TABLE 1.

Physicochemical soil parameters were measured at the sampling site and included radiocarbon dating (¹⁴C), which was measured only in 2019 and was calculated in fM (*) for samples younger than 1963 or BP (**) for samples older than 1945.

Depth [cm]	14C [*fM **BP]	H2O [%]		SOM [%]		pH		Horizon	Layer
		2019	2020	2019	2020	2019	2020		2019	2020
0–10	*1.04	7.94 ± 1.03	28.80 ± 3.38	16.01 ± 4.22	8.73 ± 1.82	3.87 ± 0	4.22 ± 0.03	O1	AL
10–20	*1.13	11.77 ± 0.93	22.52 ± 0.73	7.09 ± 1.71	5.39 ± 0.83	4.46 ± 0.05	4.02 ± 0.05	M1
20–30	*1.16	11.83 ± 0.34	22.05 ± 3.30	5.75 ± 0.21	10.19 ± 3.22	4.25 ± 0.02	4.29 ± 0.01
30–40	*1.20	13.13 ± 3.12	26.57 ± 0.83	5.85 ± 2.23	13.68 ± 0.44	4.73 ± 0.09	4.25 ± 0.01
40–50	**2,635	28.27 ± 4.92	7.73 ± 1.58	24.42 ± 4.78	2.59 ± 0.68	5.08 ± 0.05	4.63 ± 0.03	O2	TZ	TZ
50–60	**3,770	23.49 ± 1.92	15.61 ± 6.28	15.76 ± 4.50	2.93 ± 0.30	5.45 ± 0.10	4.13 ± 0.02
60–70	**26,500	14.14 ± 8.43	8.72 ± 2.53	3.78 ± 0.09	1.52 ± 0.16	6.54 ± 0.05	4.86 ± 0.05	M2
70–80	**22,100	16.31 ± 1.09	6.35 ± 0.60	3.99 ± 0.25	1.10 ± 0.24	7.01 ± 0.01	4.48 ± 0		PF
80–90	**26,200	1.65 ± 4.43	7.96 ± 0.61	1.78 ± 0.30	1.00 ± 0.20	6.61 ± 0	4.57 ± 0.01
90–100	NA	NA	7.80 ± 0.59	NA	1.04 ± 0.26	NA	4.91 ± 0.01			PF

In both years, weight-based relative soil moisture (H₂O) and soil organic matter (SOM) were measured based on loss on ignition and the pH was determined in triplicates and standard deviation is indicated (±). Layers included the active layer (AL, 0-40 cm) as long-term seasonally thawing material above the former ice lens, the transition zone (TZ, 2019: 40-70 cm, 2020: 40-90 cm) as the newly thawed material since the collapse, and permafrost (PF, 2019: > 70 cm, 2020: > 90 cm) as the still frozen ground. Based on SOM and ¹⁴C, four separate horizons were visible, namely the recent surface organic horizon (O1, 0-10 cm), the recent underlying mineral horizon (M1, 10-40 cm), the older buried organic horizon (O2, 40-60 cm), and an ancient mineral horizon (M2, > 60 cm).