv
• MACS3_HAWK.csv
• MACS4_HAWK.csv

MERCURY ANALYSIS

• These datasets contain concentrations of mercury measured through thermal decomposition and expressed in units of parts per billion (ppb).
• Sample ID: name of the sample using GSC curation numbers
• Hg (ppb): measurement of mercury in parts per billion
• Lab replicate (ppb): measurement of mercury using the lab replicated in parts per billion
• The certified reference materials are matrix samples that have been thoroughly analyzed by the international scientific community to establish standard concentrations of a known element (mercury, in this case). These certified reference materials are HISS-1 (marine sediment), STSD-3 (stream sediment), MESS-4 (marine sediment), and MCR-277R (estuarine sediment).
• HISS-1: developed by the National Research Council of Canada, it is a near-shore marine sediment sample collected from the Atlantic coast of Canada. It represents a relatively clean, unpolluted marine environment and can therefore detect very low, baseline concentrations.
• STSD-3: developed by the Geological Survey of Canada, it is a stream sediment sample composite and is used to validate data when tracking industrial or natural mercury runoff in freshwater river systems.
• MESS-4: developed by the National Research Council of Canada, it is a marine sediment sample collected from the Beaufort Sea and is used as a mid-range, natural background concentration of metals, particularly for oceanographic and environmental monitoring.
• BCR-277R: developed by the European Commission's Joint Research Centre, it is sampled from a tidal river mouth where freshwater meets the ocean. This reference material is a replacement standard, indicated by the R in the name. This reference material is critical for evaluating whether the laboratory's acid digestion process is strong enough to break the bonds between mercury and complex organic matter.
• Notes: any sample that were not homogenous or were overly woody is indicated in this column and is otherwise blank or non-existent. Caution should be used to interpret these samples.
• Null values are samples that were not analyzed for mercury or were not analyzed using one of the aforementioned reference materials.

DATA FILES:

• 16PS1_Hg.csv
• 16PS2_Hg.csv
• MACS1_Hg.csv
• MACS2_Hg.csv
• MACS3_Hg.csv
• MACS4_Hg.csv

INDUCTIVELY COUPLED PLASMA MASS SPECTROMETRY (ICP-MS)

• ICP-MS is a highly sensitive technique used to detect and measure trace elements.
• The first few rows provide information on the trace elements (analyte), including 1) the chemical symbol of the element in question, 2) the unit of measurement, either in microgram per gram (μg/g), parts per million (ppm), parts per billion (ppb), or percentage, and 3) the MDL (method detection limit) and LOD (limit of detection).
• Sample name: the name of the sample
• Sample ID: internal laboratory identification number for the sample
• Weight (g): the weight of the sample in grams
• Type: the type of sample (e.g., peat, REP (replicate), STD (standard), or BLK (blank)).
• Some ICP-MS datasheets will have values using replicates and reference materials provided further down the table, separated by blank cells (i.e,, 16PS1, 16PS2 datasheets).
• Blank cells are intentional in order to organize the data and do not denote NA or Null values.

DATA FILES:

• 16PS1_ICPMS.csv
• 16PS2_ICPMS.csv
• 18GTA292_ICPMS.csv
• 18GTA79_ICPMS.csv
• MACS1_ICPMS.csv
• MACS2_ICPMS.csv
• MACS3_ICPMS.csv
• MACS4_ICPMS.csv

POLYCYCLIC AROMATIC HYDROCARBON (PAH)

• PAHs are a large class of organic chemical compounds composed of carbon and hydrogen atoms in two or more fused benzene rings. They form during the incomplete combustion of organic material. They enter the environment through industrial emissions, forest fires, and volcanic eruptions. They also naturally occur in crude oil, shale, and coal deposits. They are heavily monitored as they can be toxic, mutagenic, and highly carcinogenic. PAHs are broadly separated into two categories: parent PAHs and alkylated PAHs.
• The first few rows are organized to show minimum and maximum sample masses and LOQ (limit of quantification or quantitation), measured in nanograms per gram (ng/g), which is the lowest concentration that the laboratory instrument can reliably measure with precision and accuracy. A maximum LOQ is the highest reporting limit applied to the dataset.
• Samples: the labelled name on the samples.
• Mass (g): mass of the samples in grams.
• Mid-depth (cm): the mid-point of the indicated depth of the sample.
• Recoveries (%): the percentage of the target compound recovered from the original peat sample, acting as a quality control check.
• Parent PAHs (ng/g): one of the two broad categories of PAHs consisting of those chemical compounds with fused benzene rings, typically formed at high temperatures.
• Alkylated PAHs (ng/g): the second broad category of PAHs consisting of parent PAHs that have one or more alkyl groups, typically associated with petroleum sources.
• Blank cells are solely for data organization and do not indicate NA or Null values.

DATA FILES:

• 16PS1_PAH.csv
• 16PS2_PAH.csv

pH, ELECTRICAL CONDUCTIVITY, AND TOTAL DISSOLVED SOLIDS

• Sample ID: name of the sample
• Depth (cm): top depth of the sample in the core, measured in centimetres. Each sample is 1 cm thick with the exception of the living layer. The living layer is above zero depth.
• pH: potential of Hydrogen, a numerical scale to measure acidity/alkalinity. It is unitless.
• EC (µS): electrical conductivity, measured in microSiemens per centimetre, it is a measurement of a material/solution's ability to conduct an electric current and therefore give insight to the amount of dissolved salts and inorganic chemicals.
• TDS (ppm): Total dissolved solids, representing the total weight of all dissolved inorganic and organic substances, measured in parts per million.

DATA FILES:

• MACS1_pH_EC_TDS.csv
• MACS2_pH_EC_TDS.csv
• MACS3_pH_EC_TDS.csv
• MACS4_pH_EC_TDS.csv

PLANT MACROFOSSILS

• Volumetric percentages of moss and stem leaves from peat material alongside macroscopic charcoal. The volumetric percentage of the different vegetative remains were estimated in 5% increments.
• The top row are groups of mosses that were identified
• Depth (cm): the mid-depth of the sample in question, in centimetres.

DATA FILES:

• MACS1_Plant_macrofossils.csv
• MACS2_Plant_macrofossils.csv
• MACS3_Plant_macrofossils.csv
• MACS4_Plant_macrofossils.csv

TESTATE AMOEBAE

• Raw counts of testate amoebae morphological species. Tests were enumerated to 100 specimens where possible, and a minimum of 50 counts for water table depth reconstruction. Intervals with very low concentrations of tests (<50 tests per three slides) were removed from the dataset.
• The top three rows indicate the sample number, and the top and bottom depth for each sample. For example, sample 1 has a top depth of -4 centimeters (it is above the surface) and a bottom depth of zero (the surface); sample 2 has a top depth of zero centimeters and a bottom depth of one centimetre, etc.
• The blank row of cells is intentional for data organization.
• The left most column succeeding this blank row of cells is a list of testate amoebae species that were identified in the core.

DATA FILES:

• 16PS1_Testate_amoebae.csv
• 16PS2_Testate_amoebae.csv
• 18GTA292_Testate_amoebae.csv
• 18GTA79_Testate_amoebae.csv
• MACS1_Testate_amoebae.csv
• MACS2_Testate_amoebae.csv
• MACS3_Testate_amoebae.csv
• MACS4_Testate_amoebae.csv

Other files:

• GPScoord.csv: the latitude and longitude of each of the core locations based on GPS.
  • Site: the name of the core
  • Latitude: latitude expressed in decimal degrees
  • Longitude: longitude expressed in decimal degrees
  • Depth (cm): depth of the core in centimetres
  • Depth after slicing (cm): the length of the core after slicing into subsamples
  • Collection date: date when the core was collected from the Northwest Territories
• MACS1-4_Environmental.csv: Description of the core locations and the cores themselves according to the field notes, transcribed directly.
  • Date: date of the core collection
  • Time: time at which the core was collected
  • Field team: the individuals that were a part of the Gwich’in Renewable Resources Board team that undertook the core collection
  • Core: the core label
  • Site description: brief description of the site according to the field notes
  • Site vegetation: vegetation that was identified at the core location according to the field notes. This is likely redundant with the column “Vegetation at core site”
  • Core description: field notes describing the core and its visible layers once extracted from the ground
  • Vegetation at core site: vegetation that was identified at the core location according to the field notes.
  • Lat (N): latitude expressed in decimal degrees in the North direction
  • Long (W): longitude expressed in decimal degrees in the West direction
  • Length (cm): length of the core once extracted from the ground, in centimetres
  • Width (cm): width of the core once extracted from the ground, in centimetres
  • Height (cm): height of the core once extracted from the ground, in centimetres
  • Depth to water table (cm): measurements of depth to the water table after the core has been extracted from the ground. There are multiple values due to the uneven surface designating zero depth.  
  • pH: potential of Hydrogen of the water at the core site, a numerical scale to measure acidity/alkalinity. It is unitless. Measured upon core collection.
  • SP conductivity (S/m): specific conductivity, the measure of the water’s ability to conduct an electrical current, in siemens per meter.
  • Elevation (m ASL): elevation of the site location in metres above sea level  
• MAC_Moss_Veg_Surface_samples.csv: summarized field notes detailing location and description of collected surface samples, microform, local vegetation, depth to water table, pH, and SP conductivity (specific conductivity - the electrical conductivity of water standardized to a temperature of 25 degrees Celsius).
  • Date: date of the collection
  • Time collected: time of the sample collection
  • Field team: names of the individuals involved in the collection of samples
  • Site: location of the collection of samples, differentiated by numbers
  • Moss & Veg samples: numerical label of each moss or vegetation sample collected at each individual site
  • Lat (N): latitude in decimal degrees, in the North direction
  • Long (W): longitude in decimal degrees, in the West direction
  • Vegetation: brief description of the surface sample and the vegetal components   
  •  Microform description: brief description of the microform at each collection site
  • Depth to water table (cm): measurement of depth to the water table. There are multiple measurements or ranges of measurements due to the uneven surface acting as zero depth.
  • pH: potential of Hydrogen of the water at the core site, a numerical scale to measure acidity/alkalinity. It is unitless.
  • SP conductivity: SP conductivity (S/m): specific conductivity, the measure of the water’s ability to conduct an electrical current, in siemens per meter.
  • Time recorded: time at which all measurements were completed.
  • Notes: Further comments from the field team providing additional information or context. Blank cells indicate no further notes were provided from the field team.
  • N/A values signify either times at which the team forgot to measure, the instrument broke, or it was not possible to collect the data.