Temperature and accumulation at the Greenland Summit: Comparison of high‐resolution isotope profiles and satellite passive microwave brightness temperature trends

Abstract

Long‐term satellite passive microwave brightness temperature trends, supported by short‐term automatic weather station (AWS) temperature data, show that the Greenland Summit area experiences secondary warm periods in the late fall and/or winter as well as primary midsummer warmth. High‐resolution isotope profiles from snow pits dug in 1989, 1990, and 1991 near the Greenland Ice Sheet Project II; (GISP2) site reveal that stable isotope ratios (δ18O and δD) preserve this distinctive temperature cycle. This indicates that snow accumulation occurs frequently through the year at the Greenland Summit and that the isotope record initially contains temperature information from many times of the year. Through an empirically derived emissivity model using AWS air temperature data and satellite microwave brightness temperatures, our approach allows isotope values preserved in the snow to be related to estimated near‐surface air temperatures. Density‐corrected profiles allow the amounts and timing of accumulation to be determined as well. Our results indicate that stable isotope ratios from the near‐surface snow at the Greenland Summit are currently a reliable, high‐resolution temperature proxy. This result increases confidence in the paleoclimatic interpretation of isotope signal variations in the GISP2 and Greenland Ice Core Project (GRIP) deep ice cores.

Multiyear accumulation and temperature history near the North Greenland Ice Core Project site, north central Greenland

“…The research presented here is consistent with previous efforts [Shuman et al, 1995a[Shuman et al, , 1998] Depositional processes act to "homogenize" the near-surface snow through the microscale redistribution of snow grains and water vapor. The ability of the sampling "increment" to capture a specific event that can be matched also plays a role.…”

“…One possible explanation of this result is that the slope is generally related to the accumulation across the central Greenland area. Although not published by Shuman et al [1995aShuman et al [ , 1998], the multiyear averages for the pits studied were 23.0 and 19.7 cm/yr, compared to 17.6 cm/yr in this study. The regression slope for all points declined from 0.46-0.39 in the first two studies to 0.28 in this study.…”

“…The comparison of these two proxy temperature records is qualitative and is based on similarities in trend shape. This allows dates to be assigned to specific pit depths and allows accumulation per interval to be determined [see Shuman et al, 1995aShuman et al, , 1998]. Overall, Figure 6 illustrates the relative abilities of the two techniques to resolve subseasonal accumulation.…”

Isotopic diffusion in polar firn: implications for interpretation of seasonal climate parameters in ice-core records, with emphasis on central Greenland

“…Fi rs t, it supports o ur including th e e nh a ncement 0 (' diffusivit y at hig h Herron and LangwCl..-Y, 1980 ( Dye 3, Vostok, Grele), Alley andfloci, 1990 andBolzan andSlrobel, 1994 (G1SP2), Hammer and olli ers, 1978 ( Mileent), Aristamill andothers, 1986 ( Dalinger Dome), J ou::eL andothers, 1983 ( South Pole) altitude. Seco nd, it shows th a t a significant enh a nce ment of water-vapor diffusivity in snow rel ativc to a ir is not appropriate in this case.…”

Snow Facies Over Ice Sheets Derived From Envisat Active and Passive Observations

“…Emissivity of snow is influenced by snow characteristics, such as grain size, density, and crystal structure [32]. Nonetheless, TB is dominantly forced by the seasonal air temperature cycle, as shown by their high correlations with in situ [44], [45] and reanalysis records of surface temperature and by radiative transfer modeling studies [26], [46]. Depending on their frequency, TBs are correlated to the temperature of a layer of snow at different depths near the surface.…”