Ice-covered ponds in the Untersee Oasis (East Antarctica): Distribution, chemical composition, and trajectory under a warming climate

Figures & data

Figure 1. (a) Location map of Untersee Oasis in Dronning Maud Land (LIMA Landsat high-resolution virtual mosaic; Bindschadler et al. 2008); (b) Map showing the location of sampled ponds (background is a WorldView satellite image acquired 7 December 2017). The ponds are located on the west (blue dots) and east (red dot) lateral moraines of the Anuchin Glacier, the terminal moraine (yellow dots) and on the glacial diamicton a few meters above the eastern shore of Lake Untersee (green dots); (c) Map of Potential Incoming Solar Radiation (PISR; Wm^-2) of the Untersee Oasis during the austral summer; (d) Hierarchical cluster plot of the ponds (based on their pH, total inorganic carbon, total organic carbon, PISR, δ¹⁸O, and D-excess values).

Figure 2. (a) Aerial photo of some ponds along the west lateral moraine. (b) Scatterplot of surface area (m²) and elevation of ponds in the Untersee Oasis. Note a negative relationship between pond elevation and surface for the west lateral moraine ponds (blue dots). (c) Scatterplot of the surface area (m²) and elevation relation for lakes and ponds in the McMurdo Dry Valleys (data from Lyons et al. [2012] and Fountain et al. [2017]). See Figure 1 for location of the ponds.

Table 1. Morphometric characteristics of ponds and their ice blisters in the Untersee Oasis. See Figure 1 for the location of ponds

				Ice blister
Pond ID	Elevation (m.a.s.l.)	Surface area (m^2)	PISR (Wm^−2)	Height (m)	Area (m^2)	Volume (m^3)
P1	666.5	413	128	0.45	112	16.5
P2	657.5	751	129	—	—	—
P3	631.0	5,879	126	—	—	—
P4	665.0	334	119	0.48	46	6.3
P5	939.5	1,707	134	—	—	—
P6	837.9	2,422	136	—	—	—
P7	827.2	354	142	0.38	73	11.5
P8	816.7	611	136	0.54	153	29.7
P9	620.3	810	144	0.42	277	42.3
P10	612.4	303	162	—	—	—
P11	615.1	1,085	154	0.61	278	58.3
P12	610.9	116	159	—	—	—
P13	615.9	114	123	—	—	—

Figure 3. Scatterplot of the relation between total pond surface area (m²) and ice blister volume (m³).

Table 2. pH, conductivity, and major ions of ponds in the Untersee Oasis. See Figure 1 for the location of ponds

Pond ID	pH	Conductivity (µS/cm^−1)	Ca (ppm)	K (ppm)	Mg (ppm)	Na (ppm)	NO3 (ppm)	SO4 (ppm)	Cl (ppm)
P1	8.6	387	38.51	10.07	7.29	58.37	10.81	80.67	91.80
P2	10.4–10.6	850–900	31.18	4.433	0.186	24.25	0.18	43.1	32.40
P3	10.4–11.8	291–300	82.53	11.716	2.254	96.69	8.32	113.9	184.50
P4	8.4	90	9.31	1.28	1.37	10.87	8.02	2.52	23.15
P5	7.1	232	9.52	2.33	3.37	9.14	1.70	19.94	12.63
P6	8.6	93	12.68	4.62	10.43	14.89	0.21	34.48	18.73
P7	8	166	5.40	1.57	2.38	5.43	0.04	8.58	6.43
P8	9.7	59	18.08	4.91	8.23	31.86	1.78	61.98	45.97
P9	9.7	120	12.70	4.03	3.10	11.45	0.06	28.16	14.70
P10	6.9	2,380	317.36	44.64	77.71	400.65	163.56	1,072.79	496.43
P11	7.2	162	18.50	3.41	3.67	18.97	4.41	48.68	20.06
P12	7.8	946	142.56	17.67	24.67	110.69	239.22	308.09	115.19
P13	7.4	84	11.10	2.32	1.67	8.03	4.02	10.40	12.51

Figure 4. Geochemical composition of ponds in the Untersee Oasis. (a) Cations ternary plot; (b) anions ternary plot; (c) concentration of major cations; and (d) Cl⁻ normalized molar ratios line chart for Ca, Na, SO₄, and TIC. Values from the oxic waters of Lake Untersee and nearby snow/firn samples have been added for comparisons (from Isaksson et al. 1996).

Figure 5. Scatterplots of (a) δD-δ¹⁸O of near-surface water and (b) ice cover samples of ponds in the Untersee Oasis. (c) Modeling of the evolution of δ¹⁸O and [Cl⁻] in the ponds under steady-state freezing (group 1) and evaporation (group 2; relative humidity set at 80 percent). In both simulations, the initial δ¹⁸O is set to −32 per mill, and the initial Cl⁻ values are set to 5 and 10 ppm (similar to that of the nearby DML firn core; Isaksson et al. 1996). Also shown is steady-state freezing assuming initial δ¹⁸O = −35 per mill and 1 percent mixing rate. Grey dotted lines show the evolution of δ¹⁸O-[Cl⁻] for freezing only of well-sealed pond (no annual recharge). Black dots with decimal numbers indicate the fraction of residual water remaining. Squares and circles indicate ponds with and without ice cover blisters, respectively.

Table 3. Stable water isotope (δD-δ¹⁸O) ratios, TIC, TOC, δ¹³C_TIC, F¹⁴C_TIC, and ³H composition of pond in the Untersee Oasis. See Figure 1 for the location of ponds

Pond ID	δ^18O (‰)	δD (‰)	D-excess (‰)	TIC (ppm C)	TOC (ppm C)	δ^13CTIC (‰)	δ^13CTOC (‰)	F^14CTIC	^3H (TU)
P1	−36.4	−285.0	5.7	2.4	4.2	−18.0	−26.1	—	4.1 ± 0.8
P2	−41.9	−317.9	17.3	1.0	1.4	−3.4	−7.6	0.9947 ± 0.0058	<0.8
P3	−40.9	−315.9	11.5	1.0	1.2	−3.7	−7.8	0.9757 ± 0.006	1.5 ± 0.8
P4	−35.9	−285.4	2.5	7.7	12.6	−13.4	−23.7	—	—
P5	−29.3	−239.3	−5.3	5.2	4.6	−13.6	−25.0	1.0011 ± 0.0036	3.5 ± 0.8
P6	−29.9	−247.2	−7.7	13.8	7.1	−4.2	−19.1	—	—
P7	−31.2	−252.6	−2.7	3.3	5.6	−12.7	−23.3	—	—
P8	−30.9	−250.4	−2.9	6.4	5.0	−16.3	−22.4	—	—
P9	−28.7	−239.8	−10.2	3.5	1.3	−10.1	−11.0	—	—
P10	−21.6	−213.3	−40.7	24.0	6.7	−1.9	−12.8	—	—
P11	−24.3	−217.0	−22.7	4.2	5.3	−14.4	−22.8	0.9872 ± 0.0033	11.7 ± 0.8
P12	−20.9	−212.9	−45.4	4.2	4.9	−14.6	−23.6	—	—
P13	−30.3	−251.3	−9.0	6.6	10.6	−17.6	−18.3	—	10.8 ± 0.8

Figure 6. Scatterplots of relation between (a) TIC and δ¹³C_TIC; (b) TOC and δ¹³C_TOC; (c) TIC/Cl (molar ratio) and δ¹³C_TIC, including data from MDV lakes (Neumann et al. 2004); and (d) δ¹³C_TOC and δ¹³C_TIC of ponds in the Untersee Oasis.

Figure 7. (a) Cross-sectional view of the perennially ice-covered Lake Untersee and the ponds in the Untersee Oasis with their differing ice cover types (i.e., from well-sealed perennial ice cover to moat-forming perennial ice cover and seasonal ice cover). Panels (b-g) indicate the pH, conductivity (uS/cm^-1), δ¹⁸O, F14CTIC, Tritium (3H), and TIC (ppm C) values of near-surface waters in the ponds as a function of ice cover type. PIC-WS = perennially ice-covered and well-sealed; PIC-MF = perennially ice-covered and moat-forming; SIC = seasonally ice-covered.

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