Difference between revisions of "Category:Chronologies Working Group"

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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.
 
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 | Christof Pearce (Stockholm University)]]
  
  
__MEMBERS__
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We recommend that discussions focus on the following techniques, and explore potential commonalities.
 
We recommend that discussions focus on the following techniques, and explore potential commonalities.
 +
 +
[[File:MetadataDefinitions.png | thumb | right | 400px | Definition of essential, recommended, and desired in regards to paleoclimate data standards]]
  
 
For each chronology type, we recommend:
 
For each chronology type, we recommend:
 
* structuring discussions around what scientific questions one would want to ask of the data
 
* structuring discussions around what scientific questions one would want to ask of the data
−
* listing essential, recommended, and optional information for:
+
* listing essential, recommended, and desired information for:
 
** the age models themselves
 
** the age models themselves
 
** the chronological measurements (ChronData tables, in LiDP/LinkedEarth parlance)
 
** the chronological measurements (ChronData tables, in LiDP/LinkedEarth parlance)
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While it is recognized that most real-word chronologies are of mixed types (e.g. a Holocene lake sediment chronology may blend radiocarbon dates,  {{SimpleNuclide2|Lead|210}} 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.
 
While it is recognized that most real-word chronologies are of mixed types (e.g. a Holocene lake sediment chronology may blend radiocarbon dates,  {{SimpleNuclide2|Lead|210}} 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 [[Linked_Paleo_Data | 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'.
 +
 +
'''Note''': Do not edit the polls (even for typos) once voting has started as it will reset the vote counts to zero. If a change needs to be made, make an annotation above the old poll (i.e., above the poll tags) and place the new poll below the first one.
 +
 +
[[File:TwitterPoll Chronology AgevsYear.png | 400px |right | thumb | Results of the poll placed on Twitter between July 12th and 19th 2017]]
 +
 +
<poll>
 +
Should we keep these two separate concepts?
 +
Yes
 +
No
 +
</poll>
 +
 +
If yes, is the current nomenclature adopted by LiPD correct?
 +
 +
=== Age ===
 +
 +
[[File:TwitterPoll Chronology AgeReporting.png | 400px | thumb | right | Results of the poll placed on Twitter between July 15th and 22nd 2017]]
 +
 +
<poll>
 +
How should we report age?
 +
Using BP, the present being defined as 1950
 +
Using BP, the present being defined as the latest year in a record
 +
Using BP, the present being defined as 2000
 +
Something else (Comment below)
 +
</poll>
 +
 +
=== Year ===
 +
 +
[[File:TwitterPoll Chronology YearReporting.png | 400px | thumb | right | Results of the poll placed on Twitter between July 15th and 22nd 2017]]
 +
 +
<poll>
 +
How should we report year?
 +
Using AD (anno Domini)
 +
Using CE (Common Era)
 +
</poll>
 +
 +
 +
=== Unifying representations ===
 +
The aforementioned concepts are in fact the same: time.
 +
One way to unify its representation is to recognize that all known applications use something of the form:
 +
 +
'''prefix _ yearlyIncrement _ suffix'''
 +
 +
 +
* Possible instances of '''yearlyIncrement''' are : ''year, years, annum, annums'', etc
 +
* Possible instances of '''prefix''' are: ''none, kilo, mega, giga''; this conveys information about the multiplicative factor that needs to be applied to the increments.
 +
*  Possible instances of '''suffix''' are: ''none, BP, CE, AD''. the suffix conveys  information about the direction of time flow, and the reference point (with some ambiguity that needs resolving).
 +
 +
- For ''years CE'', the prefix is none, the yearlyIncrement is years, the suffix is CE. Thus time flows forward from the origin of the Common Era, which is sometimes placed at year 0 (astronomical calendar, or [https://www.iso.org/iso-8601-date-and-time-format.html ISO8601]), sometimes at year 1. A system for disambiguation is needed (perhaps by attaching an ISO standard).
 +
 +
- For ''kyr BP'' the suffix conveys that time flows in reverse from the present day, again defined with some ambiguity as 1950 CE or 2000 CE (see Age poll). The prefix is kilo, indicating that a factor of 1000 needs to be applied.
 +
 +
- For "Ga", the prefix is giga, indicating a billion factor. The increment is "annum", and the suffix is none, indicating implicitly something like BP (where the 1950 or 2000 reference point is immaterial given the time spans involved.
 +
 +
Thus, the direction of time flow (forward or backward) can always been inferred from context; however, the diversity of spelling and abbreviations makes it difficult for machines to guess this, and thus a more disciplined representation would be helpful. For all representations, one might consider an internal representation like `kilo_years_BP`, and an external representation for display purposes  like `kyr BP`.
 +
 +
Lastly, we note that the excellent ontology of geologic time by Cox & Richard<ref>Cox, S. J. D., and S. M. Richard (2015), A geologic timescale ontology and service, Earth Science Informatics, 8(1), 5–19, doi:10.1007/s12145-014-0170-6.</ref>, which deals with >1Ma time scales, does not encompass such distinctions, and thus a new representation is needed.
 +
 +
== Recommendations from the literature  ==
 +
 +
The recommendations below are from Govin et al. 2015 <ref name = govin2015> Govin. A., E. Capron, P.C. Tzedakis, S. Verheyden, B. Ghaleb, C. Hillaire-Marcel, G. St-Onge, J.S. Stoner, F. Bassinot, L. Bazin, T. Blunier, N. Combourieu-Nebout, A. El Ouahabi, D. Genty, R. Gersonde, P. Jimenez-Amat, A. Landais, B. Martrat, V. Masson-Delmotte, F. Parrain, M.-S. Seidenkrantz, D. Veres, C. Waelbroeck, R. Zahn, 2015. Sequence of events from the onset to the demise of the Last Interglacial: Evaluating strengths and limitations of chronologies used in climatic archives. Quaternary Science Reviews, 129, 1-36, doi:10.1016/j.quadcirev.2015.09.018.</ref>.
 +
 +
<blockquote> "Future climate-stratigraphic alignments should provide (1) a clear statement of climate hypotheses involved, (2) a detailed understanding of environmental parameters controlling selected tracers and (3) a careful evaluation of the synchronicity of aligned paleoclimatic records. We underscore the need to (1) systematically report quantitative estimates of relative and absolute age uncertainties, (2) assess the coherence of chronologies when comparing different records, and (3) integrate these uncertainties in paleoclimatic interpretations and comparisons with climate simulations."</blockquote>
 +
 +
=== Absolute dating of aragonitic corals ===
 +
 +
Dating fossil corals often requires the use of U-series age.
 +
 +
==== Age calculation and its intrinsic uncertainties ====
 +
 +
'''Note''': Do not edit the polls (even for typos) once voting has started as it will reset the vote counts to zero. If a change needs to be made, make an annotation above the old poll (i.e., above the poll tags) and place the new poll below the first one.
 +
 +
<blockquote> "In recent years, most ages have been obtained through high precision TIMS or MC-ICP-MS measurements are are generally given with a ±2&sigma;. Earlier, they were mostly obtained through alpha particle counting and generally cited with a ±1&sigma; uncertainty. <ref name= govin2015 />" </blockquote>
 +
 +
[[File:TwitterPoll Coral USeries UncertaintyReporting.png | 400px | thumb | right | Results of the poll placed on Twitter between July 5th and 12th 2017]]
 +
 +
<poll>
 +
For U-series measurements in coral archive, should the uncertainty be reported as
 +
±2&sigma;
 +
±1&sigma;
 +
something else (comment below).
 +
</poll>
 +
 +
<blockquote> "Some vagueness persists with respect to the way quoted uncertainties include or not all potential sources of analytical errors (internal vs external precision), which makes direct comparison of databases somewhat hazardous. <ref name= govin2015 />" </blockquote>
 +
 +
<blockquote> "Moreover, radiometric age equations include decay constants of all concerned isotopes, which are known with some uncertainty. The comparison of such U-series ages to any other time scale, such as glaciological ages, astronomically-tunes ages and other radiometric ages, requires the U-series decay constant uncertainties to be carried into the final age error calculation <ref name= govin2015 />" </blockquote>
 +
 +
[[File:TwitterPoll Coral Useries DecayConstant New.png | 400px | thumb | right | Results of the poll placed on Twitter between July 5th and 12th 2017]]
 +
 +
<poll>
 +
For U-series uncertainty in coral archive, should the uncertainty in the U-series decay constant for new datasets be:
 +
Essential Metadata
 +
Recommended Metadata
 +
Desired Metadata
 +
</poll>
 +
 +
[[File:TwitterPoll Coral USeries DecayConstant Legacy.png | 400px | thumb | right | Results of the poll placed on Twitter between July 5th and 12th 2017]]
 +
 +
<poll>
 +
For U-series uncertainty in coral archive, should the uncertainty in the U-series decay constant for legacy datasets be:
 +
Essential Metadata
 +
Recommended Metadata
 +
Desired Metadata
 +
</poll>
 +
 +
Comment from [[User:Kcobb]] made on [https://twitter.com/coralsncaves/status/882698713004683264 Twitter] on July 5th 2017: <blockquote> "Should be propagated through full uncertainty analysis in published dating table. But if not there, it's easy to figure out by pub date." </blockquote>
 +
 +
=== Dating of speleothems ===
 +
 +
==== Absolute dating and stratigraphic markers ====
 +
 +
Speleothems can be absolutely dated over the last 600ka with the U-Th methodology <ref> Helmstrom, J., 2006. U-Th dating of speleothems with high initial 230Th using stratigraphical constraint Quaternary Geochronology, 1, 289-295. </ref>, with a dating uncertainty better than 0.5% <ref> Dorale, J., Edwards, R.L., Alexander Jr., E.C., Shen, C.-C., Richards, D., Cheng, H., 2004. Uranium-series dating of speleothems: current techniques, limits, & applications. In: Sasowsky, I., Mylroie, J. (Eds), Studies of Cave Sediments, Springer, US, pp. 1777-197. http://dx.doi.org/10.1007/978-1-4419-9118-8_10. </ref> <ref> Li, H.-C., Ku, T.-L., You, C.-F., Cheng, H., Edwards, R.L., Ma, Z.-B., Tsai, W.-s, Li, M.-D., 2005. 87Sr/86Sr and Sr/Ca in speleothems for paleoclimate reconstruction in Central China between 70 and 280kyr ago. Geochimica and Cosmochimica Acta, 69, 3933-3947. http://dx.doi.org/10.1016/j.gca.2005.01.009. </ref> <ref> Cheng, H., Edwards, R.L., Broecker, W.S., Denton, G.H., Kong, X., Wang, Y., Zhang, R., Wang, X., 2009. Ice age terminations. Science 326, 248-252. http://dx.doi.org/ 10.1126/science.1177840. </ref>.
 +
 +
Recommendation from Govin et al. (2015) <ref name = govin2015 />
 +
 +
<blockquote> "Ideally, new [spleothem] records should present growth rates as high as possible and numerous U-Th dating points in order to (1) reduce dating uncertainty, (2) enhance the robustness of radiometric chronologies on centennial to millennial time scales, (3) maximize constraints on the 'accordion effect' induced by growth rate changes and (4) optimize the assessment of the synchronicity between records. <ref name = govin2015 />"</blockquote>
 +
 +
=== Chronologies in marine sediments ===
 +
 +
{| class="wikitable"
 +
|-
 +
|+Summary of methods used to derive chronologies in marine sediments. Adapted from Govin et al. (2015) <ref name = govin2015 />
 +
|-
 +
! Method || Hypotheses || Age Uncertainties || Strengths || Limitations/difficulties || Recommendation
 +
|-
 +
| Radiocarbon || Reservoir age correction is known and not changing over time|| See [[#Radiocarbon]] || Absolute chronologies || Reservoir Age correction ||
 +
|-
 +
| Synchronization of tephra horizons  || Correct identification of the same tephra in different archives || rowspan = "2"|
 +
*Absolute dating error (if available)
 +
*Synchronization error
 +
||
 +
* Accurate synchronisation
 +
* Several tephra horizons identified during the same interval
 +
* Absolute dating control sometimes possible
 +
||
 +
* Taphonomic issues (reworking, dissemination, dispersion of shards)
 +
* Unequivocal identification of source volcano and eruptive event via diagnostic fingerprinting
 +
||
 +
High potential of synchronization
 +
|-
 +
| Synchronization of geomagnetic excursions and of relative paleointensity records || Global signal || Potential to synchronize paleointensity to cosmogenic isotopic records from ice cores ||
 +
* Large dating uncertainty of geomagnetic excursions
 +
* Uncertainties associated with the magnetization acquisition process
 +
|| Method suitable for local to global synchronization when sediments pass criteria of paleomagnetic reliability
 +
|-
 +
| Benthic foraminifera &delta;<sup>18</sup>O alignment || In-phase benthic &delta;<sup>18</sup>O variations || rowspan = "3"|
 +
* Alignment error (e.g. resolution, matching)
 +
* Uncertainty related to the hypothesis (e.g. possibility of diachronous high-latitude temperature changes)
 +
* Dating uncertainty of the reference
 +
|| Common tracer: many available records || Diachronous deep-water temperature and &delta;<sup>18</sup>O changes across water-masses || Method suitable between sites located within the same water mass
 +
|-
 +
| SST alignment to ice cores || In-phase high-latitude sea surface and air temperature changes || High-resolution ice core records for the last 800 ka ||
 +
* Restricted to high latitudes
 +
* Precise geographical extension of synchronous temperature changes
 +
* Sensitive to uncertainties in SST reconstruction methods (e.g., seasonality, living depth, transport)
 +
|| Method suitable for North Atlantic and Southern Ocean sites
 +
|-
 +
| Marine alignment to speleothems || In-phase regional changes in marine (e.g., SST, salinity, pollen) and continental (e.g., rainfall amount) tracers ||
 +
* High dating accuracy
 +
* Very high-resolution speleothem records
 +
||
 +
* Mostly applicable in tropical and mid-latitude regions (where speleothem records are available)
 +
* Speleothem records sometimes discontinuous
 +
* Climatic drivers of speleothem tracers (moisture availability?)
 +
|| Method suitable for sites (mostly from tropical and mid-latitude regions) located close to well-dated speleothems with well-understood tracers
 +
|}
  
 
== Tie-point chronologies ==
 
== Tie-point chronologies ==
Line 29: Line 204:
 
The following came from P. Reimer by way of T. Guilderson.  
 
The following came from P. Reimer by way of T. Guilderson.  
  
−
==== Data standardization and reporting ====
+
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>
  
−
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>
+
==== metadata ====
  
−
Sample Information (metadata):
+
{| class="wikitable"
 +
|-
 +
|+Table 1: Essential/Recommended/Desired metadata for Radiocarbon measurements
 +
|-
 +
! Metadata || Essential (E)/Recommended(R)/Desired(D) || Reason || Added by (optional)
 +
|-
 +
| Sample ID|| E || Allows to provide a unique identifier to the sample || [[User:Khider|Deborah Khider]] ([[User talk:Khider|talk]]) 15:17, 15 March 2017 (PDT) on behalf of T. Guilderson
 +
|-
 +
| Type/Matrix || E || || [[User:Khider|Deborah Khider]] ([[User talk:Khider|talk]]) 15:17, 15 March 2017 (PDT) on behalf of T. Guilderson
 +
|-
 +
| Location (lat/lon/alt or sample depth) || E || ||[[User:Khider|Deborah Khider]] ([[User talk:Khider|talk]]) 15:17, 15 March 2017 (PDT) on behalf of T. Guilderson
 +
|}
  
−
Sample ID, type/matrix, location (lat, lon, masl/mbsl altitude/depth, depth/height in section/core and referenced), etc.
+
'''Note''': Do not edit the polls (even for typos) once voting has started as it will reset the vote counts to zero. If a change needs to be made, make an annotation above the old poll (i.e., above the poll tags) and place the new poll below the first one.
  
−
==== Radiocarbon Data Table ====
+
[[File:TwitterPoll_Radiocarbon_SampleID.png|thumb|500px|Results of the poll ran on Twitter from March 23rd 2017 to March 30th 2017]]
  
−
* Chemical pretreatment/preparation (oxidation, chemical leach (%), a/b/a, soxhlet, ultrafiltration, none, etc)
+
<poll>
 +
For radiocarbon measurements, should the sample ID be:
 +
Essential Metadata
 +
Recommended Metadata
 +
Desired Metadata
 +
</poll>
  
−
* Method: GPC, LSC, AMS, etc
+
<poll>
 +
For radiocarbon measurements, the type/matrix should be:
 +
Essential Metadata
 +
Recommended Metadata
 +
Desired Metadata
 +
</poll>
  
−
* Laboratory ID# (eg. OS####; CAMS####; QUB####)
+
Polls on whether [[:Category:Location  (L)| location]] information should be essential, recommended or desired metadata for new dataset can be found [[Cross_Archive_Metadata_-_New_datasets | here]] for new datasets and [[Cross_Archive_Metadata_-_Legacy_datasets | here]] for legacy datasets.
  
−
* delta-13C ratio actual/estimated (PDB/V-PDB) <ref>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. </ref>
+
==== Reporting the Radiocarbon measurements ====
  
−
* Conventional radiocarbon age as years BP and one-sigma standard deviation <ref> 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. </ref>
+
{| class="wikitable"
 +
|-
 +
|+Table 2. Essential/Recommended/Desired metadata for reporting radiocarbon measurements
 +
|-
 +
! Metadata|| Essential (E)/Recommended(R)/Desired (D) || Reason/Notes || Added by (optional)
 +
|-
 +
| Chemical pretreatment/preparation || E|| oxidation, chemical leach (%), a/b/a, soxhlet, ultrafiltration, none, etc || [[User:Khider|Deborah Khider]] ([[User talk:Khider|talk]]) 15:37, 15 March 2017 (PDT) on behalf of T Guilderson
 +
|-
 +
|[[:Property:Method (L)| Method]] || E || GPC, LSC, AMS, etc || [[User:Khider|Deborah Khider]] ([[User talk:Khider|talk]]) 15:37, 15 March 2017 (PDT) on behalf of T Guilderson
 +
|-
 +
| Laboratory ID# || E || eg. OS####; CAMS####; QUB#### || [[User:Khider|Deborah Khider]] ([[User talk:Khider|talk]]) 15:37, 15 March 2017 (PDT) on behalf of T Guilderson
 +
|-
 +
| δ{{SimpleNuclide2|Carbon|13}}  ratio actual/estimated (PDB/V-PDB) || R || Note, the AMS measured {{SimpleNuclide2|Carbon|13}} has low precision (a few per mil, compared to IRMS).  Most AMS labs do NOT report the machine measured {{SimpleNuclide2|Carbon|13}} value because it is frequently misused.  This should be estimated as per SP77 <ref name = SP77 /> or an IRMS-based value/estimate. || [[User:Khider|Deborah Khider]] ([[User talk:Khider|talk]]) 15:37, 15 March 2017 (PDT) on behalf of T Guilderson
 +
|-
 +
| Conventional radiocarbon age as years BP || E || Note, that by definition, conventional radiocarbon age is the Libby based age. ||  [[User:Khider|Deborah Khider]] ([[User talk:Khider|talk]]) 15:37, 15 March 2017 (PDT) on behalf of T Guilderson
 +
|-
 +
| one-sigma standard deviation  || E || one-sigma standard deviation ||  [[User:Khider|Deborah Khider]] ([[User talk:Khider|talk]]) 15:37, 15 March 2017 (PDT) on behalf of T Guilderson
 +
|-
 +
|  F14C ({{SimpleNuclide2|Carbon|13}} and background correction applied) || E || This is slightly different than Stuiver and Polach <ref name = SP77 /> who have "D14C" as the optional parameter.
 +
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 {{SimpleNuclide2|Carbon|13}} and background corrected Fraction Modern (aka F14C, as per Reimer et al.[2004]) as intended by SP77.
 +
|| [[User:Khider|Deborah Khider]] ([[User talk:Khider|talk]]) 16:13, 15 March 2017 (PDT) on behalf of T Guilderson
 +
|-
 +
| colspan = '4' |''Correction applied to radiocarbon date prior to, or during conversion to calibrated age''
 +
|-
 +
| colspan = '4' |''Marine Reservoir effect''
 +
|-
 +
| Marine reservoir age, , ± one-sigma sd (or square root of the variance) uncertainty, reference/source ||E|| || [[User:Khider|Deborah Khider]] ([[User talk:Khider|talk]]) 16:13, 15 March 2017 (PDT) on behalf of T Guilderson
 +
|-
 +
|<math>\Delta R</math>  value, ± one-sigma sd (or square root of the variance)  uncertainty, reference/source || E || || [[User:Khider|Deborah Khider]] ([[User talk:Khider|talk]]) 16:13, 15 March 2017 (PDT) on behalf of T Guilderson
 +
|-
 +
| hard/soft water effect: value, ± one-sigma sd (or square root of var) uncertainty, reference/source ||E|| ||[[User:Khider|Deborah Khider]] ([[User talk:Khider|talk]]) 16:13, 15 March 2017 (PDT) on behalf of T Guilderson
 +
|-
 +
| other corrections: value ({{SimpleNuclide2|Carbon|14}} years), ± one-sigma sd (or square root of var), reference/source ||E|| ||[[User:Khider|Deborah Khider]] ([[User talk:Khider|talk]]) 16:13, 15 March 2017 (PDT) on behalf of T Guilderson
 +
|-
 +
| Calibration or conversion to calibrated ages || ||
 +
As of present, the international radiocarbon community recommends the use of the INTCAL13 (aka Marine 13<ref>P. J. Reimer et al., 2013.  INTCAL13 and MARINE13 Radiocarbon age calibration curves, 0-50,000 years CAL BP.  Radiocarbon, 55, 1869-1887.</ref>) and SHCAL13 <ref>A. G. Hogg, et al., 2013.  SHCal13 Southern Hemisphere calibration, 0-50,000 years cal BP.  Radiocarbon 55, 1889-1903.</ref> 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.
 +
|| [[User:Khider|Deborah Khider]] ([[User talk:Khider|talk]]) 16:13, 15 March 2017 (PDT) on behalf of T Guilderson
 +
|}
  
−
* F14C (13C and background correction applied) <ref> This is slightly different than Stuiver and Polach who have "D14C" as the optional parameter. </ref>
+
'''Note''': Do not edit the polls (even for typos) once voting has started as it will reset the vote counts to zero. If a change needs to be made, make an annotation above the old poll (i.e., above the poll tags) and place the new poll below the first one.
  
−
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 Stuiver and Polach (1977).
+
[[File:TwitterPoll Radiocarbon chemicalpretreatment.jpeg|thumb|300px|Results of the poll conducted on Twitter between March 27th 2017 and April 3rd 2017]]
  
 +
<poll>
 +
For Radiocarbon measurements, the chemical pretreatment/preparation of the sample should be:
 +
Essential Metadata
 +
Recommended Metadata
 +
Desired Metadata
 +
</poll>
  
−
* Correction applied to radiocarbon date prior to, or during conversion to calibrated age:
+
[[File:TwitterPoll Radiocarbon Method.png|400px|thumb|right|Results of the poll placed on Twitter between July 12th and 19th 2017]]
  
 +
<poll>
 +
For radiocarbon measurements, the method should be:
 +
Essential metadata
 +
Recommended metadata
 +
Desired metadata
 +
</poll>
  
−
** marine reservoir effect:
+
[[File:TwitterPoll Radiocarbon LabID.png | 400px |thumb|right|Results of the poll placed on Twitter between July 12th and 19th 2017]]
  
−
*** Marine reservoir age, ± one-sigma sd (or square root of the variance) uncertainty, reference/source
+
<poll>
 +
For radiocarbon measurements, the laboratory ID# should be:
 +
Essential metadata
 +
Recommended metadata
 +
Desired metadata
 +
</poll>
  
−
*** DELTA_R  value, ± one-sigma sd (or square root of the variance)  uncertainty, reference/source
+
<poll>
 +
For radiocarbon measurements, the d13C ratio actual/estimated should be:
 +
Essential Metadata
 +
Recommended Metadata
 +
Desired Metadata
 +
</poll>
  
 +
<poll>
 +
For radiocarbon measurements, conventional radiocarbon age as years BP should be:
 +
Essential Metadata
 +
Recommended Metadata
 +
Desired Metadata
 +
</poll>
  
−
* hard/soft water effect: value, ± one-sigma sd (or square root of var) uncertainty, reference/source
+
<poll>
 +
For radiocarbon measurements, the 1-sigma standard deviation on the conventional radiocarbon age should be:
 +
Essential Metadata
 +
Recommended Metadata
 +
Desired Metadata
 +
</poll>
  
−
* other corrections: value (14C years), ± one-sigma sd (or square root of var), reference/source
+
<poll>
 +
For radiocarbon measurements, the F14C should be:
 +
Essential Metadata
 +
Recommended Metadata
 +
Desired Metadata
 +
</poll>
  
−
+
<poll>
 +
For radiocarbon measurements converted to calendar ages, the marine reservoir age, one-sigma sd (or square root of the variance) uncertainty, reference/source should be:
 +
Essential Metadata
 +
Recommended Metadata
 +
Desired Metadata
 +
</poll>
  
−
   
+
<poll>
 +
For radiocarbon measurements converted to calendar ages, the DELTA_R value, ± one-sigma sd (or square root of the variance) uncertainty, reference/source should be:
 +
Essential Metadata
 +
Recommended Metadata
 +
Desired Metadata
 +
</poll>
  
−
* Calibration or conversion to calibrated ages:
+
<poll>
 +
For radiocarbon measurements, the hard/soft water effect: value, ± one-sigma sd (or square root of var) uncertainty, reference/source should be:
 +
Essential Metadata
 +
Recommended Metadata
 +
Desired Metadata
 +
</poll>
  
 +
=== Lead ===
  
−
As of present, the international radiocarbon community recommends the use of the INTCAL13 (aka Marine 13<ref>P. J. Reimer et al., 2013.  INTCAL13 and MARINE13 Radiocarbon age calibration curves, 0-50,000 years CAL BP.  Radiocarbon, 55, 1869-1887.</ref>) and SHCAL13 <ref>A. G. Hogg, et al., 2013.  SHCal13 Southern Hemisphere calibration, 0-50,000 years cal BP.  Radiocarbon 55, 1889-1903.</ref> data products.  
+
Proposed standards from [https://dornsife.usc.edu/cf/faculty-and-staff/faculty.cfm?pid=1003326 Doug Hammond] (University of Southern California).
  
 +
{| class="wikitable"
 +
|-
 +
|+ Recommendation to report 210Pb measurements
 +
|-
 +
! Metadata || Description || Essential (E)/ Recommended (R)/ Desired (D)
 +
|-
 +
| calculated excess <sup>210</sup>Pb values || Total - supported || E for both New and Legacy datasets
 +
|-
 +
| <sup>226</sup>Ra || The supported <sup>210</sup>Pb  || D for both new and legacy datasets
 +
|-
 +
| Total <sup>210</sup>Pb ||  || D for both new and legacy datasets
 +
|-
 +
| Whether a salt correction is made || || D for both new and legacy datasets
 +
|-
 +
| Porosity || necessary to do a salt correction || D for both new and legacy datasets
 +
|-
 +
| Measurement methodology || alpha spectrometry, gamma spectrometry... || R for both new and legacy datasets
 +
|-
 +
| Units || Recommend to report units in Bq/kg ||
 +
|-
 +
| rowspan = "3"|Depth || A way to locate where on the archive the measurements was made || E
 +
|-
 +
| mid-depth || E for both new and legacy datasets
 +
|-
 +
| interval top/bottom || R for both new and legacy datasets
 +
|-
 +
| core collectionDate || Necessary to convert the excess <sup>210</sup>Pb values to calendar age
 +
Recommend to correct the reported activities to the collectionDate
 +
|| E for both new and legacy datasets
 +
|-
 +
| Methodology used to calculate age || || E for both new and legacy datasets
 +
|}
  
 +
The same standards (excluding supporting measurements, which do not apply) are proposed for <sup>137</sup>Cs measurements which are often made alongside <sup>210</sup>Pb.
  
−
* Software Program/Algorithm used: eg., Bacon_v2.1, Calib_v7.x, CaliBomb_vy, CalPal, OxCal_vy, etc
+
'''Note''': Do not edit the polls (even for typos) once voting has started as it will reset the vote counts to zero. If a change needs to be made, make an annotation above the old poll (i.e., above the poll tags) and place the new poll below the first one.
−
(need section on age model reporting)
+
−
+
  
−
* 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.
+
[[File:TwitterPoll 210Pb ExcessValues.png | 400px | right| thumb | Results of the poll placed on Twitter between July 17th-24th 2017]]
  
 +
<poll>
 +
Should the calculated excess <sup>210</sup>Pb values be considered:
 +
Essential Metadata
 +
Recommended Metadata
 +
Desired Metadata
 +
</poll>
  
 +
[[File:TwitterPoll 210Pb Supportedactivties.png|400px|thumb|right|Results of the poll placed on Twitter from March 30th to April 6th 2017]]
  
 +
<poll>
 +
Should the supported activities (<sup>226</sup>Ra) be considered:
 +
Essential Metadata
 +
Recommended Metadata
 +
Desired Metadata
 +
</poll>
  
 +
[[File:TwitterPoll 210Pb totalMeasured.png | 400px |thumb | right | Results of the poll placed on Twitter from July 17th to 24th]]
  
−
=== Lead ===
+
<poll>
 +
Should the measured total <sup>210</sup>Pb be considered:
 +
Essential Metadata
 +
Recommended Metadata
 +
Desired Metadata
 +
</poll>
 +
 
 +
[[File:TwitterPoll 210Pb SaltCorrection.png | 400px | right |thumb| Results of the poll placed on Twitter between July 17th and 24th 2017]]
 +
 
 +
<poll>
 +
For <sup>210</sup>Pb chronologies, should the reporting of a salt correction be considered:
 +
Essential Metadata
 +
Recommended Metadata
 +
Desired Metadata
 +
</poll>
 +
 
 +
<poll>
 +
For <sup>210</sup>Pb chronologies, should the archive porosity be considered:
 +
Essential Metadata
 +
Recommended Metadata
 +
Desired Metadata
 +
</poll>
 +
 
 +
<poll>
 +
For <sup>210</sup>Pb chronologies, should the measurement methodology be considered:
 +
Essential Metadata
 +
Recommended Metadata
 +
Desired Metadata
 +
</poll>
 +
 
 +
<poll>
 +
For <sup>210</sup>Pb chronologies, should the activities be reported in:
 +
Bq/kg
 +
other
 +
No imposed units but units should be reported
 +
</poll>
 +
 
 +
<poll>
 +
For <sup>210</sup>Pb chronologies, should depth be considered:
 +
Essential Metadata
 +
Recommended Metadata
 +
Desired Metadata
 +
</poll>
 +
 
 +
<poll>
 +
For <sup>210</sup>Pb chronologies, should the archive collectionDate be considered:
 +
Essential Metadata
 +
Recommended Metadata
 +
Desired Metadata
 +
</poll>
 +
 
 +
<poll>
 +
For <sup>210</sup>Pb chronologies, should the method used to convert to calendar age be considered:
 +
Essential Metadata
 +
Recommended Metadata
 +
Desired Metadata
 +
</poll>
  
−
no known existing standard/template
 
 
=== U-series ===
 
=== U-series ===
 +
A standard was recently proposed by Dutton et al [2017]<ref>A. Dutton, K. Rubin, N. McLean, J. Bowring, E. Bard, R.L. Edwards, G.M. Henderson, M.R. Reid, D.A. Richards, K.W.W. Sims, J.D. Walker, Y. Yokoyama, Data reporting standards for publication of U-series data for geochronology and timescale assessment in the earth sciences, Quaternary Geochronology, Volume 39, April 2017, Pages 142-149, [http://doi.org/10.1016/j.quageo.2017.03.001 DOI]</ref>. We suggest to re-use it wholesale.
  
 
== Layer-counted chronologies ==
 
== Layer-counted chronologies ==
Line 102: Line 490:
 
=== Growth rings ===
 
=== Growth rings ===
 
Trees, corals, speleothems
 
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 ===
 
=== Ice layers ===
 
Role of flow models.  
 
Role of flow models.  
  
−
== Polls ==
 
  
−
Here are polls that the group might want to consider:
+
== Age-modeling software ==
 +
 
 +
Content:
 +
* method (e.g. Bacon, OxCal, BChron, BAM)
 +
* version
 +
* parameters
 +
 
 +
'''Note''': Do not edit the polls (even for typos) once voting has started as it will reset the vote counts to zero. If a change needs to be made, make an annotation above the old poll (i.e., above the poll tags) and place the new poll below the first one.
 +
 
 +
[[File:TwitterPoll AgeModeling Software.png | thumb | 400px | right | Results of the poll placed on Twitter between April 25th and May 2nd 2017]]
 +
 
 +
<poll>
 +
Should the method by which the chronology is obtained be fully documented
 +
with the data
 +
in the paper only
 +
both with the data and in the paper
 +
</poll>
 +
 
 +
[[File:TwitterPoll PublicationSoftwareChronology.png | thumb | 400px | right | Results of the poll placed on Twitter between April 25th and May 2nd 2017]]
  
−
For '''NEW DATASETS''': (this is a dummy poll; please update)
 
 
<poll>
 
<poll>
−
What is your favorite chronology poll?
+
If documented with the data, should the publication information about the software used in the chronology be:
−
A poll that is droll
+
Essential Metadata
−
A poll with a role
+
Recommended Metadata
−
A poll with a roll
+
Desired Metadata
 
</poll>
 
</poll>
  
−
For '''LEGACY DATASETS''':
 
 
<poll>
 
<poll>
−
What should we do with legacy chronologies?
+
If documented with the data, should the code (i.e. parameters used) used for the chronology be:
−
Contact original authors to obtain their uncalibrated dates
+
Essential Metadata
−
Curse authors who were too short-sighted to archive uncalibrated dates
+
Recommended Metadata
−
Ignore them altogether
+
Desired Metadata
 +
</poll>
 +
 
 +
<poll>
 +
If documented with the data and using a technique creating ensembles of possible age models, should the ensemble age models be:
 +
Essential Metadata
 +
Recommended Metadata
 +
Desired Metadata
 +
</poll>
 +
 
 +
<poll>
 +
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:
 +
Essential Metadata
 +
Recommended Metadata
 +
Desired Metadata
 +
</poll>
 +
 
 +
== Relative chronologies ==
 +
 
 +
Example of relative chronologies include benthic &delta;18O alignment, paleomagnetic data...
 +
 
 +
{| class="wikitable"
 +
|-
 +
|+Essential/Recommended/Desired metadata for reporting relative chronologies
 +
|-
 +
! Metadata|| Essential (E)/Recommended(R)/Desired (D) || Reason/Notes || Added by (optional)
 +
|-
 +
| [[:Category:MeasuredVariable_(L)]] || E|| &delta;18O, magnetic direction/intensity || [[User:Khider|Deborah Khider]] ([[User talk:Khider|talk]]) 12:16, 14 September 2017 (PDT)
 +
|-
 +
| The target || E|| Which record was used as target for the alignment? || [[User:Khider|Deborah Khider]] ([[User talk:Khider|talk]]) 12:16, 14 September 2017 (PDT)
 +
|-
 +
| Labeling features ||E for manual alignment/D for automated alignment || Which features of the records were used as tie points || [[User:Khider|Deborah Khider]] ([[User talk:Khider|talk]]) 12:16, 14 September 2017 (PDT)
 +
|-
 +
| Method ||E || Either the software employed or if by hand, the fit strategy || [[User:Khider|Deborah Khider]] ([[User talk:Khider|talk]]) 12:16, 14 September 2017 (PDT)
 +
|-
 +
| Flag for mixed chronologies ||R || || [[User:Khider|Deborah Khider]] ([[User talk:Khider|talk]]) 12:16, 14 September 2017 (PDT)
 +
|}
 +
 
 +
<poll>
 +
For relative chronologies, should the original measurements (e.g. d18O, magnetic direction/intensity) be:
 +
Essential
 +
Recommended
 +
Desired
 +
</poll>
 +
 
 +
<poll>
 +
For relative chronologies, should the alignment target be:
 +
Essential
 +
Recommended
 +
Desired
 +
</poll>
 +
 
 +
<poll>
 +
For relative chronologies, should the labeling features be:
 +
Essential
 +
Recommended
 +
Desired
 +
</poll>
 +
 
 +
<poll>
 +
For relative chronologies, should the method (use of software, manual alignment) be:
 +
Essential
 +
Recommended
 +
Desired
 +
</poll>
 +
 
 +
== Polls ==
 +
 
 +
'''Note''': Do not edit the polls (even for typos) once voting has started as it will reset the vote counts to zero. If a change needs to be made, make an annotation above the old poll (i.e., above the poll tags) and place the new poll below the first one.
 +
 
 +
Here are polls that the group might want to consider:
 +
 
 +
For '''LEGACY DATASETS''':
 +
<poll>
 +
Should legacy chronologies be updated to the current field standard (e.g. chronologies obtained from IntCal09 should be redone with IntCal13)?
 +
Yes, if raw data is available
 +
No, but put a warning on the chronologies
 +
No
 
</poll>
 
</poll>
  
 
==References==
 
==References==
 
<references \>
 
<references \>

Latest revision as of 19:04, 18 September 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)

__MEMBERS__

Specific tasks

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

Definition of essential, recommended, and desired in regards to paleoclimate data standards

For each chronology type, we recommend:

  • structuring discussions around what scientific questions one would want to ask of the data
  • listing essential, recommended, and desired 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'.

Note: Do not edit the polls (even for typos) once voting has started as it will reset the vote counts to zero. If a change needs to be made, make an annotation above the old poll (i.e., above the poll tags) and place the new poll below the first one.

Results of the poll placed on Twitter between July 12th and 19th 2017
Should we keep these two separate concepts?
You are not entitled to vote.
You are not entitled to view results of this poll.
There were 5 votes since the poll was created on 17:59, 15 March 2017.
poll-id D2C0068BD4358B564E5E598E295FF719

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

Age

Results of the poll placed on Twitter between July 15th and 22nd 2017
How should we report age?
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 18:02, 15 March 2017.
poll-id 84A488E5E21C698D19615F535B80CA41

Year

Results of the poll placed on Twitter between July 15th and 22nd 2017
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 18:03, 15 March 2017.
poll-id EEF59B83600956C4360A6663F9661701


Unifying representations

The aforementioned concepts are in fact the same: time. One way to unify its representation is to recognize that all known applications use something of the form: 

prefix _ yearlyIncrement _ suffix


  • Possible instances of yearlyIncrement are : year, years, annum, annums, etc
  • Possible instances of prefix are: none, kilo, mega, giga; this conveys information about the multiplicative factor that needs to be applied to the increments.
  • Possible instances of suffix are: none, BP, CE, AD. the suffix conveys information about the direction of time flow, and the reference point (with some ambiguity that needs resolving).

- For years CE, the prefix is none, the yearlyIncrement is years, the suffix is CE. Thus time flows forward from the origin of the Common Era, which is sometimes placed at year 0 (astronomical calendar, or ISO8601), sometimes at year 1. A system for disambiguation is needed (perhaps by attaching an ISO standard).

- For kyr BP the suffix conveys that time flows in reverse from the present day, again defined with some ambiguity as 1950 CE or 2000 CE (see Age poll). The prefix is kilo, indicating that a factor of 1000 needs to be applied.

- For "Ga", the prefix is giga, indicating a billion factor. The increment is "annum", and the suffix is none, indicating implicitly something like BP (where the 1950 or 2000 reference point is immaterial given the time spans involved.

Thus, the direction of time flow (forward or backward) can always been inferred from context; however, the diversity of spelling and abbreviations makes it difficult for machines to guess this, and thus a more disciplined representation would be helpful. For all representations, one might consider an internal representation like `kilo_years_BP`, and an external representation for display purposes like `kyr BP`.

Lastly, we note that the excellent ontology of geologic time by Cox & Richard[1], which deals with >1Ma time scales, does not encompass such distinctions, and thus a new representation is needed.

Recommendations from the literature

The recommendations below are from Govin et al. 2015 [2].

"Future climate-stratigraphic alignments should provide (1) a clear statement of climate hypotheses involved, (2) a detailed understanding of environmental parameters controlling selected tracers and (3) a careful evaluation of the synchronicity of aligned paleoclimatic records. We underscore the need to (1) systematically report quantitative estimates of relative and absolute age uncertainties, (2) assess the coherence of chronologies when comparing different records, and (3) integrate these uncertainties in paleoclimatic interpretations and comparisons with climate simulations."

Absolute dating of aragonitic corals

Dating fossil corals often requires the use of U-series age.

Age calculation and its intrinsic uncertainties

Note: Do not edit the polls (even for typos) once voting has started as it will reset the vote counts to zero. If a change needs to be made, make an annotation above the old poll (i.e., above the poll tags) and place the new poll below the first one.

"In recent years, most ages have been obtained through high precision TIMS or MC-ICP-MS measurements are are generally given with a ±2σ. Earlier, they were mostly obtained through alpha particle counting and generally cited with a ±1σ uncertainty. [2]"
Results of the poll placed on Twitter between July 5th and 12th 2017
For U-series measurements in coral archive, should the uncertainty be reported as
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 19:39, 29 March 2017.
poll-id 8F6390D1C46244A8CB20D9F3BFE83F22

"Some vagueness persists with respect to the way quoted uncertainties include or not all potential sources of analytical errors (internal vs external precision), which makes direct comparison of databases somewhat hazardous. [2]"
"Moreover, radiometric age equations include decay constants of all concerned isotopes, which are known with some uncertainty. The comparison of such U-series ages to any other time scale, such as glaciological ages, astronomically-tunes ages and other radiometric ages, requires the U-series decay constant uncertainties to be carried into the final age error calculation [2]"
Results of the poll placed on Twitter between July 5th and 12th 2017
For U-series uncertainty in coral archive, should the uncertainty in the U-series decay constant for new datasets 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 20:57, 20 March 2017.
poll-id 9F38149046E9E5931EB22346B63BE3C8

Results of the poll placed on Twitter between July 5th and 12th 2017
For U-series uncertainty in coral archive, should the uncertainty in the U-series decay constant for legacy datasets 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 20:57, 20 March 2017.
poll-id 383DEB45E82A99D8069455AB247EFC4F

Comment from User:Kcobb made on Twitter on July 5th 2017:
"Should be propagated through full uncertainty analysis in published dating table. But if not there, it's easy to figure out by pub date."

Dating of speleothems

Absolute dating and stratigraphic markers

Speleothems can be absolutely dated over the last 600ka with the U-Th methodology [3], with a dating uncertainty better than 0.5% [4] [5] [6].

Recommendation from Govin et al. (2015) [2]

"Ideally, new [spleothem] records should present growth rates as high as possible and numerous U-Th dating points in order to (1) reduce dating uncertainty, (2) enhance the robustness of radiometric chronologies on centennial to millennial time scales, (3) maximize constraints on the 'accordion effect' induced by growth rate changes and (4) optimize the assessment of the synchronicity between records. [2]"

Chronologies in marine sediments

Summary of methods used to derive chronologies in marine sediments. Adapted from Govin et al. (2015) [2]
Method Hypotheses Age Uncertainties Strengths Limitations/difficulties Recommendation
Radiocarbon Reservoir age correction is known and not changing over time See #Radiocarbon Absolute chronologies Reservoir Age correction
Synchronization of tephra horizons Correct identification of the same tephra in different archives
  • Absolute dating error (if available)
  • Synchronization error
  • Accurate synchronisation
  • Several tephra horizons identified during the same interval
  • Absolute dating control sometimes possible
  • Taphonomic issues (reworking, dissemination, dispersion of shards)
  • Unequivocal identification of source volcano and eruptive event via diagnostic fingerprinting

High potential of synchronization

Synchronization of geomagnetic excursions and of relative paleointensity records Global signal Potential to synchronize paleointensity to cosmogenic isotopic records from ice cores
  • Large dating uncertainty of geomagnetic excursions
  • Uncertainties associated with the magnetization acquisition process
 Method suitable for local to global synchronization when sediments pass criteria of paleomagnetic reliability
Benthic foraminifera δ18O alignment In-phase benthic δ18O variations
  • Alignment error (e.g. resolution, matching)
  • Uncertainty related to the hypothesis (e.g. possibility of diachronous high-latitude temperature changes)
  • Dating uncertainty of the reference
Common tracer: many available records Diachronous deep-water temperature and δ18O changes across water-masses Method suitable between sites located within the same water mass
SST alignment to ice cores In-phase high-latitude sea surface and air temperature changes High-resolution ice core records for the last 800 ka
  • Restricted to high latitudes
  • Precise geographical extension of synchronous temperature changes
  • Sensitive to uncertainties in SST reconstruction methods (e.g., seasonality, living depth, transport)
 Method suitable for North Atlantic and Southern Ocean sites
Marine alignment to speleothems In-phase regional changes in marine (e.g., SST, salinity, pollen) and continental (e.g., rainfall amount) tracers
  • High dating accuracy
  • Very high-resolution speleothem records
  • Mostly applicable in tropical and mid-latitude regions (where speleothem records are available)
  • Speleothem records sometimes discontinuous
  • Climatic drivers of speleothem tracers (moisture availability?)
 Method suitable for sites (mostly from tropical and mid-latitude regions) located close to well-dated speleothems with well-understood tracers

Tie-point chronologies

Radiocarbon

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

Key references: Stuiver & Polach [1977] [7] and Reimer et al., [2004] [8]

metadata

Table 1: Essential/Recommended/Desired metadata for Radiocarbon measurements
Metadata Essential (E)/Recommended(R)/Desired(D) Reason Added by (optional)
Sample ID E Allows to provide a unique identifier to the sample Deborah Khider (talk) 15:17, 15 March 2017 (PDT) on behalf of T. Guilderson
Type/Matrix E Deborah Khider (talk) 15:17, 15 March 2017 (PDT) on behalf of T. Guilderson
Location (lat/lon/alt or sample depth) E Deborah Khider (talk) 15:17, 15 March 2017 (PDT) on behalf of T. Guilderson

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Results of the poll ran on Twitter from March 23rd 2017 to March 30th 2017
For radiocarbon measurements, should the sample ID be:
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There were 4 votes since the poll was created on 22:21, 15 March 2017.
poll-id E6013E78D3258F7514048F352CC002B6

For radiocarbon measurements, the type/matrix should be:
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There were 4 votes since the poll was created on 22:23, 15 March 2017.
poll-id 3A6E5ACD2E51DC714A46792D5F2145B1

Polls on whether location information should be essential, recommended or desired metadata for new dataset can be found here for new datasets and here for legacy datasets.

Reporting the Radiocarbon measurements

Table 2. Essential/Recommended/Desired metadata for reporting radiocarbon measurements
Metadata Essential (E)/Recommended(R)/Desired (D) Reason/Notes Added by (optional)
Chemical pretreatment/preparation E oxidation, chemical leach (%), a/b/a, soxhlet, ultrafiltration, none, etc Deborah Khider (talk) 15:37, 15 March 2017 (PDT) on behalf of T Guilderson
Method E GPC, LSC, AMS, etc Deborah Khider (talk) 15:37, 15 March 2017 (PDT) on behalf of T Guilderson
Laboratory ID# E eg. OS####; CAMS####; QUB#### Deborah Khider (talk) 15:37, 15 March 2017 (PDT) on behalf of T Guilderson
δ13C ratio actual/estimated (PDB/V-PDB) R 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 [7] or an IRMS-based value/estimate. Deborah Khider (talk) 15:37, 15 March 2017 (PDT) on behalf of T Guilderson
Conventional radiocarbon age as years BP E Note, that by definition, conventional radiocarbon age is the Libby based age. Deborah Khider (talk) 15:37, 15 March 2017 (PDT) on behalf of T Guilderson
one-sigma standard deviation E one-sigma standard deviation Deborah Khider (talk) 15:37, 15 March 2017 (PDT) on behalf of T Guilderson
F14C (13C and background correction applied) E This is slightly different than Stuiver and Polach [7] who have "D14C" as the optional parameter. 
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.
Deborah Khider (talk) 16:13, 15 March 2017 (PDT) on behalf of T Guilderson
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 E Deborah Khider (talk) 16:13, 15 March 2017 (PDT) on behalf of T Guilderson
\Delta R value, ± one-sigma sd (or square root of the variance) uncertainty, reference/source E Deborah Khider (talk) 16:13, 15 March 2017 (PDT) on behalf of T Guilderson
hard/soft water effect: value, ± one-sigma sd (or square root of var) uncertainty, reference/source E Deborah Khider (talk) 16:13, 15 March 2017 (PDT) on behalf of T Guilderson
other corrections: value (14C years), ± one-sigma sd (or square root of var), reference/source E Deborah Khider (talk) 16:13, 15 March 2017 (PDT) on behalf of T Guilderson
Calibration or conversion to calibrated ages 
As of present, the international radiocarbon community recommends the use of the INTCAL13 (aka Marine 13[9]) and SHCAL13 [10] 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.
Deborah Khider (talk) 16:13, 15 March 2017 (PDT) on behalf of T Guilderson

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Results of the poll conducted on Twitter between March 27th 2017 and April 3rd 2017
For Radiocarbon measurements, the chemical pretreatment/preparation of the sample should be:
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There were 5 votes since the poll was created on 23:17, 15 March 2017.
poll-id 78202BE8846AE9F82E3C8D0FF8873D02

Results of the poll placed on Twitter between July 12th and 19th 2017
For radiocarbon measurements, the method should be:
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There were 4 votes since the poll was created on 23:17, 15 March 2017.
poll-id 6DB651F90B192B8EE2EFDDAAFF6C2B4F

Results of the poll placed on Twitter between July 12th and 19th 2017
For radiocarbon measurements, the laboratory ID# should be:
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There were 5 votes since the poll was created on 23:17, 15 March 2017.
poll-id 5054B8790D14CB3C1B3D267F3E22DE4C

For radiocarbon measurements, the d13C ratio actual/estimated should be:
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There were 4 votes since the poll was created on 23:18, 15 March 2017.
poll-id 8CF78D6D9F4CA9393100A7667DBE8A3F

For radiocarbon measurements, conventional radiocarbon age as years BP should be:
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There were 4 votes since the poll was created on 23:19, 15 March 2017.
poll-id 6654AC7134BAA4FBBA27A25B263B69B1

For radiocarbon measurements, the 1-sigma standard deviation on the conventional radiocarbon age should be:
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There were 4 votes since the poll was created on 23:20, 15 March 2017.
poll-id C7413E58CD0E740BE1015BF471706D18

For radiocarbon measurements, the F14C should be:
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There were 3 votes since the poll was created on 23:21, 15 March 2017.
poll-id 1F95A055C058CCD63002CDE71C31592F

For radiocarbon measurements converted to calendar ages, the marine reservoir age, one-sigma sd (or square root of the variance) uncertainty, reference/source should be:
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There were 5 votes since the poll was created on 23:22, 15 March 2017.
poll-id ECDA562DFA3D428A56997248E0D36175

For radiocarbon measurements converted to calendar ages, the DELTA_R value, ± one-sigma sd (or square root of the variance) uncertainty, reference/source should be:
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There were 5 votes since the poll was created on 23:38, 15 March 2017.
poll-id BABD6BFB79107997D8EDABC556177F82

For radiocarbon measurements, the hard/soft water effect: value, ± one-sigma sd (or square root of var) uncertainty, reference/source should be:
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There was one vote since the poll was created on 23:38, 15 March 2017.
poll-id 873E0B9012B11CAB074C44F049C17B87

Lead

Proposed standards from Doug Hammond (University of Southern California).

Recommendation to report 210Pb measurements
Metadata Description Essential (E)/ Recommended (R)/ Desired (D)
calculated excess 210Pb values Total - supported E for both New and Legacy datasets
226Ra The supported 210Pb D for both new and legacy datasets
Total 210Pb D for both new and legacy datasets
Whether a salt correction is made D for both new and legacy datasets
Porosity necessary to do a salt correction D for both new and legacy datasets
Measurement methodology alpha spectrometry, gamma spectrometry... R for both new and legacy datasets
Units Recommend to report units in Bq/kg
Depth A way to locate where on the archive the measurements was made E
mid-depth E for both new and legacy datasets
interval top/bottom R for both new and legacy datasets
core collectionDate Necessary to convert the excess 210Pb values to calendar age

Recommend to correct the reported activities to the collectionDate

E for both new and legacy datasets
Methodology used to calculate age E for both new and legacy datasets

The same standards (excluding supporting measurements, which do not apply) are proposed for 137Cs measurements which are often made alongside 210Pb.

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Results of the poll placed on Twitter between July 17th-24th 2017
Should the calculated excess 210Pb values be considered:
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There were 3 votes since the poll was created on 04:31, 23 March 2017.
poll-id F2B50A2D9E7A28C350C863BC5344EFAC

Results of the poll placed on Twitter from March 30th to April 6th 2017
Should the supported activities (226Ra) be considered:
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There were 3 votes since the poll was created on 04:31, 23 March 2017.
poll-id 6B9986C74DE1D835AD2134D0FBC42F88

Results of the poll placed on Twitter from July 17th to 24th
Should the measured total 210Pb be considered:
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There were 3 votes since the poll was created on 04:32, 23 March 2017.
poll-id 340D1FB46BC1E0E0A44950EE33A97108

Results of the poll placed on Twitter between July 17th and 24th 2017
For 210Pb chronologies, should the reporting of a salt correction be considered:
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There were 3 votes since the poll was created on 04:40, 23 March 2017.
poll-id 05501AFC8D35560467941FCD24576B8A

For 210Pb chronologies, should the archive porosity be considered:
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There were 3 votes since the poll was created on 04:40, 23 March 2017.
poll-id 181DCFBC24604291F434FB9CD7F51A20

For 210Pb chronologies, should the measurement methodology be considered:
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There were 2 votes since the poll was created on 04:40, 23 March 2017.
poll-id 891B68A7B5BA1B1C466ACAA587B9F439

For 210Pb chronologies, should the activities be reported in:
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There were 2 votes since the poll was created on 04:40, 23 March 2017.
poll-id AE0852F3B711AAAB64C353C8FA5E4940

For 210Pb chronologies, should depth be considered:
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There were 2 votes since the poll was created on 04:40, 23 March 2017.
poll-id 02CFD3844C4DAF8F0EA94040B9D17EE3

For 210Pb chronologies, should the archive collectionDate be considered:
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There were 2 votes since the poll was created on 04:40, 23 March 2017.
poll-id CB743DD19273EF77DC03BD5640161C9B

For 210Pb chronologies, should the method used to convert to calendar age be considered:
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There was one vote since the poll was created on 04:40, 23 March 2017.
poll-id 0885F6472066B693111BCD8598DAA74E

U-series

A standard was recently proposed by Dutton et al [2017][11]. We suggest to re-use it wholesale.

Layer-counted chronologies

Comboul et al[12] 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

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Results of the poll placed on Twitter between April 25th and May 2nd 2017
Should the method by which the chronology is obtained be fully documented
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There were 3 votes since the poll was created on 23:38, 14 March 2017.
poll-id 995EC7654FD3A7F32B1C6029C31FB20A

Results of the poll placed on Twitter between April 25th and May 2nd 2017
If documented with the data, should the publication information about the software used in the chronology be:
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There were 4 votes since the poll was created on 23:38, 14 March 2017.
poll-id 857C1D02FA05E58B01A0BEB496D1E564

If documented with the data, should the code (i.e. parameters used) used for the chronology be:
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There were 3 votes since the poll was created on 23:39, 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:
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There were 2 votes since the poll was created on 23:41, 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:
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There were 2 votes since the poll was created on 23:42, 14 March 2017.
poll-id 7D3C2523FB122801F0BC56D8D9926882

Relative chronologies

Example of relative chronologies include benthic δ18O alignment, paleomagnetic data...

Essential/Recommended/Desired metadata for reporting relative chronologies
Metadata Essential (E)/Recommended(R)/Desired (D) Reason/Notes Added by (optional)
Category:MeasuredVariable_(L) E δ18O, magnetic direction/intensity Deborah Khider (talk) 12:16, 14 September 2017 (PDT)
The target E Which record was used as target for the alignment? Deborah Khider (talk) 12:16, 14 September 2017 (PDT)
Labeling features E for manual alignment/D for automated alignment Which features of the records were used as tie points Deborah Khider (talk) 12:16, 14 September 2017 (PDT)
Method E Either the software employed or if by hand, the fit strategy Deborah Khider (talk) 12:16, 14 September 2017 (PDT)
Flag for mixed chronologies R Deborah Khider (talk) 12:16, 14 September 2017 (PDT)
For relative chronologies, should the original measurements (e.g. d18O, magnetic direction/intensity) be:
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There were 0 votes since the poll was created on 19:02, 18 September 2017.
poll-id 5035647457EDB001BB5C9F11BB0646D4

For relative chronologies, should the alignment target be:
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There were 0 votes since the poll was created on 19:03, 18 September 2017.
poll-id E36DC4B0DBAD68DDE9F48ECBF13DD3DB

For relative chronologies, should the labeling features be:
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There were 0 votes since the poll was created on 19:03, 18 September 2017.
poll-id 3F96717E063710F9175843431F321EC1

For relative chronologies, should the method (use of software, manual alignment) be:
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There were 0 votes since the poll was created on 19:04, 18 September 2017.
poll-id 0D62CB36B8D1031ED5393B66BA417388

Polls

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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)?
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There were 4 votes since the poll was created on 23:35, 14 March 2017.
poll-id EE9B5AC53196826693167AAFFAD2B738

References

  1. ↑ Cox, S. J. D., and S. M. Richard (2015), A geologic timescale ontology and service, Earth Science Informatics, 8(1), 5–19, doi:10.1007/s12145-014-0170-6.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Govin. A., E. Capron, P.C. Tzedakis, S. Verheyden, B. Ghaleb, C. Hillaire-Marcel, G. St-Onge, J.S. Stoner, F. Bassinot, L. Bazin, T. Blunier, N. Combourieu-Nebout, A. El Ouahabi, D. Genty, R. Gersonde, P. Jimenez-Amat, A. Landais, B. Martrat, V. Masson-Delmotte, F. Parrain, M.-S. Seidenkrantz, D. Veres, C. Waelbroeck, R. Zahn, 2015. Sequence of events from the onset to the demise of the Last Interglacial: Evaluating strengths and limitations of chronologies used in climatic archives. Quaternary Science Reviews, 129, 1-36, doi:10.1016/j.quadcirev.2015.09.018.
  3. ↑ Helmstrom, J., 2006. U-Th dating of speleothems with high initial 230Th using stratigraphical constraint Quaternary Geochronology, 1, 289-295.
  4. ↑ Dorale, J., Edwards, R.L., Alexander Jr., E.C., Shen, C.-C., Richards, D., Cheng, H., 2004. Uranium-series dating of speleothems: current techniques, limits, & applications. In: Sasowsky, I., Mylroie, J. (Eds), Studies of Cave Sediments, Springer, US, pp. 1777-197. http://dx.doi.org/10.1007/978-1-4419-9118-8_10.
  5. ↑ Li, H.-C., Ku, T.-L., You, C.-F., Cheng, H., Edwards, R.L., Ma, Z.-B., Tsai, W.-s, Li, M.-D., 2005. 87Sr/86Sr and Sr/Ca in speleothems for paleoclimate reconstruction in Central China between 70 and 280kyr ago. Geochimica and Cosmochimica Acta, 69, 3933-3947. http://dx.doi.org/10.1016/j.gca.2005.01.009.
  6. ↑ Cheng, H., Edwards, R.L., Broecker, W.S., Denton, G.H., Kong, X., Wang, Y., Zhang, R., Wang, X., 2009. Ice age terminations. Science 326, 248-252. http://dx.doi.org/ 10.1126/science.1177840.
  7. ↑ 7.0 7.1 7.2 Minze Stuiver and H. A. Polach, 1977. Discussion: Reporting of 14C Data. Radiocarbon 19, 3, 355-363.
  8. ↑ 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.
  9. ↑ P. J. Reimer et al., 2013. INTCAL13 and MARINE13 Radiocarbon age calibration curves, 0-50,000 years CAL BP. Radiocarbon, 55, 1869-1887.
  10. ↑ A. G. Hogg, et al., 2013. SHCal13 Southern Hemisphere calibration, 0-50,000 years cal BP. Radiocarbon 55, 1889-1903.
  11. ↑ A. Dutton, K. Rubin, N. McLean, J. Bowring, E. Bard, R.L. Edwards, G.M. Henderson, M.R. Reid, D.A. Richards, K.W.W. Sims, J.D. Walker, Y. Yokoyama, Data reporting standards for publication of U-series data for geochronology and timescale assessment in the earth sciences, Quaternary Geochronology, Volume 39, April 2017, Pages 142-149, DOI
  12. ↑ 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"

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