Peat geochemistry, grain size, organic compounds and vegetation variability in northwestern Ireland during the last 8000 years

Jenny K. Sjöström

This dataset contains results of multi-proxy analysis of a 487 cm long peat sequence covering the last 8000 years from Roycarter Bog, County Mayo, northwestern Ireland. The chronology was established through AMS (accelerator mass spectrometry) radiocarbon dating of plant macrofossils. The sequence was analysed for bulk density, plant macrofossils, elemental composition, organic compounds, mineral content and grain size distribution.

This dataset also contains the results of elemental, grain size and mineral analysis of two beach sediments from Roycarter Beach and Doolough Beach, located nearby (within ~1.5 km) of the bog. The sediment samples were collected to infer the sources of the minerals deposited on Roycarter Bog.

Field-work was conducted in February 2022. The peat sequence was retrieved with a Russian peat corer equipped with a 100×7.5 cm chamber. The sediment beach samples were collected in pits, ca 10 cm below the surface.

The data were used to infer past storminess variability during the last 8000 years in north-western Ireland, primarily based on the results of the grain size analysis. The bulk density and organic compound results were used to infer local hydrological variability in the bog during the studied period, also verified by plant macrofossil analysis at selected depths.

Citation

Jenny K. Sjöström (2024) Peat geochemistry, grain size, organic compounds and vegetation variability in northwestern Ireland during the last 8000 years. Dataset version 1. Bolin Centre Database. https://doi.org/10.17043/sjostrom-2024-ireland-1

References

Sjöström JK, Gyllencreutz R, Martínez Cortizas A, Nylund A, Piilo SR, Schenk F, McKeown M, Ryberg EE, Kylander ME (2024) Holocene storminess dynamics in northwestern Ireland: Shifts in storm duration and frequency between the mid- and late Holocene. Quaternary Science Reviews 337:108803. https://doi.org/10.1016/j.quascirev.2024.108803

Blaauw M, Christen JA (2011) Flexible paleoclimate age-depth models using an autoregressive gamma process. Bayesian Analysis 6. https://doi.org/10.1214/11-ba618

Blott SJ, Pye K (2001) GRADISTAT: a grain size distribution and statistics package for the analysis of unconsolidated sediments. Earth Surface Processes and Landforms 26:1237–1248. https://doi.org/10.1002/esp.261

Friedman GM, Sanders JE (1978) Principles of Sedimentology. Wiley, New York, p. 792.

Reimer PJ, Austin WEN, Bard E, Bayliss A, Blackwell PG, Bronk Ramsey C, Butzin M, Cheng H, Edwards RL, Friedrich M, Grootes PM, Guilderson TP, Hajdas I, Heaton TJ, Hogg AG, Hughen KA, Kromer B, Manning SW, Muscheler R, Palmer JG, Pearson C, van der Plicht J, Reimer RW, Richards DA, Scott EM, Southon JR, Turney CSM, Wacker L, Adolphi F, Büntgen U, Capano M, Fahrni SM, Fogtmann-Schulz A, Friedrich R, Köhler P, Kudsk S, Miyake F, Olsen J, Reinig F, Sakamoto M, Sookdeo A, Talamo S (2020) The IntCal20 Northern Hemisphere Radiocarbon Age Calibration Curve (0–55 cal kBP). Radiocarbon 62:725–757. https://doi.org/10.1017/rdc.2020.41

Data description

The dataset was used and discussed in the study by Sjöström et al. (2024). It is provided in nine .csv files with semicolon as value separator. Specification of the content in each file is outlined below, in most cases in the following way:

• column_header (unit) Data specification

royc_age_depth.csv

Results of the age-depth model, constructed using r.Bacon (ver 2.5, Blaauw and Christen 2011) and IntCal20 (Reimer et al. 2020). The file is organised in 6 columns and 450 rows (including header). Each row represents one centimeter. The indicated depth represents the vertical location (in cm) from the surface. The data is presented in ascending order.

1. depth (cm) Vertical depth from surface
2. age_min (cal yr BP) Minimum calibrated age, years before present
3. age_max (cal yr BP) Maximum calibrated age, years before present
4. age_median (cal yr BP) Median calibrated age, years before present
5. age_mean (cal yr BP) Mean calibrated age, years before present
6. mean_acc_rate (yr cm⁻¹) Mean accumulation rate

royc_peat_properties.csv

Information on peat properties such as bulk density and inorganic ash content. The file is organised in 7 columns and 440 rows (including header), with downcode results presented in rows (one row per cm).

1. depth (cm) Vertical depth from surface
2. sample_id Sample ID, including core number (e.g. C1) followed by a comma and the depth (cm) of sample in core (e.g. 7).
3. age (cal yr BP) Calibrated age of a given sample
4. bulk_density (g m⁻³) Measured bulk density values
5. PAR (g m⁻² yr⁻¹) Peat accumulation rate
6. ash (%) Percentage of inorganic ash content in the peat sample (residue left after ignition at 550 °C)
7. AAR (g m⁻² yr⁻¹) Ash accumulation rate

royc_ftir_absorbance.csv

Raw data of the FTIR-ATR analysis, organised in 121 columns and 1933 rows (including header). The first column contains the wavelength (WN), while columns 2⁠ – ⁠121 contain the result (absorbance spectra, per wavelength) of each analysed samples. The digits in header names of columns 2⁠ – ⁠121 represent the age in calibrated years before present of each analysed sample.

royc_ftir_indices.csv

FTIR indices, derived following statistical analysis of the raw data (see above), used to interpret variance of peat decomposition and organic compounds throughout the sequence. The calculation of the indices are detailed in Sjöström et al. (2024), chapter 3.4. The file is organised in 6 columns and 121 rows (including header). The results are presented in ascending order from the surface. The abbreviation IR used in the header names stands for infrared.

1. depth (cm) Vertical depth from the surface
2. age (cal yr BP) Calibrated age
3. IR_pd Peat decomposition
4. IR_al Aliphatic compounds
5. IR_cb Carbonyl content
6. IR_ar Aromatic compounds

royc_plant_macrofossils.csv

Result of the plant macrofossil analysis. The file is organised in 8 columns and 35 rows (including header).

1. depth (cm) Vertical depth from the surface
2. sample_id Sample ID, including core number (e.g. C1) followed by a comma and the depth (cm) of sample in core (e.g. 7).
3. age (cal yr BP) Calibrated age of the analysed sample
4. UOM (%) Occurrence of unidentified organic matter
5. monocotyledons (%) Occurrence of grasses and sedges
6. ericaceous_woody (%) Occurrence of heather and woody organic matter
7. sphagnum (%) Occurrence of sphagnum mosses
8. non_sphagnum_bryophytes (%) Occurrence of non-sphagnum mosses

royc_elemental_composition.csv

Results of the EMMA-XRF analysis (both concentration and accumulation rates). The file is organised in 14 columns and 120 rows (including header).

1. depth (cm) Vertical depth from the surface
2. sample_id Sample ID, including core number (e.g. C1) followed by a comma and the depth (cm) of sample in core (e.g. 7)
3. age (cal yr BP) Calibrated age of a given sample
4. PAR (g m⁻² yr⁻¹) Peat accumulation rate
5. Ca (%) Calcium concentration
6. S (%) Sulphur concentration
7. Cl (%) Chloride concentration
8. Si (%) Silicon concentration
9. Ti (%) Titanium concentration
10. Ca_AR (mg m⁻² yr⁻¹) Calcium accumulation rate
11. S_AR (mg m⁻² yr⁻¹) Sulphur accumulation rate
12. Cl_AR (mg m⁻² yr⁻¹) Chloride accumulation rate
13. Si_AR (mg m⁻² yr⁻¹) Silicon accumulation rate
14. Ti_AR (mg m⁻² yr⁻¹) Titanium accumulation rate

royc_grain_size.csv

Result of downcore grain-size analysis of the Roycarter peat sequence. The file is organised in 80 columns and 96 rows (including header), with one row displaying the result of one analysed sample.

Columns 1⁠ – ⁠3 (sample information)

1. depth (cm) Vertical depth from the surface
2. sample_id Sample ID, including core number (e.g. C1) followed by a comma and the depth (cm) of sample in core (e.g. 7).
3. age (cal yr BP) Calibrated age of a given sample

Columns 4⁠ – ⁠7 (summary statistics)

4. dx_10 (µm) 10th percentile of particle diameter; 10% of the particles are smaller than this size
5. dx_50 (µm) Median of particle diameter; 50% of the particles are smaller than this size
6. dx_90 (µm) 90th percentile of particle diameter; 90% of the particles are smaller than this size
7. mode (µm) Most commonly occurring grain size

Columns 8⁠ – ⁠67 (grain-size occurrence, by size in µm)

% volume occurrence of a given grain size class. The grain size class (in µm) is indicated by the digits in each column header.

Columns 68⁠ – ⁠69 (grain-size sorting)

68. ASD Grain size sorting using the arithmetic method of moments (Blott & Pye 2001)
69. GSD Grain size sorting using the method of moments, geometric (Blott & Pye 2001)

Columns 70⁠ – ⁠79 (grain-size occurrence, by size type)

% volume occurrence in grain size classes following Friedman and Sanders (1978):

70. clay (%) Occurrence of grain size =< 2 µm
71. very_fine_silt (%) Occurrence of grain size 2⁠ – ⁠4 µm
72. fine_silt (%) Occurrence of grain size 4⁠ – ⁠8 µm
73. medium_silt (%) Occurrence of grain size 8⁠ – ⁠16.4 µm
74. coarse_silt (%) Occurrence of grain size 16⁠ – ⁠31 µm
75. very_coarse_silt (%) Occurrence of grain size 31⁠ – ⁠63 µm
76. very_fine_sand (%) Occurrence of grain size 63⁠ – ⁠125 µm
77. fine_sand (%) Occurrence of grain size 125⁠ – ⁠250 µm
78. medium_sand (%) Occurrence of grain size 250⁠ – ⁠500 µm
79. coarse_sand (%) Occurrence of grain size 454⁠ – ⁠756 µm

Column 80 (cluster analysis)

80. cluster The result of hierarchical cluster analysis of the grain size distributions, clusters 1⁠ – ⁠5.

royc_dool_xrd.csv

The results of XRD (X-ray diffraction) analysis of two beach sediment samples (Roycarter beach and Doolough beach) together with downcore results from peat sequence.

The file contains the result of the XRD analysis, with results reported in columns. The file is organised in 25 columns and 3891 rows (including header). Column 1 indicates the 2θ (2Theta) position. Columns 2⁠ – ⁠25 contain the result (counts per second, for a given 2θ angle) per sample.

Column 1

1. angle (degrees) 2θ angle

Columns 2⁠ – ⁠9 (Doolough beach)

XRD results for a beach sediment sample from Doolough beach. Both a bulk sample, and different size fractions were analysed. The header name contains information about the site (dool), followed by an indication if it was a bulk, dune or size fractionated (in µm) sub-sample. For example, dool_38_63 contains the result a size fractionated subsample from Doolough beach, particles in the grain size between 38⁠ – ⁠63 µm.

2. dool_bulk (counts s⁻¹) Result for bulk sample
3. dool_dune (counts s⁻¹) Result for dune sample
4. dool_38 (counts s⁻¹) Result for grain size < 38 µm
5. dool_38_63 (counts s⁻¹) Result for grain size 38⁠ – ⁠63 µm
6. dool_63_125 (counts s⁻¹) Result for grain size 63⁠ – ⁠125 µm
7. dool_125_250 (counts s⁻¹) Result for grain size 125⁠ – ⁠250 µm
8. dool_250_500 (counts s⁻¹) Result for grain size 250⁠ – ⁠500 µm
9. dool_500 (counts s⁻¹) Result for grain size >500 µm

Columns 10⁠ – ⁠16 (Roycarter beach)

XRD results for a beach sediment sample from Roycarter beach. Both a bulk sample, and different size fractions were analysed. The header name contains information about beach name (royc) and analysed size fraction (in µm).

10. royc_bulk (counts s⁻¹) Result for bulk sample
11. royc_38 (counts s⁻¹) Result for grain size < 38 µm
12. royc_38_63 (counts s⁻¹) Result for grain size 38⁠ – ⁠63 µm
13. royc_63_125 (counts s⁻¹) Result for grain size 63⁠ – ⁠125 µm
14. royc_125_250 (counts s⁻¹) Result for grain size 125⁠ – ⁠250 µm
15. royc_250_500 (counts s⁻¹) Result for grain size 250⁠ – ⁠500 µm
16. royc_500 (counts s⁻¹) Result for grain size >500 µm

Columns 17 – ⁠25 (Peat sequence)

Downcore XRD results from the peat sequence. The header contains information about the type of sample (peat) followed by the age, in calibrated years before present (cal yr BP), that the sample represents.

17. peat_surface (counts s⁻¹) Result for surface sample
18. peat_2550 (counts s⁻¹) Result for sample with age 2550 cal yr BP
19. peat_3030 (counts s⁻¹) Result for sample with age 3030 cal yr BP
20. peat_4610 (counts s⁻¹) Result for sample with age 4610 cal yr BP
21. peat_4810 (counts s⁻¹) Result for sample with age 4810 cal yr BP
22. peat_5140 (counts s⁻¹) Result for sample with age 5140 cal yr BP
23. peat_7300 (counts s⁻¹) Result for sample with age 7300 cal yr BP
24. peat_7470 (counts s⁻¹) Result for sample with age 7470 cal yr BP
25. peat_8070 (counts s⁻¹) Result for sample with age 8070 cal yr BP

measurement_conditions.csv

Information about the measurement settings for the analysis results provided in file royc_dool_xrd.csv. Most information is provided in column 1. There are also some technical details on rows 4 and 5 in columns 5 and 6.

Comments

Abbreviations

• XRD: X-ray Diffraction Analysis
• FTIR-ATR: Fourier Transform Infrared-Attenuated Total Reflectance
• EMMA-XRF: Elemental Miniprobe Multielemental Analyser X-ray Fluorescence

Site coordinates

• Doolough Beach: 54° 7’ 56.98” N, 9° 56’ 25.95” W
• Roycarter Beach: 54° 4’ 16.83” N, 9° 57’ 46.69” W
• Roycarter Bog: 54° 5’ 59.82” N, 9° 57’ 10.91” W