IntCal data

The information here covers the data within the IntCal database and is relevant for those using this data or preparing data for possible inclusion in future iterations of the IntCal curve series. There are four key types of data which are included in the IntCal repository. These are:

• Record information
• Radiocarbon datasets
• Dendrochronological data
• Publications

See also details on preparing data for inclusion.

Record information

The records for IntCal are in the standard format described in the IntChron schema.  The key parameters relevant to the calibration curve are:

• record (Record): the unique record code; this will typically be the same as the marine core code, dendrochronology code etc
  
• country (Country): country in which the record was taken - or null if marine
  
• site (Site): the site name
• latitude (Latitude): the latitude for the record
  
• longitude (Longitude): the longitude for the record
• site_type (Site type): for IntCal normally Dendrochronogical, Marine, Terrestrial or Speleothem
  
• t_source (Timescale): this is the ultimate source for the the timescale - normally DendroNH, DendroSH, UTh or a specific calibration curve
  
• z_type (z  type): one of depth (cores), height (speleothems) or rings (dendrochronological)
  
• z_units (z_units): either a unit of length (mm,cm,m) or rings; all lengths are stored in m but presented and exchanged in the format given
  

Records can be created and edited as normal within IntChron but for dendrochronogical records it is most convenient to create them from the dendrochronologial data  which will provide much of the necessary detail.

Radiocarbon datasets

Radiocarbon datasets included in IntCal have a special format within the IntChron package which is based around the needs of the statistical procedures for curve production.   They are series stored within the record file.

The series should be of series_type "IntCal_Data" which, in addition to the standard series headers has the following:

• intcal_set_type (Type): This is "Int" for IntCal or "SH" for SHCal etc
  
• intcal_set (Set): This is the set number for data sets included within IntCal/SHCal
  
• intcal_division (Division): This is the set subdivision

All of these can be null if the data set is only provisional or being considered for inclusion.

This is followed by the data table, which has parameters which can be broken down into several groups:

Standard IntChron tool parameters

These are used for plotting and other purposes within the database and are common to other types of data series.  Details are given in the IntChron schema but are also described here for convenience:

• z (Depth/Ring): general depth or ring measurement (see below)
  
• z_range (z range):  range in z (see below)
• t (Date): general date parameter - the timescale is defined at the record level; internally this is stored as fractional astronomical years but can be displayed in a number of different formats (calBP, fractional years, BC/AD etc)
  
• t_sigma (±1σ): one sigma uncertainty in t
• sample (Sample): the sample name (see below)
• ring_segment (Seg.): the segment of a ring measured (EW, LW, EW/LW, EW1, EW2, LW1, LW2 etc.)
• labcode (Lab code): the radiocarbon lab code in standard format
• batch (Batch): the measurement batch (magzine/wheel) in which the measurements were made
  
• r_date (R_Date): the uncalibrated radiocarbon date in ¹⁴C years BP
  
• r_date_sigma (±1σ): the one sigma uncertainty in r_date

Special IntCal parameters

• calage (CalAge): required for all data - this is the age of the sample in years calBP;  in normal circumstances t will be 1950.5 - calage
  
• calage_range (CalSpan): this is the range of the sample material (see below); the default value is 1
  
• calage_sigmaI (±1σ): this is the one sigma independent uncertainty in the age (0 for dendrochronologically dated material)
  
• calage_sigmaD (±1σ): this is the one sigma systematic uncertainty in the age of the entire dataset (typically for tree ring series)
  
• calage_sigmaC (±1σ): correlated uncertainty (used for example in the Cariaco Basin varved sediments)
  
• intcal_reservoir (Reservoir): the marine reservoir offset (relative to the atmosphere) of this sample set
  
• intcal_reservoir_sigma (±1σ): the one sigma uncertainty in intcal_reservoir_sigma
  

• intcal_data_id (Id): the unique ID number for this data point in IntCal
  
• intcal_seq_no (Seq): the sequence number (for series with multiple sequences)
  
• r_date_sigma_extra (+ ±1σ): extra uncertainty in the radiocarbon value
  
• r_date_sigma_mult (× ±1σ): an error multiplier (typically 1 as a default)
  

Sample naming conventions

The sample (Sample) in the dataset is important.  This should be different for each sample which has a different age - but it should be identical for the same sample measured by different labs.  The labcode should be different for every measurement and is a unique key in the IntCal database.
For dendrochronological samples the sample name should tie up with the dendrochronological series name - suffixed with ring information in the following way.  Supposing the record name is TOW, and the tree sequence name is TOW32A.  The rings within this sequence should be numbered from 1 (the oldest sample) to the last ring.  The radiocarbon sample names will then be like TOW32A_r8 for measurement of a single ring 8 or TOW32A_r1-5 for measurements on a block from ring 1 to 5

Ring numbers and depth information (z, z_range, ring, calage_range)

Most samples come with information either on depth (in a sedimentary sequence, speleothem etc) or ring numbers.  The parameters z and z_range are used to store this information.  At the record level you can define what z is used for (depth, height, rings etc), and this data can be imported/exported and displayed in three different ways:

• z,z_range: this is the internal format and is in two columns; for the ring example above TOW32A_r1-5 would be 3 (the central ring) and 4 (the range from 1 to 5).
• z_from-z_to: this is a single column format which is either a single number (like 8 for TOW32A_r8) or a string with - (like 1-5 for TOW32A_r1-5)
• z ± dz: this is another single column format which is either a single number (like 8 for TOW32A_r8) or a string with ± (like 1±2 for TOW32A_r1-5)

In the case of tree rings this information is also given in the two columns ring and cal_age_range.  Normally ring and z will be the same but cal_age_range should be 1 for single year rings (like 1 for TOW32A_r8) and 1+z_range for higher numbers (like 5 for TOW32A_r1-5).  Although this arrangement in some ways duplicates information the cal_age_range is directly used in the curve construction and can be checked against the z_range information.  In the case of non-dendro samples z_range is not directly related to cal_age_range.

Dendrochronological data

The most important dendrochronolocal data is the ring-width measurement series for the samples that have been analyzed for radiocarbon.  These should be included within the relevant record for any new submissions but is not always available for historical data.  If the data is available either on the NOAA ITRDB or as a Tuscon format rwl file, the easiest way to import this information is to create the record using the tree ring data because this includes much of the needed information in one place.
Each dendrochronologial sequence has a unique code and ring numbers (z) starting from 1 - these should correspond to the ring numbers in the radiocarbon datasets.  The whole series might be floating (undated) in which case the t values will start from 1 for the oldest ring in the whole series.
In addition to record-based dendrochronological series, it is also possible to store master chronologies as 'Project data' - these are relevant where the radiocarbon dated samples have been dated against a main master chronology for which the details are not provided in the IntCal dataset.

Publications

Details on the referencing system are given in the main instructions for the IntChron tool.

Preparing data for inclusion

If you have data which you think might usefully be included in future versions of IntCal you can prepare it for checking, consideration and inclusion using the IntChron tool.  The steps are:

Data preparation

• Prepare you radiocarbon dataset with reference to the details above using the spreadsheet at:
• import_IntCal.xlsx
• If the project is a dendrochronological one, there are several approaches to prepare your dendrochronogical data. If working with material from an established chronology the best solution is to lodge the data with the ITRDB using the NOAA template:
      https://www.ncei.noaa.gov/pub/data/paleo/templates/noaa-wds-paleo-template-instructions.txt
  This makes the next stages easier. If not, generating your data in the Tucson .rwl or Heidelberg format will also work. Files can be converted to these formats using the Tricycle dendro data conversion tool: http://www.tridas.org/tricycle/. Please note that file conversion can result in a loss of meta-data that must them be added manually to the IntChron project.
  

Data compilation

• Start a blank IntChron project using the IntCal format by visiting:
  
• https://intchron.org/tools/integrate/integrate.html?filename=Intcal_Project_Base.json
• Log in to IntChron as you will wish to save the project - using [File > Login] for this you can use an OxCal username/password or register for a new username; this data will not be seen by anyone but you and is for your own use.
  
• Save the project using [File > Save as] and giving it a project name
• If your project is a dendrochronological one you can create the record by importing the dendrochronological data using [File > Import > Dendro] and choosing your format; the ideal is to use the ITRDB study number or doi as this includes the relevant references and other metadata. If not import the file and add this information manually, see the general instructions for entering references in the IntChron Integration tool..
• If your project is not dendrochronological create the record by pressing the [+Record] on the Records/Sites window.  This will prompt you for a record name which should be unique and is typically the core code or some other single word identifier; Edit the record information by double clicking on the Information  tab or using the edit button at the top left;  fill in the record information as explained above.
• Click on the [Data Series] tab and then on [Add to data series] - give your series a unique identifier (single word) which will create the data series.
• Select the data series type to be "IntCal_Data" which will set the correct parameters.
• Press [Import/Export]
• Next, for all data types check that the Options are set up to be correct:
• For dendrochronological projects (using the spreadsheet) set z units to "rings" and z style to "z,z_range"; critically set the t units to the units you have used for t in your spreadsheet (so calBP or AD etc);  leave the header option ticked
• For other projects set the z units to whichever units you have entered z in your spreadsheet - other settings as for the dendrochronogical case
• Copy the data (including the header line) from the import_IntCal.xlsx spreadsheet and paste it into the data exchange window
• Press [OK]
• Check that the data looks ok
• From the main project menu press [File > Save]

Adding references

Data will not normally be included in IntCal before it has been published in a peer-reviewed journal. The reference information which gives most of the details on the methodology and background for the study should be included in the data submission.  References should be given for each radiocarbon data-set submitted. This can be done by navigating the the relevant data series within the record and adding to the references.  See the general instructions for entering references in the IntChron Integration tool.  References can also be entered for the record where this is appropriate (particularly for dendrochronological series) to give background information on the record.  The radiocarbon data-sets should have references entered specifically for the radiocarbon aspects though even if this repeats records at the record level.
The most straight-forward way of entering publications is using the doi and so where possible have this ready when preparing your dataset.

Checking your data

All of the tools can be used to check that the data is correct.  In particular from the record you can use the [Plot] function to plot the data series and see if this looks correct.  The timescales used for plotting can be set using [Edit > Time] from the top level menu.  You can also check the location information using the [Map] function.

Sending your data

You can share your project with other people, including members of the IntCal committee by downloading the project as a JSON file.  To do this press [File > Download] from the top level menu - include all of the data normally.  The JSON file generated in this way can be stored locally and emailed to colleagues.  They can view the file by going to:

• Start a blank IntChron project using the IntCal format by visiting:
  
• https://intchron.org/tools/integrate/integrate.html
• Pressing [File > Upload] and uploading your project - this can either be opened as a new project or merged into another one.
  

Further details on working with project files is given in the main instructions for the IntChron tool.