Bulletin of Glaciological Research ,1 (,**3) +/ῌ,ῌJapanese Society of Snow and Ice

15

Resolution of environmental variation by detailed analysis of YM2/ shallow ice corein Antarctica
Hirotake TAKAHASHI+, Taeko YOKOYAMA+, Makoto IGARASHI,, Hideaki MOTOYAMA- andKeisuke SUZUKI+, .
+ Department of Environmental Sciences, Shinshu University, Matsumoto -3*ῌ20,+, Japan, RIKEN, Wako, Saitama -/+ῌ*+32, Japan- National Institute of Polar Research, Tachikawa +3*ῌ2/+2, Japan. Institute of Mountain Science, Shinshu University, Matsumoto -3*ῌ20,+, Japan(Received August 1, ,**3; Revised manuscript accepted December +*, ,**3)

Abstract
An ice core with a length of 11.1+ m water equivalent (w. e.) obtained in January ,**, from YM2/
in East Dronning Maud Land, Antarctica, has been subjected to detailed analysis. The ice core isdated at 101 years (+,--ῌ+333 A.D.) on the basis of the tritium concentration and volcanic signal time
markers and by annual layer counting. Large volcanic eruptions such as those of Tambora in +2+/
and Kuwae in +./- are likely to have caused the decrease in the temperature at YM2/. During +./-ῌ
+2+0 A.D., the surface mass balance at YM2/ was signiﬁcantly lower than that observed prior to andsubsequent to this period. This is thought to be because of LIA (little ice age) and the hiatus in snow
deposition. Observation of the annual surface mass balance from +2+0 A.D. to +332 A.D. shows that it
decreases sharply from the +3th century to the ,*th century. The correlation coe$cient between theﬁve-year average values of d +2O and those of the annual surface mass balance is positive (R῎*.0,) forthe period +2+0ῌ+332 A.D. The decrease in the Naῌ concentration with an increase in the temperature
is inferred to be a consequence of the diluting with a large amount of snowfall.

+.

Introduction

Japanese Antarctic Research Expeditions (JAREs)
have collected shallow ice cores from East Dronning
Maud Land, Antarctica, in order to reconstruct the
paleoenvironment. The reconstruction of the paleoenvironment is a part of the International TransAntarctic Scientiﬁc Expedition (ITASE) program,which is an international e#ort to obtain paleoclimate
records and clarify the environmental variations during the last few hundred years in Antarctica (Kameda
et al., ,**,). Under these plans, a shallow core is drilled
at YM2/, Antarctica.
Ice sheets are formed by the deposition of snow
over a long period, and the reconstruction of pastvariations in the atmospheric environment on thebasis of the analysis of ice cores is thought to bepossible. The ice cores are expected to contain information on the temperature variation by stable isotopic ratio, volcanic eruptions, surface mass balanceetc., in the past. It is also supposed to contain recordsof seasonal variations in the concentrations of chemical components that can help in the determination of
the origins of these chemical components. It is im-

portant to clarify how these environmental factors
interact with each other in the process recorded in ice
cores in resolving the environmental variations.
The objective of this study is to investigate therelationship between temperature variations andother environmental factors at YM2/ by performing adetailed analysis of the shallow ice core obtained fromthe location. We also report the result of the datingof the ice core.

,.
,.+

Methods

Drilling site
In January ,**,, a +*/./+ m ice core was collectedfrom the YM2/ (1+῏-/῍+.ῐS, .*῏-2῍/ῐE; ,,.0 m a.s.l.) in
East Dronning Maud Land, Antarctica (Fig. +) by JARE.,. This site is located in the Shirase Glacier, at the
midpoint between Mizuho Station and the Yamato
Mountains. Sastrugi are often observed around theYM2/; hence, this area is thought to be characterized
by strong katabatic winds. The average ﬂow speedof the surface ice sheet is ,/./ m year῍+ northward and/.2 m year῍+ westward (Motoyama et al., ,**,).

Bulletin of Glaciological Research

16

scribed in Watanabe et al. (+331) and Igarashi et al.
(+332). The liquid scintillation method is used for thedetermination of tritium content in the liquid phase.
Detailed analysis method of tritium is described in
Kamiyama et al. (+331).
,. - Conversion of the depth of the ice core to waterequivalent depth
The ice core is composed of ﬁrn and ice, and thedensity varies considerably along the core; the densities at the top and bottom of the core are *..- g cm῍and *.3+ g cm῍-, respectively (Motoyama et al., ,**,).
The depth of ice core must be converted into thewater equivalent depth (w. e.) scale using the density
data along the core. The water equivalent length of
the sample is obtained by multiplying the density of
the ice core by the length of the sample, and the total
water equivalent depth of the ice core is obtained by
the summation of the water equivalent lengths of all
the samples. For layers whose density data is unavailable, the average density of the top and bottom
layers is used. The water equivalent depth at thebottom of the ice core is 11.1+ m w. e.

-.

Fig. +. Location of the YM2/ shallow ice core drillingsite, East Dronning Maud Land, Antarctica.

,., Analysis
The YM2/ shallow ice core was transported toJapan in a cold storage. The core is then cut into
pieces with lengths of , to 0 cm in a low-temperaturelaboratory so that every piece provides at least ,* mlof liquid upon being melted. Subsequently, the surface of the ice core was scraped with a ceramic knife
washed in ultrapure water to remove contaminants.
The decontaminated sample was melted in a Teﬂon
bottle washed with ultrapure water in a clean room
for melting, and the resulting liquid sample was poured into a plastic bottle washed with ultrapure water,
and the plastic bottle was refrigerated until the beginning of chemical analysis. We used the melted sample to perform chemical and isotope analyses. Afterelectrical conductivity (EC) and pH of the samples
were measured, the concentrations of the major chemical components (Naῌ, NH.ῌ, Kῌ, Mg,ῌ, Ca,ῌ, F῍,
MSA῍ , Cl῍, SO.,῍, NO-῍)were measured by ion chromatography (anions: DIONEX DX--,*, cations: DIONEX ICS-+/**). We determined the isotopic composition of oxgen-+2 (d +2O) using a mass spectrometer(THERMO FISHER Delta Plus) on CO, equilibrated
with samples. Detailed analysis methods are de-Results and Discussion-.+ Chemical proﬁle of the YM2/ ice core
Figure , shows the ﬂuctuations in the value of d+2O,
the concentrations of Naῌ, MSA῍, non-sea-salt sulfate(nssSO.,῍) and NO-῍. The value of d +2O in the surface
snow is associated with the +* m snow temperature(Satow and Watanabe, +33,), and hence, we can use theﬂuctuation in d +2O in the core as an indicator of thetemperature. In the approximate depth ranges of +2ῌ
,, m w. e. and -0./ῌ-2 m w. e., the ﬂuctuations in d +2O
and nssSO.,῍ concentration appear to be signiﬁcantly
high, while MSA῍ concentration appears to be signiﬁcantly low (Fig. ,).
The NO-῍ concentration also shows a signiﬁcantdecrease in the depth ranges of +2ῌ,, m w. e. and -0./ῌ
-2 m w.e. (Fig. ,). The NO-῍ concentration has been
observed to decrease with an increase in temperaturein ice cores obtained from Greenland and Antarctica,
and the post-depositional loss of NO-῍ from the top
snow layers is caused by the release of HNO- and thephotolysis of NO-῍ (Rothlisberger et al., ,**,). The
large decrease in the NO-῍ concentration in the approximate depth range of ,*ῌ-1 m w. e. can be attributed to the post -depositional loss since a signiﬁcant
increase in d +2O is observed at these depths.
Comparing the ﬂuctuation in d +2O with that inῌ
Na concentration, it is found that d +2O is inversely
proportional to the Naῌ concentration (Fig. ,). It issuggested that the source of Naῌ in the ice core is sea
salt (Fig. -), and Naῌ concentration is expected to behigh during cold climatic conditions (Suzuki et al.,,**/); however, observations show that the reverse isTakahashi et al.

Fig. ,.

17

Vertical proﬁles of chemical components of the YM2/ ice core.

year῍+ (Toyama et al., ,**/), and hence, it could bethought that annual layer has several samples. However, the annual surface mass balance is not always
constant for long periods of time throughout the icecore. We attempted to identify the annual layers as
follows: ﬁrst, we employed several highly reliable
time markers. We then counted the number of annual layers using several ionic concentrations believed to show seasonal variations.

Fig. -. The relationship between cencentrations ofNaῌ and Cl῍ in YM2/ ice core. The broken line inthis ﬁgure indicates the ratio of concentrations ofNaῌ and Cl῍ in seawater.

true. In section -. .. ,, using the surface mass balance
information obtained from the ice core, we shall explain the relationship among the ﬂuctuations in d +2O,
the Naῌ concentration, the MSA῍ concentration, andthe NO-῍ concentration.
-., Dating of the YM2/ ice core
As a result of snow pit work at the drilling site,
the annual surface mass balance for the last two to
three years is estimated to be about ,** mm w. e.

-.,.+ Time markers
The ﬁrst time marker is the tritium concentration(Fig. .). During the early +3/*s and +30*s, the testingof thermonuclear atmospheric bombs resulted in theemission of a large amount of artiﬁcial radioactive
nuclides into the earth’s atmosphere, and hence, annual layers with remarkably high tritium concentrations are observed in the Antarctic ice cores (Stenni etal., +333; Nishio et al., ,**,). The graph of tritium
concentration vs. the depth for the ice core is shown inthe basic analytical report of the YM2/ shallow ice
core. The graph shows large peaks at depths of ..2.,..+3, and /.*, m w. e., corresponding to the years +300,+303, and +30/, respectively (Igarashi et al., ,**-). We
set these three tritium peaks as the ﬁrst time markers.
The second time marker is the signals generated
by large volcanic eruptions. Large volcanic eruptions release large amounts of sulfur oxides into theatmosphere. These oxides are eventually precipitated on the polar ice sheet surface. Hence, the presence of large amounts of nssSO.,῍ in the Antarctic
shallow ice cores can be attributed to the volcanic
eruptions (Kohno et al., +333; Stenni et al., +333; Kohno,,***; Nishio et al., ,**,; Suzuki et al., ,**/; Zhou et al.,18

Bulletin of Glaciological Research,**0). A plot of the nssSO.,῍ concentration against
the depth of the YM2/ ice core shows large peaks at
depths of ,0.+ m w. e., ./.2 m w. e., and 1,.- m w. e. (Fig.
,), and the ﬂuctuation pattern of these peaks is similar
to that of the nssSO.,῍ concentration in the DT,0- icecore (Zhou et al., ,**0). According to Zhou et al.
(,**0), these peaks correspond to the volcanic eruptions of Tambora in +2+/, Kuwae in +./- and Unknown in +,/3, respectively. By taking into accountthe time taken for the transportation of the oxides
from the site of the volcanic eruptions to the Antarctic ice sheets, we estimated the deposition of nssSO.,῍
on the layer at depths of ,0.+ m w. e., ./.2 m w. e., and1,.- m w. e. to have occurred in +2+0, +./., and +,0* A.
D., respectively. We set these three years that correspond to the years of generation of volcanic signals as
the second time markers.
Table + shows the mean annual surface mass balance calculated for the period between the time markers mentioned above. The mean annual surface massbalance from the surface snow layer to the layer
formed in +2+0 A.D. and from the layer formed in +./.
A.D. to the layer formed in +,0* A.D. is in the range of+,1 mm-,+1 mm w. e. year῍+ (Table +), and we could
observe several annual layers corresponding to theabove range. On the other hand, the mean annual
surface mass balance from the layer formed in +./.
A.D. to the layer formed in +2+0 A.D. is about /. mm
w. e. year῍+ (Table +), we could not observe many
annual layers corresponding to this range. We attempted to identify the annual layers by assumingthat the annual surface mass balance was constantfrom +./. A.D. to +2+0 A.D. In section -. .. +, we shall
explain the reason for the decrease in the surface massbalance during this period.
Identiﬁcation of annual layer
We use the seasonal variations in the concentrations of MSA῍, NO-῍, and Naῌ in order to identify theannual layers of the ice core. As described above, thesource of MSA῍ is marine phytoplankton; this implies
that the MSA῍ should be high in summer and low in
winter (Suzuki et al, ,**/). It is thought that NO-῍
contained in the Antarctic ice core mainly derived
from the stratosphere (Stenni et al., +333); the nssSO.,῍
and NO-῍ concentrations indicate high peaks in summer (Li et al., +333; Nishio et al., ,**,). As describedabove, sea salt is the source of Naῌ (Fig. -); this implies that the Naῌ concentration should be high in
winter and low in summer (Li et al., +333; Zhou et al.,,**0). It is suggested that the maximum MSA῍ concentration nearly corresponds to that of the maximum NO-῍ concentration in the layer formed during
summer, and this layer is considered as the boundary-.,.,

Fig. .. The ﬂuctuation of tritium concentration in the
YM2/ shallow ice core.

Table +. Mean annual surface mass balance calculated between tritium andlarge volcanic time markers in YM2/ ice core.

Takahashi et al.

Fig. /.

19

Proﬁles of the concentrations of MSA῍, NO-῍, Naῌ, and d +2O value from the surface layer to +31* A.D.

of the annual layer (Fig. /). When the MSA῍ concentration is signiﬁcantly low at a depth of around ,* mw. e. (Fig. ,), the layer with the maximum NO-῍ concentration corresponds to that of the minimum Naῌconcentration is considered as the boundary of theannual layer. We corrected the time obtained fromthe annual layer counting by using the tritium concentration and volcanic signal time markers describedabove.
Using the time markers and by annual layer counting, the annual layer at a depth of 11.1+ m w. e. in the
YM2/ ice core is dated at +,-- A.D.
-.- Signals generated by volcanic eruptions-.-.+ Estimation of volcanic signals
Following the approach that is widely employed,
the nssSO.,῍ concentration values exceeding the average (‹x) plus ,s (s: standard deviation) are considered
as volcanic signals (Nishio et al., ,**,; Suzuki et al.,,**/; Zhou et al., ,**0). However, in the present study,
it is supposed that only a small number of volcanic
signals are observed because the background ﬂuctuation in the nssSO.,῍ concentration is added to thee#ect of large volcanic eruptions. The average (‹xῌ ;*.0/ meq L῍+) and standard deviation (sῌ; *.., meq L῍+)
values of nssSO.,῍ concentration in the layers, except
those layers for which the values exceed ‹xῌῌ,s arecalculated. It is suggested that the layers in which
the value of the nssSO.,῍ concentration exceeds‹
xῌῌ,sῌ
(+./* meq L῍+) is a#ected by volcanic eruptions. However, as described in section -. +, nssSO.,῍ is producedby the oxidation of DMS (Nishio et al., ,**,; Suzuki etal., ,**/). In addition, a layer with high nssSO.,῍
concentration resulting from volcanic eruptions has alow pH value (Suzuki et al., ,**/). By consideringboth the MSA῍ and Hῌ concentrations in the layers,
we classify the volcanic signals into three grades.
The layers whose nssSO.,῍ concentration exceeds‹xῌῌ,sῌ, Hῌ concentration exceeds the average value (../.
meq L῍+), and MSA῍ concentration doesn’t indicate thepeak were considered to preserve highly reliable volcanic signals and were classiﬁed as grade I. The
layers whose nssSO.,῍ concentration exceeds ‹xῌῌ,sῌ,and for which either the Hῌ concentration exceeds theaverage value or the MSA῍ concentration doesn’t indicate the peak were classiﬁed as grade II. The layers
whose Hῌ concentration does not exceed the averagevalue and whose MSA῍ concentration indicate thepeak were classiﬁed as grade III. Grade II and III
layers were considered to be less a#ected by the volcanic eruptions and less reliable than grade I. Figure
0 shows the concentrations of Hῌ, MSA῍, and nssSO.,῍
in the layers. It also shows a record of volcanic eruptions that occurred to the south of ,*῎N and that arethought to correspond to volcanic signals in the volcanic explosivity index (VEI) along with the degree of
reliability of the layers (grade I, II, and III) in the rightcolumn. It can be seen that the ice core is a#ected by
the volcanic eruptions of Pinatubo and Cerro Hudson
in +33+, Agung in +30-, Tarawera in +220, Krakatau in+22- etc., except the three large volcanic eruptions
used as time markers.

Bulletin of Glaciological Research

20

Fig. 0. Proﬁles of the concentrations of Hῌ, MSA῍ and nssSO.,῍ for last ,** years and the records of volcanic eruptions.
The broken and the chain line in this ﬁgure indicate the average and ‹xῌῌ,sῌ, respectively. Symbols indicate degrees
of reliabilities of volcanic eruptions (῎῎: grade I, ῎: grade II, ῏: grade III). VEI values are compiled from the Global
Volcanism Program (http: //www.volcano.si.edu/world/largeeruptions.cfm)-.-.,

Relationship between climatic conditions and volcanic eruptions
Figure 1 shows the ﬂuctuation in the nssSO.,῍
concentration and d +2O in the vicinity of the Tambora
and Kuwae eruptions. d +2O decreased signiﬁcantly
shortly after the nssSO.,῍ peaks that are considered toinclude the e#ect of large volcanic signals. Sulfuric
acid aerosols generated by volcanic eruptions remainsuspended in the stratosphere for a period of a few
years and are dispersed by solar radiation. These
aerosols cause a decrease in the temperature on theearth’s surface (Sigurdsson, +33*). It is suggested
that large volcanic eruptions such as those of Tambora and Kuwae caused the decrease in the temperature at the YM2/ site.
-.. Surface mass balance-...+ Surface mass balance in YM2/
During +./-ῌ+2+0 A.D., the surface mass balance
at YM2/ was signiﬁcantly lower than those observed
both prior to and subsequent to this period (Table +).
This is thought to be caused by two factors. One is
the Little Ice Age (LIA) in the Northern Hemisphere.
LIA is the cold period that lasted from the +.th to the+3th century in the Northern Hemisphere, and the ice
cores obtained from the Southern Hemisphere also
corroborate the occurrence of the LIA (Thompson etal., +320; Benoist et al., +32,; Morgan et al., +32/). It

Fig. 1. Proﬁles of nssSO.,῍ concentration and d+2O in thevicinity of Tambora (above) and Kuwae (bottom)
eruption. The broken and the chain line in thisﬁgure indicate the average and‹xῌῌ,sῌ, respectively.

Takahashi et al.

has been reported that the mean annual accumulation
rate of snow at DT,0-, Antarctica is signiﬁcantly low
during the LIA. The other factor is a period during
which there was a hiatus in snow deposition. The
hiatus was observed at alternate regions separated by+*-km distances in the areas in the upper basin of theYM2/ site (Furukawa et al., +330). Considering theannual average ﬂow rate of the surface ice sheet at
YM2/ (as mentioned in section ,.+), the surface layerof the YM2/ site is expected to have moved at the rateof 3 km yearῌ+ for -0- years from +./. to +2+0 A.D.
There is a possibility that the site where the next
hiatus in snow deposition is likely to occur can be
determined from the records preserved in the YM2/
ice core. However, a sharp decrease in d +2O during
the period +./-ῌ+2+0 A.D. is not observed in the icecore. The parameter that contains evidence of the
hiatus in snow deposition preserved in the YM2/ shallow ice core is as yet unknown. Further studies arenecessary for explaining the signiﬁcantly low surface
mass balance during +./-ῌ+2+0 A.D. at YM2/.
Figure 2 shows the annual surface mass balance,
which is calculated using the identiﬁed annual layers,
for +2, years from +2+0 to +332 A.D. The average,
maximum, and minimum values of the annual surface
mass balance for this period are +.+ mm w. e. yearῌ+,--0 mm w. e. yearῌ+ in +23/, and /* mm w. e. yearῌ+ in+3-1, respectively. The annual surface mass balance
for the abovementioned period indicates a sharp decrease from the +3th to the ,*th century, and thesurface mass balance during the +3th century is higher than that during the ,*th century. This pattern
appears to be similar to that observed in the H1, icecore (Suzuki et al., ,**/), and hence, it could be expected that from the +3th to the ,*th century, theannual surface mass balance showed a similar pattern
throughout the area extending from the coastal region to approximately ,** km inland in East Dronning
Maud Land.
Relationship between climatic conditions andsurface mass balance
It has been previously reported that the ﬂuctuation in d +2O in the H1, ice core showed seasonalvariations: the ﬂuctuation was high in summer andlow in winter (Suzuki et al., ,**/). However, the ﬂuctuation in d +2O in the YM2/ shallow ice core did notshow clear seasonal variations (Fig. /). Using snow
stake measurements, the average surface mass balance at the H1, site was calculated to be -*1 mm w. e.
yearῌ+ for the period +31-ῌ+332 (Nishio et al., ,**,);
this value is much higher than the average surface
mass balance at YM2/ for the period +2+0ῌ+332 A.D.
It is suggested that the value of d +2O in the surface
snow layer gradually changes because of isotopic ﬂuctuations, and that the seasonal variations in d +2O are
not preserved in the YM2/ core due to a low accumu-

21

Fig. 2. Annual surface mass balance from +2+0 to +332 A.D.

-...,

Fig. 3. The relationship between the /-year-average ofd +2O and the /-year-average of annual surface massbalance from +2+0 to +332 A.D. The broken line inthis ﬁgure indicates a linear regression.

lation rate.
Figure 3 shows the relationship between the ﬁveyear average values of d +2O and those of the annual
surface mass balance for the period +2+0ῌ+332 A.D. If
the ﬁve-year average of d +2O is high, then the ﬁve-year
average of annual surface mass balance is also high;Bulletin of Glaciological Research

22

this indicates that the correlation coe$cient (R῎*.0,)
between the two parameters is positive. According
to the relationship between the average temperatureand the accumulation rate obtained for Greenland andAntarctica, the site with a high temperature tends tohave a high accumulation rate (Satow et al., +333;
Röthlisberger et al., ,**,). It is suggested that theperiod with a high temperature tends to show a highsurface mass balance at YM2/. The decrease in theconcentration of Naῌ with an increase in the temperature, as mentioned in section -.+, could be because of
the occurrence of a large amount of snowfall. The
decrease in the MSA῍ and NO-῍ concentrations at theapproximate depth ranges of +2ῌ,, m w. e. and -0./ῌ
-2 m w. e. (Fig. ,) may be, to some extent, because ofmelting of the snow as a result of high temperature.
However, the e#ect having the peculiar reaction processes by preserving into ice core, as described abovein -.+ section, can exceed the e#ect by the diluting
since both MSA῍ and NO-῍ concentrations show asigniﬁcant decrease.

..

served in the H1, ice core, and hence, it could be
expected that from the +3th century to the ,*th century, the annual surface mass balance showed a similar pattern throughout the area extending from thecoastal region to approximately ,** km inland in East
Dronning Maud Land.
There is a clear relationship between the ﬂuctuation in d +2O and that in the MSA῍ and NO-῍ concentrations in the YM2/ ice core; hence, it is suggested
that the processes of preservation of these ions isrelated to the temperature at which they are deposited. When comparing the ﬂuctuation in d +2O withthat in the Naῌ concentration, a high d +2O is found at
low Naῌ concentrations. This is inferred to be because of the occurrence of a large amount of snowfall,
which is in turn a consequence of a high surface massbalance.
It is necessary to assess the implications of thepresent study for the whole Antarctic ice sheet. Additionally, further research on the methods of analyzing ice cores is necessary to tackle unresolved problems.

Conclusions
Acknowledgments

An ice core with a length of 11.1+ m w. e. that wascollected in January ,**, at YM2/ in East Dronning
Maud Land, Antarctica, by JARE-., has been subjected to a detailed analysis. The layer at a depth of
11.1+ m w. e in the ice core is dated at +,-- A.D using
the tritium concentration and volcanic signal time
markers and by annual layer counting, which involved counting of the number of annual layers using
several ionic concentrations that were believed toshow seasonal variations.
The ice core appears to have been a#ected by the
volcanic eruptions of Pinatubo and Cerro Hudson in+33+, Agung in +30-, Tarawera in +220, Krakatau in+22-, Tambora in +2+/, Unknown in +2*3, Kuwae in+./-, and Unknown in +,/3. d +2O shows a signiﬁcantdecrease shortly after large volcanic signals such as
those from Tambora in +2+/ and Kuwae in +./-, andhence, it is concluded that these large volcanic eruptions could have caused a decrease in the temperature
at the YM2/ site.
During +./-ῌ+2+0 A.D., the surface mass balance
at YM2/ was signiﬁcantly lower than that observed
both prior to and subsequent to this period. This isthought to be caused by the LIA and a hiatus in snow
deposition. However, this is debatable. Further studies are required to elucidate the reason for the low
surface mass balance during this period.
An observation of the annual surface mass balance at YM2/ for +2, years, from +2+0 to +332 A.D.,
indicates a sharp decrease from the +3th century tothe ,*th century; the surface mass balance during the+3th century is higher than that during the ,*th century. This pattern appears to be similar to that ob-

We are indebted to the JARE-., ice-coring teamfor their e#orts to obtain the ice core at the YM2/ site
under severe weather conditions.

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