MOISTURE TRANSPORT DYNAMICS IN THE NORTH PACIFIC OVER THE LAST MILLENNIUM AND IMPACTS ON THE MT. HUNTER (ALASKA) ICE CORE ISOTOPE RECORD

The mechanisms and outcomes of teleconnections between the tropical and North Pacific regions over the past millennium remain elusive. Here we evaluate hydroclimate variability in the North Pacific using an array of glaciochemical proxy records from ice cores recovered on Mt. Hunter, Alaska (within Denali National Park). In particular, we present a newly updated stable water isotope record developed from the combined analysis of two surface to bedrock ice cores. The cores were processed using a continuous flow analysis (CFA) system, and dated using a combination of annual chemical and dust signals, and radioactive and volcanic horizons. The resulting annually-resolved timescale spans 2013-810 AD. We analyzed ~6000 stable water isotope samples for d¹⁸O, dD, and the derived deuterium excess (dxs) parameter, yielding a subannually resolved isotope record from 2013-1234AD, and 1-3 year resolution from 1233-810AD. Previous analysis of the annual accumulation record from the cores reveals a doubling of snowfall rate at the site since ~1850AD. Roughly coeval increases in sodium (Na+) concentration and melt layer frequency imply a deepening of the Aleutian low pressure system and increased advection of warm air masses. We suggest these changes were driven by warming sea surface temperatures in the tropical Pacific. Here we focus on the Mt. Hunter deuterium excess (dxs) record, which contains trends that correspond to the large-scale climate features of the Common Era. The most obvious feature of the dxs record is a decreasing trend beginning in ~1850AD that continues to present, mirroring changes in snowfall, temperature, and atmospheric circulation. Recent observational and modeling work suggests that broad-scale dxs patterns may primarily reflect ocean evaporation source relative humidity (higher RH = lower dxs). If correct, then the temporal dxs pattern in the Mt. Hunter cores implies a progressive southerly shift in moisture source and transport beginning ~1850 AD. We discuss the validity and implications of this hypothesis in the context of overall North Pacific hydroclimate.