Gas isotope thermometry in the South Pole and Dome Fuji ice cores provides evidence for seasonal rectification of ice core gas records
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Published:2022-07-22
Issue:7
Volume:16
Page:2947-2966
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ISSN:1994-0424
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Container-title:The Cryosphere
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language:en
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Short-container-title:The Cryosphere
Author:
Morgan Jacob D., Buizert ChristoORCID, Fudge Tyler J., Kawamura KenjiORCID, Severinghaus Jeffrey P.ORCID, Trudinger Cathy M.ORCID
Abstract
Abstract. Gas isotope thermometry using the isotopes of molecular nitrogen and argon
has been used extensively to reconstruct past surface temperature change
from Greenland ice cores. The gas isotope ratios δ15N and
δ40Ar in the ice core are each set by the amount of
gravitational and thermal fractionation in the firn. The gravitational
component of fractionation is proportional to the firn thickness, and the
thermal component is proportional to the temperature difference between the
top and bottom of the firn column, which can be related to surface
temperature change. Compared to Greenland, Antarctic climate change is
typically more gradual and smaller in magnitude, which results in smaller
thermal fractionation signals that are harder to detect. This has hampered
application of gas isotope thermometry to Antarctic ice cores. Here, we present an analytical method for measuring δ15N and
δ40Ar with a precision of 0.002 ‰ per atomic
mass unit, a two-fold improvement on previous work. This allows us to
reconstruct changes in firn thickness and temperature difference at the South
Pole between 30 and 5 kyr BP. We find that variability in firn thickness is
controlled in part by changes in snow accumulation rate, which is, in turn,
influenced strongly by the along-flowline topography upstream of the ice
core site. Variability in our firn temperature difference record cannot be
explained by annual-mean processes. We therefore propose that the ice core
gas isotopes contain a seasonal bias due to rectification of seasonal
signals in the upper firn. The strength of the rectification also appears to
be linked to fluctuations in the upstream topography. As further evidence
for the existence of rectification, we present new data from the Dome Fuji
ice core that are also consistent with a seasonal bias throughout the
Holocene. Our findings have important implications for the interpretation of ice core
gas records. For example, we show that the effects of upstream topography on
ice core records can be significant at flank sites like the South Pole – they
are responsible for some of the largest signals in our record. Presumably
upstream signals impact other flank-flow ice cores such as EDML, Vostok, and
EGRIP similarly. Additionally, future work is required to confirm the
existence of seasonal rectification in polar firn, to determine how spatially
and temporally widespread rectifier effects are, and to incorporate the
relevant physics into firn air models.
Funder
Office of Polar Programs Japan Society for the Promotion of Science
Publisher
Copernicus GmbH
Subject
Earth-Surface Processes,Water Science and Technology
Reference88 articles.
1. Albert, M., Shuman, C., Courville, Z., Bauer, R., Fahnestock, M., and
Scambos, T.: Extreme firn metamorphism: impact of decades of vapor transport
on near-surface firn at a low-accumulation glazed site on the East Antarctic
plateau, Ann. Glaciol., 39, 73–78, https://doi.org/10.3189/172756404781814041, 2004. 2. Beem, L. H., Cavitte, M. G. P., Blankenship, D. D., Carter, S. P., Young, D.
A., Muldoon, G. R., Jackson, C. S., and Siegert, M. J.: Ice-flow
reorganization within the East Antarctic Ice Sheet deep interior, Geol. Soc. Lon. Spec. Publ., 461,
35–47, https://doi.org/10.1144/SP461.14, 2018. 3. Beem, L. H., Young, D. A., Greenbaum, J. S., Blankenship, D. D., Cavitte, M. G. P., Guo, J., and Bo, S.: Aerogeophysical characterization of Titan Dome, East Antarctica, and potential as an ice core target, The Cryosphere, 15, 1719–1730, https://doi.org/10.5194/tc-15-1719-2021, 2021. 4. Bender, M., Sowers, T. A., and Lipenkov, V.: On the concentrations of O2,
N2, and Ar in trapped gases from ice cores, J. Geophys. Res.-Atmos., 100, 18651–18660, https://doi.org/10.1029/94JD02212, 1995. 5. Bender, M. L.: Orbital tuning chronology for the Vostok climate record
supported by trapped gas composition, Earth Planet. Sc. Lett.,
204, 275–289, https://doi.org/10.1016/S0012-821X(02)00980-9, 2002.
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