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Radiocarbon age-modelling I – introduction to age-models Dr. Maarten Blaauw School of Geography, Archaeology and Palaeoecology Queens University Belfast Northern Ireland

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My background Born 1974 in Hardenberg (nl) Msc Biology, Groningen (nl) PhD Palaeoecology, Amsterdam (nl) Postdoc Trinity College Dublin (ie) Postdoc CIMAT (mx) Postdoc Queens Univ Belfast (uk)

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Today Lectures Introduction to age-depth modelling Bayesian age-depth modelling Practicals Calibrating Basic age-depth modelling Bayesian age-depth modelling

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4 Pollen-diagram Blaauw et al. in press, The Holocene

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5 Poisson random walk Blaauw et al. in press, The Holocene

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Types of chronologies No uncertainties Yearly resolution Decadal / centennial – (multi-) millennial resolution

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Annually layered ice cores

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History peat dating Pre 14 C dating (relative dating) Peat stratigraphy (Sernander ) & pollen Link pollen with archaeology (bronze age etc.) Link with Swedish varve chronology (de Geer) (Sub) millennial precision Von Post 1946

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History peat dating Carbon dating 'absolute', independent dates Smith & Pilcher 1973: 14 C dating vs. pollen zones 'Wishful thinking obscures reality' (von Post 1946) 14 C date depths along peat core At levels with major proxy changes At regular intervals Assume linear accumulation between dated levels e.g.: Aaby 1976, van Geel 1978

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History peat dating High-resolution 14 C dating wiggle-match dating (van Geel&Mook 1989) Bayesian (e.g., Blaauw&Christen 2005) post-bomb dating (e.g., van der Linden et al. 2008) Tephra (e.g., Pilcher et al. 1995, Davies et al. 2003) 210 Pb dating (e.g., Turetsky et al. 2004) All form age estimates for age-depth models The estimates and models are uncertain

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Carbon dating

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14 C dating 14 C unstable, half-life 5568 yr Ratio 14 C/C gives age fossil

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Tree-ring coverage for IntCal04: until 12.4 kcal BP Belfast Groningen Pretoria Heidelberg Waikato Seattle PNW/CAGerman Oak German Pine Swiss Pine Irish Oak German Oak

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Tree-ring coverage for IntCal04

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Age-depth modelling So now we have dates... what's next? Estimate ages of non-dated levels Use available information all dates together environmental settings site other comparable archives

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Age-depth modelling 14 C and other dates Basic age-modelling techniques interpolation, regression, spline,... Bayesian approaches chron. ordering, wiggle-match dating Compare multiple archives tuning, eye-balling, Bayesian

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Age-depth modelling

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Uncertainty accumulation

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Many date$

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Few dates

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Which age-depth model? 800 cm core 9 14 C dates surface = recent

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Which age-depth model? 800 cm core 9 14 C dates surface = recent Linear interpol. Too much weight on individual dates?

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Which age-depth model? 800 cm core 9 14 C dates surface = recent Linear interpol. date 6 = outlier

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Which age-depth model? 800 cm core 9 14 C dates surface = recent Linear interpol. 470 cm = hiatus

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Which age-depth model? 800 cm core 9 14 C dates surface = recent Linear interpol. Linear regression 470 cm = hiatus Too narrow error ranges?

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Which age-depth model? 800 cm core 9 14 C dates surface = recent Linear interpol. Linear regression Polyn. regression 470 cm = hiatus second degree wide uncertainties when extrapolating!

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Which age-depth model? 800 cm core 9 14 C dates surface = recent Linear interpol. Linear regression Polyn. regression Smooth spline

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Which age-depth model? 800 cm core 9 14 C dates surface = recent Linear interpol. Linear regression Polyn. regression Smooth spline date 6 = outlier

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Which age-depth model? 800 cm core 9 14 C dates surface = recent Linear interpol. Linear regression Polyn. regression Smooth spline 470 cm = hiatus

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Age-depth modelling How did our sediment accumulate over time? Constant? Varying? Pulses? Hiatuses? Site settings Should we try to fit a curve through all dates? Balance belief in dates and belief in model Use stratigraphic information How many dates do I need? The more, the better? The more problems? Depends on your questions is my sediment of glacial age? early 8.2 k event?

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Dating uncertainties

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14 C dating

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Uncertainties dates 5 calibrated dates surface = recent simulate yr every date draw age-model linear interpolation repeat

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Uncertainties dates 5 calibrated dates surface = recent simulate yr every date draw age-model polynomial regression does not cross all dots weighted by error sizes repeat

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Uncertainties dates

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Basic age-modelling Choose which one looks nicest... How treat point estimates? (mid/max, multimodal) Why just one line? Not much literature Bennett 1994, Bennett and Fuller 2002, The Holocene, Telford et al. 2004, QSR Software Calib + Excel clam, Blaauw in press (Quaternary Geochronology)

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Today Lectures Introduction to age-depth modelling Bayesian age-depth modelling Practicals Calibrating Basic age-depth modelling Bayesian age-depth modelling

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