Synoptic and Mesoscale Mechanisms Drive Winter Precipitation δ¹⁸O/δ²H in South‐Central Alaska

Abstract

Measurements of oxygen and hydrogen stable isotopes in precipitation (δ18OP and δ2HP) provide a valuable tool for understanding modern hydrological processes and the empirical foundation for interpreting paleoisotope archives. However, long‐term data sets of modern δ18OP and δ2HP in southern Alaska are entirely absent, thus limiting our insight and application of regionally defined climate‐isotope relationships in this proxy‐rich region. We present and utilize a 13‐year‐long record of event‐based δ18OP and δ2HP data from Anchorage, Alaska (2005–2018, n = 332), to determine the mechanisms controlling precipitation isotopes. Local surface air temperature explains ~30% of variability in the δ18OP data with a temperature‐δ18O slope of 0.31 ‰/°C, indicating that δ18OP archives may not be suitable paleo‐thermometers in this region. Instead, back‐trajectory modeling reveals how winter δ18OP/δ2HP reflects synoptic and mesoscale processes in atmospheric circulation that drive changes in the passage of air masses with different moisture sources, transport, and rainout histories. Specifically, meridional systems—with either northerly flow from the Arctic or southerly flow from the Gulf of Alaska—have relatively low δ18OP/δ2HP due to progressive cooling and removal of precipitation as it condenses with altitude over Alaska's southern mountain ranges. To the contrary, zonally derived moisture from either the North Pacific and/or Bering Sea retains relatively high δ18OP/δ2HP values. These new data contribute a better understanding of the modern Alaska water isotope cycle and provide an empirical basis for interpreting paleoisotope archives in context of regional atmospheric circulation.

Moisture origin and stable isotope characteristics of precipitation in southeast Siberia

“…Atmospheric precipitation is the primary source of water for terrestrial and aquatic ecosystems (Brázdil, 1992; Galloway & Cowling, 1978). Hence, the detailed understanding of circulation processes and background mechanisms controlling precipitation of a given region and its temporal and spatial variations is an important issue for assessment and forecast of weather and water regimes worldwide (Bailey, Klein, & Welker, 2019; Brázdil, 1992; Tang et al, 2017; Trenberth, 2011). In particular, hydrogen and oxygen isotopes in precipitation are natural tracers, which help to understand the atmospheric moisture cycle (Araguás‐Araguás, Froehlich, & Rozanski, 2000).…”

Ice Core δ18O Record Linked to Western Arctic Sea Ice Variability

“…Observations discussed by Bailey et al () indicate that δ 18 O in precipitation over Anchorage is enriched when storms approach from the west and southwest due to fewer topographical barriers and associated rainout. Storms more commonly approach from the west during the spring season (Bailey et al, ), which partially explains why western station temperatures were most strongly correlated to B‐C δ 18 O during spring (Figure b and Table S5). Isotopes at B‐C are similarly enriched when storms approach from the west or southwest, but whether this is explained by the original moisture source characteristics, topography, or a combination of these factors has yet to be determined.…”

“…Logan. Storms from the west and southwest may be less subject to the coastal orography thereby enriching B‐C δ 18 O, and storms may preferentially traverse topographic lows such as the Cook Inlet and other prominent river valleys (Bailey et al, ; Lachniet et al, ). Without automatic weather station data or high‐resolution models capable of accurately capturing the complex terrain, it is uncertain how an individual storm system would uniquely affect each site in this region.…”

“…Logan occurs when moisture originates from more local, rather than distant, sources and is associated with zonal flow. Observations discussed by Bailey et al (2019) indicate that δ 18 O in precipitation over Anchorage is enriched when storms approach from the west and southwest due to fewer topographical barriers and associated rainout. Storms more commonly approach from the west during the spring season , which partially explains why western station temperatures were most strongly correlated to B-C δ 18 O during spring (Figure 4b and Table S5).…”

“…However, the δ 18 O records from the aforementioned cores and other paleo‐isotope records from this region exhibit little consistency (Kaufman et al, ). Characteristics of δ 18 O in this region vary greatly with elevation (Holdsworth et al, ), and the complex mountainous topography has been shown to influence δ 18 O in precipitation (Bailey et al, ). Due to its high elevation (5,340 m above sea level, masl), δ 18 O from the Mt.…”