Dissolved organic carbon in Alaskan Arctic snow: concentrations, light-absorption properties, and bioavailability

Figures & data

Fig. 1. Distribution of (a) DOC (mg L⁻¹), (b) TN (mg L⁻¹), (c) BC (μg L⁻¹), and (d) major ions (μg L⁻¹) in Alaskan snow cover in the spring of 2017. (Detailed sampling information can be referred to supplementary Table S1.).

Table 1. DOC concentrations measured in snow of Alaska and Barrow and comparison with previous studies.

Region	Sampling period	Snow types	DOC conc. (mg L^−1)	Sample size	References
Barrow	Apr to May 2017	Surface snow	0.17 ± 0.05	35	This study
Across Alaskan regions	Apr 2017	Surface snow	0.30 ± 0.18	27	This study
Juneau Icefield, Southeast Alaska	May 2013	Glacial surface snow	0.20	10	Fellman et al. (2015)
Mendenhall Glacier, Alaska		Snowpit	0.19	1	Stubbins et al. (2012)
Mt. Blanc, French Alps	Sept. 2012	Surface snow	0.11 ± 0.01	4	Legrand et al. (2013)
Mt. Blanc, French Alps	Sept. 2012	Snowpit	0.30	4	Legrand et al. (2013)
Glacier No.1, Tienshan	Aug. 2014	Snowpit	0.52 ± 0.14	6–16	Liu et al. (2016)
Glacier No.1, Tienshan	May 26 to Oct 4, 2013	Surface snow	0.35 ± 0.09	78	Li et al. (2018)
LHG glacier No.12, northern Tibetan Plateau	Jul to Aug 2015	Surface snow	0.34 ± 0.14	184	Yan et al. (2016)
LHG glacier No.12, northern, Northern Tibetan Plateau	Aug. 2014	Snowpit	0.66 ± 0.08	6–16	Liu et al. (2016)
XDKMD glacier, central Tibetan Plateau	May 29 to Sep30, 2013	Surface snow	1.17 ± 0.34	374	Li et al. (2018)
XDKMD glacier, Central Tibetan Plateau	Aug 2014	Snowpit	0.64 ± 0.50	6–16	Liu et al. (2016)
Mountain glaciers	Mean	Surface snow	0.49 ± 0.07	35	Hood et al. (2015)
Greenland Ice Sheet	Mean	Surface snow	0.20 ± 0.01	4	Hood et al. (2015)
Greenland Ice Sheet	May to Aug 2012	Snow	0.06	1	Musilova et al. (2017)
Greenland Ice Sheet	May to Aug 2012	Ice	0.18		Musilova et al. (2017)
Dry Valleys, Antarctic Ice Sheet	Mean	Surface snow	0.46 ± 0.12	7	Hood et al. (2015)
Vostok, Antarctic Ice Sheet	Ice, 8300 BP	Ice core	0.0058 ± 0.0014	3	Legrand et al. (2013)
Dome C	Ice, 10300 BP	Ice core	0.021 ± 0.005	4	Legrand et al. (2013)

Fig. 2. Vertical variations of DOC concentrations and other parameters recorded in the snowpack at Barrow, Alaska.

Fig. 3. Comparison of DOC (mg L−1), TN (mg L−1), BC (μg L−1), and major ions (μg L−1) in surface and subsurface snow cover at Barrow.

Table 2. Absorption Ångström Exponent (AAE_{330 − 400}) and mass absorption cross section of DOC in snow across Alaska and at Barrow, as well as a comparison with other studies on snow and aerosols from other regions.

Study area/source	Average AAE330-400	Average MACDOC365 (m^2 g^-1)	λ (MAC, nm)	Reference
Surface snow, Barrow	2.11 ± 1.18	0.32 ± 0.24	365	This study
Surface snow, across Alaska	2.34 ± 0.78	0.37 ± 0.32	365	This study
HULIS, Arctic snow	6.1^a	2.6 ± 1.1	250	Voisin et al. (2012)
Non-BC light absorbing constituents, Arctic snow	2.3 ± 0.3			Doherty et al. (2010)
LHG glacier, Tibetan Plateau	5.0 ± 5.9	1.4 ± 0.4	365	Yan et al. (2016)
DOC in precipitation, Tibetan Plateau		0.25 − 0.64	365	Li et al. (2017)
Water-soluble organic carbon aerosols, South Tibetan Plateau		0.84 − 1.18	365	Li et al. (2017)
Water-soluble organic carbon aerosols, northern China	6.4 ± 0.6	0.7 ± 0.2	365	Kirillova et al. (2014)
Secondary organic carbon	5.2 − 8.8	0.001 − 0.088	405	Lambe et al. (2013)
Water-soluble OC, Wood smoke	8.6 − 17.8	0.13 − 1.1	400	Chen and Bond (2010)
Humic-like organic carbon aerosol	4	1.2	300 − 650	Sun et al. (2007)
Biomass smoke	4.8	5.0	350	Kirchstetter et al. (2004)
BrC aerosol, Beijing, China (winter)	7.1^b	1.45	365	Cheng et al. (2016)
BrC aerosol, North American continental troposphere	6.82 ± 2.63^c			Liu et al. (2015)
Water-soluble OC, Indian Ocean		0.5 ± 0.2	365	Bosch et al. (2014)
BrC aerosol, India	5.1 ± 1.9	1.3 ± 0.7	365	Srinivas et al. (2016)

^a Wavelength range for AAE in this study is 300 − 550 nm.

^b Wavelength range for AAE in this study is 310 − 450 nm.

^c Wavelength range for AAE in this study is 300 − 450 nm.

Fig. 4. Relationship between (a) MAC_DOC365 values and DOC concentrations, (b) MAC_DOC365 values and AAE_330-400, and (c) SUVA₂₅₄ and DOC concentrations for Alaskan snow samples, and temporal variation in MAC_DOC365 values (d), and SUVA₂₅₄ Values (e) in snow cover on the sea ice at Barrow during the study period of April to May in 2017.

Fig. 5. Variation for ratios (a) of RF by DOC to BC, and relationships between ratios of RF by DOC to BC and (b) MAC_DOC365 and (c) ratios of DOC/BC in the snow at Barrow, Alaska.

Fig. 6. Exponential decrease of DOC concentrations in snow cover on Chukchi sea ice during the biodegradation experiment in May of 2017 at Barrow.

Fig. 7. Footprint analyses of the backward trajectories launched over the snow sampling site at Barrow, Alaska, during April and May in 2017 for pass by (a) 48 h and (b) 120 h, respectively, and HYSPLIT model seven day back trajectories for air masses arriving in Barrow on (c) April 17, 2017 and (d) May 2, 2017. (Different colors of backward trajectories in c and d represent the air mass arrived at the different date.).

Table 3. Principal component analysis of DOC with other parameters in snow over across the Alaska and on sea ice at Barrow.

	Barrow snow			Snow across Alaska
	PCA1 (%)	PCA2 (%)	PCA3 (%)	PCA1 (%)	PCA2 (%)	PCA3 (%)
DOC	0.87	1.79	80.69	1.09	33.61	5.71
TN	11.06	16.15	55.13	51.11	0.61	30.06
BC	3.24	41.18	2.27	1.86	0.07	67.81
Cl^-	88.73	3.42	1.78	7.96	40.32	12.92
SO4^2-	13.29	63.59	0.39	86.27	4.44	0.97
NO3^-	0.05	50.38	20.57	69.87	0.01	11.99
Na^+	87.82	4.78	0.90	3.21	61.31	10.92
NH4^+	14.31	62.23	0.27	34.00	0.24	50.68
K^+	84.46	8.53	0.69	1.78	65.41	1.28
Mg^2+	63.66	9.34	2.40	81.21	0.00	0.26
Ca^2+	10.97	3.02	26.96	51.94	2.10	1.59
Variance of extraction	34.41%	24.04%	17.46%	35.48%	18.92%	17.65%
Accumulated variance	75.90%			72.05%

Fig. 8. Biplot analyses of DOC with other parameters for (a) snow samples in Barrow, and (b) snow samples across Alaska.

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