Deuterium excess and ¹⁷O-excess variability in meteoric water across the Pacific Northwest, USA

Figures & data

Fig. 1. Location map showing two east–west transects that were sampled across mountain ranges in the Pacific Northwest. The southern transect is at ∼44.6° and crosses Oregon (red circles). The northern transect is at ∼47.8° and crosses Washington (blue circles). Both transects dissect two major mountain ranges, the Coast Range and Cascade Mountains in Oregon and the Olympic and Cascade Mountains in Washington. Moisture is typically brought into the study area by westerlies with significant rainout on the windward (western) flank of the Coast Range, Olympic Mountains, and Cascade Mountains. A substantial rain shadow exists east of the Cascade Mountains. The background digital elevation map (DEM) is from the Shuttle Radar Topography Mission (SRTM).

Fig. 2. Plot of climate parameters versus longitude for both the Washington (A) and Oregon (B) transects. For the Olympic Mountains (Washington) and Coast Range (Oregon), precipitation amount increases to the highest elevations. For the Cascades, precipitation amount and relative humidity start to decrease before reaching the range crest. Climate information is derived from the PRISM 30-year normals at 800 m resolution. Relative humidity is estimated from mean annual temperature and mean annual dew point temperature using Eq. (4) in Supplementary Materials. Elevation information is derived from a 200 m resolution digital elevation model (DEM) from the Shuttle Radar Topography Mission (SRTM). Each curve represents the average value along a 100 km swath centered along each transect at (A) 47.8° and (B) 44.5° latitudes.

Table 1. Location information, isotopic data, and meteorological parameters for each sample site and associated watershed. δ¹⁷O values are shown to 4 decimal places per Schoenemann et al. (2013).

ID	Type	d^18O	d^17O	dD	d excess	^17O-excess (D^17O)	Latitude	Longitude	Latitude (Centroid)	Longitude (Centroid)	Elevation (m)	MBH (m)	Basin area (km^2)	Date sampled	Side of range	State	Region
DHOW-06	Stream	−11.42	−6.0192	−84.9	6.5	27	44.4284	−121.7257	44.3986	−121.7980	1,030	1,363	57.4	10/4/2015	Leeward	OR	Cascades
DHOW-09	Stream	−10.90	−5.7488	−79.4	7.8	19	44.4121	−122.0431	44.3993	−122.0890	986	1,312	28.5	10/4/2015	Leeward	OR	Cascades
DHOW-11	Stream	−9.95	−5.2361	−71.9	7.7	31	44.4025	−122.2698	44.3925	−122.2810	467	815	1.1	10/4/2015	Windward	OR	Cascades
DHOW-13	Stream	−9.06	−4.7556	−64.0	8.5	38	44.4041	−122.4388	44.4422	−122.3710	307	794	54.1	10/4/2015	Windward	OR	Cascades
DHOW-14	Stream	−9.01	−4.7356	−64.6	7.5	32	44.3727	−122.6232	44.3276	−122.5270	233	740	134.5	10/4/2015	Windward	OR	Cascades
DHOW-15	Stream	−8.59	−4.5151	−63.0	5.7	28	44.3975	−122.7345	44.3641	−122.6930	167	360	29.8	10/4/2015	Windward	OR	Cascades
DHOW-18	Stream	−9.16	−4.8213	−65.6	7.7	27	44.6302	−123.0042	44.5724	−122.9480	69	93	25.8	10/4/2015	Windward	OR	Cascades
WA16-1	Stream	−9.11	−4.8131	−72.7	0.2	7	48.5298	−122.1367	48.5509	−122.1327	41	476	3.9	8/11/2015	Windward	WA	Cascades
WA17-1	Stream	−12.51	−6.6008	−98.4	1.7	26	48.6316	−121.3253	48.8823	−121.0506	126	1,387	3,262.9	8/11/2015	Windward	WA	Cascades
WA17-2	Stream	−11.94	−6.2997	−93.5	2.0	20	48.5876	−121.3953	48.6746	−121.4323	428	1,094	132.2	8/11/2015	Windward	WA	Cascades
WA17-3	Stream	−10.67	−5.6200	−82.7	2.6	26	48.5239	−121.7135	48.5583	−121.6100	60	951	63.9	8/11/2015	Windward	WA	Cascades
WA18-1	Stream	−11.25	−5.9326	−88.0	2.1	26	48.7173	−121.1500	48.7544	−121.2012	271	1,247	58.9	8/11/2015	Windward	WA	Cascades
WA19-2	Stream	−14.08	−7.4335	−112.4	0.2	24	48.5992	−120.5348	48.5663	−120.6140	928	1,690	102.5	8/11/2015	Leeward	WA	Cascades
WA36-1	Stream	−14.37	−7.5834	−116.1	−1.1	29	48.3632	−119.7204	48.4014	−119.7181	722	1,067	20.0	8/11/2015	Leeward	WA	Cascades
WA36-2	Stream	−14.90	−7.8692	−120.5	−1.3	25	48.3669	−120.0064	48.3818	−119.9420	678	1,197	48.6	8/11/2015	Leeward	WA	Cascades
WA47-1	Stream	−9.90	−5.2279	−79.7	−0.5	11	47.8366	−121.6594	47.7716	−121.3378	77	1,059	1,391.5	8/12/2015	Windward	WA	Cascades
WA47-2	Stream	−10.77	−5.6843	−84.4	1.7	17	47.7280	−121.3384	47.8069	−121.2566	322	1,100	251.6	8/12/2015	Windward	WA	Cascades
WA48-1	Stream	−11.42	−6.0216	−90.2	1.2	26	47.7737	−120.9673	47.7650	−121.0439	812	1,315	72.0	8/12/2015	Leeward	WA	Cascades
WA48-2	Stream	−12.36	−6.5087	−97.3	1.6	36	47.7854	−120.8474	47.7550	−120.9820	665	1,372	184.8	8/12/2015	Leeward	WA	Cascades
WA48-3	Stream	−12.54	−6.6074	−99.6	0.7	32	47.6640	−120.7361	47.8859	−120.8785	583	1,287	1,738.1	8/12/2015	Leeward	WA	Cascades
WA50-1	Stream	−13.95	−7.3848	−117.6	−6.0	6	47.6282	−120.0344	47.6353	−120.0804	783	870	48.0	8/12/2015	Leeward	WA	Cascades
DHOW-07	Lake	−11.38	−5.9928	−84.8	6.3	35	44.4274	−121.7297	44.3984	−121.7984	1,039	1,364	57.1	10/4/2015	Leeward	OR	Cascades
DHOW-20	Stream	−7.07	−3.7247	−50.8	5.8	15	47.7110	−124.4143	47.7143	−124.4015	18	73	1.4	9/10/2016	Windward	WA	Coast
DHOW-22	Stream	−10.18	−5.3597	−74.6	6.8	28	47.9541	−123.8332	47.9395	−123.8372	559	1,069	1.5	9/10/2016	Windward	WA	Coast
DHOW-23	Stream	−10.40	−5.4708	−76.1	7.1	34	47.9505	−123.8119	47.9563	−123.8110	640	993	0.2	9/10/2016	Windward	WA	Coast
DHOW-24	Stream	−10.66	−5.6048	−78.9	6.4	37	47.9425	−123.7836	47.9269	−123.7944	720	1,232	1.4	9/10/2016	Windward	WA	Coast
DHOW-25	Stream	−11.06	−5.8247	−80.9	7.5	28	47.9345	−123.7690	47.9421	−123.7644	804	1,139	0.3	9/10/2016	Windward	WA	Coast
DHOW-26	Stream	−11.28	−5.9334	−83.1	7.1	37	47.9321	−123.7488	47.9404	−123.7489	962	1,367	0.5	9/10/2016	Windward	WA	Coast
DHOW-27	Stream	−11.08	−5.8364	−80.8	7.9	32	47.9245	−123.7345	47.9187	−123.7358	1,173	1,372	0.8	9/10/2016	Windward	WA	Coast
DHOW-28	Stream	−11.16	−5.8857	−81.0	8.3	24	47.9154	−123.7300	47.9100	−123.7299	1,333	1,454	1.2	9/10/2016	Windward	WA	Coast
DHOW-29	Lake	−10.18	−5.3646	−77.4	4.0	24	47.9113	−123.7320	47.9113	−123.7349	1,428	1,494	0.2	9/10/2016	Windward	WA	Coast
DHOW-38	Stream	−12.47	−6.5527	−92.4	7.4	50	47.7205	−123.2778	47.7335	−123.2833	760	1,594	0.2	9/27/2016	Leeward	WA	Coast
DHOW-40	Stream	−10.85	−5.7042	−79.7	7.1	38	47.7070	−123.3145	47.7085	−123.3225	1,031	1,518	0.7	9/27/2016	Leeward	WA	Coast
DHOW-43	Stream	−12.31	−6.4831	−90.5	8.0	36	47.7417	−123.0546	47.7531	−123.0562	202	999	0.4	9/27/2016	Leeward	WA	Coast
DHOW-44	Stream	−11.22	−5.9061	−82.1	7.7	35	47.7191	−122.9432	47.7466	−122.9726	92	769	21.3	9/27/2016	Leeward	WA	Coast
JBOW-16	Stream	−8.35	−4.3865	−56.1	10.7	32	44.5039	−123.5639	44.5049	−123.5640	918	1,022	0.2	8/21/2015	Windward	OR	Coast
JBOW-17	Stream	−8.19	−4.2944	−54.9	10.6	41	44.4742	−123.5286	44.4754	−123.5280	672	803	0.3	8/21/2015	Windward	OR	Coast
JBOW-20	Stream	−7.83	−4.1055	−52.5	10.2	37	44.3850	−123.6208	44.4066	−123.6320	85	403	16.3	8/21/2015	Windward	OR	Coast
JBOW-21	Stream	−7.70	−4.0384	−51.9	9.7	37	44.3786	−123.7306	44.4339	−123.7290	54	410	70.7	8/21/2015	Windward	OR	Coast
JBOW-22	Stream	−6.76	−3.5460	−45.0	9.1	28	44.4056	−123.9494	44.3844	−123.9650	6	215	11.9	8/21/2015	Windward	OR	Coast
JBOW-39	Stream	−8.35	−4.3893	−57.9	8.9	30	44.4569	−123.3372	44.4444	−123.4047	85	287	58.1	8/26/2015	Leeward	OR	Coast
JBOW-40	Stream	−8.09	−4.2852	−55.8	9.0	−3	44.4878	−123.4408	44.4730	−123.4760	133	333	23.3	8/26/2015	Leeward	OR	Coast
JBOW-41	Stream	−8.29	−4.3493	−57.9	8.4	34	44.5003	−123.4394	44.5143	−123.5040	121	460	34.5	8/26/2015	Leeward	OR	Coast
JBOW-42	Stream	−6.83	−3.5801	−51.3	3.3	30	44.5400	−123.3867	44.5989	−123.5124	92	300	275.6	8/26/2015	Leeward	OR	Coast
DHOW-30	Lake	−10.20	−5.3713	−77.8	3.8	27	47.9109	−123.7332	47.9108	−123.7362	1,418	1,528	0.1	9/10/2016	Windward	WA	Coast
OR431	Stream	−12.64	−6.6702	−103.4	−2.3	21	45.3466	−118.2220	45.1948	−118.3800	905	1,421	1,545.0	8/13/2015	Leeward	OR	Eastern
OR432	Stream	−14.19	−7.4921	−109.2	4.4	27	45.6199	−117.7280	45.4084	−117.4330	779	1,587	2,385.2	8/13/2015	Leeward	OR	Eastern
OR441	Stream	−15.12	−7.9762	−118.3	2.7	37	45.4199	−117.2704	45.3166	−117.1860	2,298	1,700	380.3	8/13/2015	Leeward	OR	Eastern
OR571	Stream	−16.22	−8.5604	−124.2	5.5	36	45.1816	−117.0539	45.1756	−117.1210	1,681	2,267	38.8	8/13/2015	Leeward	OR	Eastern
OR572	Stream	−14.87	−7.8460	−112.5	6.5	32	45.1509	−116.8779	45.1161	−117.0990	1,219	1,972	243.3	8/13/2015	Leeward	OR	Eastern
OR573	Stream	−15.21	−8.0293	−116.2	5.5	33	45.0082	−116.9107	45.0430	−117.0140	975	1,735	79.7	8/14/2015	Leeward	OR	Eastern
OR631	Stream	−13.33	−7.0342	−105.1	1.5	29	44.4137	−120.4961	44.4633	−120.4230	1,229	1,485	82.8	8/14/2015	Leeward	OR	Eastern
OR641	Stream	−8.82	−4.6432	−86.2	−15.6	26	44.5328	−119.8806	44.4994	−120.0090	1,142	1,439	233.5	8/14/2015	Leeward	OR	Eastern
OR651	Stream	−13.46	−7.1019	−108.9	−1.2	30	44.4662	−119.5327	44.1769	−119.4310	714	1,459	1,573.3	8/14/2015	Leeward	OR	Eastern
OR661	Stream	−13.84	−7.3041	−109.1	1.6	27	44.4177	−118.9090	44.4185	−118.6790	959	1,525	1,012.7	8/14/2015	Leeward	OR	Eastern
OR671	Stream	−12.87	−6.7986	−104.4	−1.5	18	44.6649	−117.9638	44.7408	−118.1360	1,166	1,622	449.6	8/14/2015	Leeward	OR	Eastern
OR672	Stream	−15.44	−8.1584	−118.1	5.5	25	44.5852	−118.5033	44.5058	−118.4580	1,253	1,660	95.1	8/14/2015	Leeward	OR	Eastern
WA22-2	Stream	−14.23	−7.5082	−117.4	−3.6	29	48.6589	−118.8471	48.6706	−118.9015	947	1,292	86.0	8/10/2015	Leeward	WA	Eastern
WA25-1	Stream	−13.40	−7.0812	−113.0	−5.8	18	48.5108	−117.2771	47.4523	−114.3130	624	1,506	64,991.0	8/10/2015	Leeward	WA	Eastern
WA67-1	Stream	−13.94	−7.3763	−116.4	−4.9	8	47.4460	−118.1859	47.4831	−118.1714	671	701	41.9	8/13/2015	Leeward	WA	Eastern
WA55-2	Lake	−12.48	−6.5846	−104.9	−5.0	26	47.9039	−117.3435	48.0491	−117.1649	826	816	1,155.4	8/12/2015	Leeward	WA	Eastern
JBOW-26	Ocean	0.05	0.0367	−2.4	−2.8	10	42.8331	−124.5564			0	0		8/22/2015		OR

Fig. 3. (A) Plot of δ¹⁸O versus δ²H for all samples analyzed in this study. Circles are stream samples and squares are lake samples. Solid symbols are from west of the Cascades Mountains and open symbols are from east of the Cascades. The slope of the Local Meteoric Water Line (LMWL) (solid) is slightly higher than the Global Meteoric Water Line (GMWL) (dashed) at 8.86 versus 8, respectively. Significant evaporation in the rain shadow of the Cascade Mountains (east) lowering d-excess in more distilled (continental) samples is likely the primary cause as the LMWL for Oregon Coast Range and Olympic Mountain samples (not shown) has a slope similar to the GMWL (y = 8.1x + 9.3; R² = 0.99). (B) Plot of ln(δ¹⁸O/1000 + 1) and ln(δ¹⁷O/1000 + 1) for all samples analyzed in this study. This is the same sample population shown in (A). The mass-dependent fractionation coefficient (λ) for all samples is 0.5280 ± 0.0005. This is close to the theoretically determined coefficient for equilibrium fractionation of water (λ = 0.529 ± 0.001) (Barkan and Luz, 2005) and the same as that observed in meteoric waters (λ = 0.528) (Meijer and Li, 1998; Luz and Barkan, 2010). Uncertainty in δ¹⁸O, δ²H, d-excess, δ¹⁷O, and ¹⁷O-excess are 0.07‰, 0.42‰, 0.46‰, 0.04‰, and 8 ppm, respectively.

Fig. 4. (A) Plot of δ¹⁸O versus δ²H for stream samples in the rain shadow (east) of the Cascade Mountains in Washington (> −119° longitude) and Oregon (> −121° longitude). The slope, m, of the Local Meteoric Water Line (LMWL) is significantly lower than the Global Meteoric Water Line (GMWL) (m = 5.15 versus m = 8), reflecting the influence of evaporation under relatively arid conditions. (B) Plot of ln(δ¹⁸O/1000 + 1) and ln(δ¹⁷O/1000 + 1) for the same sample population as (A). The slope (λ) is 0.5235, significantly lower than that observed for meteoric water globally (λ = 0.528) (Luz and Barkan, 2010). Sample OR641 has been excluded from plots due to anomalously high δ¹⁸O, δ¹⁷O, and δ²H values. Uncertainty in δ¹⁸O and δ²H values are less than 0.07‰ and 0.42‰, respectively.

Fig. 5. Plot of δ¹⁸O versus elevation for the windward side of the Olympic Mountains (solid circles) and Cascades (solid triangles) in Washington, and the Coast Range (open circles) and Cascades (open triangles) in Oregon. Note that elevation is on the x-axis and δ¹⁸O is on the y-axis. A linear regression through these data shows an isotopic lapse rate of −3.2‰/km of elevation gain, similar to the global average of −2.8‰/km (Poage and Chamberlain, 2001). Elevation is reported as mean basin hypsometry and is derived from a DEM from the SRTM at ∼200 m resolution.

Fig. 6. Plot of d-excess versus elevation for samples from the windward side of the (A) Olympic Mountains (triangles) and (B) Oregon Coast Range (circles). Right-angle arrows show where the cloud base is inferred to intersect with the ground surface, above which there is no subcloud evaporation (relative humidity is 100%). We estimate this is roughly ∼750 m for the Olympics and 500 m for the Oregon Coast Range based on the elevation of maximum precipitation amount (Fig. 2). The open symbols show d-excess values of precipitation at the cloud base estimated from a subcloud evaporation model. Subcloud evaporation explains much of the difference between high and low elevation samples. Linear regressions through each transect have similar slopes suggesting that there is a similar reduction in subcloud evaporation with elevation for both ranges. The difference in y-intercept is likely due to unique moisture provenance for each transect as shown in Fig. 9. Elevation is reported as mean basin hypsometry and is derived from a DEM from the SRTM at ∼200 m resolution. Uncertainty in d-excess values is ±0.46‰.

Fig. 7. Plot of ¹⁷O-excess versus elevation for samples from the windward side of (A) the Olympic Mountains (triangles) and (B) Oregon Coast Range (circles). Right-angle arrows show where the cloud base is inferred to intersect with the ground surface, above which there is no subcloud evaporation (relative humidity is 100%). This is roughly ∼750 m for the Olympics and 500 m for the Oregon Coast Range based on the elevation of maximum precipitation amount (Fig. 2). The open symbols show ¹⁷O-excess values of precipitation at the cloud base estimated from a subcloud evaporation model. Though there is significant scatter, the disparity between low- and high-elevation samples does not appear to be explained by subcloud evaporation alone. Elevation is reported as mean basin hypsometry and is derived from a DEM from the SRTM at ∼200 m resolution. Uncertainty in ¹⁷O-excess values is ±8 ppm.

Fig. 8. Plot of d-excess (A) and ¹⁷O-excess (B) versus relative humidity (H) for samples from the windward sides of the Coast Range and Cascades. Circles are colored by elevation which is reported as mean basin hypsometry (MBH). Two anomalous samples are not included in this regression. They are DHOW-20 from Ruby Beach, whose PRISM-derived H is anomalously high, likely because it is right next to the ocean, and WA16-1, a shallow, slow moving, and likely highly evaporated stream. Uncertainty in d-excess and ¹⁷O-excess values are less than 0.46‰ and 8 ppm, respectively.

Fig. 9. Surface relative humidity during winter months (Oct–Mar) with an overlay of the difference between air parcel provenance for the Olympic Mountains (blue circle and solid contours) compared to the Oregon Coast Range (red circle and dashed contours). Relatively low d-excess values in Olympic mountain water samples compared to Oregon Coast Range samples for the same elevations (Fig. 6) are likely due to comparatively high relative humidity (H) over its source area (∼90% H over SW British Columbia compared to ∼80% H over the Pacific Ocean offshore California). A similar pattern is observed in ¹⁷O-excess with relatively low values in the Olympic Mountains relative to the Oregon Coast Range (Fig. 7). Refer to the Supplementary Materials section for details on how this map was created including parameters for HYSPLIT back trajectory analysis. Relative humidity is derived from the NCEP/NCAR reanalysis dataset for years 2015–2016 (Kalnay et al., 1996).

Fig. 10. Plot of (A) d-excess and (B) ¹⁷O-excess versus elevation for samples from the leeward (east) side of the Cascade Mountains in Washington (triangles) and Oregon (circles). Eastern population is defined as sample watersheds with a centroid that is > −119° longitude (Washington) and > −121° longitude (Oregon). Elevation is reported as mean basin hypsometry and is derived from a DEM from the SRTM at ∼200 m resolution. Uncertainty in d-excess and ¹⁷O-excess values are less than 0.46‰ and 8 ppm respectively.

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