# Paleodust deposition and peat accumulation rates – Bog size matters

Jenny Sjöström, Antonio Martínez Cortizas, Sophia Hansson, Noemí Silva Sánchez, Richard Bindler, Johan Rydberg, Carl-Magnus Mörth, Eleonor Ryberg, Malin Kylander

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## To cite this version:

Jenny Sjöström, Antonio Martínez Cortizas, Sophia Hansson, Noemí Silva Sánchez, Richard Bindler, et al.. Paleodust deposition and peat accumulation rates – Bog size matters. Chemical Geology, 2020, 554, pp.119795. 10.1016/j.chemgeo.2020.119795. hal-03412734

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Submitted on 12 May 2023

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Distributed under a Creative Commons Attribution 4.0 International License
<figure><img src="image_3.png" /><figcaption>**Fig. 1.** A) Location map of Scandinavia, B) Quaternary deposit map, including the modeled shoreline of a former ice-lake (Fornbolmen) indicated by white lines, and C) satellite image of Draftinge Mosse (Google Earth, 2018). Location and soil map from Kylander et al. (2016, 2018).</figcaption></figure>

2012; Kylander et al., 2013a, 2016; Pratte et al., 2016; Martínez Cortizas et al., 2019), (2) there are changes in the character and source of the deposited dusts over time (Kylander et al., 2013a, 2016) and (3) that this dust can significantly affect terrestrial nutrient limited eco-systems, such as peatlands (Yu et al., 2015; Aciego et al., 2017; Arvin et al., 2017; Kylander et al., 2018), by altering ecosystem productivity and carbon uptake. Furthermore, changes in the mineral composition of paleodust through time can be indicative of source area changes, which in turn is indicative of changes in wind strength, atmospheric circulation and/or vegetation cover.

Peat paleodust reconstructions are achieved through down-core geochemical analysis of conservative lithophile elements such as Sc, Ti, Zr, or rare earth elements (REE) (Steinmann and Shotyk, 1997; Shotyk et al., 2002; Krachler et al., 2003; Aubert et al., 2006) with the goal to quantify variations in dust deposition rates, mineralogy, grain size and provenance. Over the past two decades our ability to extract paleodust records from peat has evolved with improvements in analytical methods (Krachler et al., 2002; Givelet et al., 2004; Sapkota et al., 2005; Le Roux and De Vleeschouwer, 2010), tools for dust provenance tracing (Shotyk et al., 2002; Kylander et al., 2007; Marx et al., 2005; Kylander et al., 2016), and the increasing application of statistical analysis, such as elemental correlation matrices (Martínez Cortizas et al., 2005), principal component analysis (PCA) with fractionation of communalities (Muller et al., 2008; Horák-Terra et al., 2014; Silva-Sánchez et al., 2014), and changepoint modelling (Kylander et al., 2007).

A number of geochemical approaches have been applied to study changes in the grain size, mineralogy and thereby, source, of dust deposited in peatlands such as Pb and Nd isotope analysis (Kylander et al., 2005, Meyer et al., 2011; Le Roux et al. 2012) and elemental ratios (Shotyk et al., 2002; Kylander et al., 2016). Elemental ratios can be used to infer changes in grain size or mineralogy because some elements are enriched or depleted in certain grain sizes and/or mineral groups. For example, ratios between an element that is enriched in finer grain sizes, e.g. Ti (Taboada et al., 2006) can be plotted against an element that is distributed across a wider range of size classes (e.g. Sc or

Si) in order to detect grain size changes (e.g. Shotyk et al., 2002; Kylander et al., 2013b). In terms of mineral hosts, Ga/Al can be used to represent changes in mica and/or plagioclase feldspar (Kylander et al., 2006), while ratios between light, middle and heavy REE (L/M/HREE) can be used to identify changes in the mineralogy in peat paleodust studies (Kylander et al., 2007; Le Roux et al. 2012; Pratte et al., 2020). REE occur, often together, in accessory minerals such as phosphates, carbonates, fluorides, and silicates in pegmatites, granites and other metamorphic and igneous rocks (Tyler, 2004). In addition to these indirect mineralogical identification tools, X-ray diffraction (XRD) mineral analysis can be a valuable complement to geochemical datasets in peat paleodust studies (Sjöström et al., 2019).

Despite the established use of peat records, methodological questions remain. Peat paleodust studies rarely compare within site deposition rates, or explore links between peatland development, mineral dust deposition and peat accumulation rates (PAR). This leads to a lack of understanding regarding the links between dust deposition and accumulation rates; the role of local factors (i.e. bog specific) on peat paleodust records; and the spatial representativeness of single-site reconstructions. These unknowns can be approached by making comparisons between sites that share a similar climate, bedrock, and landscape development and therefore, dust sources. To this end, we present a high-resolution analysis of a peat sequence from Draftinge Mosse (400 ha) which is located ~18 km to the southwest of the only Scandinavian paleodust record published to date, Store Mosse (7700 ha) (Kylander et al., 2013a, 2016, 2018). We take the approach of pairing elemental data with XRD mineral results to gain a more in-depth understanding of the mineral composition and related changes in geochemistry. The aim of this work is to construct a peat paleodust and growth rate record from southern Sweden with the specific objectives to: (1) identify peatland development stages, dust events (DE) and PAR variations; (2) detect changes in mineral composition and lastly, (3) compare our results with the nearby paleodust study from Store Mosse. These objectives are met using a high-resolution (sub-sampling at 1 cm with an average temporal span of 20 years) peat sequence, analysed for ash content, peat composition, bulk density, organic and inorganic
<caption>**Table 1**</caption>

Vertical sample depth (cm), lab-id, specification of samples used for dating, ¹⁴C ages and calibrated age ranges. Calibration and age-depth model constructed using Bacon (Blaauw and Christen, 2011), including IntCal13 calibration curve (Reimer et al., 2013).

<table><thead><tr><th>Sample Depth (cm)</th><th>Laboratory no.</th><th>Material used for dating</th><th>¹⁴C Yr ± 1 σ</th><th>Calibrated age range, BP. 2 σ</th></tr></thead><tbody><tr><td>39</td><td>D-AMS 10650</td><td>Bulk peat</td><td>554 ± 23</td><td>525–663</td></tr><tr><td>60</td><td>D-AMS 10654</td><td>Sphagnum leaves and stems</td><td>835 ± 24</td><td>695–785</td></tr><tr><td>88</td><td>D-AMS 10651</td><td>Bulk peat</td><td>1259 ± 24</td><td>1093–1279</td></tr><tr><td>108</td><td>Beta 418758</td><td>Sphagnum stems, seeds</td><td>1970 ± 30</td><td>1868–1992</td></tr><tr><td>124</td><td>Beta 418759</td><td>Sphagnum stems, seeds, insect remains</td><td>2390 ± 30</td><td>2346–2667</td></tr><tr><td>136</td><td>Beta 498599</td><td>Sphagnum stems and leaves, twigs</td><td>3860 ± 30</td><td>4159–4410</td></tr><tr><td>144</td><td>Beta 385361</td><td>Sphagnum leaves, insect remains, charcoal</td><td>4070 ± 30</td><td>4785–4445</td></tr><tr><td>152</td><td>Beta 458209</td><td>Sphagnum leaves and <i>Eriophorum</i> sp. stems</td><td>4070 ± 30</td><td>4440–4799</td></tr><tr><td>176</td><td>Beta 458208</td><td>Sphagnum leaves and stems</td><td>4370 ± 30</td><td>4857–5036</td></tr><tr><td>186</td><td>D-AMS 10655</td><td>Sphagnum leaves and stems</td><td>4401 ± 26</td><td>4873–5042</td></tr><tr><td>226</td><td>D-AMS 10656</td><td>Sphagnum leaves and stems</td><td>4485 ± 25</td><td>5041–5289</td></tr><tr><td>250</td><td>Beta 387826</td><td>Sphagnum leaves and stems</td><td>4690 ± 30</td><td>5320–5575</td></tr><tr><td>296</td><td>Beta 853262</td><td>Pine cone</td><td>4740 ± 30</td><td>5450–5585</td></tr><tr><td>326</td><td>Beta 387827</td><td>Charcoal, <i>Carex</i></td><td>5180 ± 30</td><td>5900–5985</td></tr><tr><td>353</td><td>Beta 385363</td><td>Charcoal, <i>Carex</i></td><td>6470 ± 30</td><td>7310–7425</td></tr><tr><td>391</td><td>Beta 385364</td><td>Seed, insect remains, <i>Carex</i></td><td>7510 ± 30</td><td>8190–8350</td></tr><tr><td>300*</td><td>D-AMS 10652</td><td>Bulk peat</td><td>5763 ± 26</td><td>6494–6638</td></tr><tr><td>329*</td><td>D-AMS 10653</td><td>Bulk peat</td><td>6932 ± 27</td><td>7690–7827</td></tr></tbody></table>

elemental concentrations, and mineral composition, set into a temporal perspective using an age-depth model based on 16 AMS radiocarbon ages. In order to identify processes governing the paleorecord we use principal component analysis (PCA) to reduce dimensionality and explore associations between variables (elements and ash content).

### 1.1.1. Site description

Draftinge Mosse (57°06'27.6"N 13°42'54.1"E; 149 m asl; 400 ha) is located in a peat-rich area in south-central Sweden (Fig. 1). The study area has a maritime climate dominated by westerly Atlantic winds, with relatively cool summers (average temp: 17 °C), mild winters (average temp: 1 °C) and high moisture availability (Länsstyrelsen i Jönköpings län, 2012). The annual average temperature is 5.5 °C and the average precipitation is 800 mm yr⁻¹ (SMHI, klimatdata, 2009). The study site is located in an area dominated by granite and granitoid gneisses of 1.67 Ga age (Wik et al., 2007) consisting of minerals such as quartz, feldspar, biotite mica and amphiboles. The bedrock is covered by glaciogenic sediments deposited directly by the ice or by glaciofluvial and/or aeolian processes (Malmberg Persson, 2010) (Fig. 1B). Peatland initiation in the study area occurred directly on sandy sediments deposited by the retreat of a former ice lake, Lake Fornbolmen (Nilsson, 1968; Svensson, 1988). In the initiation stage the peatlands were generally minerotrophic fens (Granlund, 1932), that transitioned into being rain-fed (ombrotrophic) around 6000 to 5000 years ago (Svensson, 1988). The shift to ombrotrophy was caused by a combination of peatland succession, climate change (Svensson, 1988, Kylander et al., 2013a) and isostatic uplift (Påsse and Andersson, 2005). The present day bog vegetation is dominated by Cyperaceae (sedges), Ericaceae (heather), Sphagnum (mosses) and lichens.

## 2. Materials and methods

To construct a peat paleodust and growth rate record, analysis of peat stratigraphy, physical properties (bulk density, pH), organic and inorganic elemental concentrations, and plant macro-fossil content was conducted, coupled to a high resolution age-depth model (n = 16). Three analytical approaches were applied to capture a wide range of elements (details outlined in chapter 2.2, 2.3, and 2.4). In total three peat sequences were retrieved from Draftinge Mosse, collected with a Russian peat corer equipped with a 100 × 10 cm barrel. The main sequence, which underwent the bulk of the analyses and radiocarbon

dating, was collected in May 2014 (57° 6'29.61"N, 13°42'46.58"E). Five one-meter cores with 25 cm overlap were retrieved from two alternating holes (total length: 390 cm). Pictures of cores and coring site are found in the Supplementary file (Appendix B). The cores were stored frozen (−18 °C), and subsequently cut into one-centimeter slices with a stainless-steel band saw. The volume and weight of each slice was measured to calculate the bulk density, which was used to align the cores and make a composite sequence. Peat accumulation rates (PAR) was calculated by dividing the bulk density (g cm⁻³) of each slice by the accumulation rate estimated by the age-depth model. Loss-on-ignition (LOI), the weight loss after combustion at 500–550 °C (Dean, 1974), was determined at 1 to 3 cm intervals. The resolution of the geochemical analyses varied by method with elemental concentrations measured every 5 cm by WD-XRF and 2–5 cm by ICP-OES. The results of the WD-XRF and ICP-OES were combined into one data-set, calculated to mass accumulation rates (MAR), which were transformed to z-scores, followed by PCA analysis to quantitatively explore elemental associations. X-ray diffraction analysis (XRD) was conducted on 24 samples distributed throughout the profile. The second core (57° 6'49.45"N, 13°42'41.15"E, total length: 465 cm), collected in September 2017 underwent pH measurements, directly on the fresh peat, every 10 cm, with an Extech pH 100 (n = 48). The third core collected in September 2019 (57° 6'29.61"N, 13°42'46.58"E, total length: 355 cm) underwent a modified macrofossil analysis (n = 28), identifying percentages of Cyperaceae, Ericaceae (including roots), Sphagnum, brown mosses, and unidentified organic material (UOM) as well as the presence of wood and charcoal (method and results described in Supplementary file, Appendix A). The sequences were correlated to each other based on peat stratigraphy and bulk density data.

### 2.1. Radiocarbon dating and age-depth modelling

Four bulk, and fourteen macrofossil samples (n = 18) were sent for AMS radiocarbon dating (Table 1). Prior to analysis, samples underwent both acid and alkali treatment to remove carbonates. Calibration and age-depth modelling was conducted with Bacon (Blaauw and Christen, 2011), version 2.2, using the default settings. The Bacon script constructs an age-depth model by applying an iterative Markov Chain Monte Carlo process by which several thousands of independent likely age-depth models and accumulation rates are constructed between each dated level (Blaauw and Christen, 2011). In this process the sequence is divided into sections, with a priori memory of accumulation rate inherited from the previous sections. This process avoids sharp

<footnote>* Samples not used in age-depth model.</footnote>
accumulation rate changes to occur at dated points.

## 2.2. Total carbon, nitrogen and δ¹³C analysis

Total C, N, and δ¹³C of the bulk peat samples was measured using a Carlo Erba NC2500 elemental analyzer, coupled to a Finnigan MAT Delta + mass spectrometer at the Department of Geological Sciences, Stockholm University. The relative error for the measurement was < 3%. The δ¹³C data are reported in per mil (‰) relative to V-PDB. In order to evaluate the presence of carbonates in the ash residues, selected samples (n = 14) were also analysed for total (%C<sub>tot</sub>), organic (%C<sub>org</sub>) carbon, and δ¹³C values, before and after a dilute acid treatment. A positive difference between %C<sub>tot</sub> and %C<sub>org</sub> values indicates the presence of carbonates (%C<sub>carb</sub>) in a given sample. The result can also be used to calculate the δ¹³C values of the carbonates, indicative of origin of the mineral, by applying a two-component mixing model calculation:

$$ \%C_{org} \delta^{13}C_{org} + \%C_{carb} \delta^{13}C_{carb} = \%C_{tot} \delta^{13}C_{tot} $$

Were δ¹³C<sub>carb</sub> can be solved for by

$$ \delta^{13}C_{carb} = \frac{\%C_{tot} \delta^{13}C_{tot} - \%C_{org} \delta^{13}C_{org}}{\%C_{carb}} $$

## 2.3. Wavelength dispersive X-ray fluorescence analysis (WD-XRF)

WD-XRF analysis was conducted at the Department of Ecology and Environmental Science, Umeå University, using a Bruker X8-Tiger analyzer equipped with a Rh-anticathod X-ray tube. Elemental concentrations were measured in dried and milled subsamples (400–500 mg), which were placed in plastic cups covered with 2,5 Mylar® film. Calibration was conducted based on a loose sediment method developed by Rydberg (2014), adapted to peat and plant samples by Hansson et al. (2014).

## 2.4. Induced coupled plasma OES (ICP-OES) analysis

ICP-OES analysis was conducted at the Department of Geological Sciences, Stockholm University. Prior to acid digestion, samples were combusted at either 500 °C or 550 °C which has been shown to efficiently remove organic matter from peat samples (Sjöström et al. 2019) with only minor losses of the elements of interest to this study (Koh et al., 1999; Llorente and García, 2006). The digestion procedure followed Krachler et al. (2002) and was conducted in a MARS 6 microwave (MW) system. Prior to use, all vessels and beakers where acid cleaned (6 M HCl) for 48 h. High purity water (18.2 MΩ) from MilliQ (Millipore, Milford, MA, USA) was used in all solutions and for rinsing lab utensils. The samples were digested in 6 ml of ultrapure 65% HNO₃ and, depending on sample weight, 11–45 µl of HBF₄. The MW program ramped to 180 °C during 30 min, followed by a 20 min hold and a 30 min cool down. The samples were evaporated to near dryness in Savillex beakers on hot plate (60 °C) after which 5 ml of 1% HNO₃ was added. Blanks and reference material (LKDS-4, LKDS-1 and NIST-CRM 2711a) were included in all digestion rounds. In total 149 samples, including 15 blanks and 14 standards, were digested and analysed by ICP-OES. The samples were run twice, first with a c-spray nebulizer and a read time of 7 s for both axial and radial position (mainly for major elements) and then with an ultra-sonic nebulizer (Cetac U5000AT+) having a read time of 60 s in axial position to get the highest sensitivity as possible. Merck multi-elements standard solutions were used. Based on internal standards and certified standards (e.g. NIST 1640a) the analytical error was within ± 5%.

## 2.5. Statistical analysis

Following Martínez Cortizas et al. (2019) concentration values from the LOI, WD-XRF and ICP-OES analysis were re-calculated into mass accumulation rates (MAR) prior to statistical analysis (concentration X PAR (g m⁻² yr⁻¹)). Principal component analysis (PCA) was conducted using the software JMP 14, in correlation mode with a varimax rotation on z-score transformed data. The z-score transformation avoids scaling effects of the data and transforms it to average-centered distributions (Eriksson et al., 1999).

## 2.6. X-ray diffraction (XRD) mineral analysis

XRD analyses were conducted at the Department of Geological Sciences, Stockholm University, using a PANalytical X-ray diffraction system (X'Pert Powder) equipped with a point detector. Pre-treatment of samples followed Sjöström et al. (2019). The samples were analysed from 2° to 70° 2θ, with CuKα radiation at 45 kV and 40 mA, passing through a curved graphite monochromator, programmable fixed divergence and receiving slits (1°), step size 0.020° and a count time of 2 s. Prior to analysis the ash residues were washed three times in deionized water in order to remove soluble salts. Processing of the diffractograms, such as determination of background, smoothing, peak localization, and mineral identification was done in HighScore, a PANalytical software with integrated mineral reference patterns from the ICSD database (2012). Brown and Brindley (1984) and Moore and Reynolds (1997) were also used to guide mineral identification. To verify the results, two samples were also analysed at the Swedish Natural Museum hosting similar XRD equipment but equipped with a multi-detector (X100).

# 3. Results

All original quantitative data as well as calculated AAR, MAR and PAR can be found on the Bolin Centre Database (https://www.bolin.su.se/sjostrom-2020).

## 3.1. AMS radiocarbon dating and age-depth model

Table 1 shows the result of the AMS radiocarbon dating and the calibrated age ranges. The lowermost sample was dated to 8275 cal BP, showing that the Draftinge Mosse sequence covers the last ~8300 years. The results of the age-depth model are displayed in Fig. 2. Two bulk samples (329 and 300 cm) were excluded from the age depth model as they showed older ages than proximal macrofossil samples (Table 1). In the context of ¹⁴C dating, macro-fossil samples are generally preferred over bulk samples, as the former constitutes a known, that typically grew on the location (e.g. Mauquoy et al. 2007) whereas the latter is a mixture of unknowns. Two younger bulk samples located higher up in the sequence (88 and 39 cm) were, however, still included in the age-depth model since bulk samples from ombrotrophic peat have been shown to largely display reliable ¹⁴C ages (Blaauw et al., 2004). The acquired weighted mean and the accumulation rate (cm yr⁻¹), together with the bulk density, is used here to calculate peat, ash and elemental mass accumulation rates (PAR, AAR and MAR, respectively), as well as to plot data on a calendar age scale. All results reported in the following sections are described relative to the calendar ages (cal. BP).

## 3.2. Peat properties

The lowermost section, between ~8300 to ~5750 cal BP, consists of a woody Carex peat that is replaced by Sphagnum peat, along with some occurrence of brown mosses, between ~5750 and ~5560 cal BP (Fig. 3, Appendix A). Thereafter non-humified Sphagnum peat dominates until c. 4570 cal BP, after which an abrupt transition to Carex and Ericaceae peat occurs. Carex and Ericaceae peat thereafter dominates until
<figure><img src="image_4.png" /><figcaption>Fig. 2. Age-depth model based on 16 AMS radiocarbon dates. The grey scale indicates the likely age-depth models with 95% confidence range.</figcaption></figure>

Calibrated distributions of the ¹⁴C dates shown by blue objects. The red dotted line represents the weighted mean. Two outliers indicated by red asterisks. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

~420 cal BP, followed by *Sphagnum* peat towards the present.

The ash content throughout the sequence ranges from 0.15 to 7.3%, with an average of 1.8 ± 2.7% (n = 321, all standard deviations given as 2σ)(Fig. 3). Between ~8300 and ~5580 cal BP the ash content is higher (3.4 ± 1.6%, n = 100) compared to after ~5580 cal BP (1 ± 1.3%, n = 272). The highest ash content occurs in the uppermost sample (11 cm, 7.3%). The average AAR is 1.1 ± 1.9 g m⁻² yr⁻¹

(n = 321), displaying a decreasing trend from ~8300 to ~6180 cal BP after which the AAR increases steadily, peaking at ~5665 cal BP with a fivefold increase above the average (5.2 g m⁻² yr⁻¹). Thereafter the AAR drops sharply and by ~5580 cal BP the rate is 1.6 g m⁻² yr⁻¹. This is followed by a more gradual decrease until ~4390 cal BP. Low, but relatively stable values are subsequently recorded (0.2 ± 0.2 g m⁻² yr⁻¹, n = 14) until ~2630 cal BP when an increase occurs. Between ~2630 cal BP and present there are four episodes of increased AAR (cal BP): ~2340–2170 (n = 6); ~1385–1150 (n = 11); ~740–600 (n = 15); and from ~420 towards the present (n = 15). The results of the pH measurements showed that the pH ranged from 5.2 in the lowermost parts of the sequence to 3.5 at the top (Fig. 3).

Bulk densities range from 0.02 to 0.23 g cm⁻³, with an average of 0.10 ± 0.07 g cm⁻³ (n = 381)(Fig. 3). Between ~5540 and ~4620 cal BP bulk density minima occur (0.06 ± 0.03 g cm⁻³, n = 134), while sequence maxima occur between ~4220 and ~2540 cal BP (0.17 ± 0.05 g cm⁻³, n = 12). In terms of PAR, the values decrease from ~45 to ~15 g m⁻² yr⁻¹ between ~8275 and ~6180 cal BP, followed by an increase between ~6090 and ~4530 cal BP (97 ± 73 g m⁻² yr⁻¹, n = 174) where the profile maxima (220 g m⁻² yr⁻¹) occur at 5630 cal BP. Between ~4530 and ~4200 cal BP the rates decrease to an average of 40 ± 36 g m⁻² yr⁻¹ (n = 11), followed by a sharp decline to minimal PAR between ~4000 and ~2480 cal BP (10 ± 5 g m⁻² yr⁻¹, n = 10). Here the lowest PAR of the profile is observed at 3810 cal BP (8 m⁻² yr⁻¹). From ~2480 cal BP towards the present, the average PAR is 61 ± 48 g m⁻² yr⁻¹ (n = 115), with four periods of elevated values noted (cal BP): ~2225–2170 (67 ± 2 g m⁻² yr⁻¹, n = 3); ~1240–1185 (~80 ± 10 g m⁻² yr⁻¹, n = 4); ~755–505 (94 ± 30 g m⁻² yr⁻¹, n = 25), and from ~280 cal BP towards the present (78 ± 25 g m⁻² yr⁻¹, n = 12).

Total carbon and nitrogen (%C, %N, n = 163) co-vary between ~8300 and ~5580 cal BP, with higher concentrations and lower variability (55 ± 5% and 1.9 ± 0.6%, respectively, n = 41) compared to after ~5580 cal BP (50 ± 6% and 0.8 ± 0.8%, n = 122). Lower

<figure><img src="image_5.png" /><figcaption>Fig. 3. Peat composition, pH, ash content, bulk density, peat accumulation rates (PAR), total C and N content (%), C/N ratio, and δ¹³C.</figcaption></figure>
concentrations are recorded between ~5580 and ~4500 cal BP (278–140 cm), after which %C values decrease towards the present while %N is more variable (Fig. 3). C/N ratios range from 26 to 185 (average 76 ± 87) throughout the record with lower average values between ~8300 and ~5580 cal BP (35 ± 28, n = 43) compared to after ~5580 cal BP (90 ± 83, n = 119). Highly elevated C/N ratios occur between ~5580 and ~4500 cal BP (119 ± 68, n = 66), decreasing from ~4500 cal BP towards the present (55 ± 26, n = 122), interrupted by a period of increased values between ~1120 and ~795 cal BP (78 ± 20, n = 4).

δ¹³C values range from -29 to -23‰ (-26.9 ± 2.1, n = 163) throughout the sequence, with less variability and more depleted values recorded between 8300 and 5600 cal BP (-28.2 ± 1.1, n = 42) compared to after 5600 cal BP (-26.5 ± 1.6‰, n = 121). Less depleted values occur between 5600 and 4500 cal BP, followed by more depleted values until 2480 cal BP. A trend towards less depleted δ¹³C values is seen between 2480 and 1090 cal BP, followed by the sequence maximum (-23.1‰) at ~1040 cal BP. After this, the values get progressively more depleted towards the present. TOC and δ¹³C measurements of the ash residues (n = 14) indicate the presence of carbonates in all samples (Table 2). The δ¹³C values of the carbonates range between -8.96‰ (lowermost sample) to -18.29‰ (average -15.03 ± 4.81‰, n = 14). The samples between ~5550 to ~4800 cal BP are enriched in carbonates (on average 2.47 ± 0.76%, n = 6) compared to the other samples (0.67 ± 0.74%, n = 8).

### 3.3. Analytical performance WD-XRF and ICP-OES

Eighty-eight samples were analysed by WD-XRF acquiring concentration data for Al, Ca, Fe, K, Mg, Na, P, S, Si, and Ti. Accuracy and precision were assessed using NIST 8437 (n = 3) and an internal peat standard (QC PM) (n = 3). Accuracy expressed as the relative deviation from the certified values was generally 10% or better with the exception of Ca, which is present in very low concentrations in NIST 8437. Absolute deviations from the certified values were never larger than 0.02% or 2 ppm. The precision (relative standard deviation, % RSD) was within 10% for a majority of elements with the exception of Na, which was within 15% (presented in Appendix C: Table 1). Aluminium was below the detection limit (1‰) in 34 samples. The concentration values were set to half the detection limit in these samples for the statistical analysis and inter-analytical comparison.

For the ICP-AES analysis 149 samples were analysed (122 ashed peat samples, 14 blanks, and 15 standards) acquiring data for Al, Ca, Fe, K, Mn, Mg, REE (Dy, Eu, Ga, Ho, La, Nd, Y), Rb, Sc, Ti, P and Sr. In order to quantify the accuracy of the wide range of analysed elements, we used a set of three certified reference materials (standards): NIST

<caption>**Table 2**</caption>

Result of carbon (% C) and isotope (δ¹³C) analysis of ash residues. All samples contained carbonates and the δ¹³C values of these carbonates range from -18.29 to -8.96‰.

<table><thead><tr><th>Age, Cal BP</th><th>δ¹³C<sub>tot</sub></th><th>% C<sub>tot</sub></th><th>δ¹³C<sub>org</sub></th><th>% C<sub>org</sub></th><th>δ¹³C<sub>carb</sub></th><th>% C<sub>carb</sub></th></tr></thead><tbody><tr><td>4355</td><td>-15,12</td><td>1,17</td><td>-27,91</td><td>0,14</td><td>-13,37</td><td>1,03</td></tr><tr><td>4500</td><td>-16,30</td><td>1,47</td><td>-28,04</td><td>0,14</td><td>-15,08</td><td>1,33</td></tr><tr><td>4790</td><td>-17,03</td><td>2,29</td><td>-28,25</td><td>0,20</td><td>-15,96</td><td>2,09</td></tr><tr><td>5180</td><td>-17,26</td><td>3,22</td><td>-27,72</td><td>0,11</td><td>-16,89</td><td>3,11</td></tr><tr><td>5340</td><td>-16,51</td><td>2,89</td><td>-26,98</td><td>0,15</td><td>-15,95</td><td>2,74</td></tr><tr><td>5440</td><td>-17,91</td><td>2,52</td><td>-27,97</td><td>0,13</td><td>-17,35</td><td>2,39</td></tr><tr><td>5490</td><td>-16,94</td><td>2,61</td><td>-27,37</td><td>0,33</td><td>-15,41</td><td>2,28</td></tr><tr><td>5545</td><td>-18,84</td><td>2,38</td><td>-27,06</td><td>0,15</td><td>-18,29</td><td>2,23</td></tr><tr><td>5605</td><td>-19,03</td><td>0,80</td><td>-27,18</td><td>0,12</td><td>-17,55</td><td>0,68</td></tr><tr><td>5660</td><td>-19,08</td><td>0,35</td><td>-27,52</td><td>0,15</td><td>-13,13</td><td>0,21</td></tr><tr><td>6130</td><td>-18,64</td><td>0,41</td><td>-28,51</td><td>0,12</td><td>-14,36</td><td>0,29</td></tr><tr><td>6700</td><td>-16,82</td><td>0,60</td><td>-27,86</td><td>0,08</td><td>-15,06</td><td>0,51</td></tr><tr><td>7800</td><td>-15,20</td><td>0,82</td><td>-27,56</td><td>0,12</td><td>-13,04</td><td>0,70</td></tr><tr><td>8180</td><td>-12,99</td><td>0,72</td><td>-27,85</td><td>0,15</td><td>-8,96</td><td>0,56</td></tr></tbody></table>

CRM - 2711a (n = 4), a contaminated top soil and LKSD-1 (n = 5) and LKSD-4 (n = 6), two composites of Canadian lake sediments issued by Geological Survey of Canada (Lynch 1990, Lynch 1999). Two of the analysed reference samples were removed due disproportionally low reported values for several elements. Here, accuracy is expressed as deviations from the certified values. Calcium, Dy, Eu, Fe, Ga, K, La, Mg, Mn, Nd, Na, P, Sr, Sc, Y, and Yb were within 15% of the certified/recommended values while the recovery of Al and Ti was lower (72% and 75%, respectively) (Appendix C: Table 2). The precision (2σ) of the majority of elements was within 10%, while somewhat higher variability was reported for Al (23%), Na (13%), La (16%) and Yb (13%).

Maxima values from the procedural blanks (n = 14) indicate that contamination accounted for less than 0.1% of the average sample concentration for elements Al, Ca, Fe, Mg, Na, P, and Y. Somewhat higher values were reported for K (0.7%), Mn (0.4%), and Ti (0.2%). For trace elements maximum background contamination contributed with less than 1% (Dy, Er, Eu, Ga, Ho, La, Nd, Sc, Y, and Yb). Some elements were analysed by WD-XRF and ICP-OES, which allowed inter-analytical comparison (Al, Ti, P, Ca, Fe) presented in Appendix D. Prior to statistical handling concentration values were calculated to MAR. Selected MAR profiles are displayed in Appendix E.

### 3.4. Statistical analysis

Based on the analytical performance and relevance to the study questions a number of elements were selected from the WD-XRF (Al, Ca, Fe, K, Na, Si, Ti, and Sr) and the ICP-OES data (P, Dy, Eu, Ga, Ho, La, Sc, Nd, and Y) and combined to a composite data-set for the statistical analysis. Since the data-sets had slightly different resolution (WD-XRF n = 88, ICP-OES n = 107) samples from within 2 cm (~40 years) distance are here regarded as from the same depth to maximize the number of data points (n = 71). Three components (CPs) were extracted in order to explain at least 90% of the variance. Two separate PCA were conducted, one covering the entire sequence, denoted PCA₈₃₀₀ (Table 3), and one covering the last ~5500 cal BP (i.e. containing only ombrotrophic peat), denoted PCA₅₅₀₀ (Table 4). The first component of PCA₈₃₀₀ (CP1) explains 51% of the total variance and strongly associated variables (loading > 0.7) include the REE, Sc, Al, Ga, while Si, AAR, Fe, Mn, Ti and P display a partial association (0.3–0.7). We note that the variance of the REE and Sc dominate CP1 and that this is due to highly elevated concentration of these elements between ~8300 and ~5500 cal BP compared to later in the sequence. CP2 explains 22% of the variance and strongly associated variables

<caption>**Table 3**</caption>

Result of PCA₈₃₀₀ analysis. The associations displayed in descending order with the strength indicated by bold (> 0.7), regular (0.3–0.7), and grey font (< 0.3).

<table><thead><tr><th>Variables</th><th>CP1</th><th>CP2</th><th>CP3</th></tr></thead><tbody><tr><td>Expl. var. %</td><td>51</td><td>22</td><td>20</td></tr><tr><td>Cum. var. %</td><td>51</td><td>73</td><td>34</td></tr><tr><td>Ho</td><td><strong>0.97</strong></td><td>0.14</td><td>0.17</td></tr><tr><td>Dy</td><td><strong>0.97</strong></td><td>0.13</td><td>0.17</td></tr><tr><td>Y</td><td><strong>0.97</strong></td><td>0.15</td><td>0.17</td></tr><tr><td>Eu</td><td><strong>0.97</strong></td><td>0.12</td><td>0.18</td></tr><tr><td>Nd</td><td><strong>0.97</strong></td><td>0.13</td><td>0.17</td></tr><tr><td>La</td><td><strong>0.96</strong></td><td>0.14</td><td>0.19</td></tr><tr><td>Sc</td><td><strong>0.95</strong></td><td>0.08</td><td>0.22</td></tr><tr><td>Al</td><td><strong>0.87</strong></td><td>0.18</td><td>0.41</td></tr><tr><td>Ga</td><td><strong>0.77</strong></td><td>0.42</td><td>0.44</td></tr><tr><td>Si</td><td>0.68</td><td>0.18</td><td>0.65</td></tr><tr><td>AAR</td><td>0.64</td><td>0.49</td><td>0.55</td></tr><tr><td>Ca</td><td>0.16</td><td><strong>0.97</strong></td><td>-0.05</td></tr><tr><td>Fe</td><td>0.39</td><td><strong>0.85</strong></td><td>0.16</td></tr><tr><td>Na</td><td>-0.19</td><td><strong>0.83</strong></td><td>0.27</td></tr><tr><td>Sr</td><td>0.13</td><td><strong>0.79</strong></td><td>0.49</td></tr><tr><td>Mn</td><td>0.50</td><td>0.68</td><td>0.31</td></tr><tr><td>K</td><td>0.05</td><td>0.24</td><td><strong>0.91</strong></td></tr><tr><td>Ti</td><td>0.52</td><td>0.09</td><td><strong>0.78</strong></td></tr><tr><td>P</td><td>0.41</td><td>0.34</td><td><strong>0.73</strong></td></tr></tbody></table>
<table><caption>**Table 4**

Result of PCA<sub>5500</sub>. The associations displayed in descending order with the strength indicated by bold (> 0.7), regular (0.3–0.7), and grey font (< 0.3).</caption><thead><tr><th>Variable</th><th>CP1</th><th>CP2</th><th>CP3</th></tr></thead><tbody><tr><td>Exp. var. %</td><td>66</td><td>22</td><td>7</td></tr><tr><td>Cum. var. %</td><td>66</td><td>88</td><td>95</td></tr><tr><td>La</td><td><strong>0.99</strong></td><td>0.04</td><td>0.11</td></tr><tr><td>Eu</td><td><strong>0.98</strong></td><td>0.10</td><td>0.10</td></tr><tr><td>Y</td><td><strong>0.98</strong></td><td>0.07</td><td>0.14</td></tr><tr><td>Dy</td><td><strong>0.98</strong></td><td>0.10</td><td>0.14</td></tr><tr><td>Nd</td><td><strong>0.97</strong></td><td>0.16</td><td>0.11</td></tr><tr><td>Sc</td><td><strong>0.96</strong></td><td>0.01</td><td>0.20</td></tr><tr><td>Al</td><td><strong>0.95</strong></td><td>-0.13</td><td>0.20</td></tr><tr><td>Ti</td><td><strong>0.95</strong></td><td>-0.01</td><td>0.17</td></tr><tr><td>Si</td><td><strong>0.94</strong></td><td>0.05</td><td>0.27</td></tr><tr><td>Ho</td><td><strong>0.92</strong></td><td>0.32</td><td>0.10</td></tr><tr><td>Ga</td><td><strong>0.79</strong></td><td>0.53</td><td>0.24</td></tr><tr><td>K</td><td><strong>0.76</strong></td><td>0.27</td><td>0.43</td></tr><tr><td>AAR</td><td>0.69</td><td>0.60</td><td>0.34</td></tr><tr><td>Fe</td><td>-0.07</td><td><strong>0.97</strong></td><td>0.06</td></tr><tr><td>Na</td><td>0.11</td><td><strong>0.93</strong></td><td>0.01</td></tr><tr><td>Ca</td><td>-0.34</td><td><strong>0.92</strong></td><td>-0.12</td></tr><tr><td>Sr</td><td>0.43</td><td><strong>0.77</strong></td><td>0.18</td></tr><tr><td>Mn</td><td>0.25</td><td><strong>0.76</strong></td><td>0.42</td></tr><tr><td>P</td><td>0.59</td><td>0.30</td><td><strong>0.70</strong></td></tr></tbody></table>

include Ca, Fe, Na, and Sr, while Mn, AAR, Ga, and P are partially associated. CP3 explains 20% of the variance and strongly associated variables include K, Ti, and P. Variables Si, AAR, Sr, Ga, Al, and Mn display a partial association to CP3. The first component, CP1, of PCA<sub>5500</sub> explains 61% of the total variance and strongly associated variables include the REE, Sc, Al, Ti, Si, and Ga (Table 4). Partially associated variables include the AAR, Sr, and P. CP2 explains 25% of the variance and variables Ca, Fe, Na, Sr, and Mn are strongly associated while the AAR, Ga, and Ho are partially associated (Table 4). CP3 explains 7% of the total variance, capturing most of the variance of P, and some of the variance of Mn, K, and the AAR.

Plotting the factor scores against age enables a visual representation of the weight variability over time (Fig. 4A & B). The profiles show

deviations from the average (0). The scores of CP1 of the PCA<sub>8300</sub> analysis are positive, and generally increasing from ~8300 to ~6100 cal BP. Between ~6090 and ~5615 cal BP the scores increase sharply, peaking at 5640 cal BP, followed by a drop back to negative scores. Thereafter, CP1 scores are at, or just below the average until the present, displaying a decreasing trend from ~830 cal BP towards the present. CP2 is initially positive, displaying a generally decreasing trend after 7850 cal BP, sustained until 6090 cal BP when the scores increase again. Between 5640 and 5365 cal BP a sharp increase occurs, followed by a gradual decrease. From 4930 cal BP negative scores are recorded and the decrease continues until ~4000 cal BP. After 2480 cal BP the scores increase again, with peaks recorded at (cal BP): ~2200, ~1200, and between ~740 and ~590. CP3 scores are relatively stable between ~8300 and ~6280 cal BP, after which a steady increase occurs. CP3 peaks at ~5615 cal BP, followed by a rapid drop to below average values. Thereafter CP3 stays below the average until 2480 cal BP when a general increase towards the present occurs, intercepted by four periods of elevated scores (cal BP): at ~2200; ~1385–1150; ~750–590, and from ~450 cal BP towards the present.

In PCA<sub>5500</sub>, CP1 shows negative scores from ~5500 cal BP until ~2480 cal BP when a general increase occurs (Fig. 5A). Within the general increase, four periods of elevated scores are recorded (cal BP): at ~2200; ~1320–1120, ~740–590, and from ~310 cal BP towards the present. CP2 starts with elevated values, and thereafter generally decreases. After ~4900 cal BP CP2 scores are negative until 2480 cal BP after which greater variability is noted towards the present. Elevated values are noted at (cal BP): ~2200, 1200, ~740–590, and from ~200 cal BP towards the present. Except for a minor peak around 5365 cal BP CP3 generally shows stable scores until ~2200 cal after which greater variability is noted towards the present. Negative excursions occur at (cal BP): ~2200; ~1200; and ~740. Elevated scores are recorded at (cal BP): -1070; and -640–240. A sharp decrease is noted after -240 cal BP.

### 3.5. Elemental ratios

From the elemental datasets three elemental ratios were plotted to explore mineralogical and grain size changes: K/Al<sub>XRF</sub>, Si/Ti<sub>XRF</sub>, and La/Y<sub>ICP</sub> (Fig. 5C). The K/Al ratio (average 0.23 ± 0.31, n = 108) is relatively stable between ~8300 and 5750 cal BP. This is followed by an increase that is sustained until ~4500 cal BP (0.35 ± 0.36, n = 39), peaking at ~5200 cal BP (0.79). The ratio thereafter stays low until ~2200 cal BP, except for a minor peak around ~3070 cal BP. The ratio thereafter generally increases towards the present (from 0.10 to 0.40, n = 33) with peaks noted at ~1940 (0.17), ~1240 (0.36), ~740 (0.25), and ~240 cal BP (0.44). Initially, both Si/Ti<sub>XRF</sub> and Sc/Ti<sub>ICP</sub> ratios were explored as Si content may be associated to both inorganic and biogenic mineral phases (e.g. diatoms, phytoliths). Based on the matching trends between these ratios (data not shown) and given the relative analytical quality the focus here is put on the Si/Ti<sub>XRF</sub> ratio. The ratio (sequence average 26 ± 25, 2σ, n = 89) is initially low, followed by an increase between ~7480 and ~6800 cal BP, after which it decreases. From ~6550 cal BP a steep increase occurs, peaking at ~5625 cal BP (74), followed by a rapid drop. Low values are thereafter sustained until 2340 cal BP. Between ~1500 and ~640 cal BP the ratio increases (31 ± 18, n = 11), with peaks noted at ~1040 cal BP and ~740 cal BP, respectively. The ratio thereafter decreases until ~500 cal BP, followed by an increase towards the present. A minor peak occurs at ~420 cal BP.

The La/Y (1.4 ± 0.9, n = 107) represents changes in the light to heavy REE content (L/HREE) throughout the sequence. Yttrium does not belong to the lanthanides, but can be regarded as a HREE based on its chemical properties (e.g. Tyler, 2004). Initially La/Y ratios decrease from ~8300 to ~7680 cal BP, followed by an increase (from 0.8 to 1.7) that is sustained until ~5430 cal BP (n = 26). Starting from ~5365 cal BP a decrease occurs, reaching minimum values ~5200 cal BP (0.5),

<figure><img src="image_6.png" /><figcaption>**Fig. 4.** A) Factor scores plotted against age of the PCA<sub>8300</sub> analysis, and B) after for PCA<sub>5500</sub>. Associated variables (> 0.6) indicated below each profile. The statistical association of the lithophile elements changed when running the analysis with and without the fen.</figcaption></figure>
<figure><img src="image_7.png" /><figcaption>**Fig. 5.** Summary diagram. A. Ash accumulation rate (AAR), peat accumulation rate (PAR), and mass accumulation rate (MAR) of lithogenic element Sc. Periods of elevated mineral deposition indicated by colored boxes. B. Mineralogy as identified by XRD, relative occurrence indicated by number and color of dots. C. Elemental ratios to infer grain size (Si/Ti); deposition of K-feldspar and/or muscovite (K/Al), light to heavy REE ratio (La/Y). D. Rotated scores of PCA<sub>8300</sub> analysis.</figcaption></figure>

followed by generally increasing values. From 4790 cal BP towards the present generally higher values are recorded again (1.7 ± 0.6, n = 58) with peaks noted at (cal BP): ~4200, ~2630, ~2130, ~1640 while decreases are noted around (cal BP): ~2480, ~830, and ~640.

### 3.6. XRD mineral results

Quartz, feldspar (plagioclase and alkali feldspar), muscovite, and carbonates (hydrotalcite - a carbonate clay, dolomite and calcite) were identified throughout the sequence. The mineral composition of each analysed sample is presented in Table 5. In the lowermost sample analysed (~8180 cal BP) quartz, plagioclase feldspar, alkali feldspar, muscovite and a minor occurrence of calcite were identified. At ~7800 cal BP quartz, plagioclase feldspar, and an amorphous phase were identified. From ~5900 to ~5625 cal BP only quartz and a similar amorphous phase to that of the previous sample occur again. From ~5500 to ~4600 cal BP (n = 8) a carbonate clay (hydrotalcite), calcite and minor amounts of quartz are noted. At ~3000 cal BP quartz, plagioclase, alkali feldspar, mica, calcite and a minor occurrence of hydrotalcite were identified. In samples from ~2020 and ~1860 cal BP quartz, plagioclase, and a minor amount of orthoclase feldspar occur. At ~1300 cal BP quartz, plagioclase and alkali feldspar, together with muscovite were recorded, while at ~1040 cal BP quartz, carbonates (hydrotalcite, calcite), plagioclase and alkali feldspars were found. Around ~700 and ~200 cal BP quartz and calcite were recorded along with a minor occurrence of feldspar and one unknown mineral phase. From the most recent sample (15 cm depth, ~180 cal BP) quartz, orthoclase, plagioclase, muscovite, and montmorillonite were identified.

<caption>**Table 5**</caption>

Result of XRD analysis. Relative intensity indicated by size and number of X (x = minor, X = moderate, XX = major).

<table><thead><tr><th>Age,BP.</th><th>Qz</th><th>Pl</th><th>Kfs</th><th>Ms</th><th>Mont.</th><th>Cal /Dol</th><th>Hydro-talcite</th><th>Amorph.</th><th>Unknown</th></tr></thead><tbody><tr><td>180</td><td>X</td><td>X</td><td>X</td><td>X</td><td>x</td><td></td><td></td><td></td><td></td></tr><tr><td>310</td><td>X</td><td>x</td><td></td><td></td><td></td><td>x</td><td></td><td></td><td></td></tr><tr><td>690</td><td>X</td><td>x</td><td></td><td></td><td></td><td>x</td><td></td><td></td><td>x</td></tr><tr><td>960</td><td>Xx</td><td>X</td><td>X</td><td></td><td></td><td></td><td>X</td><td></td><td></td></tr><tr><td>1040</td><td>X</td><td>X</td><td>X</td><td></td><td></td><td>X</td><td>X</td><td></td><td></td></tr><tr><td>1320</td><td>XX</td><td>XX</td><td>XX</td><td>X</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>1860</td><td>Xx</td><td>X</td><td>x</td><td></td><td></td><td></td><td>x</td><td></td><td></td></tr><tr><td>2020</td><td>XX</td><td>X</td><td>x</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>3070</td><td>XX</td><td>X</td><td>X</td><td>X</td><td></td><td>X</td><td></td><td></td><td></td></tr><tr><td>4660</td><td>x</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>4990</td><td>X</td><td></td><td></td><td></td><td></td><td>X</td><td></td><td></td><td></td></tr><tr><td>5120</td><td>X</td><td></td><td></td><td></td><td></td><td></td><td>X</td><td></td><td>x</td></tr><tr><td>5390</td><td>X</td><td></td><td></td><td></td><td></td><td>X</td><td>XX</td><td></td><td></td></tr><tr><td>5390</td><td>X</td><td></td><td></td><td></td><td></td><td>XX</td><td>XX</td><td></td><td>x</td></tr><tr><td>5450</td><td>X</td><td></td><td></td><td></td><td></td><td>X</td><td>XX</td><td></td><td></td></tr><tr><td>5460</td><td>X</td><td></td><td></td><td></td><td></td><td>X</td><td>X</td><td></td><td></td></tr><tr><td>5480</td><td>X</td><td></td><td></td><td></td><td></td><td>X</td><td>XX</td><td></td><td></td></tr><tr><td>5500</td><td>X</td><td></td><td></td><td></td><td></td><td>X</td><td>X</td><td></td><td></td></tr><tr><td>5630</td><td>X</td><td></td><td></td><td></td><td></td><td></td><td></td><td>X</td><td></td></tr><tr><td>5660</td><td>X</td><td></td><td></td><td></td><td></td><td></td><td></td><td>X</td><td></td></tr><tr><td>5880</td><td>X</td><td></td><td></td><td></td><td></td><td></td><td></td><td>X</td><td></td></tr><tr><td>6540</td><td>X</td><td></td><td></td><td></td><td></td><td></td><td></td><td>X</td><td></td></tr><tr><td>7750</td><td>X</td><td>X</td><td></td><td></td><td></td><td></td><td></td><td>X</td><td></td></tr><tr><td>8180</td><td>X</td><td>X</td><td>X</td><td></td><td></td><td>X</td><td></td><td></td><td>x</td></tr></tbody></table>

Qz: quartz, Pl: plagioclase feldspar, Kfs: K-feldspar, Ms.: muscovite, Cal: calcite, Dol: dolomite, Amorph: amorphous phase.
# 4. Discussion

The objectives of this study were to produce a high resolution peat paleodust and growth rate record, and to compare the results with an existing paleodust record of the region (Kylander et al., 2013a, 2016, 2018). We aim to understand the links between dust deposition and accumulation rates; the role of local factors (i.e. bog specific) on peat paleodust records; and the spatial representativeness of single-site reconstructions. In this chapter, the main peatland development stages and PAR of Draftinge Mosse are outlined. This is followed by an assessment of the processes governing the elemental MAR; identification of DE, and; linking mineralogy to the elemental data. Finally, a comparison of DE and PAR between Draftinge Mosse and Store Mosse is conducted, and common and divergent trends explored.

## 4.1. Peatland development

Peat accumulation at Draftinge Mosse started ~8300 cal BP through paludification of the underlying lake sediments. Sedges dominated the assemblage until 5700 cal BP when *Sphagnum* mosses were introduced (Appendix A). The timing of the fen-bog transition is inferred from several lines of evidence: the peat composition, ash content and nitrogen concentration (Tolonen, 1984; Yliruokanen and Lehto, 1995). The transition started around 5700 cal BP and was complete by 5580 cal BP, as indicated by a dominance of *Sphagnum* mosses and a drop in both ash and nitrogen content (< 1.2% and < 1.5%, respectively) (Fig. 3, Fig. 6A, Appendix A).

The PAR gradually decreases between ~8300 and ~6180 cal BP, followed by increasing rates from 6010 cal BP. During the transition to ombrotrophy a significant increase occurs, peaking at 5610 cal BP with values three times higher (220 g m⁻² yr⁻¹) than the profile average

(70 g m⁻² yr⁻¹). Non-humified *Sphagnum* peat, coupled to high C/N ratios, are recorded during this high peat accumulation event (HPAE). The continued dominance of *Sphagnum* moss would suggest that the high C/N ratios are a result of low levels of decomposition (Kuhry and Vitt, 1996), likely as a consequence of high water tables during this phase. The HPAE lasted until ~4530 cal BP after which the PAR dropped back to background values. Between ~4000 and ~2480 cal BP PAR fall to the lowest values observed in the sequence (10 g m⁻² yr⁻¹). This slowdown in PAR could be the result of lowered plant productivity and/or high levels of decomposition or, alternatively, part of the record may be missing. Decreased wetness was reported in peat records from south and central Sweden around this time (Rundgren, 2008; Kylander et al., 2013a, 2016) indicating that dry conditions may explain the reduced PAR at Draftinge Mosse during this period. After ~2480 cal BP the peat is dominated by Carex and Ericaceae, with an average PAR of 60 g m⁻² yr⁻¹, which is overprinted by four periods of elevated PAR (cal BP: ~2225–2170; ~1240–1185; ~755–505, and from ~280 towards the present) (Fig. 5A).

## 4.2. Processes controlling elemental concentrations in the bog

In peat paleodust studies, conservative lithophile elements (Al, Sc, REE, Ti) are used as proxies for atmospheric mineral dust input (Steinmann and Shotyk, 1997; Shotyk et al., 2002; Aubert et al., 2006). At Draftinge Mosse these elements are associated with two components (CP1 and CP3) in the full sequence analysis (PCA₈₃₀₀), and to one component (CP1) when only the ombrotrophic part of the sequence is considered (PCA₅₅₀₀). The second component (CP2) of both PCA analyses included most of the variance of elements that are associated with soluble phases in peat (Ca, Fe, Mn, Na and Sr) (Tables 3 and 4, Fig. 4) (Boyle, 2001; Malmer, 1988).

The change in elemental groupings when running the PCA with and without the fen stage suggests that the processes governing the elements shifted over the fen-bog transition. When a mire transitions to ombrotrophy a shift in both in the floral (sedges to *Sphagnum* mosses) and geochemical (lower pH) contexts as well as mineral transport processes (fluvial and aeolian to aeolian alone) is expected. As a consequence of the latter, finer grain sizes should increase when fluvial transport ceases and aeolian transport dominates. At Draftinge Mosse the Si/Ti ratio (Fig. 5D) drops in accordance with the fen to bog transition. Suggesting that the split of lithogenic elements into two components (Tables 3 and 4) reflect a shift in grain size, likely related to the shift in the trophic status and dominating mineral transport processes.

In PCA₅₅₀₀ all lithophile elements are associated to CP1 (Table 4), indicating that the rotated factor scores of CP1, which, together with the trophic state of the bog, indicates that this CP represents atmospheric mineral input (Fig. 4B). Apart from the conservative lithophiles (Al, REE, Sc, and Ti) in CP1, a few other elements are also found in CP1, namely Si, Ga, and K. Silicon is a common minerogenic element, dominant in quartz (SiO₂), but can also be associated with biogenic phases (phytoliths, diatoms). Here, Si is strongly associated with the lithophile elements, suggesting that any biogenic Si is of minor relevance. Gallium is associated with plagioclase feldspar (e.g. Kylander et al., 2006), and K to alkali minerals (e.g. muscovite and K-feldspar) (e.g. Nesse, 2017). Despite the fact that muscovite and feldspars are subject to dissolution in acidic environments (e.g. Boyle, 1973; Oelkers and Schott, 1998) the association of these elements with the lithophile elements (Table 4) suggests the most of the Ga and K are retained in the peat, at least on the timescale of the ombrotrophic stage (~5500 cal BP).

We note that, towards the end of the fen stage, the REE and Sc content increase significantly (1–3 order of magnitude) when fluvial and/or topogenous transport mechanisms of relatively coarse grained minerals likely dominated. The elevated values persist into the ombrotrophic stage (until ~5520 cal BP). During this time, the REE and Sc, show a contrasting behavior to other lithogenic elements (e.g. Si, Al, Ti)

<figure><img src="image_8.png" /><figcaption>**Fig. 6.** Sc MAR and PAR at A) Draftinge Mosse and B) Store Mosse between 8300 and 300 cal BP. Uncertainties in timing indicated by grey color. Mean indicated by the black line.</figcaption></figure>
and the AAR (Tables 3 and 4; Fig. 5A). This could indicate that a distinct mineralogy, enriched in high REE and Sc content minerals, (Aubert et al., 2001) such as monazite, xenotime, allanite (e.g. Sadeghi et al., 2013), was deposited, or alternatively, that other processes affected the concentration. These processes could include pH changes, changes in organic matter character, inflow of geogenic groundwater, and/or microbial activity (Davranche et al., 2015; Rinklebe et al., 2017; Broder and Biester, 2017; Sjöberg et al. 2017).

In both PCAs (Fig. 4A & B) CP2 groups elements that are associated with phases that are soluble in acidic reducing environments (Fe, Mn, Na, Ca, and Sr)(Boyle, 2001) that are out washed from the bog. Calcium is delivered to bogs both via atmospheric deposition and diffusion from underlying sediments, and therefore expected to display an upwards decreasing trend in peat records (Malmer, 1988). At Draftinge Mosse, the second component generally decreases from ~8300 cal BP towards the present except between ~5670 and ~4000 cal BP when a sharp increase occurs. This increase is contemporary with the HPAE and carbonates are identified at this time (Fig. 5). A second, more moderate increase, also occurs between ~740 to ~590 cal BP. CP2 thus appears to be controlled not only by leaching and outwashing, and/or diffusion, but, given the surprising presence of carbonates, by increased Ca content, carbonate precipitation and/or preservation (see below) in certain parts of the record.

The third component of PCA<sub>5500</sub> explains only a minor part of the total dataset variance (7%) but most of the variance of P. Phosphorous is derived via aeolian deposition to bogs, both as inorganic minerals (i.e. apatite)(Wieder, 2006) and organic particles (Newman, 1995), but has a different fate after deposition than conservative lithophile elements (Le Roux et al., 2006). Phosphorous is an important nutrient and is therefore expected to be rapidly taken up by plants in the biologically active layer (Wieder, 2006), although deposited P seems to be largely retained in the peat (Schillereff et al., 2016), slight losses are expected as reabsorption by plants is never complete (Walbridge and Navaratnam, 2006). The general decrease from the top and downwards of CP3 observed here, likely reflects enrichment, and losses, of P in the active layer of the peat.

### 4.3. Atmospheric mineral dust deposition

During the fen stage mineral deposition occurred both through fluvial and aeolian transport, with fluvial transport likely dominating. As such, the focus here is on the ombrotrophic section, after 5570 cal BP, when the system was exclusively rain-fed. Some lithophile elements dropped in accordance with the fen bog transition (Al, Sc, Si, Ti) while others decreased at a somewhat slower pace (REE), causing the split of lithophile elements to persist ~70 years after the system became ombrotrophic. Here, DE are identified based on periods of elevated Sc MAR (Fig. 5A) in combination with the rotated factor scores of CP1 (PCA<sub>5500</sub>) (Fig. 4B). Scandium is a conservative lithophile element that is not typically involved in biological uptake and cycling (Steinmann and Shotyk, 1997), often used as a dust proxy (Shotyk et al., 2001).

At Draftinge Mosse, low levels of dust deposition are in inferred in the early ombrotrophic phase (Fig. 5A). Due to the low resolution between ~4000 and ~2480 cal BP, no paleodust information is available. A general trend of increasing dust deposition is noted from ~2480 cal BP onwards, overprinted by four DE dated to (cal BP) ~2200 (DE1), ~1385 to ~1150 (DE2), ~830 to ~640 (DE3), and from ~420 towards the present (DE4). PAR increase in parallel, or with a slight temporal off-set, to all four DEs (Fig. 5A.). Drier conditions have been recorded regionally, contemporary with DE1 and DE2 (e.g. Kylander et al., 2016) while DE3 and DE4 occurred during the Little Ice Age, when both colder and drier conditions have been reconstructed (Wanner et al., 2011). We note that the DEs are also reflected in the AAR data (Fig. 5), indicating that the AAR could be used as to detect dust deposition in peat paleodust records, as previously suggested by Martínez Cortizas et al. (2019).

### 4.4. Mineral composition and elemental associations

Shifts in the mineralogy in the Draftinge Mosse sequence were detected by coupling XRD mineral results with elemental MAR and ratios. The lowermost sample analysed (~8180 cal BP), corresponds to the early fen development and likely reflects the mineralogy of the underlying sediment. Identified minerals includes quartz, plagioclase, alkali feldspar and calcite. In the sample at ~7755 cal BP the alkali feldspars and calcite disappear leading into the period between ~6540 and ~5625 cal BP (n = 4) where only two phases occur: quartz and an amorphous phase.

Just prior to, and during the early ombrotrophic stage, we find the HPAE (~5690 to ~4530 cal BP) where two phases, quartz and carbonates, are recorded (Fig. 5). The 813C values of ash residues indicate that these carbonates have an authigenic origin and that the isotopic values in the lowermost sample are distinct in comparison to samples further up in the sequence (Table 2). An increased supply of Ca is recorded between ~5670 and ~4000 cal BP and although Ca can diffuse upwards in peat (Steinmann and Shotyk, 1997), this process alone is unlikely to explain the significant increase observed here. As the peatland was ombrotrophic at this time, aeolian deposition might have contributed with Ca. A potential local Ca source could be carbonates from the local (former) lake sediments of the area, re-mobilized by aeolian activity. That carbonates are present in the local soils is also evidenced by the occurrence of calcite in the oldest, and lowest, sample analysed by XRD (Fig. 5). During the same period the La/Y ratio decreases markedly (Fig. 5), likely reflecting the tendency for heavy REE enrichment in electronegative ligands, e.g. carbonates and/or oxalates (e.g. Tyler, 2004; Stolpe et al., 2013). Carbonates are expected to be rapidly dissolved in the acidic conditions of the bog (Le Roux et al., 2006). Despite this, carbonates have been observed in peat sequences, precipitated within the cell of the *Sphagnum* moss peat (Rudmin et al., 2018). Plants can precipitate carbonates and Ca-oxalates to remove excess Ca (Bauer et al., 2011). The location of the precipitate, within the cell walls, might protect the mineral from dissolution by organic acids and/or acidic bog water. Additional analyses are required to fully untangle the processes governing these carbonates, but their presence nevertheless indicates an increased role of authigenic processes in parts of the sequence, that Ca content was abundant during the HPAE, and that these carbonates can affect the REE ratio. This is in line with a study by Arbuzov et al. (2018) showing that the bulk of the REE were associated with hydrolyzable and acidolyzable phases in peat sequences in Western Siberia.

We note that following the fen to bog transition Al, Sc, and Ti MAR drop rapidly while other lithophile elements (K and Ga) are decrease at a slower rate, indicating a shift in the mineral composition. Potassium is enriched in alkali feldspars and muscovite, both of which occur in the sequence, but were not identified by XRD analysis for this period. This might be related to peak overlap and/or dilution from the carbonates or that the minerals have been weathered. By plotting K/Al (Fig. 5C) the relative contribution of K containing minerals throughout the sequence can be depicted. In the upper parts of the sequence increases coincide with periods when K-feldspar and muscovite are present (Fig. 5B & C) suggesting that this ratio reflects alkali mineral input. Both muscovite and alkali feldspar can be weathered in acidic conditions (e.g. Boyle, 1973; Oelkers and Schott, 1998) but the strong association of K with the immobile lithophile elements in the ombrotrophic section indicates that the bulk of the element is still retained in the peat (Table 4). The ratio increases in parallel with the HPAE, suggesting an increased input of K containing minerals. Gallium is associated with plagioclase feldspars, and is also relatively enriched during the HPAE. Taken together, the increased input of Ca, K, Y, and Ga indicates a distinct mineralogy being deposited at this time, enriched in plagioclase, alkali minerals and carbonates, that together with high water tables might have supported the rapid peat growth. Elevated nutrient availability is also supported by the presence of brown mosses (Vitt and Wieder, 2008) during the
early part of HPAE (Appendix A). The undecomposed peat observed during this phase, indicates increased wetness, possibly related to strengthening of westerly airflows and increasing regional precipitation around mid-Holocene (Rundgren, 2008).

Between ~4000 and ~2480 cal BP the temporal resolution of the record is low and only one sample was analysed for mineralogical composition (~3070 cal BP). From this time and onwards, the mineralogy becomes more diverse with typical felsic minerals (quartz, feldspars, muscovite) occurring in varying amount along with occurrence of carbonates. This change is also reflected in the elemental dataset with concordant increases in Al, K, and Na when feldspars and muscovite are identified (Appendix E).

When exploring the mineralogy of the DEs we note that during DE1 (~2200 cal BP) the elemental ratios show no significant change indicating that the mineralogy of the event did not differ much from the background dust deposition. DE2 (~1400–1150 cal BP) and DE4 (~420 cal BP towards the present) are enriched in alkali minerals compared to non-dust events (Fig. 5B & C). In DE3 (~830–640 cal BP) only quartz and minor amounts of plagioclase and calcite were recorded, with no presence of alkali minerals. This is also reflected in a stagnant K/Al ratio. The Si/Ti ratio is however somewhat elevated, indicating increased coarser grains being deposited. Increased grain size in late Holocene have previously also been recorded in inland sand dunes from south and central Sweden, attributed to increased wind strengths (Bernhardson et al., 2019). Between 1040 and 310 cal BP carbonates occur again (Fig. 5B), coinciding with decreased La/Y ratios. In the most recent sample analysed (~180 cal BP), the ash residues are relatively enriched in quartz, plagioclase, alkali feldspar with no presence of carbonates or amorphous phases, coupled to increasing La/Y and K/Al ratios (Fig. 5B.).

## 4.5. Comparison with Store Mosse

Here, mineral deposition as indicated by Sc MAR and PAR are compared between Draftinge Mosse and the nearby paleodust record from Store Mosse (Kylander et al., 2013a, 2016, 2018). The comparison covers 8300 to 310 cal BP, confined by the basal age of Draftinge Mosse. Prior to the comparison, an updated age-depth model was made for Store Mosse using the approach described for Draftinge Mosse. In order to visualize the effect of temporal uncertainties stemming from the age models the Sc MAR profiles are plotted using the ghost plot function in Bacon (Blaauw and Christen, 2011) (Fig. 6).

Overall, the two sites show many similarities in Sc MAR and PAR (Fig. 6), although the magnitude, and sometimes timing, differ somewhat. Higher Sc MAR are generally recorded at Draftinge Mosse, particularly between ~8300 and ~5600 cal BP. Higher ash content are also recorded at Draftinge Mosse (1.8 ± 2.7%, *n* = 321) compared to Store Mosse (1.3 ± 1.0, *n* = 472). The HPAE at Draftinge Mosse has a slightly earlier initiation (~6090 cal BP) and peak (5610 cal BP), compared to that of Store Mosse (initiation ~5750 cal BP, peaking at ~5220 cal BP, using the updated age model). While dust deposition rates were low during the HPAE, a nutrient rich mineral assemblage was inferred at both sites. At Store Mosse, enrichment of feldspars and phosphates was inferred (Kylander et al., 2013a, 2016), while at Draftinge Mosse feldspar and carbonates were identified. However, elevated P input is recorded early in the HPAE (Appendix E), indicating increased fluxes of a P source, such as phosphates, might have occurred also at Draftinge Mosse. Given that PAR in bogs is mainly governed by the height of the water table (Clymo, 1984), the presence of the HPAE at both sites, suggest that this was a period with regionally elevated water tables. Temperatures were also elevated during this period (Seppä et al., 2009), possibly extending the growth season, and contributing to elevated PAR.

After the HPAE PAR decline at both sites and Draftinge Mosse in particular sees very low PAR, preventing comparison of the two records until ~2480 cal BP. Within a short timespan however, Sc MAR and PAR

increases at both sites (Draftinge and Store Mosse at ~2200 and ~2300 cal BP, respectively). Between ~1400 and ~1250 cal BP another period of elevated dust deposition was recorded at both sites but a concurrent PAR increase is only seen at Draftinge Mosse. Between ~840 and ~590 cal BP a period of elevated Sc MAR and PAR is seen at Draftinge but not Store Mosse. From ~400 cal BP, Sc MAR increase again at both sites.

That elevated Sc MAR are recorded at both sites within the same periods (given the uncertainties of the respective age-models), despite different analytical approaches, resolution, and dominant vegetation, strongly point to a common external forcing mechanism. Between ~8300 and ~5500 cal BP significantly higher Sc MAR are recorded at Draftinge Mosse in comparison to Store Mosse. As mentioned previously, this likely reflects a larger input of sologenous or topogenous water flows, higher ash contents and the later transition to bog conditions at Draftinge Mosse (~5580 cal BP) compared to Store Mosse (~6000 cal BP). That Sc MAR still peak within the same period (Draftinge Mosse: ~5640 and Store Mosse: ~5675 cal BP) during this first event indicates that at least part of the minerals was derived via the same transport process at the two sites. Between ~5520 and ~5360 cal BP, two short, but distinct peaks are recorded at Store Mosse, which are not seen at Draftinge Mosse. This could reflect local events, or alternatively, differences in the analytical resolution during this period. When only the ombrotrophic parts of the sequences are compared the average Sc MAR are more similar, but individual events still differ in recorded intensities (Fig. 6). This would imply a common forcing mechanism, such as dry conditions causing more exposed soils, increased land use, and/or increased wind strengths. But given the differences in intensities between the bogs, local dust sources likely dominate. At Draftinge Mosse, increases in PAR consistently occur during or towards the end of dust events. This pattern is mostly also reflected at Store Mosse, with an exception around the DE recorded at ~1200 cal BP. Another notable difference between the two sites is that the PAR are more extreme at Draftinge Mosse compared to Store Mosse, the former having both higher maximum (220 g m⁻² yr⁻¹) and lower minimum values (8 g m⁻² yr⁻¹), indicating a stronger, and sometimes faster, response to the factors governing peat accumulation. PAR in bogs are affected by several factors such as dominating vegetation and nutrient availability (Malmer and Wallén, 1999, Clymo, 1984), with the most important factor being the height of the water table (Clymo, 1984). Given the differences in size between the two bogs, with the contemporary Draftinge Mosse covering 400 ha, while the significantly larger Store Mosse extends over 7700 ha, the smaller bog might have responded faster to hydrological changes than the larger, and thus more buffered, bog.

## 5. Conclusions

Five episodes of increased mineral deposition were recorded at Draftinge Mosse (cal BP): ~6280–5570, ~2200, ~1385–1150, ~830–590, and from ~420 to the present. The earliest event in the succession occurred during the fen-bog transition and was enriched in coarse grain particles, suggesting a fluvial origin. Following the transition into ombrotrophy the grain size decreased and a shift in the mineral composition occurred, highlighting the importance within peat paleodust studies to carefully asses the peatland development stages, preferably from multiple proxies, as this can inform on the dominant transport processes. Between ~5600 and ~4700 cal BP a HPAE occurred, previously observed in the region by Kylander et al. (2013a). This work shows that the HPAE was reflected regionally and thus likely induced by common climate forcing mechanisms: regionally wet conditions coupled to deposition of nutrient rich minerals. Authigenic carbonates were identified throughout the record, with enrichments recorded during the HPAE. The excess Ca observed during this period could be derived both via diffusion from underlying sediments, but also likely via aeolian transport of local carbonates. From ~2500 cal BP to
the present a general increase in deposited dust is recorded, along with four dust events. Increases in PAR concurrently followed dust events, suggesting a coupling between these processes. Comparison of Sc MAR and PAR between Draftinge Mosse and the previously studied Store Mosse showed many similarities, indicating that the dust events were regional. Despite the synchronicity, both bogs showed different intensities of change under the same external forcing: greater variability and earlier responses in terms of PAR, and higher Sc MAR at the moderately sized Draftinge Mosse compared to the larger Store Mosse. The differences in PAR are likely related to a greater buffering capacity, and more inert response to hydrological changes of the larger bog ecosystem compared to the smaller bog. Draftinge Mosse records a higher Sc MAR, and also over all higher ash content, indicating that the size of the bog also might be important for mineral accumulation rates, and that that local dust sources likely dominate. During the studied period the PAR have been highly variable, ranging from 15 to 220 g m⁻² yr⁻², with the highest values recorded during a warm and wet episode coupled to elevated input of nutrient rich minerals. Similar climate conditions are projected for the region ahead (Länsstyrelsen i Jönköpings län, 2012), that together with elevated mineral dust input might promote accelerated PARs in bogs.

## Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

## Acknowledgements

We wish to thank the students at Per Brahegymnasiet for conducting the modified macro-fossil analysis, Heike Siegmund, Scientific engineer at the Dept. of Geological Science, (Stockholm Uni.) for the C, N, and ¹³C analysis and Pär Hjemlquist, Scientific engineer at Dept. of Environmental Science (Stockholm University) for support during the clean lab digestion procedure. Jenny Söderlind (MSc) assisted with ashing of peat samples. Carina Johansson, Scientific engineer, Mikaela Holm (MSc), and Dr. Richard Gyllencreutz (Dept. of Geological Sciences, Stockholm University) are thanked for support in the field, lab, and interpretation discussions. Prof. Henrik Skogby (Swedish Museum of Natural History) and Inés Fernández Cereijo (Molecular structure specialist, Universidade de Santiago de Compostela) are thanked for XRD mineral identification. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

## Appendices. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.chemgeo.2020.119795.

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