Journal of Biogeography

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Journal of Biogeography

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Origin of the forest steppe and exceptional grassland diversity in Transylvania

(central-eastern Europe)

Angelica Feurdean, Elena Marinova, Anne B. Nielsen, Johan Liakka, Daniel Veres, Simon M.

Hutchinson, Mihaly Braun, Alida Timar-Gabor, Ciprian Astalos, Volker Mosburgger and

Thomas Hickler

Appendix S1

Chronology and age

–depth construction at Lake Stiucii.

The construction of the chronology of the first 626 cm, i.e. the top 12,000 years of the profile, was established on the basis of 15 AMS

14

C ages and

210

Pb

137

Cs and

241

Am measurements of the recent sediments (Table 1; Feurdean

et al

., 2013). The

14

C AMS age estimates were converted into calendar years BP (cal. yr

BP

) via C

LAM

software (Blaauw, 2010) using the

INTCAL13 data set of Reimer

et al

. (2009). An age

–depth curve was derived based on a smoothing spline model (with 0.3 smooth; 10,000 iteration; Fig. S1), thus following the same setting as in Feurdean

et al

. (2013). Pollen stratigraphic markers were used to slightly adjust the Younger Dryas / Holocene transition as this appeared to be about 300 years too young based on the radiocarbon ages. The newly obtained age

–depth based on INTCAL13 is largely similar to Feurdean

et al

. (2013) based on INTCAL09. The gamma based age

–depth model was calculated using constant rate of supply (CRS) model, which was joined to the radiocarbon chronology by assuming a constant sedimentation rate between the two types of dated points (Fig. S1). The sediment accumulation rate in the 0

–12,000 cal. yr

BP

interval varies between 8 and 40 cm/yr.

In the lower part of the sediment profile stretching between 626 and 726 cm, the chronology was based on two AMS

14

C and two optically stimulated luminescence ages (OSL;

Fig. S2). The

14

C AMS age of 38,375

± 1177 (44,650–41,200 cal. yr

BP

; 43,000 cal. yr

BP average; INTCAL13 data set) at 680 cm depth agrees with the OSL age obtained on quartz at

685 cm

(48,300 ± 2900) and at 710 cm (52,500 ± 2900) respectively. However, the radiocarbon age of 19,654 (22,000

–21,000 cal. yr

BP

; 21,500 cal. yr

BP

average 2 sigma) at

692 cm is too young and suggests either an age reversal or contamination by younger carbon or organic remains. We therefore retained the 43,000 cal. yr

BP

date as most likely to be valid and reject the age of 21,500 cal. yr

BP

until further results are available (Fig. S2). Support for the assumption that the radiocarbon age at 692 cm may be too young comes from the pollen record. This indicates one of the greatest extensions of the tree cover. This according to the

1

radiocarbon date should correspond to the Last Glacial Maximum (LGM), a period when we expect a marked reduced tree cover similar to that recorded above 645 cm. Overall, these combined radiocarbon and OSL age estimates indicate that the Lake Stiucii basin has recorded environmental conditions from about 55,000 cal. yr

BP

(early Marine Isotope Stage

(MIS) 3

– full glacial). However, several erosional events appear to have affected the integrity of the record between approximately 35,000 and

c

. 13,000 cal. yr

BP

.

Figure S1

Age

–depth model for Lake Stiucii for the period 0–12,000 cal. yr

BP

. Data points used for the construction of the age

–depth model (blue); data points rejected from the age– depth model (red); pollen stratigraphical markers used to adjust the age

–depth (green).

2

Figure S2

Age

–depth model at Lake Stiucii for the glacial period based on AMS

14

C and OSL measurements. Uncalibrated radiocarbon dates and weighted average OSL measurements

(black squares), whereas midpoint of calibrated dates (radiocarbon) and weighted average

(OSL) are plotted in grey triangles.

3

*UBA-21062

UBA-20364

UBA-19030

*UBA-19031

*UBA-19033

UBA-19035

UBA-20365

UBA-18402

UBA-19034

UBA-19035

UBA-19037

UBA-19036

UBA-20362

UBA-20361

UBA-20363

UBA-21555

*UBA-21562

Table S1

(a)

210

Pb and

137

Cs; (b) AMS

14

C and (c) optically stimulated luminescence ages (1 sigma). Ages treated as outliers in the age

–depth model are marked with asterisks.

(a)

210

Pb and

137

Cs

210

Pb

210

Pb

210

Pb

210

Pb

210

Pb

210

Pb

210

Pb

210

Pb

210

Pb

210

Pb

210

Pb

210

Pb

Core Depth

(cm) gravity 0 gravity 1 gravity 3 gravity 4.5 gravity 5.5 gravity 6.5 gravity 7.5 gravity 9.5 gravity 11.5 gravity 12.5 gravity 13.5 gravity 14.5

Age

210

Pb

2012

2012

2005

1961

± 0

± 2

±2

1998± 2

1994

± 2

1988±3

1984

± 3

1977

± 3

1969

± 4

1964

± 4

1963

± 4

± 4

(b)

Lab no. Core Material dated

14

C age

13

C gravity

4.2

2.1

2.2

2.3

2.2

2.3

2.3

2.4

2.5

2.6

2.6

4.8

4.8

4.8

4.9

4.9

226

238

258

296

330

390

511

570

577

597

619

680

692

Depth

(cm)

33

110

149

164

Gyttja

Phragmites

Phragmites

Phragmites

Phragmites

Phragmites

Phragmites

Phragmites

Peat

Peat

Phragmites

Peat

Phragmites

Plant macros

Phragmites

Charcoal

Juniperus

twigs

611

± 23

1197

± 23

1210

± 33

1076

± 35

1574

± 22

2675

± 25

3018

± 31

3269

± 36

35.6

-24.2

-34.2

-35.7

-29.8

-22.6

-25.8

-25.6

4105

± 25

6404

± 42

8387

± 41

9349

± 38

9445

± 50

-28.7

-25.2

-30.5

-29.0

-26.1

9547

± 54

9962

± 39

27.3

-27.0

38,375

± 1177 -24.6

19,654

± 158

-19.5

(c)

Sample code

OSL 2

OSL 1

Core

4.9

4.9

Depth (cm)

42-47 (682-687)

62-68 (707-713)

OSL age

48,300

± 2400

52,500

± 2900

4

OSL dating methodology

Equivalent dose measurements have been conducted using the single aliquot regeneration

(SAR) protocol (Murray & Wintle, 2000, 2003), which is generally accepted as a robust technique for dating quartz from relatively young sediments.

In order to increase the confidence in the OSL dating results, besides the application of the standard intrinsic rigour tests of the protocol [recycling, infrared (IR) depletion-purity tests, recuperation, dose recovery, preheat plateau], analyses were carried out on all available quartz grain size fractions (4

–11 μm, 63–90 μm, 90–125 μm and 125–180 μm, respectively).

The ages were found to be in agreement within the error limits and there was no systematic offset of any of the grain sizes. Moreover, the fact that there was no dependency in age with grain size rules out the possibility of partial bleaching affecting the coarser grains.

Consequently, the final ages tabulated in Table S1 is the average of the individual ages obtained on each grain size. More details regarding OSL dating are given below.

Sample preparation

Sample preparation for luminescence measurements was performed under low intensity red light conditions. A 3-day HCl (10% concentration) treatment was employed for carbonate removal followed by further 3-day H

2

O

2

(30%) treatment for organic matter removal. The coarse grain fractions (63

–90 μm, 90–125 μm, 125–180 μm) were separated through wet sieving. As this fraction consisted in an undifferentiated mixture of polyminerals including quartz, feldspars and heavy minerals, a two-step density separation by centrifugation using a heavy liquid solution [sodium metatungstate Na

6

(H

2

W

12

O

40

)

× distilled water] was performed..

First the quartz (density 2.65

–2.66 g/cm

3

) and plagioclase grains were separated by centrifugation in a 2.65 g/cm

3

heavy liquid solution from the lighter minerals as potassium and sodium feldspars with a density of 2.62 g/cm

3

. The second step employed a 2.75 g/cm

3

heavy liquid solution, in which the quartz and plagioclase feldspars were isolated from the heavy minerals such as zircons and apatite. Quartz grains were isolated from this fraction employing a treatment with hydrofluoric acid HF (40% concentration) for 40 minutes as they could no longer be differentiated from plagioclase by density separation. Etching was also removed from the outer surface of the quartz grains, reducing the external ionizing alpha radiation contribution to the grains to a negligible level. Precipitated fluorides resulting from the HF attack were rinsed with a 60 minute HCl (10%). For fine grain fraction of quartz (4

–11 μm) to be extracted, t he fraction less than 11 μm were isolated by settling in Atterberg cylinders a ccording to Stokes’ Law. This fraction was etched with hexafluorosilicic acid H

2

SiF

6

for 10 days. Subsequently, the removal of the grains < 4 μm was carried out by centrifugation. For measurement the coarse quartz grains were mounted on stainless steel disks. Silicon oil was

5

used as adhesive. For the fine quartz grains aluminum disks were used. Aliquots were made by pipetting a 1 ml suspension of the fine grains (2 mg of grains /1 ml acetone) onto each aluminum disc.

Equipment and measurement protocol

Luminescence measurements were performed on a standard Risø TL/OSL-DA-20 reader equipped with blue light emitting diodes (LEDs;

470 ± 30 nm). IR (875 ± 80 nm) LEDs were used for infrared stimulation. The blue light stimulated OSL signal was detected through a 7.5 mm thick Hoya U-340 UV filter. Irradiations were carried out using an incorporated

90

Sr-

90

Y radioactive source that was calibrated against gamma dosed calibration quartz supplied by

Risø National Laboratory. A dose rate of 0.155 Gy/s for the coarse quartz grain mounted on stainless steel disks was obtained. For the fine grains on aluminium disks the dose rate was

0.123 Gy/s.

The single aliquot regeneration (SAR) protocol (Murray & Wintle, 2000, 2003) was applied on quartz extracts. The measurement parameters (unless otherwise mentioned) consisted of: preheat 10 s at 220 o

C; cut heat (ramp heating 5

o

C/s) to 180

o

C; ETOSL consisting of blue

LED stimulation (36 mW/cm

2

) at 280 o

C for 40s; IR stimulation for 100s at 125

o

C (IR bleach) before each blue LED OSL stimulation (40s at 125

o

C) to reduce any possible contribution from signals derived from feldspars; test dose magnitude of 15.5 Gy; five regeneration doses applied to construct the dose response curve; exponential + linear model used for interpolating the growth curve. The intrinsic rigour tests applied included recycling, recuperation, dose recovery, preheat plateau test (for OSL1 90

–125 μm). For all measurements the net CW-OSL signal was determined from the initial 0.308 s of the decay curve less an early background integrated between 1.69 and 2.31 s.

6

Table S2

Equivalent dose measurement. Errors quoted are random errors.

SAMPLE Grain size aliq size no of aliq used

3

Equivalent dose

DE(Gy)

162

± 4

Recycling Recuperation

(%)

OSL 1

OSL 2

4-11

μm

9 mm

63-90

μm

9 mm

90-125

μm 9 mm

2 mm

125-180

μm

4-11

μm

9 mm

9 mm

63-90

μm

9 mm

90-125

μm 9

125-180

μm mm

9 mm

6

9

37

8

4

3

9

8

135 ± 15

136 ± 11

122 ± 8

98 ± 17

142 ± 3

153 ± 11

120 ± 15

108 ± 13

1.03 ± 0.05 0.40 ± 0.44

0.96 ± 0.02 0.20 ± 0.12

1.00 ± 0.02 0.20 ± 0.17

0.97 ± 0.01 0.74 ± 0.22

0.99 ± 0.03 1.29 ± 0.66

1.05 ± 0.04 0.37 ± 0.18

0.98 ± 0.01 0.30 ± 0.14

0.96 ± 0.01 0.77 ± 0.30

1.00 ± 0.02 0.61 ± 0.08

Table S3

Equivalent dose dependency as function of preheat treatment applied. The cut heat temperature was kept at 180 o

C.

SAMPLE

OSL 1

Grain size

90-125

μm aliq size

2 mm no aliq used

3 of

37

3

3

4

Preheat treatment

200

220

240

260

280

Equivalent dose

DE(Gy)

139 ± 12

122 ± 8

86 ± 19

106 ± 8

1

24 ± 46

7

Table S4

Results of dose recovery tests. Measurement parameters: preheat of 10s at 220 o

C, cut heat to 180

°C, bleaching consisting of 2 repeated OSL stimulations of 100 s at room temperature with an intercalated pause of 10,000s, given dose 77.5 Gy.

SAMPLE

OSL1

OSL 2

Grain size

Aliq size

No. of aliq used

63-90

μm

9 mm 3

90-125

μm 9 mm 3

125-180

μm

9 mm 4

90-125

μm 9 mm 3

Annual dose determination

Recovered/ given dose

1.09 ± 0.08

1.09 ± 0.08

1.06 ± 0.08

1.03 ± 0.06

Recycling

1.00 ± 0.04

0.98 ± 0.03

1.00 ± 0.05

0.98 ± 0.03

Recuperation

(%)

0.09 ± 0.14

0.60 ± 0.25

1.62± 0.55

0.62 ± 0.12

Radionuclide (

238

U/

226

Ra,

232

Th,

40

K) specific activities were measured using high resolution gamma-ray spectrometry and the dose rates were calculated using the conversion factors tabulated by Adamiec & Aitken (1998).

Table S5

Radionuclide specific activity. Errors quoted are representing the total (random and systematic) uncertainty.

SAMPLE

OSL 1

OSL 2

Pb-210

(Bq/kg)

29 ± 4

27 ± 4

Ra-226(Bq/kg)

23 ± 2

32 ± 3

Th-232(Bq/kg)

27 ± 3

35 ± 3

K-40(Bq/kg)

495 ± 12

457 ± 12

8

Table S6

Summary of OSL age.

n

represents the number of accepted aliquots. Beta attenuation and etching factor for 63

–90 μm quartz was assumed to 0.94 ± 0.050; beta attenuation and etching factor for 90

–125 μm was assumed to 0.90 ± 0.045; beta attenuation and etching factor for 125

–180 μm was assumed to 0.88 ± 0.044; alpha efficiency factor considered was 0.04

± 0.02; the uncertainties mentioned with the optical ages are the overall uncertainties. All uncertainties represent 1σ.

Quartz

Fraction

4-11

μm

63-90

μm

90-125

μm

90-125

μm

Small

125-180

μm

WEIGHTED

AVERAGE

References

OSL 1

AGE

(ka)

Random error (%)

System error

(%)

7.2

57.1 ±

5.0

55.0 ±

7.6

56.9 ±

6.2

50.8 ±

5.3

41.6 ±

7.9

4.9

11.2

7.5

6.9

17.4

52.5 ± 2.9 ka

7.9

7.9

7.9

7.9 8

n

3

6

9

37

OSL 2

AGE

(ka)

44.6

± 4.3

61.5

± 6.9

49.0

± 7.6

-

Random error (%)

4.8

8.0

13.4

-

System error(%)

7.9

7.9

7.9

-

45.2

± 6.7

12.6

48.3 ± 2.4 ka

7.9

n

4

3

9

-

8

Adamiec, G & Aitken, M.J. (1998) Dose-rate conversion factors: update.

Ancient TL

,

16

, 37-

50.

Blaauw, M. (2010) Methods and co de for ‘classical’ age-modelling of radiocarbon sequences.

Quaternary Geochronology

,

5

, 512

–518.

Feurdean, A, Liakka, J, Vanniere, B, Marinova, Hutchinson S.M., E., Mossbruger V. & Hickler

T. (2013) Holocene fire regime drivers in the lowlands of Transylvania (Central-Eastern

Europe): a data-model approach.

Quaternary Science Reviews

,

81

, 48-61.

Murray, A.S. & Wintle, A.G. (2000) Luminescence dating of quartz using an improved singlealiquot regenerative-dose protocol.

Radiation Measurements

,

32

, 57-73

Murray, A.S. & Wintle, A.G. (2003) The single aliquot regenerative dose protocol: 350 potential for improvements in reliability.

Radiation Measurements

,

37

, 377-381

Reimer, P.J., Bard, E. & Bayliss A. (2013) IntCal13 and Marine13 Radiocarbon Age

Calibration curves 0

–50,000 years cal BP.

Radiocarbon

,

55

, 1869

–1887.

9

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