Difference between revisions of "Category:Chronologies Working Group"

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The following came from P. Reimer by way of T. Guilderson.  
 
The following came from P. Reimer by way of T. Guilderson.  
  
  Key references: Stuiver & Polach [1977] <ref name="SP77">Minze Stuiver and H. A. Polach, 1977. Discussion: Reporting of 14C Data. Radiocarbon 19, 3, 355-363. </ref> and  Reimer et al., [2004] <ref>Paula J. Reimer, T. A. Brown, and R. W. Reimer, 2004.  Discussion: Reporting and calibration of post-bomb 14C Data. Radiocarbon, 46, 3, 1299-1304.</ref>
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  Key references: Stuiver & Polach [1977] <ref name=SP77>Minze Stuiver and H. A. Polach, 1977. Discussion: Reporting of 14C Data. Radiocarbon 19, 3, 355-363. </ref> and  Reimer et al., [2004] <ref>Paula J. Reimer, T. A. Brown, and R. W. Reimer, 2004.  Discussion: Reporting and calibration of post-bomb 14C Data. Radiocarbon, 46, 3, 1299-1304.</ref>
  
 
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Revision as of 13:51, 15 March 2017

An imaginary chronology based on U/Th dates, generated via Bchron
Credit: Julien Emile-Geay (Own work)

Overview

In the Linked Earth context, a working group (WG) is a self-organized coalition of knowledgeable experts, whose activities are governed herewith. This page is dedicated to the discussion of data and metadata standards for chronologies, and aims to formulate a set of recommendations for such a standard.

This WG needs to work closely with other WGs, as constraints will vary by archive. Nevertheless, some aspects are common enough that it is worth pursuing some general recommendations, and devise ad hoc adjustments for individual archives if need be. It is recommended that every WG coordinator join this WG to keep track of discussions.

Members

The chronologies Working Group has one coordinator, Christof Pearce (Stockholm University)

Specific tasks

We recommend that discussions focus on the following techniques, and explore potential commonalities.

For each chronology type, we recommend:

  • structuring discussions around what scientific questions one would want to ask of the data
  • listing essential, recommended, and optional information for:
    • the age models themselves
    • the chronological measurements (ChronData tables, in LiDP/LinkedEarth parlance)
    • their uncertainties, and what those numbers correspond to (e.g. 1-sigma or 2-sigma?)
  • provide an ideal chronology table, so the community knows what to report and how to report it.
  • provide separate recommendations for new and legacy datasets

While it is recognized that most real-word chronologies are of mixed types (e.g. a Holocene lake sediment chronology may blend radiocarbon dates, 210Pb dates, and volcanic ash markers), it is critical to first define guidelines for how to report pure chronologies. Once the foundations are sound, they will be easier to compose together.

Nomenclature

In paleoclimatology, scientists tend to reference the time axis either starting from the present (present often being taken as 1950) and counting positively back in time. In the current LiPD model, this concept is referred to as 'age'. On the other hand, some scientists, especially focusing on the last 2,000 years, use the Gregorian Calendar. In LiPD, this concept is referred to as 'year'.

Should we keep these two separate concepts?
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There were 5 votes since the poll was created on 09:59, 15 March 2017.
poll-id D2C0068BD4358B564E5E598E295FF719

If yes, is the current nomenclature adopted by LiPD correct?

Age

How should we report age?
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There were 6 votes since the poll was created on 10:02, 15 March 2017.
poll-id 84A488E5E21C698D19615F535B80CA41

Year

How should we report year?
You are not entitled to vote.
You are not entitled to view results of this poll.
There were 6 votes since the poll was created on 10:03, 15 March 2017.
poll-id EEF59B83600956C4360A6663F9661701


Tie-point chronologies

Radiocarbon

The following came from P. Reimer by way of T. Guilderson.

Key references: Stuiver & Polach [1977] [1] and  Reimer et al., [2004] [2]

metadata

  • Sample ID
  • type/matrix
  • location (lat, lon, masl/mbsl altitude/depth, depth/height in section/core and referenced)

Radiocarbon Measurements

  • Chemical pretreatment/preparation (oxidation, chemical leach (%), a/b/a, soxhlet, ultrafiltration, none, etc)
  • Method: GPC, LSC, AMS, etc
  • Laboratory ID# (eg. OS####; CAMS####; QUB####)
  • δ13C ratio actual/estimated (PDB/V-PDB) [3]
  • Conventional radiocarbon age as years BP and one-sigma standard deviation [4]
  • F14C (13C and background correction applied)[5]:
We suggest the inclusion of the background and d13C corrected Fraction modern (F14C) as it is the primary reported value.  In the past there has been some inconsistencies in the literature/laboratories with regards to fraction modern.  By using/requesting F14C you will be explicitly requesting 13C and background corrected Fraction Modern (aka F14C, as per Reimer et al.[2004]) as intended by SP77).
  • Correction applied to radiocarbon date prior to, or during conversion to calibrated age:
    • marine reservoir effect:
      • Marine reservoir age, ± one-sigma sd (or square root of the variance) uncertainty, reference/source
      • DELTA_R value, ± one-sigma sd (or square root of the variance) uncertainty, reference/source
  • hard/soft water effect: value, ± one-sigma sd (or square root of var) uncertainty, reference/source
  • other corrections: value (14C years), ± one-sigma sd (or square root of var), reference/source
  • Calibration or conversion to calibrated ages:
As of present, the international radiocarbon community recommends the use of the INTCAL13 (aka Marine 13[6]) and SHCAL13 [7] data products. 
  • Calibration of post-bomb (post 1954/1957) samples should also include the calibration data-set utilized, description/reference of any corrections applied, and the software/algorithm utilized to convert the F14C data to years AD.

Lead

no known existing standard/template

U-series

Layer-counted chronologies

Comboul et al[8] argue that it is critical to report uncertainties in layer-counted chronologies, and that these can be expressed in terms of an undercounting and overcounting rate. However, there needs to be agreement about how to measure and report this rate for various archives.

Varves

Growth rings

Trees, corals, speleothems

Tree-rings typically provide an absolute chronology but there needs to be the facility to also work with 'floating' chronologies anchored typically by radiocarbon. A hybrid dendro-radiocarbon chronological framework should be supported.

Tree-rings data can also be stored at subannual level e.g. with early and latewood parameters. These are typically stored as two different data series as they are normally used to reconstruct different climatic parameters. In chronological terms these datasets represent portions of the year but precisely which portions depends on the species and location. In the southern hemisphere the earlywood will typically grow in the final months of the year and the latewood the first months of the following year. For paleoclimate reconstructions it's therefore essential to include metadata regarding the months each data point covers.

A convention that continues to cause confusion when representing dendrochronological data is the use of the astronomical calendar. The astronomical calendar includes the year 0 so matches the AD calendar, but is one year different in the BC period. Astronomical dates are easier to handle in statistical analyses but have been erroneously quoted as BC years in even some very prestigious articles. Whatever method is used, it should be clear and consistent.

Ice layers

Role of flow models.


Age-modeling software

Content:

  • method (e.g. Bacon, OxCal, BChron, BAM)
  • version
  • parameters
Should the method by which the chronology is obtained be fully documented
You are not entitled to vote.
You are not entitled to view results of this poll.
There were 3 votes since the poll was created on 15:38, 14 March 2017.
poll-id 995EC7654FD3A7F32B1C6029C31FB20A

If documented with the data, should the publication information about the software used in the chronology be:
You are not entitled to vote.
You are not entitled to view results of this poll.
There were 4 votes since the poll was created on 15:38, 14 March 2017.
poll-id 857C1D02FA05E58B01A0BEB496D1E564

If documented with the data, should the code (i.e. parameters used) used for the chronology be:
You are not entitled to vote.
You are not entitled to view results of this poll.
There were 3 votes since the poll was created on 15:39, 14 March 2017.
poll-id AFB996C4DF36B3A5D1E9EC6DF2938178

If documented with the data and using a technique creating ensembles of possible age models, should the ensemble age models be:
You are not entitled to vote.
You are not entitled to view results of this poll.
There were 2 votes since the poll was created on 15:41, 14 March 2017.
poll-id 44A4F1955E6EC42862A54AA52689BCA9

If documented with the data and using a technique creating ensembles of possible age models, should the ensemble statistics (e.g., mean, median, standard deviation, quantiles) be:
You are not entitled to vote.
You are not entitled to view results of this poll.
There were 2 votes since the poll was created on 15:42, 14 March 2017.
poll-id 7D3C2523FB122801F0BC56D8D9926882

Polls

Here are polls that the group might want to consider:

For LEGACY DATASETS:

Should legacy chronologies be updated to the current field standard (e.g. chronologies obtained from IntCal09 should be redone with IntCal13)?
You are not entitled to vote.
You are not entitled to view results of this poll.
There were 4 votes since the poll was created on 15:35, 14 March 2017.
poll-id EE9B5AC53196826693167AAFFAD2B738

References

  1. Minze Stuiver and H. A. Polach, 1977. Discussion: Reporting of 14C Data. Radiocarbon 19, 3, 355-363.
  2. Paula J. Reimer, T. A. Brown, and R. W. Reimer, 2004. Discussion: Reporting and calibration of post-bomb 14C Data. Radiocarbon, 46, 3, 1299-1304.
  3. Note, the AMS measured 13C has low precision (a few per mil, compared to IRMS). Most AMS labs do NOT report the machine measured 13C value because it is frequently misused. This should be estimated as per SP77 or an IRMS-based value/estimate.
  4. Note, that by definition, conventional radiocarbon age is the Libby based age. Most AMS laboratories report 1-sigma sd of the analysis or the 1-sigma sd reproducibility for similar aged/sized material.
  5. This is slightly different than Stuiver and Polach who have "D14C" as the optional parameter.
  6. P. J. Reimer et al., 2013. INTCAL13 and MARINE13 Radiocarbon age calibration curves, 0-50,000 years CAL BP. Radiocarbon, 55, 1869-1887.
  7. A. G. Hogg, et al., 2013. SHCal13 Southern Hemisphere calibration, 0-50,000 years cal BP. Radiocarbon 55, 1889-1903.
  8. Comboul, M., J. Emile-Geay, M. N. Evans, N. Mirnateghi, K. M. Cobb, and D. M. Thompson (2014), A probabilistic model of chronological errors in layer-counted climate proxies: applications to annually banded coral archives, Climate of the Past, 10(2), 825–841, doi:10.5194/cp-10-825-2014

Pages in category "Chronologies Working Group"

This category contains only the following page.

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