Open AccessInterpreting H 2 O isotope variations in high‐altitude ice cores using a cyclone model
Author(s) -
Holdsworth Gerald
Publication year - 2008
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2007jd008639
Subject(s) - altitude (triangle) , thermometer , geology , ice core , atmospheric sciences , climatology , isotopes of oxygen , physics , geometry , thermodynamics , mathematics , geochemistry
Vertical profiles of isotope ( δ 18 O or δ D) values versus altitude (z) from sea level to high altitude provide a link to cyclones, which impact most ice core sites. Cyclonic structure variations cause anomalous variations in ice core δ time series which may obscure the basic temperature signal. Only one site (Mount Logan, Yukon) provides a complete δ versus z profile generated solely from data. At other sites, such a profile has to be constructed by supplementing field data. This requires using the so‐called isotopic or δ thermometer which relates δ to a reference temperature (T). The construction of gapped sections of δ versus z curves requires assuming a typical atmospheric lapse rate (dT/dz), where T is air temperature, and using the slope (d δ /dT) of a site‐derived δ thermometer to calculate d δ /dz. Using a three‐layer model of a cyclone, examples are given to show geometrically how changes in the thickness of the middle, mixed layer leads to the appearance of anomalous δ values in time series (producing decalibration of the δ thermometer there). The results indicate that restrictions apply to the use of the δ thermometer in ice core paleothermometry, according to site altitude, regional meteorology, and climate state.