STABLE H AND O ISOTOPE ANALYSES OF MODERN WATER SAMPLES FROM COLORADO AND UTAH, USA: IMPLICATIONS FOR (PALEO)ALTIMETRY

Seventy water samples, collected along the routes through Colorado and Utah, USA in 2014 and 2015, have been analyzed for stable H and O isotopes. Linear regressions of the data acquired, relating elevation to such variables as δD, δ¹⁸O, latitude, or longitude, revealed some interesting and perhaps unsettling results: (1) the relationships between elevation and δD or δ¹⁸O were weak or nonexistent, with r² less than 0.1; comparatively, there are better relationships between elevation and latitude or longitude, with r² about 0.2; (2) there are very little (if any) relationships between δD and latitude or longitude, perhaps due to the much larger error in δD analyses than in δ¹⁸O analyses; and (3) compared to the very weak or nonexistent relationship between δ¹⁸O and latitude, the relationship between δ¹⁸O and longitude is much better (with r² = ~0.12), perhaps because longitude is related more to the moisture source distance than latitude is in the study area. The weak or nonexistent relationships between elevation and δD or δ¹⁸O place serious doubts on (paleo)altimetry in the central Rockies through Colorado and Utah, perhaps because of the many factors that could affect the δD and δ¹⁸O values, including but are not limited to the distance to moisture source, evaporation, temperature, humidity, and raining amounts, etc. That is, (paleo)altimetry may not be applicable in the study area.

Other interesting observations include: (1) flowing water is generally more enriched than snow or ice in the same area due to melting and evaporation enrichment; (2) water puddles next to each other in the desert or the same puddle some time later may have very different δD and δ¹⁸O values, with the smaller puddle being more enriched and more easily affected due to higher percentages of evaporation; (3) standing water usually has more enriched values than running water; (4) wetter year (e.g., 2015) generally yields more depleted δD and δ¹⁸O values than drier years (e.g., 2014); and (5) lower reaches of a river may have higher δD and δ¹⁸O values than the upper reaches, perhaps due to evaporation.