Search

Rapidly changing climate is disrupting the High Arctic's water systems. As tracers of hydrological processes, stable water isotopes can be used for high quality monitoring of Arctic waters to better reconstruct past changes and assess future environmental threats. However, logistical challenges typically limit the length and scope of isotopic monitoring in High Arctic landscapes. Here, we present a comprehensive isotopic survey of 535 water samples taken in 2018 and 2019 of the lakes and other surface waters of the periglacial Pituffik Peninsula in far northwest Greenland. The δ18O, δ2H, and deuterium‐excess values of these samples, representing 196 unique sites, grant unprecedented insight into the environmental drivers of the regional hydrology and water isotopic variability. We find that the spatial variability of lake water isotopes can best be explained through evaporation and the hydrological ability of a lake to replace evaporative water losses with precipitation and snowmelt. Temporally, summer‐long evaporation can drive lake water isotopes beyond the isotopic range observed in precipitation, and wide interannual changes in lake water isotopes reflect annual weather differences that influenced evaporation. Following this, water isotope samples taken at individual times or sites in similar periglacial landscapes may have limited regional representativeness, and increasing the spatiotemporal extent of isotopic sampling is critical to producing accurate and informative High Arctic paleoclimate reconstructions. Overall, our survey highlights the diversity of isotopic compositions in Pituffik surface waters, and our complete isotopic and geospatial database provides a strong foundation for future researchers to study hydrological changes at Pituffik and across the Arctic. Plain Language Summary: Water isotopes can help us track how rapidly changing climate is disrupting High Arctic water systems, but the challenging Arctic environment has limited the monitoring required to understand these isotopes. To address this, we collected 535 water isotope samples from lakes and other waters on the Pituffik Peninsula in northwest Greenland in 2018 and 2019. We found that differences in lake water isotopes are mainly due to water evaporation and how connected a lake is to sources of precipitation and snowmelt that can replace evaporated water in the summer. The information we collected about isotopes is a good starting point for other scientists who want to study how water is changing, not just in Pituffik, but also in the whole Arctic. Our findings tell us that if we only collect water samples once or twice, or only in one place, we might not get the full picture of what is happening with the isotopes across the whole region. To get a better understanding of how the climate is changing in the High Arctic, water isotopic samples should be collected from a wide range of locations over long periods of time. Key Points: Five hundred and thirty five water isotope samples taken over 2 years in Pituffik, Greenland, provide insight into High Arctic isotope hydrologySpatially, lake water isotopic composition reflects the degree that evaporation losses are offset by precipitation and snowmelt rechargeEvaporation drives summer‐long lake water isotopic evolution and best explains interannual isotopic differences [ABSTRACT FROM AUTHOR]

The Arctic Ocean and adjacent seas are undergoing increased freshwater influx due to enhanced glacial and sea ice melt, precipitation, and runoff. Accurate delineation of these freshwater sources is vital as they critically modulate ocean composition and circulation with widespread and varied impacts. Despite this, the delineation of freshwater sources using physical oceanographic measurements (e.g., temperature, salinity) alone is challenging and there is a requirement to improve the partitioning of ocean water masses and their mixing relationships. Here, we complement traditional oceanographic measurements with continuous surface seawater isotopic analysis (δ18O and deuterium excess) across a transect extending from coastal Alaska to Baffin Bay and the Labrador Sea conducted from the US Coast Guard Cutter Healy in Autumn 2021. We find that the diverse isotopic signatures of Arctic freshwater sources, coupled with the high freshwater proportion in these marine systems, facilitates detailed fingerprinting and partitioning. We observe the highest freshwater composition in the Beaufort Sea and Amundsen Gulf regions, with heightened freshwater content in eastern Baffin Bay adjacent to West Greenland. We apply isotopic analysis to delineate freshwater sources, revealing that in the Western Arctic freshwater inputs are dominated by meteoric water inputs—specifically the Mackenzie River—with a smaller sea ice meltwater component and in Baffin Bay the primary sources are local precipitation and glacial meltwater discharge. We demonstrate that such freshwater partitioning cannot be achieved using temperature‐salinity relationships alone, and highlight the potential of seawater isotopic tracers to assess the roles and importance of these evolving freshwater sources. Plain Language Summary: Freshwater inputs to the Arctic seas, including glacial and sea ice meltwater, precipitation, and river runoff, are increasing as the Arctic warms. The impacts of these changing freshwater influxes are varied depending on the type of freshwater source, and thus it is important to delineate and trace these different freshwater sources, which represents a significant challenge using only traditional physical oceanographic measurements (e.g., temperature, salinity). In this study, we utilize a new approach to identify and trace freshwater sources using continuous seawater isotopic measurements during a cruise extending from coastal Alaska, through the Canadian Archipelago, and across Baffin Bay and the Labrador Sea. We show that these isotopic measurements, which have been commonly used in other media (e.g., precipitation, water vapor, ice cores), hold important and distinct information about the source and mixing of different freshwater sources. We use these measurements to identify the freshwater sources (e.g., Mackenzie vs. Yukon River) contributing to ocean surface waters across the Arctic region. Key Points: Seawater isotopic measurements (δ18O, δ2H, deuterium excess) show heightened freshwater content in the Beaufort Sea and Baffin BayIsotopic observations enable freshwater source delineation not feasible from traditional physical oceanographic methodsFreshwater source delineation includes the Mackenzie and Yukon Rivers around coastal Alaska and glacial meltwater in Baffin Bay [ABSTRACT FROM AUTHOR]

Hydrogen (δD) and oxygen (δ18O) isotopic ratios are strongly correlated in precipitation over time and space, defining the meteoric water line, and the slope of this δD‐δ18O relationship reflects covariations of deuterium excess (d‐excess) with δD or δ18O. This δD‐δ18O line provides a tool for inferring hydrologic processes from the evaporation source to condensation site. Here, we present δD‐δ18O relationships on seasonal and annual timescales for daily precipitation, snow pits, and a 15‐m ice core (Owen) at Summit, Greenland. Seasonally, precipitation δD‐δ18O slopes are less than 8 (summer = 7.70; winter = 7.77), while the annual slope is greater than 8 (8.27). We suggest that intra‐season slopes result primarily from Rayleigh distillation, which, under prevailing conditions, produces slopes less than 8. The summer line has a greater intercept (higher d‐excess) than the winter line. This separation causes annual slopes to be greater than seasonal ones. We attribute high summer d‐excess primarily to contributions of vapor sublimated from the Greenland Ice Sheet and other terrestrial sources. High sublimated moisture proportions result in a large separation between seasonal δD‐δ18O lines, and thus high annual slopes. Inter‐seasonal weighting of precipitation amount also influences annual slopes because slopes are weighed by the number of storms each season. Using snow pit measurements, we demonstrate that precipitation isotopic signals translate to the snowpack. We generate indices to determine Sublimation Proportion Index and Precipitation Weighting Index, and find that annual Owen core δD‐δ18O line slopes are significantly related to these indices, demonstrating that these factors are recorded in ice cores. Plain Language Summary: We present water isotope measurements in precipitation, snow pits, and a shallow ice core from Summit, Greenland. We investigate the relationship between hydrogen and oxygen isotope ratios, emphasizing the temporal variation in the slope of the local meteoric water line and its relationship with climate conditions. We demonstrate that, on the annual scale, variations in the hydrogen (δD) versus oxygen (δ18O) isotopic ratio slope is significantly controlled by moisture contribution from sublimation off the Greenland Ice Sheet and by variations in the seasonal weighting of precipitation. We demonstrate that these isotopic signals of precipitation translate directly to the snowpack and thus are potentially transferred to ice cores. We obtained annual δD versus δ18O slopes from a 32‐year ice core and show that the slope variations are related to the relative amount of sublimation and seasonal weighting of the precipitation. These results open a new way of interpreting ice cores for their climatic significance. The work may also help better understand ice sheet mass balance through the quantification of sublimation‐sourced precipitation. Key Points: Deuterium excess annual cycles in precipitation, snow pits, and an ice core at Summit, Greenland have phases opposite to most Arctic sitesSlope of local meteoric water line (LMWL) can be measured in ice cores and can be used to extract past hydroclimatesLMWL slope contains information about sublimation off the Greenland Ice Sheet and seasonal precipitation distribution [ABSTRACT FROM AUTHOR]

At Thule Air Base on the coast of Baffin Bay (76.51 ∘ N, 68.74 ∘ W), we continuously measured water vapor isotopes (δ18O , δ2H) at a high frequency (1 s -1) from August 2017 through August 2019. Our resulting record, including derived deuterium excess (dxs) values, allows an analysis of isotopic–meteorological relationships at an unprecedented level of detail and duration for high Arctic Greenland. We examine isotopic variability across multiple temporal scales from daily to interannual, revealing that isotopic values at Thule are predominantly controlled by the sea ice extent in northern Baffin Bay and the synoptic flow pattern. This relationship can be identified through its expression in the following five interacting factors: (a) local air temperature, (b) local marine moisture availability, (c) the North Atlantic Oscillation (NAO), (d) surface wind regime, and (e) land-based evaporation and sublimation. Each factor's relative importance changes based on the temporal scale and in response to seasonal shifts in Thule's environment. Winter sea ice coverage forces distant sourcing of vapor that is isotopically light from fractionation during transport, while preventing isotopic exchange with local waters. Sea ice breakup in late spring triggers a rapid isotopic change at Thule as the newly open ocean supplies warmth and moisture that has ∼10 ‰ and ∼70 ‰ higher δ18O and δ2H values, respectively, and ∼10 ‰ lower dxs values. Sea ice retreat also leads to other environmental changes, such as sea breeze development, that radically alter the nature of relationships between isotopes and many meteorological variables in summer. On synoptic timescales, enhanced southerly flow promoted by negative NAO conditions produces higher δ18O and δ2H values and lower dxs values. Diel isotopic cycles are generally very small as a result of a moderated coastal climate and the counteracting isotopic effects of the sea breeze, local evaporation, and convection. Future losses in Baffin Bay's sea ice extent will likely shift mean annual isotopic compositions toward more summer-like values, and local glacial ice could potentially preserve isotopic evidence of past reductions. These findings highlight the influence that the local environment can have on isotope dynamics and the need for dedicated, multiseason monitoring to fully understand the controls on water vapor isotope variability. [ABSTRACT FROM AUTHOR]

At Thule Air Base on the coast of Baffin Bay (76.51° N 68.74° W), we continuously measured water vapor isotopes (δ18O, δD) at high frequency (1 s-1) from August 2017 through August 2019. Our resulting record, including derived deuterium-excess (dxs) values, allows for analysis of isotopic-meteorological relationships at an unprecedented level of detail and duration for High Arctic Greenland. We examine isotopic variability across multiple temporal scales from daily to annual, revealing that isotopic values at Thule are determined by five interacting factors: (a) local air temperature, (b) local marine moisture availability, (c) the NAO, (d) surface wind regime, and (e) land-based evaporation/sublimation. Each factor's relative importance changes in response to seasonal shifts in Thule's environment, largely driven by the sea ice extent in northern Baffin Bay. Winter sea ice coverage forces distant sourcing of vapor that is isotopically light from fractionation during transport and prevents isotopic exchange with local waters. Late spring sea ice breakup triggers a rapid isotopic change at Thule as the newly open ocean supplies warmth and moisture that is 10 ‰ and 70 ‰ higher in δ18O and δD, respectively, and 13 ‰ lower in dxs. Sea ice retreat also leads to other environmental changes, such as sea breeze development, that dramatically alter the nature of relationships between isotopes and many meteorological variables in summer. On shorter temporal scales, enhanced southerly flow promoted by negative NAO conditions produce higher δ18O and δD values and lower dxs values. Diel isotopic cycles are generally very small as a result of a moderated coastal climate and counteracting isotopic effects of the sea breeze and local evaporation. Future losses in Baffin Bay sea ice extent will likely shift mean annual isotopic compositions toward more summer-like values, and past reductions should be similarly preserved in local glacial ice. These findings highlight the strong influence local environment has on isotope dynamics and the need for dedicated, multi-season monitoring to fully understand the controls on water vapor isotope variability. [ABSTRACT FROM AUTHOR]

The meteoric water line, defined by the correlation of hydrogen (δD) and oxygen (δ18O) values, is one of the earliest described characteristics of precipitation isotopic variations. However, spatial and temporal variations in the slope of this line are less studied. The slope of the δD-δ18O relationship is coupled with how d-excess covaries with δD or δ18O, and may provide an integrated tool for inferring hydrologic processes from the evaporation to condensation site. We present a study of δD-δ18O relationships on seasonal and annual timescales for event-based precipitation and a 15-meter ice core (Owen) at Summit, Greenland. Seasonally, precipitation δD-δ18O slopes are less than eight (summer = 7.71; winter = 7.77), while the annual slope is greater than eight (8.27). We suggest intra-season slopes result primarily from Rayleigh distillation, which, under prevailing conditions, produces slopes less than eight. The summer line has a greater intercept (higher d-excess) than the winter line. This separation causes annual slopes to be greater than seasonal ones. We attribute high summer d-excess to contributions of vapor sublimated from the Greenland Ice Sheet. Higher sublimated moisture proportions in summer cause larger separations between seasonal δD-δ18O lines, and thus higher annual slopes. Intra-seasonal distributions of precipitation amount also influence annual slopes because slopes are weighed by the number of storms each season. We generate indices to quantify sublimation proportion (SPI) and precipitation distribution (PDI), and find that annual Owen core slope measurements are significantly related to these indices, demonstrating that sublimation and precipitation distribution represent important climate conditions recorded in ice cores. [ABSTRACT FROM AUTHOR]