A landscape-isotopic approach to the geochemical characterization of lakes in the Kangerlussuaq region, west Greenland

Figures & data

Figure 1. (A) Location of study area in the south west of Greenland. (B) Transect of studied lakes extending to coast. (C) Map detailing most heavily sampled area and indicating which lakes were sampled for the Greenland Analogue Project and which were sampled by Dr. John Anderson. The study area is divided into three regions: ice marginal (area 1), upper fjord (area 2), and coastal (area 3). (A) and (B) are adapted from Anderson and Brodersen (2001)

Table 1. Summary of major geochemical and isotopic results. Alkalinity is expressed as mmol/L as CaCO₃. Meltwater lakes, lakes that receive meltwater directly, and the thaw lakes on the Leverett Glacier till plain are separated here to illustrate the similarity between these two groups

		EC	pH	δ^18O	δ^2H	^3H	Ca	Mg	K	Na	Cl	SO4	Alk
Group		µS/cm		‰ VSMOW		TU	mg/L	mg/L	mg/L	mg/L	mg/L	mg/L	mmol/L
Ponds n = 8	Avg.	845	7.8	−10.5	−107.9	10.2	84.5	46.7	16.7	17.8	21.4	360	1.6
	Min.	164	3.4	−16.2	−134.1	9.4	3.5	1.1	1.7	0.9	1.4	6.1	0.2
	Max.	1797	9.2	−5.2	−84.5	12.0	210	135	45	78	102	949	3.0
Dilute Lakes n = 26	Avg.	256	8.2	−11.0	−109.0	9.5	16.5	13.8	6.9	13.5	17.7	7.2	1.8
	Min.	50	7.2	−15.1	−131.6	7.4	2.7	2.2	0.7	1.3	1.7	0.0	0.1
	Max.	616	9.6	−6.8	−91.9	12.9	42	36	28	53	69	88	4.5
Saline Lakes n = 14	Avg.	2,848	8.9	−8.8	−99.9	10.5	25.9	161	113.9	350	487	174	14.0
	Min.	902	8.2	−11.4	−113.2	8.2	4.0	57.3	35.3	74.2	121	18.2	6.6
	Max.	4,500	9.2	−6.5	−93.9	13.2	108	254	190	590	782	403	22
Meltwater Lakes	L6	223	7.7	−15.1	−128.8	10.5	25.5	9.3	3.4	3.1	3.0	43.6	1.23
	L36 (P660)	62	6.8	−18.1	−145.5	9.4	5.9	3.3	0.4	1.8	1.8	3.3	0.43
Thaw Lakes n = 5	Avg.	238	8	−14	−130	8	32.7	5.0	6.3	4.2	2.6	57.2	0.9
	Min.	61	7	−15	−136	7	7.2	0.9	1.7	1.1	0.9	12.0	0.3
	Max.	327	8.4	−13.1	−127.2	10.5	46	7.3	8.5	5.2	3.8	77	1.6

Table 2. Summary of representative chemistry and isotopic results. P = pond, DL = dilute lake, SL = saline lake, and MW = meltwater lake. *Indicates that the results for dissolved chemical species are average results throughout multiple years as measured by John Anderson (ex., Anderson et al. 2001). Alkalinity is expressed as mg/L as CaCO₃. NM = not measured

	Location	Name	Sample Date	Lake Type	EC	pH	Ca	Mg	K	Na	Cl	SO4	Alk	Sr	Br	δ^18O	δ^2H	^3H	^87/86Sr
					µS/cm		mg/l	mg/l	mg/l	mg/l	mg/l	mg/l	mg/L	µg/l	µg/l	‰ VSMOW		TU
Ice Marginal	L8		2008–06-28	P	342	7.9	32	20	2	3.5	2	132	76	62	36	−16.2	−134	10	NM
	L20 2	Acid Lake	2010–09-05	P	1750	3.4	182	74	29	17	14	949	<2	217	123	−10.6	−107	10	NM
	L18		2008–07-01	P	1797	8.9	130	135	45	78	102	725	304	540	420	−5.2	−85	10	0.7459
	L1		2008–06-27	DL	381	8.4	27	19	11	19	31	2	303	94	156	−11.0	−111	11	0.7553
	L15		2008–06-30	DL	74	8.0	5	4	1	1.8	2	1	57	15	16	−14.8	−132	8	0.7536
	L26 26m	Talik Lake	2010–05-11	DL	232	7.7	18	11	6	6.7	10	3	190	63	40	−12.9	−118	10	0.7385
	L41		2011–09-12	DL	550	8.6	26	36	18	29	40	<1	451	93	141	−7.5	−95	9	0.7487
	L43		2011–09-12	DL	150	7.7	12	7	3	6.9	9	3	112	40	84	−12.5	−115	8	0.7439
	SS32		2003–08-21	DL	51	7.3	4	3	1	2	2	1	<1	NM	NM	NM	NM	NM	0.7557
	L17		2008–07-01	DL	902	9.0	23	85	35	74	121	24	816	72	277	−11.4	−113	10	0.7510
	L29		2010–09-04	SL	1250	9.2	15	85	88	105	152	<1	859	70	79	−6.5	−96	10	NM
	L6		2008–06-28	MW	223	7.7	26	9	3	3.1	3	44	123	52	40	−15.1	−129	11	0.7514
	L12		2008–06-29	TH	297	7.8	40	6	8	4.9	4	71	130	130	27	−13.6	−128	7	0.7533
Upper Fjord	L33	Lake Ferguson	2010–09-04	DL	66.1	7.6	7	3	2	2.6	3	2	57	41	21	−12.7	−112	12	0.7187
	SS2*		2003–08-20	DL	321	7.9	26	13	4	18	15	3	NM	NM	NM	NM	NM	NM	0.7353
	SS8/L46		2012–09-03	DL	236	8.9	23	15	11	21	28	2	237	96	103	−10.2	−95	7	0.7310
	L45		2012–08-28	SL	3470	8.3	108	150	80	340	722	384	656	883	1960	−9.0	−101	9	0.7267
	L21	Hunde Sø		SL	4030	8.8	16	203	182	545	797	180	2060	574	980	−10.1	−101	15	0.7298
	L32	Store Saltsø	2010–09-04	SL	3110	8.9	21	155	181	343	372	18	1880	238	667	−9.9	−104	8	0.7540
	L22/SS4	Braya Sø	2011–09-10	SL	3000	8.9	20	149	128	362	493	91	1560	356	759	−8.9	−95	12	0.7295
	L39/SS5	Limnea Sø	2011–09-10	SL	4500	9.0	15	233	190	588	782	190	2230	337	944	−7.7	−93	11	NM
	SS1122*			SL	3167	8.8	58	141	156	418	664	243	NM	NM	NM	NM	NM	NM	0.7275
	SS1421 2m*		2004–06-23	SL	2690	9.1	18	155	4181	337	415	175	NM	NM	NM	NM	NM	NM	0.7314
Coastal	SS48*			DL	29.1	6.6	3	1	<1	2	4	2	NM	NM	NM	NM	NM	NM	0.7154
	SS76*		12.08.03	DL	345.5	7.7	42	10	3	9	13	88	NM	NM	NM	NM	NM	NM	0.7410
	SS75*		12.08.03	DL	226.3	5.0	16	7	1	6	7	76	NM	NM	NM	NM	NM	NM	NM

Figure 2. (A) Isotopic composition of lakes. Local evaporation lines are adapted from Leng and Anderson (2003) for zones 3 (mid fjord), 4 (upper fjord), and 5 (close to ice sheet). The zones from Leng and Anderson (2003) correspond to area 3 (zone 3), area 2 (zone 4), and area 1 (zone 5). Average annual precipitation estimated from intercept of LEL with GMWL. Local meteoric water lines for Grönnedal and Thule were generated using isotopic monitoring data from IAEA stations. (B) Isotopic composition of lakes compared to groundwaters and meltwaters from Kangerlussuaq region

Table 3. Results of δ³⁷Cl and δ⁸¹Br analyses on lakes and borehole groundwaters. Analytical uncertainty on δ³⁷Cl and δ⁸¹Br is ±0.2‰. Locations with * next to the name indicate average lake chemistries. NM = not measured

	Cl	Br	δ^37Cl	δ^81Br
Location	mg/l	µg/l	‰ SMOC	‰ SMOB
L32	372	667	−0.2	−0.1
L22/SS4	493	759	0.0	0.8
SS1122 8m*	664	NM	0.0	0.9
L29	152	79	−0.3	1.0
L41	40	141	0.0	1.7
SS1421 18m*	415	NM	−0.5	1.8
SS1421 2m	NM	NM	−0.3	NM
SS1421	NM	NM	0.1	NM
SS3*	669	NM	−0.6	NM
L18	102	420	−0.4	NM
L21	797	980	−0.2	NM
SS6*	567	NM	−0.2	NM
L26 5m	10	40	−0.1	NM
SS5 0.5m	782	944	0.0	NM
SS1164 8m*	173	NM	0.0	NM
L12	4	27	0.0	NM
DH-GAP01	8	90	−0.1	0.3
DH-GAP04U	94	1,260	0.3	0.4
DH-GAP04M	109	1,520	0.2	NM
DH-GAP04L	173	2,390	0.4	0.6

Table 4. Isotopic composition and concentration of sulfate in surface waters and groundwaters. Sulfate minerals (predominantly gypsum) from fracture infillings and sulfide minerals from the rock matrix are included from the DH-GAP01 and DH-GAP04 cores. Gypsum was found abundantly as a fracture filling below a depth of 300 m in the DH-GAP04 borehole, while only one occurrence of gypsum was noted in the DH-GAP01 borehole. NM is not measured because of insufficient sample material. NA = not applicable

Location	Sample Type	δ^34S	δ^18O
		SO4
		‰ CDT	‰ VSMOW
L20 2	pond	−0.7	−3.0
L20 1	pond	0.4	−3.9
L18	pond	1.1	3.4
SS75	dilute lake	1.2	−2.2
L43	dilute lake	12.5	−1.0
L45	saline lake	14.1	NM
SS5	saline lake	19.3	8.1
SS5	saline lake	20.2	8.0
SS4	saline lake	22.9	5.5
SS4	saline lake	23.3	4.6
L21	saline lake	23.4	5.3
1371	saline lake	28.5	7.8
L12 1	thaw lake	3.8	−11.0
DH-GAP01	groundwater BH	4.9	5.9
DH-GAP04-Up	groundwater BH	5.0	3.9
DH-GAP04-Mid	groundwater BH	4.5	3.1
DH-GAP04-Low	groundwater BH	5.0	2.9
Leverett Spring	groundwater Spr	10.9	5.9
DH-GAP01	sulfide minerals	2.3–3.7	NA
DH-GAP04	fracture sulfate	2.6–10.7	4.5–9.1

Figure 3. (A) δ³⁷Cl compared to δ¹⁸O isotopic composition. δ⁸¹Br values compared to (B) δ¹⁸O isotopic values and (C) δ³⁷Cl isotopic values. Analytical error corresponds to symbol size except where otherwise indicated by error bars

Figure 4. Relationship between Na/Ca ratios compared to Cl/SO₄ ratios indicates the relative importance of processes such as sulfate reduction, sulfide oxidation, and CaCO₃ precipitation

Figure 5. The ⁸⁷Sr/⁸⁶Sr signature of lakes increases toward the ice sheet where weathering of biotite becomes increasingly important

Figure 6. Comparison of the ratio of (Mg + K)/Na to ⁸⁷Sr/⁸⁶Sr isotope ratios for all lake types. The ratio of (Mg + K) to Na increases with increasingly radiogenic ⁸⁷Sr/⁸⁶Sr isotopic ratios

Figure 7. (A) the isotopic composition (δ³⁴S and δ¹⁸O) of sulfate in lakes and groundwaters as well as gypsum found as a fracture mineral in the bedrock. δ³⁴S of sulfide minerals found in the bedrock are indicated by the stippled area. (B) A comparison of the δ³⁴S of sulfate in lakes to the Cl/SO₄ ratio shows that as δ³⁴S is enriched during bacterial sulfate reduction, sulfate is removed and the Cl/SO₄ ratio increases

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