Industrial-age doubling of snow accumulation in the Alaska Range linked to tropical ocean warming

Abstract

Future precipitation changes in a warming climate depend regionally upon the response of natural climate modes to anthropogenic forcing. North Pacific hydroclimate is dominated by the Aleutian Low, a semi-permanent wintertime feature characterized by frequent low-pressure conditions that is influenced by tropical Pacific Ocean temperatures through the Pacific-North American (PNA) teleconnection pattern. Instrumental records show a recent increase in coastal Alaskan precipitation and Aleutian Low intensification, but are of insufficient length to accurately assess low frequency trends and forcing mechanisms. Here we present a 1200-year seasonally- to annually-resolved ice core record of snow accumulation from Mt. Hunter in the Alaska Range developed using annual layer counting and four ice-flow thinning models. Under a wide range of glacier flow conditions and layer counting uncertainty, our record shows a doubling of precipitation since ~1840 CE, with recent values exceeding the variability observed over the past millennium. The precipitation increase is nearly synchronous with the warming of western tropical Pacific and Indian Ocean sea surface temperatures. While regional 20th Century warming may account for a portion of the observed precipitation increase on Mt. Hunter, the magnitude and seasonality of the precipitation change indicate a long-term strengthening of the Aleutian Low.

Denali Ice Core Methanesulfonic Acid Records North Pacific Marine Primary Production

“…Hunter shows a predominant marine aerosol source region in the Gulf of Alaska (GOA) to the south‐southwest of the central Alaska Range (Figure ). This is consistent with most precipitation events being associated with southerly flow on the eastern side of low‐pressure systems in the GOA (Winski et al, ). Figure shows some trajectories along a more zonal path originating in the southern Bering Sea, but the vast majority of back trajectories intersect the boundary layer east of the Aleutian Islands.…”

“…Stable water isotopes were measured at the University of Maine using a Picarro L2130i stable water analyzer. Core sections from 84‐ to 124‐m depth were also analyzed by nondestructive gamma spectrometry at the University of New Hampshire to identify the radioactive cesium‐137 peak from atmospheric nuclear weapons testing in 1963 (Osterberg et al, ; Winski et al, ). We analyzed Denali Core 2 (hereafter the “Denali ice core”) in its entirety (back to 800 Common Era) for MSA.…”

“…The depth‐age scale was validated by the presence of sulfate spikes corresponding with the dates of known volcanic eruptions (e.g., Katmai in 1912, Shiveluch in 1856, and Laki in 1783) and by the cesium‐137 spike in 1963 matching the timing of peak atmospheric nuclear weapons testing (Holdsworth et al, ). The ice core time scale uncertainty from 1998 to 2010 is estimated to be <0.25 years (Osterberg et al, ; Winski et al, ).…”

“…Ice cores collected from North Pacific mountain glaciers provide subannual‐to‐decadal glaciochemical records of temperature, atmospheric circulation, pollution, volcanism, and dust deposition over the late Holocene (Fischer et al, ; Neff et al, ; Osterberg et al, , ; Zdanowicz et al, , ). Given their high temporal resolution and multiproxy capability, North Pacific alpine ice cores such as the new Denali ice core (Osterberg et al, ; Winski et al, ) provide a unique opportunity to investigate the long‐term context and cause(s) of the recent productivity declines in the North Pacific.…”

A 400‐Year Ice Core Melt Layer Record of Summertime Warming in the Alaska Range

“…However, previous work on winter‐biased Mt. Hunter archives (Osterberg et al, ; Winski et al, ) demonstrate that there is a wide spread among models in their ability to capture the magnitude of tropical teleconnections in the North Pacific. Improving agreement between North Pacific paleoclimate archives and gridded climate data sets is a potential area for future advances.…”