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Abstract The Arctic hydrological cycle is predicted to intensify as the Arctic warms, due to increased poleward moisture transport during summer and increased evaporation from seas once ice‐covered during winter. Records of past Arctic precipitation seasonality are important because they provide a context for these ongoing changes. In some Arctic lakes, stable isotopes of oxygen and hydrogen (δ18O and δ2H, respectively) vary seasonally, due to seasonal changes in precipitation δ18O and δ2H. We reconstruct precipitation seasonality from Lake N3, a well‐dated lake sediment archive in Disko Bugt, western Greenland, by generating Holocene records of two proxies that are produced at different times of the year, and therefore record different lake water seasonal isotopic compositions. Aquatic plants synthesize waxes throughout the summer, and their δ2H reflects winter‐biased precipitation δ2H at Lake N3, whereas chironomids synthesize their head capsules between late summer and winter, and their δ18O reflects summer‐biased precipitation δ18O at Lake N3. During the middle Holocene at Lake N3, aquatic plant leaf wax was strongly2H‐depleted, while chironomid chitin was18O‐enriched. We guide interpretations of these records using sensitivity tests of a lake water and energy balance model, where we change precipitation amount and isotope seasonality inputs. The sensitivity tests suggest that the contrasting trends between proxies were likely caused by an increase in precipitation amount during all seasons and an increase in precipitation isotope seasonality, in addition to proxy‐specific mechanisms, highlighting the importance of understanding lake‐ and proxy‐specific systematics when interpreting records from sediment archives.
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An Isotope Mass Balance Analysis of Evaporative Loss From Lake Turkana, Kenya Using δ 18 O and δD of Natural Waters
Abstract Measurements of oxygen and hydrogen stable isotope ratios (δ18O and δD) in meteoric waters provide insight to overlapping effects of evaporation, precipitation, and mixing on basin scale hydrology. This study of waters collected between 2016 and 2021 in the Turkana Basin, northern Kenya, uses δ18O and δD to understand water balance in Lake Turkana, a large, low‐latitude, alkaline desert lake. The Omo River, a major river system in the Ethiopian Highlands, is historically understood to provide approximately 90% of the water input to Lake Turkana. Discharge of the Omo is prohibitively difficult to measure, but stable isotope ratios in the lake may provide a meaningful method for monitoring the lake's response to changes in input. Precipitation in the Turkana Basin is low (<200 mm/year) with negligible rainfall on the lake's surface, and all water loss from the lake is evaporative. We compare new measurements with previous data from the region and records of lake height and precipitation from the same time period. We show that a Bayesian approach to modeling evaporation using atmospheric conditions and river δ18O and δD yields results consistent with published water balance models. Continued sampling of lake and meteoric waters in the Turkana Basin will be a useful way to monitor the lake's response to regional and global climate change.
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- PAR ID:
- 10577064
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Water Resources Research
- Volume:
- 60
- Issue:
- 6
- ISSN:
- 0043-1397
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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