II-7. Astrophysics and Astro-Glaciology

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Annually resolved d-excess record from a shallow ice core (DFS10) near
Dome Fuji station, East Antarctica
Y. V. Sahoo,∗1 , Y. Motizuki,∗1 , Y. Nakai,∗1 , and K. Takahashi,∗1Ice cores are well preserved and utilized as proxies forpast climates and temperature reconstruction. A secondorder equation given by the deuterium excess 1) (referredto as d-excess), d = δD − 8 × δ 18 O, is defined fromthe Meteoric Water Line. Here, δD and δ 18 O are theisotopic water compositions given by δD or δ 18 O () =(Rmeasured − RVSMOW )/RVSMOW , where R is the ratio
2
H/1 H or 18 O/16 O, RVSMOW is the reference standard,
Vienna Standard Mean Ocean Water, and Rmeasured isthe measured ratio of a sample.
The d-excess is primarily related to physical parameters such as relative humidity, air temperature, sea surface temperature of the oceanic source or precipitation
at the site, and the trajectory of moisture source.2) On
a global scale, an annual average value of d is relatively
constant around 10.
Vimeux et al.3) demonstrated the d-excess changes
during transition from the glacial and interglacial periods of Vostok deep ice core data; the changes were wellcharacterized in the plot of d-excess versus δD, implicating changes in oceanic moisture sources as a resultof changes in Earth’s orbital obliquity. The d-excess
records for the Dome Fuji site have been studied withdaily snow precipitation 4,5) and a deep ice core spanningthe past 360,000 years.6) So far, moisture sources andclimate changes have been studied for deep ice cores in
Antarctica which span a long period; however, is it possible to determine the same tendency on short scales withannually-resolved d-excess data from shallow ice cores?
Here, we briefly report the correlation of d-excess withδ 18 O in a shallow ice core.
The shallow ice core (DFS10) was drilled in 2010 fromthe site at 10 km south of Dome Fuji station, East
Antarctica. The DFS10 site is located (77◦ 40’S, 39◦ 62’E)
at 3,800 m above sea level. The ice core drilling project
was conducted by Japanese Antarctic Research Expedition. The analyzed samples represent a temporal resolution of about one year ranging from 2 m to 60 m in depth(∼1300 years). All samples were analyzed using Liquid
Water Isotope Analyzer (Los Gatos Research, Inc.) atRIKEN.
A linear relation between δD and δ 18 O, with a slope of7.77, R2 = 0.987 for DFS10 was determined. This is close
to the local meteoric water line. The d-excess shows nocorrelation with δ 18 O (δD) on an annual or short scale;
however, simulation studies established a correlation onlonger scales with other ice cores drilled in Antarctica.
Fig. 1a shows a smoothed 50 data points running average of d-excess plotted against smoothed δ 18 O, andclusters into groups are evident. This case shows hierarchal structures: For groups of ∼500 years, a gen∗1Fig. 1. (a) Deuterium excess versus δ 18 O; the data aresmoothed using 50 data points running average. The color
highlights the bunched ∼500 years period to show thechanges in d-excess. (b) The same, but for data points
from 1496 to 1973 CE (blue highlight from a) are subdivided into ∼50 years period.

eral decrease in d-excess with time is observed, suggesting that the moisture source could have systematicallychanged through the years. Each group subdivided into
shorter time scales (∼50 years) reveals smaller clusters ofd-excess pattern changing with time (Fig. 1b). As seen
here, the d-excess/δ 18 O small clusters follow a patternwith time. This pattern is not observed in a similar plot
with the raw data (R2 = 0.04, Pearson’s R = −0.19).
The d-excess variation depends on a number of factors and intensive simulation or modeling studies arenecessary to provide an insight into climate change ona shorter scale, which needs to be assessed using shallow
ice cores.
References

RIKEN Nishina Center- 74 -1) W. Dansgaard, Tellus 16, 436 (1964).
2) L. Merlivat, J. Jouzel, J. Geophys. Res. 84, 5029 (1979).
3) F. Vimeux et al., Nature 398, 410 (1999); J. Geophy.
Res. 106(31), 863 (2001).
4) H. Motoyama et al., J. Geophy. Res. 110, D11106 (2005).
5) K. Fujita, O. Abe, Geophys. Res. Lett. 33, L18503 (2006).
6) R. Uemura et al., Clim. Past. 8, 1109 (2012).

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